Effect of cocaine on left ventricular function. Relation to increased wall stress and persistence after treatment

BACKGROUND

To determine whether alterations in left ventricular (LV) function after a cocaine infusion are due to reduced myocardial contractility or changes in loading conditions, we examined LV function in 30 morphine-sedated, closed-chest dogs. We also wanted to determine the time course of the effects of cocaine on LV function after the infusion was stopped.

METHODS AND RESULTS

Two-dimensional echocardiography and hemodynamics provided LV fractional shortening and end-systolic wall stress data. Radionuclide ventriculography was also performed. Four groups of dogs received saline or cocaine infusions of 10, 30, or 100 micrograms.kg-1.min-1. Cocaine was infused for 90 minutes with ECG and arterial pressure monitoring. Animals were monitored for an additional 120 minutes after the infusion ended. Arterial pressure rose over the course of the experiment in all four groups, but saline and cocaine 10 micrograms.kg-1.min-1 did not significantly change ejection fraction. Cocaine 30 and 100 micrograms.kg-1.min-1 acutely increased arterial pressure and heart rate but decreased ejection fraction from 0.64 +/- 0.06 to 0.45 +/- 0.08 and from 0.65 +/- 0.10 to 0.46 +/- 0.11, respectively. Additionally, cocaine 100 micrograms.kg-1.min-1 decreased fractional shortening from 36 +/- 9% to 23 +/- 12%. However, cocaine 30 and 100 micrograms.kg-1.min-1 also increased wall stress from 42 +/- 15 to 65 +/- 11 g/cm2 and from 37 +/- 15 to 90 +/- 33 g/cm2, respectively. These results were analyzed by use of the relation between wall stress and fractional shortening as an index of contractility. Fractional shortening after cocaine infusion was displaced downward as a result of increased wall stress rather than changes in contractility. In addition, alteration of afterload with phenylephrine (6 micrograms/kg) and sodium nitroprusside (10 micrograms/kg) before and during infusion of cocaine 100 micrograms.kg-1.min-1 showed similar regression lines for wall stress to fractional shortening.

CONCLUSIONS

Ejection-phase indexes of LV function were reduced by cocaine in this model of conscious, sedated dogs, but effects were attributable to increased wall stress rather than to reduced myocardial contractility. These effects persisted for at least 2 hours after the infusion was stopped.

Exercise testing in patients with electrocardiographic evidence of left ventricular hypertrophy

The purpose of this study was to determine the influence of left ventricular hypertrophy, based on electrocardiographic evidence, on the results of exercise thallium testing. Patients with electrocardiographic evidence of left ventricular hypertrophy (ECG-LVH) and suspected of having coronary artery disease underwent exercise thallium testing. Retrospective analysis of 107 consecutive patients with ECG-LVH showed transient myocardial perfusion defects (TMPD) in 12 (11%), indicative of myocardial ischemia; 12 (11%) had fixed myocardial perfusion defects (FMPD), indicative of probable myocardial infarction; 5 had TMPD plus FMPD (5%), and scan results for 78 were normal (73%). In patients with ECG-LVH, additional ST changes were observed in 76% and chest pain in 7% of patients with ECG-LVH. In a matched comparison group of 255 patients not prescreened for ECG-LVH, TMPD was observed in 20%, FMPD in 16%, and TMPD plus FMPD in 26% of patients, and normal results were found in 38%. Electrocardiographic changes were found in 49% and chest pain in 20%. Hemodynamic responses to exercise were comparable between subgroups. Lung thallium uptake was quantified as the lung-to-heart thallium activity ratio (L-H) on the immediate exercise anterior planar images. In controls, a significant increase in L-H was observed in patients with TMPD and TMPD plus FMPD. This was not observed in patients with ECG-LVH, possibly because of elevated thallium myocardial activity as a result of increased left ventricular mass. The conclusion is that patients with ECG-LVH often had normal perfusion scan results (73%) on exercise despite a high incidence of additional ECG changes (76%).(ABSTRACT TRUNCATED AT 250 WORDS)

Norepinephrine-induced left ventricular dysfunction in anesthetized and conscious, sedated dogs

