[ECG-dipyridamole and ECG-exercise test in the assessment of ischemic cardiopathy: effects of the acute administration of nitroglycerin]

It is known that intravenous administration of dipyridamole can induce chest pain and ECG signs of ischemia in patients with coronary artery disease. In the present study we evaluated ECG and hemodynamic changes in response to dipyridamole (0.56 mg/kg in 10 min) under basal conditions and 3 hours after administration of nitroglycerin (10 mg/24 h patch) in 14 patients with coronary artery disease. The effects of nitroglycerin were also compared to those induced by the same drug on a bicycle stress test in the same patients. Exercise stress test induced specific ST changes in all patients when performed off-drug. Nitroglycerin administration completely prevented exercise-induced ischemia in 2 patients, and significantly prolonged exercise time in the remaining patients (p < 0.01). This effect was accompanied by a significant increase in heart rate (HR) and rate-pressure product at the threshold of ischemia (HRBP, p < 0.01); furthermore we observed a significant increase in HR at the maximal work load (p < 0.05). In the absence of treatment, dipyridamole infusion induced ST segment changes and/or typical chest pain in 12/14 patients. Moreover we observed a significant increase (p < 0.05) in HR, BP and HRBP during the test with respect to basal conditions. Following nitroglycerin administration, dipyridamole infusion failed to induce ischemia in 4 patients, and the time to ST depression in the remaining 8 patients (459 +/- 69 vs 610 +/- 127 s; p < 0.05) was significantly prolonged.(ABSTRACT TRUNCATED AT 250 WORDS)

Transforming G protein-coupled receptors potently activate JNK (SAPK). Evidence for a divergence from the tyrosine kinase signaling pathway

The expression of human muscarinic acetylcholine receptors (mAChRs) in NIH 3T3 cells has been used as a model for studying proliferative signaling through G protein-coupled receptors. In this biological system, the m1 class of mAChRs can effectively transduce mitogenic signals (Stephens, E.V., Kalinec, G., Brann, M.R., and Gutkind, J.S. (1993) Oncogene 8, 19-26) and induce malignant transformation if persistently activated (Gutkind, J.S., Novotny, E.A., Brann, M.R., and Robbins, K.C. (1991) Proc. Natl. Acad. Sci. U.S.A. 88, 4703-4708). Moreover, available evidence suggests that the m1-signaling pathway converges at the level of p21ras with that emerging from tyrosine kinase receptors (Crespo, P., Xu, N., Simonds, W.F., and Gutkind, J.S. (1994) Nature 369, 418-420). To explore nuclear events involved in growth regulation by G protein-coupled receptors in this setting, we compared the effect of platelet-derived growth factor (PDGF) and the cholinergic agonist, carbachol, on the expression of mRNA for members of the jun and fos family of nuclear proto-oncogenes. We found that activation of m1 receptors by carbachol induces the expression of a distinct set of nuclear transcription factors. In particular, carbachol caused a much greater induction of c-jun mRNA and AP-1 activity. These responses did not correlate with protein kinase C stimulation nor with the activation of mitogen-activated protein (MAP) kinases. Recently, it has been shown that a novel family of kinases structurally related to MAP kinases, stress-activated protein kinases, or Jun kinases (JNKs), phosphorylate in vivo the amino-terminal transactivating domain of the c-Jun protein, thereby increasing its transcriptional activity. In view of our results, this observation prompted us to ask whether m1 and PDGF can differentially activate JNKs. Here, we show that m1 mAChRs can induce a remarkable increase in JNK activity, which was temporally distinct from that of MAP kinase and was entirely protein kinase C independent. In contrast, PDGF failed to activate JNK in these cells, although it stimulated MAP kinase to an extent even greater than that for carbachol. These findings demonstrate that G protein-coupled receptors can signal through pathways leading to the activation of JNK, thus diverging at this level with those signaling routes utilized by tyrosine kinase receptors.

Recombinant tissue-type plasminogen activator therapy in prosthetic mitral valve thrombosis: assessment by transthoracic and transesophageal echocardiography

Prosthetic cardiac thrombosis is a life-threatening complication that needs prompt diagnosis and therapy. We used recombinant tissue-type plasminogen activator (rT-PA), followed by heparin, in three patients with mitral prosthetic thrombosis, which was evident in two and suspect in one. Transthoracic and transesophageal echocardiography were employed in the diagnosis of both thrombosis and its resolution. No complications occurred. Immediately after the end of treatment with rT-PA, clinical status and echocardiographic data improved in all cases: transthoracic echocardiography showed the normalization of prosthetic function and transesophageal echocardiography showed resolution of thrombosis. One patient needed reoperation for rethrombosis due to the presence of prosthetic fibrous clot. rT-PA, followed by heparin, led to a good clinical result without bleeding and embolic complications in selected patients with mitral prosthetic thrombosis. Transthoracic and transesophageal echocardiography are complementary diagnostic tools in the diagnosis and management of patients with prosthetic thrombosis.

[Coronary angioplasty for the recovery of myocardial function after acute myocardial infarction: mid- and long-term results]

Sixty-three patients with previous myocardial infarction and documented hypoperfused reversibly dysfunctional myocardium after 201thallium tomography and/or echo-dobutamine were candidates to coronary angioplasty. Patients were enrolled at four hospitals (Naples, Milan, Pisa and Varese) and evaluated by different study protocols, while endpoint (presence of myocardial viability and efficacy of coronary angioplasty to improve dysfunctional myocardium) was similar. Sixty-two patients underwent successful angioplasty, and early evaluation (between 1 and 3 months after procedure) showed the ability of either 201thallium tomography and/or dobutamine echocardiography, to identify hypoperfused reversibly dysfunctional myocardium. Ten patients underwent late (after 8 +/- 2 months) evaluation of both wall motion and myocardial perfusion showing a sustained improvement in 25/32 hypoakinetic myocardial segments. Our data confirm the efficacy of revascularization of hypoperfused dysfunctional myocardial segments by coronary angioplasty. Further studies are warranted to obtain a better patient stratification and to evaluate the long-term results.

[Interstitial changes and ventricular hypertrophy in man]

Left ventricular hypertrophy is accompanied by the remodeling of the collagen network. We have studied collagen network in left ventricular hypertrophy secondary to aortic stenosis by cardiac catheterization and endomyocardial biopsies. We have demonstrated that collagen architecture is abnormal in 2/3 of patients with aortic stenosis and is more important than collagen concentration in influencing myocardial stiffness and ejection fraction. Furthermore, we observed that relaxation and asynchrony were influenced by the degree of hypertrophy instead of by the collagen network. The postoperative regression of left ventricular hypertrophy and the changes in interstitial tissue after valve replacement have been studied in a subgroup of patients. The major finding is that the regression of myocardial hypertrophy is a process that occurs over many years after correction of primary hemodynamic abnormality. Six to 7 years after valve replacement we observed, together with the normalization of diastolic stiffness, the complete normalization of interstitial fibrosis that was primarily increased (both pre and early postoperatively).

[Gene therapy for the treatment of restenosis after coronary angioplasty]

Accumulation and proliferation of vascular smooth muscle cells are associated with atherosclerosis and hypertension. Proliferation of smooth muscle cells constitutes a major pathological event responsible for long-term failure of coronary and peripheral arterial bypass graft as well as the development of restenosis after percutaneous transluminal coronary angioplasty (PTCA). The incidence of restenosis after PTCA has been reported to be as high as 40-45% within 3-6 months. Major advantages in recombinant deoxyribonucleic acid (DNA) technology and eukaryotic gene regulation allow to hypothesize gene therapy as a potential treatment for inherited and acquired diseases. Gene therapy is the introduction of genes into somatic cells to correct an inherited or acquired disorder through the synthesis of missing or defective protein. Although no disease has yet been treated by gene therapy, several gene transfer protocols have recently been undertaken. We have studied the expression of foreign DNA that has been introduced into smooth muscle cells after balloon carotid injury in a rat model of angioplasty. The effects of different degree of balloon injury on neointima formation and c-fos expression was also assessed. Our data demonstrate that site-specific gene expression can be achieved by direct gene transfer in vivo and could be applied to the treatment of restenosis after PTCA.

Coronary artery vasoconstriction after successful single angioplasty of the left anterior descending artery

Percutaneous transluminal coronary angioplasty is associated with spontaneous transient vasoconstriction. The mechanisms by which coronary vasoconstriction occurs distally to a successful dilated stenosis after coronary artery angioplasty are still unknown. The present study was planned to investigate the effect of successful coronary artery angioplasty on coronary vasomotion distal to a dilated stenosis and in the control vessel and the role of alpha-adrenergic receptors on coronary vasomotion after successful coronary artery angioplasty. We prospectively studied 32 consecutive patients scheduled for elective single coronary artery angioplasty of the left anterior descending coronary artery. Only aspirin, 325 mg, or nitroglycerin was allowed in the week before the study; no premedication with diazepam or other drugs was given. In group 1 (control patients, n = 20), quantitative coronary angiography was performed in the control state; 5 and 15 minutes after coronary artery angioplasty; and after intracoronary nitroglycerin infusion, 300 micrograms. In group 2 (n = 12), intracoronary phentolamine, 2 mg, was infused regionally through the balloon catheter before the coronary artery angioplasty, and coronary angiography was performed at baseline, 15 minutes after balloon deflation, and after nitroglycerin infusion. In group 1, constriction of the coronary segment distal to a dilated stenosis (2.4 +/- 0.8 to 2.1 +/- 0.6 mm, -14.6% vs baseline; p < 0.05) and of the circumflex coronary artery segment (2.8 +/- 0.7 to 2.5 +/- 0.6 mm, -10.7% vs baseline, p < 0.05) occurred 15 minutes after coronary artery angioplasty. The degree of vasoconstriction was not correlated with the lesion severity before coronary artery angioplasty.(ABSTRACT TRUNCATED AT 250 WORDS)

Evaluation of left ventricular asynchrony by radionuclide angiography: comparison of phase and sector analysis

The aim of this study was to assess the optimal method to evaluate asynchrony in equilibrium radionuclide angiography (RNA).