These studies were conducted to evaluate effects of high dose norepinephrine infusion on left ventricular function in anesthetized and conscious dogs. Separate groups of pentobarbital anesthetized closed-chest dogs received norepinephrine infusion for 90 min followed by 1 h of recovery. Arterial pressure, electrocardiogram, two-dimensional echocardiogram and an equilibrium radionuclide angiogram were monitored. One hour following infusion of norepinephrine, left ventricular ejection fraction was reduced in a dose-dependent fashion. Fractional shortening was similarly reduced, with increased left ventricular systolic and diastolic dimensions also observed. Left ventricular end-systolic wall stress was increased at 60 min following infusion of norepinephrine but not saline: saline, 68 +/- 8, norepinephrine, 4 micrograms/kg/min, 113 +/- 8 g/cm2. The left ventricular end-systolic wall stress/fractional shortening relationship showed reduction of contractility. In 10 conscious dogs pretreated with morphine, norepinephrine at 5 micrograms/kg/min x 90 min produced similar changes to those seen in anesthetized animals. Ejection fraction was reduced from 0.69 +/- 0.3 to 0.36 +/- 0.04 at 60 min post infusion. Fractional shortening was also reduced. Left ventricular end-diastolic dimension was increased. However, when animals were followed for 1 week, complete recovery occurred within 48 h. Histology showed mild contraction band necrosis in acute experiments and mild perivascular fibrosis in chronic experiments. Therefore, norepinephrine cardiotoxicity produced significant left ventricular dilation and reduction of ejection phase indices of left ventricular function associated with reduced contractility. In chronic dogs, histologic changes were mild, and left ventricular dysfunction was reversible.

Effect of chronic native flow competition on internal thoracic artery grafts

Residual competitive flow from the native coronary artery has been proposed as a mechanism that reduces flow in an internal thoracic artery graft (ITA), resulting in narrowing and ultimately failure of the graft. Results from acute experiments have indicated that competitive flow from a fully patent native artery did not abolish ITA graft flow. The present study was designed to examine the consequences of dynamic flow competition between the native vessel and the ITA graft in a chronic model. Fifteen mongrel dogs underwent coronary artery bypass grafting using the pedicled left ITA anastomosed to the normal, fully patent circumflex (CFX) coronary artery. The procedure was performed through a sterile thoracotomy, without systemic cardiopulmonary bypass, using a brief local occlusion to construct the anastomosis. Intraoperatively, ITA flow was measured in situ on the chest wall, before the pedicle was mobilized. Internal thoracic artery graft and distal CFX flow were measured after the anastomosis was completed, with and without brief occlusion of the proximal CFX. Angiography was performed 72 hours, 4 weeks, and 8 weeks later; graft patency and diameter were evaluated. After 8 weeks, open-chest direct flow measurements comparable with the intraoperative assessment were obtained. Two grafts (13%) occluded early, the technical result of poor anastomotic construction. In the 13 remaining animals, all grafts were widely patent at all time points. Internal thoracic artery flow in situ averaged 10.9 +/- 7.8 mL/min (mean +/- standard deviation), and was maintained after grafting (11.5 +/- 4.4 mL/min; p = not significant).(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of hyperkalemia on myocardial depression by verapamil in isolated hearts

Verapamil can produce depression of left ventricular function, delayed atrioventricular conduction, and hypotension, which can be potentiated by hyperkalemia. We sought to investigate a direct cardiac interaction between verapamil and hyperkalemia. Studies utilized isolated guinea pig hearts (Langendorff) paced at 250 beats/min. Hearts were randomly assigned to perfusion (Krebs-Henseleit buffer) with potassium concentrations ([K]+) of 1.5, 3, 6 and 9 mmol/l. Infusion of verapamil at rates of 0.2 to 60 micrograms/min (approximately 3 x 10(-8) to 10(-5) mol/l) produced concentration-dependent reduction of isovolumic left ventricular developed pressure. As [K]+ increased, concentration response curves showed parallel shifts to the left. The ED50 for reduction of left ventricular developed pressure significantly decreased: 8.2 +/- 3.7, 2.9 +/- 1.4, 1.2 +/- 0.7, 0.6 +/- 0.2 micrograms/min (mean +/- SD), respectively. Nifedipine and diltiazem were also studied in hearts perfused with 3 and 9 nmol/l [K]+. Infusion of nifedipine 0.003-1 microgram/min (approximately 10(-9) to 3 x 10(-7) mol/l) produced concentration-dependent reduction of left ventricular developed pressure but the ED50 was not affected by [K]+: 0.06 +/- 0.03 and 0.05 +/- 0.04 microgram/min, respectively. Nifedipine vehicle was without effect at the infusion rates tested. Infusion of diltiazem 2-200 micrograms/min (approximately 3 x 10(-7) to 3 x 10(-5) mol/l) also produced concentration-dependent reduction of left ventricular developed pressure. The ED50 for diltiazem-induced reduction of left ventricular developed pressure was significantly reduced by elevated [K]+: 20.1 +/- 6.7 and 3.5 +/- 0.9 micrograms/min with 3 and 9 mmol/l [K]+, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of diltiazem on norepinephrine-induced acute left ventricular dysfunction

The present study has examined the role of diltiazem as a protective agent in a canine model of norepinephrine cardiotoxicity. Effects of diltiazem, 20 micrograms/kg/min x 5 min pretreatment followed by 10 micrograms/kg/min x 90 min, or saline infusion were examined at baseline and 1 h after infusion of norepinephrine, 4 micrograms/kg/min for 90 min, in closed-chest anesthetized dogs. Left ventricular function was assessed by equilibrium radionuclide angiogram and two-dimensional echocardiogram. In 7 saline experiments, hypotension and increased heart rate were observed at 1 h post infusion. In the diltiazem-treated group (n = 7), mean arterial pressure and heart rate were unchanged. In the saline group, left ventricular ejection fraction fell from 0.50 +/- 0.04 to 0.28 +/- 0.04. Left ventricular ejection fraction was unchanged in the diltiazem-treated group: 0.52 +/- 0.03 to 0.55 +/- 0.07. Left ventricular end-diastolic volume was increased at 1 h post infusion in saline controls but not in the diltiazem-treated group. Measurement of fractional shortening from two-dimensional echocardiograms also indicated left ventricular dysfunction in the saline but not diltiazem-treated groups. Left ventricular end-systolic wall stress following norepinephrine infusion was significantly increased in the saline but not diltiazem-treated groups: 122.7 +/- 18.7 vs 67.6 +/- 19.7 g/cm2, respectively. In dogs receiving saline without norepinephrine infusion, no significant changes occurred over the course of the experiment. Histologic examination showed mild contraction band necrosis in saline controls but not in sham saline dogs. Diltiazem showed intermediate histologic evidence of injury, which was not further quantified. This study suggests that effects of norepinephrine on left ventricular function in the canine model of norepinephrine cardiotoxicity may be largely due to increased wall stress following a prolonged increase in afterload. Diltiazem pretreatment afforded significant protection of left ventricular function.

Competitive flow from a fully patent coronary artery does not limit acute mammary graft flow

The shriveled, stenotic mammary graft sometimes observed after internal mammary artery (IMA) to coronary artery bypass grafting has been attributed to competitive flow from the insufficiently stenosed native coronary vessel. To study further the effects of native coronary artery competing flow on IMA graft flow, 10 dogs (mean weight, 23.5 +/- 3.69 kg) underwent coronary artery bypass grafting using the pedicled left IMA anastomosed to a normal, fully patent proximal circumflex (CFX) coronary artery. The procedure was performed through a left thoracotomy, off pump, using a brief local occlusion to perform the anastomosis. Native in situ IMA flow, CFX flow distal to the anastomosis, and IMA graft flow were measured using calibrated electromagnetic flow probes. When the CFX proximal to the anastomosis was occluded transiently, IMA flow increased to supply 100% of the previously measured distal CFX flow (60.2 +/- 7.9 mL/min). When both the IMA graft and CFX proximal to the anastomosis were patent, total distal perfusion was maintained (58.9 +/- 7.8 mL/min) and relative IMA graft flow (26.5 +/- 3.3 mL/min) was proportional to the relative diameter of the IMA graft to the native coronary artery (r = 0.96). The mean flow in the IMA in situ on the chest wall before its division was 23.8 +/- 8.1 mL/min. These results suggest that, at least acutely in a canine model, IMA graft flow is maintained above in situ levels even when grafted to a completely patent coronary artery and that acute competitive flow probably does not cause mammary artery shriveling.