METHODS

We studied 20 patients (14 males and 6 females, age range 25-60 yr) with RNA during atrial and sequential atrioventricular (AV) pacing, which increased left ventricular (LV) asynchrony. Both studies were performed at the same heart rate. Asynchrony was assessed either on phase images, by computing the standard deviation of the phase distribution (SD-P) and by sector analysis. Systolic and diastolic asynchrony were evaluated as the coefficient of variation of time to end systole (CV-TES) and time to peak filling rate (CV-TPFR) in four sectors. In addition, phase values were computed on time-activity curves from the same sectors, and their standard deviation (SD-Psec) was computed.

RESULTS

During atrial pacing SD-P was 32.3 degrees +/- 6.7 degrees and did not change during AV pacing (32.1 degrees +/- 5.6 degrees, p = n.s.). Both CV-TES and CV-TPFR had a significant increase during AV pacing (from 7.7% +/- 3.9% to 11.5% +/- 6.4%, p < 0.01, and from 8.4 degrees +/- 5.8 degrees to 12.9 degrees +/- 6.7 degrees, p < 0.001). AV pacing led to a significant increase in SD-Psec (from 6.3 degrees +/- 4.0 degrees to 12.6 degrees +/- 9.7 degrees, p < 0.05). Moreover, reproducibility was assessed in 15 additional age-matched patients. The results of the reproducibility study indicate a better repeatability for CV-TES and CV-TPFR.

CONCLUSIONS

The findings of this study suggest that sector analysis with calculation of indices of LV systolic and diastolic asynchrony is better suited for quantitation of LV temporal nonuniformity.

[Ambulatory monitoring of left ventricular function in patients with ischemic heart disease: effects of coronary revascularization]

The aim of this study was to assess the efficacy of coronary artery bypass using an ambulatory radionuclide monitoring system of left ventricular function (VEST) during daily activities in patients with previous myocardial infarction and coronary artery disease. Ten patients with previous myocardial infarction, clinical evidence of residual angina and angiocardiographically proven coronary artery disease of at least two epicardial vessels were studied by VEST 8 +/- 2 days before and 15 +/- 3 days after surgical myocardial revascularization. VEST allows to monitor both left ventricular function and 2 ECG leads. During the radionuclide monitoring (at least 60 min) all patients underwent handgrip test (compression of a dynamometer for 2 min at the 75% of maximal capacity), a mental stress (arithmetic operation consisting in subtracting 17 from 17,000 for 4 min), walking (140 yards) and climbing stairs (8 flights). No significant changes in left ventricular function during mental stress and handgrip both before and after the surgical procedure were observed. In the preoperative evaluation, walking induced a significantly increase in heart rate from rest to peak exercise (73 +/- 13 versus 79 +/- 11 b/min, respectively; p < 0.01). After coronary artery bypass, heart rate (rest: 92 +/- 18 b/min, effort: 98 +/- 19 b/min; p < 0.01), ejection fraction (rest: 47 +/- 8%, effort: 53 +/- 10%; p < 0.01), cardiac output (rest: 43 +/- 8 edv/min, effort: 51 +/- 11 edv/min, p < 0.01), and stroke volume (rest: 47 +/- 9%, effort: 53 +/- 9%; p < 0.01) increased at maximal effort compared to the control conditions.(ABSTRACT TRUNCATED AT 250 WORDS)

Myocardial damage during ischaemia and reperfusion

Large quantities of oxygen free radicals can be generated on reperfusion of the ischemic myocardium. This phenomenon is probably responsible for a specific component of cell damage separate from ischemic injury and may blunt the beneficial effects of thrombolysis. Anti-free radical interventions may reduce the severity of this "reperfusion injury". However, reports of treatment failures indicate that reperfusion injury is a complex phenomenon, and suggest that the beneficial effects of treatment may be critically dependent on factors that are not clearly understood.

Influence of reversible segmental left ventricular dysfunction on heart period variability in patients with one-vessel coronary artery disease

OBJECTIVES

This study evaluated the relation between reversible segmental left ventricular dysfunction and frequency domain measures of heart period variability in patients with coronary artery disease.

BACKGROUND

Heart period variability is frequently reduced in patients with coronary artery disease. However, the mechanisms of this reduction are still unclear.

METHODS

Echocardiographic left ventricular wall motion and frequency domain measures of heart period variability were evaluated in 32 patients with one-vessel coronary artery disease before and 16 to 24 days after successful percutaneous transluminal coronary angioplasty. Of these, 12 patients (Group A) had normal and 20 patients (Group B) had abnormal regional wall motion. A control group of 15 healthy subjects (Group C) underwent 24-h Holter recording twice at 2-week intervals to check for spontaneous variations.

RESULTS

At baseline, low and high frequency power were lower in Group B than in Groups A and C, whereas no difference was detectable in ultra low and very low frequency and total power. After coronary angioplasty, regional wall motion and frequency domain measures of heart period variability were unchanged in Group A. In Group B the mean (+/- SD) summed segment score improved from 17.1 +/- 3.6 to 12.8 +/- 2.0 (p < 0.01), and mean low and high frequency power (logarithmic units) increased from 6.14 +/- 0.23 to 6.35 +/- 0.34 (p < 0.01) and from 5.43 +/- 0.32 to 5.68 +/- 0.52 (p < 0.01), respectively. Furthermore, low and high frequency power, lower at baseline in Group B than in the other two groups, were comparable in the three groups after coronary angioplasty.

CONCLUSIONS

This study demonstrates that segmental left ventricular dysfunction is involved in determining sympathovagal imbalance in patients with one-vessel coronary artery disease; the reversal of left ventricular dysfunction by successful coronary angioplasty improves the heart period power spectrum. Thus, alterations in cardiac geometry influence the discharge of afferent sympathetic mechanoreceptors, contributing to the derangement in autonomic control of heart rate.

Assessment of left ventricular regional function by radionuclide angiography: effects of number of sectors on repeatability

Twenty patients were studied by equilibrium radionuclide angiography (RNA) twice in the same day in order to assess the repeatability of quantitative measurements of left ventricular (LV) regional function by using a sector analysis method. RNA was performed in the best septal 45 degrees left anterior oblique projection, acquiring 150,000 counts/frame, at 20 msec/frame with 5% gate tolerance. LV regional analysis was performed using a computer algorithm written by the authors running on Digital PDP 11/34 machine. The algorithm after having identified the center of gravity of the LV, divided it into 4, 5 and 6 equiangular sectors. In the 5, and 6 sector analysis, the region including the mitral and aortic valves was excluded from subsequent analysis. In each sector Ejection Fraction (EF) and Peak Filling Rate (PFR) were computed. In addition, the Time to End Systole (TES) and Time to Peak Filling Rate were also assessed for each region. The coefficient of variation of the regional values of TES (CV-TES) and regional TPFR (CV-TPFR) were then computed and considered as indices of LV systolic (CV-TES) and diastolic (CV-TPFR) asynchrony. Repeatability was firstly assessed by linear regression analysis between the 2 RNA studies. Our data show a high correlation coefficient on regional values of EF and PFR (R: > 0.92). Moreover, the differences in a given parameter between the 2 studies were plotted against their mean value, and the coefficient of repeatability (CR) was calculated as twice the standard deviation of the differences. No significant differences were found between EF and PFR regional values in the 2 RNA studies (EF coefficient of repeatability: < 0.18; PFR coefficient of repeatability: < 0.8). A low value of coefficient of repeatability was found also for CV-TES (< 17) and for CV-TPFR (< 18). In conclusion LV regional analysis is a repeatable method of analysis, and the number of regions does not affect the repeatability.

[Atrioventricular conduction before and after the radiofrequency catheter ablation of a nodal reentry tachycardia circuit]

Aim of our study was to retrospectively evaluate atrioventricular conduction 24 hours after selective radiofrequency catheter ablation of the fast pathway or after selective ablation of the slow pathway of the atrioventricular nodal reentrant tachycardia circuit. Electrophysiologic modifications were retrospectively analyzed in 47/48 patients successfully submitted to fast pathway ablation and in 90/93 patients successfully submitted to slow pathway ablation. The atrioventricular conduction intervals (P-Q and A-H), both anterograde and retrograde Wenckebach point, the effective refractory period of atrioventricular node and the atrioventricular node function curve were evaluated before and after selective radiofrequency catheter ablation of slow and fast pathway. We identified the fast pathway ablation potential as: A:V ratio > or = 2:1, His electrogram < or = 150 microV. The slow pathway potential was identified as the widest, sharpest and latest atrial electrogram recorded during sinus rhythm in the posteroseptal region of the atrioventricular junction or as the widest, sharpest and earliest observed during retrograde conduction. We observed a significant increase in the P-Q and A-H intervals in patients submitted to fast pathway ablation, while no significant modification of these parameters was appreciated in patients submitted to slow pathway ablation. No significant modification of anterograde Wenckebach point (NS) was observed in patients submitted to successfully ablation of fast pathway while a statistically significant increase in anterograde Wenckebach point (p = 0.03) was observed in patients submitted to slow pathway ablation. After selective fast pathway ablation, retrograde conduction was absent in 82.9% of patients submitted to ablation; in the remaining 17.1% a significant increase of retrograde Wenckebach point was observed.(ABSTRACT TRUNCATED AT 250 WORDS)

Forearm vascular responsiveness to alpha 1- and alpha 2-adrenoceptor stimulation in patients with congestive heart failure

BACKGROUND

The alpha-adrenergic component of the sympathetic nervous system plays a major role in the pathophysiology, clinical manifestations, and natural history of human congestive heart failure (CHF). However, the functional integrity of vascular alpha 1- and alpha 2-adrenoceptors in CHF remains to be elucidated. The present study was designed to assess the vascular responsiveness of alpha 1- and alpha 2-adrenoceptors in patients with CHF.