A radioimaging technique for quantifying regional myocardial blood flow

We developed a radioimaging technique for measuring regional myocardial blood flow (rMBF) in 5 mm2 myocardial tissue using canine closed-chest models. RMBF was measured in three groups: (1) total occlusion of left anterior descending (LAD) coronary artery with microfibrillar collagen, (2) fixed stenosis of LAD with angioplasty balloon, and (3) comparison of clinical dose response of adenosine (AD) and dipyridamole (DP) on rMBF. In these studies, rMBF in every 5 mm2 tissue was measured throughout the epicardium and endocardium. In groups 1 and 2, rMBF was also measured during adenosine-induced coronary hyperemia (ADICH). In group 1 (n = 7), rMBF measured at 6 hours post-LAD occlusion in epicardial infarct center (IC), peri-infarct (PI) and normal zone (NZ) were 17 +/- 7, 55 +/- 8, and 132 +/- 12 ml/min/100 tissue, respectively. The area and location of infarct seen in TTC staining matched with rMBF images. During ADICH, the corresponding rMBF were 16.2 +/- 13.9, 98.3 +/- 53.0, and 226.0 +/- 103.6 ml/min/100 g tissue, respectively. RMBF measured during ADICH in group 2 (n = 4) in areas of LAD stenosis (LS), surrounding stenosis (SS), and no stenosis (NS) were 120 +/- 58, 249 +/- 123, and 432 +/- 181 ml/min/100 gm tissue, respectively. In group 3, rMBF measured during 3 min into 0.14 mg/kg/min adenosine infusion in areas perfused by LAD, circumflex (CX) and right coronary artery (RCA) were 244 +/- 22, 238 +/- 19, and 215 +/- 19 ml/min/100 g tissue, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Significance of increased Tl-201 uptake by the lungs in patients undergoing oral dipyridamole-thallium myocardial imaging

The purpose of this study was to evaluate the significance of increased Tl-201 uptake by the lungs after oral dipyridamole testing. In conjunction with myocardial perfusion scintigraphy, intravenous dipyridamole has been recently approved as an alternative to exercise for the evaluation of coronary artery disease in patients who cannot adequately exercise, and it will largely replace oral dipyridamole testing. This study contributes to the understanding of the significance of increased lung thallium uptake during pharmacologic stress testing. Oral dipyridamole, 400 mg, was administered to 192 patients undergoing Tl-201 imaging for clinical indications. Mild adverse effects occurred in 31% of patients (chest pain, nausea, headache, or flushing). Dipyridamole had minimal hemodynamic effects. The lung/heart thallium activity ratio was determined in 152 patients. These were subdivided into four groups according to the presence or absence of ischemia, transient myocardial perfusion defect, or scar as indicated by a fixed myocardial perfusion defect. In 61 patients without transient myocardial perfusion defect or fixed myocardial perfusion defect (group 1), the lung/heart thallium activity ratio was 0.39 +/- 0.01 (mean +/- SEM). In 31 patients without transient myocardial perfusion defect but with fixed myocardial perfusion defect (group 2), the lung/heart thallium activity ratio was higher, 0.44 +/- 0.02 (P less than 0.05). In 27 patients with transient myocardial perfusion defect but no fixed myocardial perfusion defect (group 3) and in 33 patients with both transient myocardial perfusion defect and fixed myocardial perfusion defect (group 4), the lung/heart thallium activity ratio was 0.51 +/- 0.03 and 0.52 +/- 0.03, respectively, both significantly higher than either group 1 or group 2 (P less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of neuropeptide Y on isolated rat hearts