METHODS AND RESULTS

To evaluate alpha 1- and alpha 2-adrenoceptor responsiveness, we studied the effects of the regional infusion into the brachial artery of increasing doses of phenylephrine (a selective alpha 1-adrenoceptor agonist) and BHT 933 (a selective alpha 2-adrenoceptor agonist) on vascular responses in 12 healthy subjects and in 24 patients with CHF secondary to primary dilated cardiomyopathy or ischemic heart disease. Left ventricular ejection fraction was measured by radionuclide angiography, and forearm blood flow was determined by venous occlusion plethysmography. Phenylephrine reduced forearm blood flow in normal subjects from 5.2 +/- 0.9 to 2.5 +/- 0.6 mL per 100 mL of tissue/min (P < .05) at the highest dose (-50.8 +/- 4.8% versus baseline). A similar vasoconstriction was obtained in patients with CHF (from 3.5 +/- 0.5 to 1.5 +/- 0.2 mL per 100 mL of tissue/min (P < .05) (-58.7 +/- 5.0% versus baseline). The dose-response curves produced by phenylephrine in the two groups were comparable. The highest dose of BHT 933 reduced forearm blood flow in normal subjects from 5.3 +/- 0.9 to 2.3 +/- 0.6 mL per 100 mL of tissue/min (P < .05) (-59.0 +/- 4.9% versus baseline). In patients with CHF, a similar vasoconstriction was obtained (from 4.2 +/- 0.8 to 1.5 +/- 0.3 mL per 100 mL of tissue/min, P < .05, -62.1 +/- 6.5% versus baseline). The dose-response curves produced by BHT 933 also were comparable in the two groups. In patients with CHF, plasma concentrations of norepinephrine were significantly higher than in normal subjects.

CONCLUSIONS

The results of the present study demonstrate that alpha 1- and alpha 2-adrenoceptor stimulations produced an equivalent vasoconstriction in patients with CHF and in normal subjects. This indicates that the vascular responsiveness to alpha-adrenoceptor agonists may be preserved in the limb vessels of patients with CHF.

Modulation of platelet function by reactive oxygen metabolites

Reactive oxygen metabolites have been reported to affect platelet aggregation. However, this phenomenon is still poorly understood. In the present study we investigated the effects of superoxide radical and hydrogen peroxide (H2O2) on platelet function in vitro and correlated those effects to possible changes of platelet concentrations of cyclic nucleotides and thromboxane, since these systems play a key role in the response of platelets to activating stimuli. Human platelets were exposed to xanthine-xanthine oxidase (X-XO), a system that generates both superoxide radicals and H2O2. Sixty seconds of incubation with X-XO impaired aggregation in response to ADP (by 48%), collagen (by 71%), or the thromboxane mimetic U-46619 (by 50%). This effect was reversible and occurred in the absence of cell damage. Impairment of aggregation in platelets exposed to X-XO was due to H2O2 formation, since it was prevented by catalase but not by superoxide dismutase. Similarly, incubation with the pure H2O2 generator glucose-glucose oxidase also markedly inhibited ADP-induced platelet aggregation in a dose-dependent fashion. Impaired aggregation by H2O2 was accompanied by a > 10-fold increase in platelet concentrations of guanosine 3',5'-cyclic monophosphate (cGMP), whereas adenosine 3',5'-cyclic monophosphate levels remained unchanged. The inhibitory role of increased cGMP formation was confirmed by the finding that H2O2-induced impairment of platelet aggregation was largely abolished when guanylate cyclase activation was prevented by incubating platelets with the guanylate cyclase inhibitor, LY-83583. Different effects were observed when arachidonic acid was used to stimulate platelets. Exposure to a source of H2O2 did not affect aggregation to arachidonate. Furthermore, in the absence of exogenous H2O2, incubation with catalase, which had no effects on platelet response to ADP, collagen, or U-46619, virtually abolished platelet aggregation and markedly reduced thromboxane B2 production (to 44% of control) when arachidonic acid was used as a stimulus. In conclusion, our data demonstrate that H2O2 may exert complex effects on platelet function in vitro. Low levels of endogenous H2O2 seem to be required to promote thromboxane synthesis and aggregation in response to arachidonic acid. In contrast, exposure to larger (but not toxic) concentrations of exogenous H2O2 may inhibit aggregation to several agonists via stimulation of guanylate cyclase and increased cGMP formation.

Oxygen radicals inhibit human plasma acetylhydrolase, the enzyme that catabolizes platelet-activating factor

Platelet-activating factor (PAF) can exert profound inflammatory effects at very low concentrations. In plasma, PAF is hydrolyzed to lyso-PAF by acetylhydrolase, an enzyme that circulates bound to LDL. Previous studies suggest that oxygen radicals may act synergistically with PAF to potentiate tissue injury. However, mechanisms underlying this interaction have not been elucidated. In this study we investigated whether oxygen radicals may inactivate PAF acetylhydrolase. PAF acetylhydrolase activity was measured in human plasma and purified LDL before and after exposure to radicals (10-20 nmol/min per ml) generated by xanthine/xanthine oxidase. Oxygen radicals induced > 50% loss of PAF acetylhydrolase activity within 60 s and almost complete inactivation by 10 min. This phenomenon was irreversible and independent of oxidative modification of LDL. Inactivation occurred without changes in the affinity constant of the enzyme (Km was 17.9 microM under control conditions and 15.1 microM after exposure to oxygen radicals). Inactivation was prevented by the scavengers superoxide dismutase or dimethylthiourea or by the iron chelator deferoxamine. Thus, superoxide-mediated, iron-catalyzed formation of hydroxyl radicals can rapidly and irreversibly inactivate PAF acetylhydrolase. Since concomitant production of PAF and oxygen radicals can occur in various forms of tissue injury, inactivation of acetylhydrolase might represent one mechanism by which oxygen radicals may potentiate and prolong the proinflammatory effects of PAF.

[Heart function in chronic pressure overload caused by aortic stenosis: the role of collagen tissue]

The purpose of this study was to evaluate left ventricular (LV) structure-function interplay in aortic stenosis. LV structure was assessed from endomyocardial biopsies obtained in 27 patients with aortic stenosis. Total collagen volume fraction, orthogonal collagen fiber meshwork (cross-hatching) and endocardial fibrosis were determined by morphologic-morphometric evaluation. Control biopsy data were obtained from 6 pre-transplantation donor hearts whereas other 11 patients with normal cardiac function served as hemodynamic controls. LV biplane cineangiography and high-fidelity LV pressure measurement were carried out in all patients. Systolic function was assessed by LV biplane ejection fraction, diastolic function by time constant of relaxation, peak filling rates and passive elastic properties. Total collagen volume fraction (7.3 versus 1.6%, p < 0.01) as well as the degree of cross-hatching (1.7 versus 0.8 grade, p < 0.01) were significantly increased in patients with aortic stenosis with respect to controls. Endocardial fibrosis was present in 11/27 patients with aortic stenosis and in no patients of control group. In aortic stenosis in presence of increased total collagen volume fraction there were no changes in systolic and diastolic function, whereas in presence of changes in collagen architecture ejection fraction was depressed and passive elastic properties increased. In conclusion, in aortic stenosis, changes in collagen architecture are associated with altered systolic function and passive diastolic properties. The sole increase in total collagen volume fraction without a change in architecture leaves systolic and passive diastolic function unaltered. A prolongation of relaxation was present in aortic stenosis and appears to be mediated by muscle hypertrophy per se.

Rab5a is a common component of the apical and basolateral endocytic machinery in polarized epithelial cells

In nonpolarized cells, the small GTPase Rab5a is localized to the plasma membrane, clathrin-coated vesicles, and early endosomes. Rab5a is required for early endosome fusion in vitro and regulates transport between the plasma membrane and early endosomes, in vivo. In polarized epithelial cells endocytosis occurs from separate apical and basolateral plasma membrane domains. Internalized molecules are initially delivered to distinct apical or basolateral early endosomes. In vitro, apical early endosomes can readily fuse with one another but not with the basolateral endosomes and vice versa, thereby indicating that the apical and basolateral early endocytic pathways are controlled by distinct machineries. Here, we have investigated the localization and function of Rab5a in polarized epithelial cells. Confocal immunofluorescence microscopy on mouse kidney sections revealed association of the protein with the apical and basolateral plasma membrane domains and underlying structures. In polarized Madin-Darby canine kidney I cells, endogenous and overexpressed Rab5a have the same distribution. Moreover, overexpression of the protein causes a 2-fold increase in fluid-phase uptake from both domains of the cell, thus showing that Rab5a functions in apical and basolateral endocytosis. Our data indicate that the apical and basolateral endocytic machineries of epithelial cells share common regulatory components and that Rab5a per se is not sufficient to target endocytic vesicles to apical or basolateral early endosomes.

[The peroxidation of human glycosylated low-density lipoproteins is mediated by the superoxide radical: the protective effects of superoxide dismutase]

Low-density lipoproteins (LDL) oxidized by oxygen radicals are a potent atherogenic stimulus. Chemically modified LDL are internalized by macrophages via a specific cell surface receptor that was termed the scavenger receptor, and could induce foam cell transformation. Post-translational nonenzymatic glycosylation of low density lipoprotein (LDL) occurs in vivo in diabetic patients. Glycosylated LDL (glcLDL) is degraded by macrophages in part by the classic LDL-receptor and in part by the scavenger receptor. This latter mechanism may contribute to the formation of foam cells and acceleration of atherosclerosis in diabetes mellitus. Oxygen free radicals (ORs) could induce LDL peroxidation and subsequent formation of foam cells. Glycosylation may alter protein conformation. A free radical is any chemical species that has an unpaired electron. This property renders it highly chemically reactive. When a radical reacts with a non radical another free radical is generated. This characteristic enables radicals to trigger chain reactions. Oxygen radicals are: superoxide anion (.O2-), hydroxyl radical (.OH) and hydrogen peroxide (H2O2). Thus, the aim of this study was to investigate whether glcLDL are susceptible to peroxidative modification by ORs. GlcLDL was prepared incubating LDL with 40 mM glucose in sterile phosphate-buffer-EDTA 1 mM for 10 days at 37 degrees C. Control LDL (cLDL) was similarly incubated with buffer but without glucose. After this preparation both forms of LDL were oxidized by CuSO4 (15 microM for 20 hours at 37 degrees C) or by xanthine/xanthine oxidase (X:2 mM/XO: 100 mU for 20 hours at 37 degrees C).(ABSTRACT TRUNCATED AT 250 WORDS)

[Protection by blockers against human low density lipoprotein peroxidation induced by oxygen free radicals]

Previous studies in other systems have shown that beta-receptor blockers may effectively inhibit oxygen radical-induced lipid peroxidation. On the other hand, it has been recently proposed that oxygen free radicals can induce peroxidation of human low density lipoproteins (LDL), and that peroxidized LDL may be an atherogenic stimulus. Chemically modified LDL are internalized by macrophages via a specific cell surface receptor that was termed the scavenger receptor. This phenomenon may induce foam cells transformation in vivo. In the present study we investigated whether beta-blockers may reduce oxygen radical-mediated LDL peroxidation. Purified human LDL were oxidized by exposure to oxygen free radicals generated by xanthine (0.2 mM) and xanthine oxidase (100 mU) at 37 degrees C after a pre-incubation (30 min) in presence of different concentrations (from 1 to 30 microM) of acebutolol, metoprolol or propranolol, three agents with a different degree of lipophilicity. Peroxidation was measured from malonyldihaldehyde (MDA) production. Data have shown a significant percent inhibition of MDA formation in presence of beta-blockers (from 33 to 85%). Thus, beta-blockers reduced peroxidation of human LDL in vitro at clinically relevant concentrations. The order of potency appears to follow the degree of lipophilicity. These data suggest that, although beta-blockers are known to adversely effect lipid metabolism, these agents might on the other hand prevent atherogenesis via a mechanism of inhibition of LDL peroxidation in vivo and reduced foam cells formation.

Local effect of serotonin released during coronary angioplasty

BACKGROUND

Serotonin is released after the aggregation of platelets, a phenomenon that may occur after coronary angioplasty. We sought to determine whether serotonin is released into the coronary circulation during coronary angioplasty and to assess whether serotonin can affect coronary-artery tone during angioplasty.

METHODS

Blood samples were drawn from the ascending aorta and the coronary sinus of eight patients scheduled to undergo angioplasty of the left anterior descending or circumflex coronary artery. Samples were obtained before angioplasty and after each balloon dilation. The dimensions of arterial segments distal to the site of dilation were measured angiographically before angioplasty and 5 and 15 minutes after the last dilation in these eight patients and in seven similar patients; the latter group was treated with ketanserin, a serotonin2-receptor antagonist, before angioplasty.

RESULTS

Before the eight patients underwent angioplasty, their mean (+/- SE) plasma serotonin level in the aorta was 2.5 +/- 0.7 ng per milliliter and that in the coronary sinus was 2.3 +/- 0.6 ng per milliliter (P = 0.34). The serotonin level in plasma from the coronary sinus rose significantly, to 31.5 +/- 13.5, 17.6 +/- 5.3, and 29.1 +/- 8.1 ng per milliliter after the first, second, and third dilations, respectively (P = 0.014 for the comparison with preoperative levels). In contrast, the serotonin level in plasma from the ascending aorta did not change. The cross-sectional area of the coronary artery was significantly reduced 5 and 15 minutes after the last dilation (from a preoperative value of 3.7 +/- 0.5 mm2 to 2.7 +/- 0.4 mm2 15 minutes after the last dilation; P = 0.011). This vasoconstriction was significantly blunted in the seven patients who received ketanserin (from 3.7 +/- 0.5 mm2 before angioplasty to 3.9 +/- 0.4 mm2 after 15 minutes) (P = 0.017 for comparison with the eight patients who did not receive ketanserin).

CONCLUSIONS

Serotonin is released into the coronary circulation during angioplasty, and this vasoactive substance may contribute to the occurrence of vasoconstriction distal to the dilated site. The vasoconstriction is attenuated by ketanserin, a serotonin2-receptor antagonist.

A monoclonal antibody against rabbit tissue factor inhibits thrombus formation in stenotic injured rabbit carotid arteries

Tissue factor (TF) is a transmembrane protein that binds factor VII/VIIa, thus activating the extrinsic blood coagulation pathway. Since this pathway appears to be involved in the formation of intravascular thrombi, the anti-rabbit TF monoclonal antibody, AP-1, was produced and tested as an antithrombotic agent in a rabbit model of recurrent intravascular thrombosis. In this model, a plastic constrictor is positioned around the injured rabbit carotid arteries, and flow is monitored with a Doppler flow probe. This produces cyclic flow variation (CFV) in the carotid artery, which is caused by recurrent formation and dislodgment of thrombi at the site of the stenosis. After monitoring CFV pattern for 30 minutes, AP-1 was infused intravenously into nine rabbits at doses of 0.05 to 1.5 mg/kg body weight, and a control monoclonal antibody that does not react with rabbit TF was infused into four additional rabbits. In all rabbits receiving AP-1, CFV was abolished, and a steady normal blood flow was restored, indicating that thrombus formation had been blocked by AP-1. By contrast, in all rabbits that received the control monoclonal antibody, CFV continued unaltered. There was no change in the partial thromboplastin time and ex vivo platelet aggregation to several different agonists after infusion of AP-1, indicating an absence of systemic effects on the coagulation process. We conclude that activation of the extrinsic coagulation pathway has a key role in triggering intravascular thrombosis and that an anti-TF monoclonal antibody is an effective antithrombotic agent that could have therapeutic potential for humans.

IPO-V2: a prospective, multicenter, randomized, comparative clinical investigation of the effects of sulodexide in preventing cardiovascular accidents in the first year after acute myocardial infarction

OBJECTIVES

This study was conducted to assess the efficacy of sulodexide, a glycosaminoglycan compound with antithrombotic properties, in preventing death and thromboembolic events after acute myocardial infarction.

BACKGROUND

Antithrombotic therapy has been found to play an important role in the prevention of cardiovascular events and death after acute myocardial infarction. Glycosaminoglycan-containing compounds, including sulodexide, show profibrinolytic and antithrombotic properties that render them suitable for use in patients after infarction.

METHODS

A total of 3,986 patients who had recovered from acute myocardial infarction were randomized to receive either the standard therapy routinely administered at each study center, excluding antiplatelet and anticoagulant drugs (control group, 1,970 patients), or the standard therapy plus sulodexide (treated group, 2,016 patients). Between 7 and 10 days after the episode of acute myocardial infarction, sulodexide was administered as a single daily 600-lipoprotein-lipase-releasing unit (LRU) intramuscular injection for the 1st month, followed by oral capsules of 500 LRU twice daily. Patients were evaluated for > or = 12 months.

RESULTS

At the end of the study, 140 deaths (7.1%) were recorded in the control group and 97 (4.8%) in the sulodexide group (32% risk reduction, p = 0.0022, chi-square test). A total of 90 patients (4.6%) in the control group had a further infarction, compared with 66 (3.3%) in the sulodexide group (28% risk reduction, p = 0.035). Furthermore, a reduction in left ventricular thrombus formation (evaluated by echocardiography) was observed in the sulodexide group (n = 12; 0.6%), compared with values in the control group (n = 25; 1.3%) (53% risk reduction, p = 0.027). Sulodexide was well tolerated and devoid of significant adverse events. All significant results were confirmed by "actual treatment" analyses.

CONCLUSIONS

The study provides evidence that long-term therapy with sulodexide started early after an episode of acute myocardial infarction is associated with reductions in total mortality, rate of reinfarction and mural thrombus formation.

[Ablation of paroxysmal tachycardia in Wolff-Parkinson-White syndrome]

Surgical or catheter ablation of accessory pathways by means of high energy shock has been substantial associated with morbidity and mortality. On the contrary radiofrequency current, an alternative energy source for ablation, has a low incidence of complications and a very high success rate. Aim of this study was to relate about the results using catheter ablation of accessory pathways by radiofrequency current in our Electrophysiologic laboratory. Radiofrequency current (20-40 W) was delivered between a large-tip catheter electrode positioned against the mitral or tricuspid anulus and a standard adhesive electrosurgical dispersive pad applied to the left chest wall. When possible radiofrequency delivery was guided by catheter recordings of accessory pathway activation. Ablation was attempted in 181 patients with 191 accessory pathways. We obtained successful ablation of 187/191 accessory pathways and accessory pathway conduction was eliminated in 177/181 patients. During a mean follow-up of 14 +/- 10 months preexcitation returned in 7 patients (3.9%). All underwent a second successful ablation. In 1 patient, during the procedure, we observed a transient ischemic attack, with no complications. In accordance to other reports we conclude that radiofrequency ablation is highly effective in ablating accessory pathways, with low morbidity and no mortality.

[Anti-angina activity of potassium-channel activators]

Recently, a new class of drugs has been developed with unique properties with regard to cardiovascular pharmacology: K(+)-channel openers. The increased K+ efflux from smooth muscle cells induced by these drugs is accompanied by a reduced intracellular availability of free Ca++, which in turn induces vascular relaxation. This property is currently being exploited to achieve peripheral and coronary artery dilatation in patients with ischemic heart disease. Cromakalim, pinacidil, and nicorandil, are the most extensively investigated agents in this class. Nicorandil, in addition to its K(+)-channel opener property, also shows a nitrate-like activity on guanylate cyclase of vascular smooth muscle cells. Clinical trials demonstrate that chronic administration of nicorandil can significantly increase exercise tolerance in patients with coronary artery disease. In experimental studies, this drug has also shown protective effects against myocardial injury induced by ischemia and reperfusion, by mechanisms partly independent of its vasodilating properties. These results suggest that K(+)-channel openers may have a relevant place in the pharmacological treatment of patients with ischemic heart disease.

[A methodological approach to the transcatheter radiofrequency ablation of anomalous Kent-type pathways]

Aim of this study is to suggest our methodological approach for transcatheter ablation of Kent bundles by radiofrequency energy as to the potential ablation sites, the need in unipolar or bipolar recording mode, single catheter or multiple catheters mapping of anomalous pathways, the vascular approach for both left sited and right sited anomalous pathways, and finally the duration and power to supply. The recording of Kent potential and/or a Va-QRS interval > or = 0 ms have been considered significant predictors of success (respectively p < 0.001 and p < 0.05). The unipolar recording mode has been considered critical in the choice of ablation site in 47 (29.9%) patients. A 6-catheter approach for both diagnostic electrophysiologic studies and mapping allowed us to easily localize accessory pathways and to record either a probable or possible Kent potential in a high percentage of patients and to reduce the permanence of the ablation catheter in the left ventricle. By transaortic retrograde approach in ablating left sited anomalous pathways, we obtained a high success rate, while right sited accessory pathway were approached from the inferior vena cava. In right sited anomalous pathway we delivered radiofrequency energy for a longer time in order to avoid a relapse soon after the procedure. We performed ablation of 174/178 (97.7%) anomalous pathways in 165/169 (97.6%) patients. We observed a 3.8% relapse during a mean follow up of 13 +/- 9 months.

Reverse redistribution in resting thallium-201 myocardial scintigraphy in patients with coronary artery disease: relation to coronary anatomy and ventricular function

We studied 25 male patients, with coronary artery disease, mean age 56 +/- 8 yr. All underwent 201Tl rest-redistribution and resting 99mTc methoxyisobutyl isonitrile (MIBI) cardiac imaging. Regional 201Tl and MIBI uptake were quantitatively analyzed. Regional left ventricular wall motion (WM) was visually assessed on MIBI gated images using a three-point scale (0 = normal, 1 = hypokinetic, 2 = a/dyskinetic). Two patterns of reverse redistribution (RR) were identified: RR-A when 201Tl uptake was normal on rest images and abnormal on redistribution images, and RR-B when 201Tl uptake was abnormal on rest images and a significant decrease in uptake was observed on redistribution images. Of the total 375 myocardial segments analyzed, 229 were classified as normal (Nl), 40 as reversible defect (RD), 74 as irreversible defect (ID); 26 showed RR-A while 6 myocardial segments had RR-B. Myocardial segments with RR-A differed from NI in the degree of coronary artery stenosis (81% +/- 33% versus 57% +/- 39%, respectively, p < 0.05), in WM score (1.1 +/- 0.7 versus 0.5 +/- 0.6, respectively, p < 0.01), and in MIBI uptake (81% +/- 10% versus 92% +/- 9%, respectively, p < 0.0001). Moreover, the percent of myocardial segments supplied by a totally occluded coronary artery was significantly higher (p < 0.05) in myocardial segments with RR-A (46%) than in NI (22%). Segments with RR-B did not show any significant difference either from RD and ID. These results suggest that myocardial segments with RR-A on resting 201Tl images have impaired function and are supplied by severely stenosed coronary arteries and should not be considered normal.

Evidence that mitochondrial respiration is a source of potentially toxic oxygen free radicals in intact rabbit hearts subjected to ischemia and reflow

Previous in vitro studies have shown that isolated mitochondria can generate oxygen radicals. However, whether a similar phenomenon can also occur in intact organs is unknown. In the present study, we tested the hypothesis that resumption of mitochondrial respiration upon reperfusion might be a mechanism of oxygen radical formation in postischemic hearts, and that treatment with inhibitors of mitochondrial respiration might prevent this phenomenon. Three groups of Langendorff-perfused rabbit hearts were subjected to 30 min of global ischemia at 37 degrees C, followed by reflow. Throughout ischemia and early reperfusion the hearts received, respectively: (a) 5 mM KCl (controls), (b) 5 mM sodium amobarbital (Amytal, which blocks mitochondrial respiration at Site I, at the level of NADH dehydrogenase), and (c) 5 mM potassium cyanide (to block mitochondrial respiration distally, at the level of cytochrome c oxidase). The hearts were then processed to directly evaluate oxygen radical generation by electron paramagnetic resonance spectroscopy, or to measure oxygen radical-induced membrane lipid peroxidation by malonyl dialdehyde (MDA) content of subcellular fractions. Severity of ischemia, as assessed by 31P-nuclear magnetic resonance measurements of cardiac ATP, phosphocreatine, and pH, was similar in all groups. Oxygen-centered free radical concentration averaged 3.84 +/- 0.54 microM in reperfused control hearts, and it was significantly reduced by Amytal treatment (1.98 +/- 0.26; p < 0.05), but not by KCN (2.58 +/- 0.96 microM; p = not significant (NS)), consistent with oxygen radicals being formed in the mitochondrial respiratory chain at Site I. Membrane lipid peroxidation of reperfused hearts was also reduced by treatment with Amytal, but not with KCN. MDA content of the mitochondrial fraction averaged 0.75 +/- 0.06 nM/mg protein in controls, 0.72 +/- 0.06 in KCN-treated hearts, and 0.54 +/- 0.05 in Amytal-treated hearts (p < 0.05 versus both groups). Similarly, MDA content of lysosomal membrane fraction was 0.64 +/- 0.09 nM/mg protein in controls, 0.79 +/- 0.15 in KCN-treated hearts, and 0.43 +/- 0.06 in Amytal-treated hearts (p < 0.05 versus both groups). Since the effects of Amytal are known to be reversible, in a second series of experiments we investigated whether transient mitochondrial inhibition during the initial 10 min of reperfusion was also associated with beneficial effects on subsequent recovery of cardiac function after wash-out of the drug. At the end of the experiment, recovery of left ventricular end-diastolic and of developed pressure was significantly greater in those hearts that had been treated with Amytal during ischemia and early reflow, as compared to untreated hearts.(ABSTRACT TRUNCATED AT 400 WORDS)

Short-term and long-term role of platelet activating factor as a mediator of in vivo platelet aggregation

BACKGROUND

Platelet activating factor (PAF) is a phospholipid released upon stimulation by a variety of cells and has been implicated in several pathophysiological events such as asthma and inflammatory diseases. However, although the ability to aggregate platelets in vitro was the first biological activity ascribed to PAF, its role in contributing to the in vivo formation of arterial thrombi has not been thoroughly clarified.

METHODS AND RESULTS

Intravascular platelet aggregation was initiated in two different animal models of arterial stenosis and endothelial injury. An external constrictor was positioned around rabbit carotid arteries and canine coronary arteries. After placement of the constrictor, a typical pattern of flow developed in the stenotic vessels. This pattern of flow, characterized by progressive reductions of carotid or coronary blood flow followed by spontaneous or induced restorations of flow (cyclic flow variations, CFVs), is related to recurrent platelet aggregation at the site of the stenosis followed by dislodgment of the thrombus. After observing CFVs for 30 minutes, BN52021 (up to 1.2 mg/kg), a potent and selective PAF antagonist, was given intravenously to rabbits (n = 12) and dogs (n = 10). BN52021 completely inhibited CFVs in 10 of 12 rabbits, whereas it was relatively ineffective in abolishing CFVs in dogs (only 2 of 10 animals inhibited). This different effect of BN52021 was not explained by too small a dose of the drug to achieve a complete blockade of PAF receptors in dogs, since ex vivo platelet aggregation was completely inhibited in both rabbits and dogs in response to exogenous PAF at concentrations up to 10(-5) mol/L. In a second group of 10 dogs, the hypothesis that PAF may become an important mediator of CFVs in dogs only several hours after endothelial injury was tested. After 30 minutes of baseline CFVs, these animals received a bolus of BN52021 up to 1.2 mg/kg. After this treatment, CFVs were completely abolished in 2 of 10 animals. The remaining 8 dogs were followed for an additional 8-hour period, at the end of which a second bolus of BN52021 was given. At this time, BN52021 was effective, as CFVs were abolished in 6 of 8 animals. These effects of BN52021 at 8 hours were not the consequence of a cumulative dose of the compound, since ex vivo platelet aggregation in response to PAF returned to baseline values immediately before administering the second dose. To identify possible sources of PAF other than aggregating platelets at the site of arterial stenosis, dogs in a third group were killed after 30 minutes (n = 7) and after 8 hours (n = 8) of CFVs. Histological sections of the stenotic coronary artery showed a marked leukocyte infiltration in these arterial segments after 8 hours of CFVs, whereas sections from dogs killed after 30 minutes showed only moderate or no infiltration.

CONCLUSIONS

These data demonstrate that PAF plays an important role as a mediator of platelet aggregation in vivo in rabbits and dogs. In the canine model, PAF appears to become more important after leukocyte infiltration of the arterial wall, as it may contribute to initiating enough platelet activation to lead to cyclic flow variations at sites of arterial stenosis and endothelial injury. Data from the present study suggest that PAF antagonists may be used as antiplatelet agents.

[The usefulness of bioimpedance in patient monitoring in an intensive-therapy heart-surgery unit: a comparison with thermodilution]

Haemodynamic monitoring of intensive care unit (ICU) patients can be carried out by thermodilution system. This method is invasive, does not give a continuous monitoring and complications can occur. Thoracic electrical bioimpedance (TB), a non invasive, fast, easily repeatable method, is able to measure some important haemodynamic parameters: end diastolic volume (EDV), stroke volume, cardiac output (CO), ejection fraction (EF), some contractility indexes, systemic vascular resistances (SVR) and cardiac work. The aim of the present study is to compare CO and SVR obtained by thermodilution with the same indexes obtained by TB. Therefore, 20 ICU patients (12 males and 8 females, mean age 54 +/- 11 years) were studied. Out of them, 16 had been submitted to cardiac surgery in the previous 7 days and 4 were waiting for cardiac surgery. The patients were divided in 2 groups: Group A (N 4) included patients with valvular malfunction and/or cardiac arrhythmias and Group B (N 16) included patients with normal valvular function and sinus rhythm. CO obtained by TB was well related with the one obtained by invasive (INV; r = 0.878; p < 0.001). The mean value of difference of the 2 methods was 12.29 +/- 11.83 for the whole group of 20 patients but it was 26.07 +/- 14.16 in the Group A and 8.84 +/- 8.09 in the Group B confirming the less reliability of the method in patients with abnormal valvular function or in the presence of cardiac arrhythmias. As a consequence, SVR obtained by TB and INV resulted well related (r = 0.752; p < 0.001). The mean value of differences was 11.14 +/- 9.01 in the group of 20 patients and particularly 19.55 +/- 10.87 in the Group A and 9.04 +/- 7.07 in the Group B. In a subgroup of 9 patients, CO was measured at successive times (0, 30, 60, 90 min) by both TB and INV; when comparing the 2 CO values a significant correlation was observed. In conclusion, TB represents a valid method in haemodynamic monitoring of the ICU patients.

The in vivo antiplatelet effects of thromboxane A2 synthase inhibitors are potentiated by simultaneous thromboxane A2/prostaglandin H2 receptor blockade

The aim of the present study was twofold: 1) to assess whether inhibition of thromboxane A2 (TxA2) synthase exerts more potent antiplatelet effects when applied concomitantly with TxA2 and prostaglandin (PG)H2 receptor blockade and 2) whether these effects are mediated through redirection of PG endoperoxides toward the synthesis of antiplatelet PGs, such as PGI2 and PGE2. Thus, cyclic flow variations (CFVs), due to recurrent platelet aggregation, were initiated in the stenotic, endothelially injured carotid arteries of 39 rabbits. After 30 min of CFVs, the animals received: 1) SQ29548 (up to 0.6 mg/kg bolus + 0.2 mg kg-1 hr-1, n = 13), a TxA2/PGH2 receptor antagonist; 2) dazoxiben (up to 15 mg/kg bolus + 5 mg kg-1 hr-1, n = 13), a TxA2 synthase inhibitor and 3) picotamide (up to 20 mg/kg bolus + 20 mg kg-1 hr-1, n = 13), a drug with simultaneous TxA2 synthase and receptor blocking properties. CFVs were abolished in 6, 7, and 12 animals treated with SQ29548, dazoxiben, and picotamide, respectively (P < .01 for picotamide versus SQ29548 and dazoxiben). The animals in which CFVs were not abolished by SQ29548 or dazoxiben received the other drug at the same dose. CFVs were abolished by dazoxiben in five of seven rabbits that initially did not respond to SQ29548 and by SQ29548 in five of six animals that did not respond to dazoxiben. All animals that responded to the combination of SQ29548 and dazoxiben, as well as those that responded to picotamide, received increasing intravenous infusions of epinephrine to restore CFVs.(ABSTRACT TRUNCATED AT 250 WORDS)

[The effects of the selective intracoronary administration of nifedipine on left ventricular filling anomalies during coronary angioplasty]

Eighteen patients with isolated stenosis of left anterior descending artery, were randomly given 0.2 mg of nifedipine (Group II) or its solvent (Group I) via balloon catheter positioned across the lesion immediately prior balloon occlusion. Peak velocity of early (E peak) and late (A peak) filling, velocity flow integral at early (E area) and late (A area) filling and their ratios (by echo-Doppler) and heart rate, mean aortic and wedge (W) pressures were measured at baseline, 15 and 30 s during balloon occlusion and 10 min after balloon deflation. In Group I we observed a significant decrease in either E peak at 15 and 30 s (-24.7%, -29.3% respectively) and E area (-32.8%, -40.0% respectively) with a non significant increase in both A peak and A area. Accordingly, either E/A peak ratio and E/A area ratio decreased significantly. In Group II no significant changes were observed in the echo-Doppler parameters of left ventricular filling. Wedge pressure also significantly increased in Group I at 15 and 30 s (68.7% and 97.9% respectively), while a significant increase in Group II occurred only at 30 s (32.5%). Heart rate significantly increased only in Group I at 15 and 30 s (10.3% and 11% respectively), while aortic pressure remained unchanged in both groups. Thus, nifedipine given intracoronary in the post-stenotic area just before balloon occlusion prevents left ventricular filling dynamic alteration by preserving early filling.

Rest-injected thallium-201 redistribution and resting technetium-99m methoxyisobutylisonitrile uptake in coronary artery disease: relation to the severity of coronary artery stenosis

To compare rest-injected thallium-201 (Tl) redistribution and resting technetium-99m methoxyisobutylisonitrile (99mTc-MIBI) myocardial uptake in chronic coronary artery disease (CAD), 15 patients with angiographically proven CAD and left ventricular (LV) dysfunction (ejection fraction 34% +/- 9%) were studied. All patients underwent rest-redistribution Tl and resting 99mTc-MIBI cardiac imaging. Gated 99mTc-MIBI images were also acquired to assess regional LV wall motion (WM). Myocardial segments (n = 225) were divided into three groups on the basis of the degree of coronary artery stenosis: group 1 (total occlusion, n = 82), group 2 (50%-99% of stenosis, n = 84) and group 3 (< 50% of stenosis, n = 59). WM was significantly worse in groups 1 and 2 compared to group 3 (P < 0.001), but no difference was observed between groups 1 and 2. Tl and 99mTc-MIBI uptake were significantly lower in groups 1 and 2 compared to group 3 (P < 0.001), and in group 1 compared to group 2 (P < 0.001). When Tl and 99mTc-MIBI uptake were directly compared. Tl uptake was higher than 99mTc-MIBI uptake in group 1 (P < 0.001), while no significant difference was observed in groups 2 and 3. Thus, both rest-injected Tl redistribution and resting 99mTc-MIBI uptake reflected the severity of coronary artery stenosis in CAD. However, in myocardial segments with total coronary occlusion Tl uptake was significantly higher than 99mTc-MIBI uptake.(ABSTRACT TRUNCATED AT 250 WORDS)

Hibernating and stunned myocardium

The term "hibernating" myocardium has been introduced to indicate the presence of regional asynergy due to persistent hypoperfusion, which can be reversed after revascularization. The mechanisms underlying the prolonged functional adaptation of myocardial cells to hypoperfusion are still not clear, although preliminary experimental data indicate that a reduced availability of intracellular Ca++ may play an important role. The identification of hibernating myocardium may have therapeutic implications, since it has been demonstrated that the revascularization of hibernating myocardial territories may lead to regional and global improvement of systolic left ventricular function. The noninvasive identification of hibernating myocardium can be accomplished by positron emission tomography, which demonstrates the presence of preserved metabolic activity in hibernating myocardial territories. However, exercise 201thallium scintigraphy, using the reinjection technique, with a quantitative regional analysis of 201thallium uptake, has also been reported to provide information comparable to that obtained by positron emission tomography. "Stunning" of the myocardium indicates a condition of transient impaired regional systolic function, following an episode of ischemia. The mechanisms determining the slow recovery of function after ischemia are still not completely understood. Experimental data suggest in this case a reduced Ca++ affinity of the myofibrils and a reduced maximal calcium-activated force.

Effects of induced asynchrony on left ventricular diastolic function in patients with coronary artery disease

OBJECTIVES

This study was designed to increase asynchrony with sequential atrioventricular (AV) pacing and to study its effects on left ventricular isovolumetric relaxation, rapid filling and stiffness.

BACKGROUND

Left ventricular nonuniformity is a major determinant of diastolic function.

METHODS

Thirteen patients with coronary artery disease were studied by simultaneous equilibrium radionuclide angiography and cardiac catheterization during atrial and AV pacing. Ejection fraction and peak filling rate were measured by radionuclide angiography. Regional analysis was obtained by analyzing time-activity curves of four left ventricular sectors; systolic and diastolic asynchrony were evaluated as the coefficient of variation of time to end-systole and, respectively, time to peak filling rate in the four sectors. Cardiac index and left ventricular pressure were measured with high fidelity catheters at cardiac catheterization. The time constant of isovolumetric relaxation was derived from left ventricular pressure. Pressure-volume loops were assembled and constants of chamber stiffness were computed.

RESULTS

Atrioventricular pacing led to a decrease in cardiac index (3.7 +/- 0.9 to 3.3 +/- 0.8 liters/min per m2, p = 0.01) and peak filling rate (352 +/- 125 to 287 +/- 141 ml/s, p = 0.03; 2.4 +/- 0.8 to 2.0 +/- 0.8 end-diastolic counts/s, p = 0.02; 4 +/- 1.3 to 3.2 +/- 1.0 stroke counts/s, p = 0.008). The time constant of isovolumetric relaxation increased (57 +/- 10 to 64 +/- 12 ms, p = 0.04) and the global diastolic pressure-volume relation shifted upward.

CONCLUSIONS

Atrioventricular pacing induces left ventricular asynchrony, which is associated with a slower rate of isovolumetric relaxation. The isovolumetric relaxation lasts after the filling phase has begun, thereby reducing the rate of rapid filling.

Evaluation of myocardial perfusion and function by technetium-99m methoxy isobutyl isonitrile before and after percutaneous transluminal coronary angioplasty. Preliminary results

Myocardial perfusion and function were evaluated with Tc-99m MIBI myocardial scintigraphy before and after percutaneous angioplasty in six patients. In addition to conventional stress-rest images (3 projections: 45 degrees left anterior oblique, anterior, and left lateral), gated images were obtained at rest and during stress before and after angioplasty. Improvement in myocardial perfusion after angioplasty was demonstrated in all patients. The increase from rest to stress of radionuclide fractional shortening (an index of global left ventricular function computed on gated images) was greater after angioplasty than before (9% +/- 7% versus--0.5% +/- 8%, respectively, p < 0.05). Systolic wall thickening (an index of regional left ventricular function) showed a significantly greater rest-to-stress increase after angioplasty than before it in the regions supplied by treated vessels. Thus, Tc-99m MIBI myocardial scintigraphy is capable of evaluating myocardial perfusion and function.

Effects of calcium antagonists on left ventricular structure and function

Effects of calcium antagonists on left ventricular hypertrophy: The goals of antihypertensive treatment are to lower systemic blood pressure and to reverse left ventricular hypertrophy. A number of different drugs can induce a decrease in left ventricular mass, some of which are calcium antagonists. In particular, verapamil, diltiazem and a number of dihydropyridines (nifedipine, isradipine, lacidipine) have proved effective in this respect. Left ventricular systolic function: Left ventricular systolic function is often normal at rest in patients with hypertension, but is quite commonly abnormal during exercise. Calcium antagonists therefore do not affect resting systolic function in this category of hypertensive patients. In contrast, in hypertensive patients with heart failure the administration of dihydropyridines improves systolic performance. Left ventricular diastolic function: Isovolumic relaxation and rapid filling are often impaired in patients with hypertension, with or without left ventricular hypertrophy. Verapamil is effective in abolishing this diastolic dysfunction when given intravenously; in contrast, medium-term therapy with calcium antagonists such as diltiazem or dihydropyridines does not improve left ventricular filling properties. However, when antihypertensive therapy achieves a reduction in left ventricular mass, a consistent improvement in diastolic properties occurs.

Comparison of left ventricular function in insulin- and non-insulin-dependent diabetes mellitus

Diabetes mellitus has been reported to have controversial effects on left ventricular (LV) function in patients with no evidence of coronary artery disease. In this study, LV function at rest was evaluated in 2 groups of diabetic patients, with insulin-dependent (IDD; n = 16) and non-insulin-dependent (NIDD; n = 23) diabetes mellitus, with no evidence of coronary artery disease. All patients underwent an electrocardiographic stress test, and first-pass and equilibrium radionuclide angiography at rest and during supine exercise. Data in each group of diabetic patients were compared with those obtained from age- and sex-matched normal subjects. In both groups of diabetic patients plasma catecholamine levels were significantly greater than in control subjects. Ejection fraction at rest and during exercise did not differ between each group of diabetic patients and their respective control group. In patients with IDD, peak ejection rate (4 +/- 1 end-diastolic count/s) was significantly greater than in control subjects (2.6 +/- 0.1 end-diastolic count/s; p < 0.001); similarly, peak filling rate (4.3 +/- 1.0 end-diastolic count/s) was significantly greater than in controls (3.0 +/- 0.2 end-diastolic count/s; p < 0.001). Cardiac output and systemic vascular resistances did not differ between patients with IDD and control subjects. In contrast, patients with NIDD had significantly reduced cardiac output compared with that of control subjects (5.7 +/- 0.2 vs 5.9 +/- 0.2 liter/min; p < 0.01), and increased systemic vascular resistances (1,422 +/- 137 vs 1,314 +/- 68 dynes.s.cm-5; p < 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)

Platelet aggregability in patients with a VVI pacemaker

Several studies have suggested an increased incidence of thromboembolic events in patients with VVI pacemaker (VVI patients); furthermore, other authors have demonstrated that a treatment with anticoagulants or antiplatelet drugs may be effective in reducing thromboembolic events, thus suggesting an increased formation of platelet thrombi in these patients. In this respect, platelet aggregability was investigated in ten VVI patients and ten age- and sex-matched subjects. beta-thromboglobulin (beta-Tg) and platelet factor 4 (PF4) plasma levels were determined as well as platelet aggregation induced by ADP, collagen, epinephrine, and arachidonic acid. Plasma beta-Tg levels were increased in the patient group (86 +/- 24 vs 24 +/- 13 ng/mL; P < 0.001) in presence of normal PF4 values (14 +/- 11 vs 13 +/- 6 ng/mL; NS). Aggregation curves showed abnormal values of maximal amplitude, slope, and lag time. In particular, maximal amplitude was significantly higher in VVI patients as compared with controls (ADP P < 0.01, collagen P < 0.001, adrenaline P < 0.01, arachidonic acid P < 0.05). These findings strongly suggest an increase of platelet activity in VVI patients.

Endogenous prostaglandin endoperoxides may alter infarct size in the presence of thromboxane synthase inhibition: studies in a rabbit model of coronary artery occlusion-reperfusion

OBJECTIVES

The aim of this study was to assess whether prostaglandin endoperoxides, which continue to be formed in the setting of thromboxane A2 synthase inhibition, might influence the fate of ischemic myocardium in a model of coronary occlusion and reperfusion.

BACKGROUND

It was recently demonstrated that thromboxane A2 synthase inhibitors reduce ischemic myocardial injury through a redirection of prostaglandin (PG) endoperoxides toward the synthesis of "cardioprotective" prostaglandins, such as PGI2, PGE2 and PGD2. However, part of these prostaglandin endoperoxides may also stimulate a receptor, shared with thromboxane A2, mediating platelet aggregation and vasoconstriction.

METHODS

New Zealand White rabbits were subjected to 30 min of coronary occlusion, followed by 5.5 h of reperfusion. Fifteen minutes before reperfusion, the animals were randomized to receive 1) saline solution (control animals, n = 8); 2) SQ 29548, a potent and selective thromboxane A2/PGH2 receptor antagonist (n = 8); 3) dazoxiben, a selective thromboxane A2 synthase inhibitor (n = 8); 4) R 68070 (Ridogrel), a drug with dual thromboxane A2 synthase-inhibiting and thromboxane A2/PGH2 receptor-blocking properties (n = 8); or 5) aspirin + R 68070 (n = 8).

RESULTS

Dazoxiben and R 68070, but not SQ 29548, significantly reduced thromboxane B2 formation and increased plasma levels of 6-keto-PGF1 alpha, PGE2 and PGF2 alpha. Ex vivo platelet aggregation induced by U46619 (a thromboxane A2 mimetic) was inhibited by SQ 29548 and R 68070 but not by dazoxiben. In control animals, infarct size determined at the end of the experiment by triphenyltetrazolium chloride staining averaged 57.7 +/- 3.2% of the area at risk of infarction. The administration of SQ 29548 did not significantly reduce infarct size compared with that in control animals, whereas dazoxiben and R 68070 significantly reduced infarct size to 36.7 +/- 2.8% and 16.6 +/- 3.6% of area at risk of infarction, respectively (p < 0.001 vs. control values). In rabbits treated with R 68070, infarct size was also significantly smaller than that of dazoxiben-treated rabbits (p < 0.01). This protective effect of R 68070 was completely abolished when the drug was administered with aspirin, infarct size in this group averaging 59.7 +/- 1.6% (p = NS vs. control values). No differences in regional myocardial blood flow, systemic blood pressure, heart rate or extent of area at risk were observed among groups.

CONCLUSIONS

Thus, prostaglandin endoperoxides play an important role in modulating the cardioprotective effects of thromboxane A2 synthase inhibitors. The simultaneous inhibition of thromboxane A2 synthase and blockade of thromboxane A2/PGH2 receptors by R 68070 identify a pharmacologic interaction of potential therapeutic importance.

[Coronary vasoconstriction induced by digoxin in normal subjects and in patients with coronary atherosclerosis]

This study evaluated the effects of digoxin infusion (0.014 mg/kg in 10 min i.v.) on large coronary arteries measured by quantitative digital angiography. Twenty-two patients (aged 47 +/- 12), divided in 3 groups were studied. The effects of digoxin infusion (after 10 and 20 min) and sublingual administration of isosorbide dinitrate were investigated in Group I (patients with angiographically normal coronary arteries, n = 9) and in Group II (patients with atherosclerotic coronary arteries, n = 8). In Group III (n = 5) to determine whether or not the effects of digoxin were mediated by activation of alpha-adrenergic receptors, coronary angiographies were performed after alpha-adrenoceptor blockade (phentolamine 0.11 mg/kg, i.v.). In Group I, 10 min after the end of digoxin infusion, cross-sectional area decreased from 7.7 +/- 4.1 mm2 to 6.0 +/- 2.2 mm2, and after 20 min to 5.6 +/- 2.6 mm2 (p < 0.05). Isosorbide dinitrate reverted digoxin-induced vasoconstriction as cross-sectional area increased to 8.5 +/- 3.4 mm2 (NS versus baseline). By 20 min after digoxin infusion heart rate was significantly reduced from 79 +/- 16 to 74 +/- 13 b/min (p < 0.01). Peripheral vascular resistances increased significantly 10 min after digoxin infusion (from 1396 +/- 693 to 1693 +/- 984 dyne*s*cm-5, p < 0.05), whereas cardiac output did not change. In Group II, minimal stenosis diameter decreased significantly 20 min after digoxin infusion from 1.6 +/- 0.5 mm to 1.4 +/- 0.5 mm (p < 0.05). Again, isosorbide dinitrate reverted digoxin-induced vasoconstriction as minimal stenosis diameter increased (NS versus control).(ABSTRACT TRUNCATED AT 250 WORDS)

Clinical experience with the transvenous Medtronic Pacer Cardioverter Defibrillator (PCD) System

We review our experience with the transvenous Medtronic Pacer Cardioverter Defibrillator System (Model 7217B), a multifunction implantable pacer defibrillator combined with a transvenous lead system (Transvene). From April 1991 to October 1992, we implanted this device in 19 consecutive patients (11 men and 8 women; average age, 56.5 years). Nine patients (47.4%), 5 with coronary artery disease and 4 with dilated cardiomyopathy, had an ejection fraction of < 30%. The average operative time was 129 minutes. In 18 patients (94.7%), the transvenous lead system provided effective sensing, pacing, and defibrillation during intraoperative testing. In each of these cases, the defibrillation threshold was less than 18 J. In 1 patient (5.3%), it was necessary to switch to epicardial leads, which were implanted through a left thoracotomy. All patients were extubated in the recovery room. The average hospital stay was 8 days. There was no early mortality or morbidity. During a maximum follow-up period of 17 months (mean, 9.2 months), no sudden death occurred. The implantable system terminated 245 ventricular tachycardia episodes in 14 patients (73.7%) and 82 ventricular fibrillation episodes in 13 patients (68.4%). Two hundred eleven (86.1%) of the ventricular tachycardia episodes were resolved by antitachycardia pacing alone. In 2 patients (10.5%), the caval electrode became dislocated; repositioning of the electrode was followed by repeat defibrillation threshold evaluation. Our experience shows that the transvenous Medtronic Pacer Cardioverter Defibrillator System provides safe, effective treatment of ventricular tachyarrhythmias. Because the perioperative mortality and morbidity are extremely low, use of this device may be particularly beneficial in patients with a high operative risk. Moreover, the lower number of unpleasant therapeutic shocks should increase patient a acceptance of the device.

The effects of calcium channel antagonist treatment and oxygen radical scavenging on infarct size and the no-reflow phenomenon in reperfused hearts

Calcium antagonists reduce ischemic injury, and anti-free-radical interventions may reduce reperfusion injury. However, the effects of treatment with both interventions have never been investigated. In the present study, anesthetized rabbits underwent 30 minutes of coronary artery ligation, which was followed by 5.5 hours of reflow. Eight animals in each group received: (1) the calcium antagonist gallopamil during ischemia, (2) the oxygen radical scavenger superoxide dismutase during reperfusion, (3) combined treatment with gallopamil and superoxide dismutase, and (4) saline solution. All groups were similar with respect to collateral flow during ischemia and extent of risk region. Infarct size averaged 60.2% +/- 5.5% of risk region in controls and was significantly smaller (p < 0.001) in rabbits that were treated with either gallopamil (28.1% +/- 3.4%) of superoxide dismutase (29.3% +/- 3.2%). Little further reduction in infarct size was observed with combination therapy (22.9% +/- 3.2% of risk region; p = NS). Superoxide dismutase had no effects on hemodynamics, whereas gallopamil significantly reduced heart rate, mean arterial pressure, and rate-pressure product. However, the reduction in infarct size that was observed in gallopamil-treated rabbits significantly exceeded the expected value in this group after corrections were made for changes in these determinants of ischemic injury. Therefore we investigated whether other factors may have contributed to the beneficial effects of gallopamil. In vitro the drug had no oxygen radical scavenging activity, nor did it exert antioxidant effects. In addition, gallopamil did not affect neutrophil function. In conclusion, in this acute model myocardial cell necrosis was significantly reduced either by administration of a calcium antagonist during ischemia or by removing oxygen radicals during reperfusion. However, superoxide dismutase administration did not further reduce infarct size when given to animals that had been treated with gallopamil. Since gallopamil has no direct effect on several mechanisms of reperfusion injury, these data suggest that calcium antagonists, by decreasing myocardial oxygen demand during ischemia, may indirectly reduce oxygen radical damage during subsequent reperfusion.

Angiotensin II directly stimulates release of atrial natriuretic factor in isolated rabbit hearts

BACKGROUND

Previous studies have shown that infusion of angiotensin II (Ang II) increases plasma concentrations of atrial natriuretic factor (ANF) in vivo. This phenomenon has been considered secondary to the effects of Ang II on cardiac and systemic hemodynamics. The present study was designed to assess whether Ang II may exert a direct stimulatory effect on ANF release from the heart independent of changes in hemodynamics.

METHODS AND RESULTS

Isolated rabbit hearts were perfused in the Langendorff mode. Heart rate, coronary flow, and atrial and left ventricular (LV) volumes were kept constant. After stabilization, Ang II was infused intracoronary at increasing doses (10(-11) to 10(-8) M) in nine hearts and at a single dose of 10(-10) M in 10 hearts. Each infusion lasted for 5 minutes and was followed by a 10-minute washout period. Four hearts received vehicle alone for 80 minutes. Ang II induced a dose-dependent increase in coronary perfusion pressure and in LV developed pressure. ANF release, measured by radioimmunoassay on the extracts of the cardiac effluent, also increased during Ang II infusion and returned to the basal values during the 10-minute washout period. In the control group, coronary perfusion pressure, LV developed pressure, and LV end-diastolic pressure did not change appreciably over the observation period, whereas ANF release progressively decreased during perfusion.

CONCLUSIONS

Ang II can directly stimulate cardiac release of ANF in isolated rabbit hearts independently of changes in hemodynamics.

Endothelium-derived relaxing factor modulates platelet aggregation in an in vivo model of recurrent platelet activation

It has been shown that endothelium-derived relaxing factor (EDRF) may inhibit platelet aggregation in vitro through activation of platelet-soluble guanylate cyclase. To assess whether EDRF may also affect platelet function in vivo, intravascular platelet aggregation was initiated by placing an external constrictor around endothelially injured rabbit carotid arteries. Carotid blood flow velocity was measured continuously by a Doppler flow probe placed proximal to the constrictor. After placement of the constrictor, cyclic flow reductions (CFRs), due to recurrent platelet aggregation, developed at the site of the stenosis. After CFRs were observed for 30 minutes, a solution of authentic nitric oxide (NO, n = 10) was infused into the carotid artery via a small catheter placed proximally to the stenosis. Before infusion of NO, CFR frequency averaged 18.3 +/- 2.9 cycles per hour, and CFR severity (lowest carotid blood flow as percentage of baseline values) was 6 +/- 1%. NO completely inhibited CFRs in all animals, as shown by the normal and constant pattern of carotid blood flow (CFR frequency, 0 cycles per hour, p < 0.001; carotid blood flow, 92 +/- 5%, p = NS versus baseline). These effects were transient; CFRs were restored spontaneously within 10 minutes after cessation of NO infusion. After CFRs returned, S-nitroso-cysteine (S-NO-cys), a proposed form of EDRF, was infused into the carotid artery. S-NO-cys also abolished CFRs in all animals but at a significantly lower dose than NO (0.3 +/- 0.1 versus 12 +/- 4 nmol/min). The role of endogenously released EDRF in modulating in vivo platelet function was then tested in additional experiments. In 10 animals, endogenous release of EDRF was stimulated by infusing acetylcholine into the aortic root during CFRs. Infusion of acetylcholine was also associated with a complete inhibition of CFRs, similar to that observed during exogenous infusion of NO or S-NO-cys. These antithrombotic effects of acetylcholine were completely lost when EDRF synthesis was prevented by administration of the L-arginine analogue NG-monomethyl L-arginine (L-NMMA). Furthermore, in six additional rabbits the basal release of EDRF was blocked by L-NMMA after CFRs had been previously abolished with aspirin or the combination of aspirin and ketanserin, a serotonin S2 receptor antagonist. L-NMMA caused restoration of CFRs in all animals, indicating that even the basal release of EDRF is important in modulating platelet reactivity in vivo. Taken together, the data of the present study demonstrate that endogenous EDRF might importantly contribute to the modulation of platelet function in vivo.

Influence of atenolol on the relationship between heart rate and QT interval in patients with exercise-induced myocardial ischemia

The aim of this study was to analyze the relationship between heart rate and QT interval (HR-QT) during exercise in control subjects (Group A) and in patients with coronary artery disease (CAD) with effort angina and without previous myocardial infarction (MI) (Group B). The diagnosis of CAD was confirmed by coronarographic examination. The correlation HR-QT was significant (p < 0.001) in both groups on effort and at recovery. The analysis of the regression HR-QT was carried out separately, both on effort in upright position and at rest in supine position, to avoid the influence of posture on QT length. During effort, the regression line showed lower slope and intercept values in Group B (p < 0.001) than those for Group A. A similar behavior was also observed at rest. Thus, at the highest heart rate, where ECG signs of ischemia (ST depression > 1 mm) frequently occurred, a longer QT interval was present in Group B. Moreover, in Group B, the QT interval in the presence of ECG signs of ischemia was significantly longer (p < 0.01) than in Group A at comparable heart rates both on effort and at rest, thereby confirming the result obtained by comparing both regression lines. The same effort protocol was repeated in Group B patients after acute administration of atenolol 100 mg per os. After atenolol administration, the analysis of the regression HR-QT in Group B clearly showed a shorter QT interval than that obtained in washout period during the baseline test at the highest heart rates where the ECG frequently showed signs of ischemia.(ABSTRACT TRUNCATED AT 250 WORDS)