Neuropeptide Y (NPY) induces coronary vasoconstriction and an associated negative inotropic effect in the isolated rat heart, but it is unclear whether NPY produces these effects directly or through the mediation of other vasoactive substances. This question has been examined in Langendorff-perfused, paced hearts using constant pressure. In 22 dose-response experiments examining single injections of NPY, 0.05-5 nmol, into the coronary perfusate, dose-dependent reduction of flow and developed pressure was observed. NPY, 0.5 nmol or approximately 5 x 10(-8) M, was chosen for further studies. This dose produced close to maximal effects on coronary flow, -22 +/- 5%, and developed pressure, -14 +/- 5% (mean +/- SD). NPY was examined during infusion of the cyclooxygenase inhibitor indomethacin (n = 6) and the 5-lipoxygenase inhibitor RG 6866 (N-methyl-4-benzyloxyphenyl acetohydroxamic acid, n = 6), using a test dose for both agents of 20 micrograms/min (approximately 3 microM) or vehicle (ethanol, 0.01 ml/min, n = 9). NPY reduced coronary flow in all three groups: vehicle 6.2 +/- 1.1 to 4.6 +/- 1.1 ml/min, indomethacin 7.0 +/- 1.1 to 5.7 +/- 1.0, and RG 6866 7.0 +/- 1.6 to 6.1 +/- 1.6; reductions of 25 +/- 7, 19 +/- 5 and 13 +/- 9%, respectively. The flow reduction was attenuated by RG 6866. Developed pressure was significantly reduced by NPY in vehicle 71 +/- 10 to 62 +/- 11 mm Hg, and indomethacin 70 +/- 10 to 64 +/- 11 but not RG 6866 74 +/- 15 to 71 +/- 15 groups, reductions of 13 +/- 3, 9 +/- 9 and 4 +/- 5%, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Changes in transmyocardial impedance during prolonged ventricular fibrillation. Implications for current flow and delivered energy during DC countershock

Transthoracic resistance (TTR) and transmyocardial resistance (TMR) were measured during 10 minutes of uninterrupted ventricular fibrillation (VF) in a canine model. TMR was measured at 10- to 50-second intervals with two wire-mesh patch electrodes in 16 dogs. TTR was measured through two identical low-impedance electrodes. A monophasic exponentially truncated pulse with a duration of 5 msec was used for measurement of TMR as well as TTR. Low-energy pulses of 100 V were used for TMR measurements and pulses of 300 V for TTR measurements. TMR showed an increase of 22.8 +/- 5.14 omega (from 96.2 +/- 12.3 omega) after 600 seconds of uninterrupted VF (p less than 0.0006). TTR showed a change of 2.4 +/- 1.94 omega, which was not statistically significant in comparison with the initial value of 69.0 +/- 11.4 omega. A mathematical model was developed to predict energy delivered to the heart after a transthoracic shock. Observed values of TMR and TTR were used in this model. With the use of this model, the predicted fall in transmyocardial current after 600 seconds of uninterrupted VF and 19.3%, and the fall in energy delivered to the heart was 14%. Our study suggests that increase in TMR may contribute to the observed lack of successful defibrillation during prolonged VF.

Evaluation of a technique for avoiding inadvertent myocardial laceration in an experimental canine model: expansion of the role of two-dimensional echocardiography

An experimental animal model was utilized to evaluate the role of simultaneous two-dimensional echocardiography combined with a modified electrocardiographic monitoring technique for improving the safety of pericardiocentesis. This technique avoids the hazards of placing the sharp pericardiocentesis needle against the heart in order to determine its location against the epicardial surface. This technique was evaluated in eight dogs in over 100 aspiration attempts. Cardiac trauma occurred only in a single incidence with the use of a 20-gauge cannula. A detailed description of this procedure is provided in the text.

Quantification of acute aortic regurgitation by color Doppler flow in an experimental animal model

Color Doppler flow studies were performed on ten anesthetized open-chest dogs. Acute aortic regurgitation was created in the dogs by a special valve-spreading catheter. The magnitude of valvular regurgitation was determined by aortic electromagnetic flow recordings of regurgitant fraction. Arbitrarily-designated grades of aortic regurgitation: mild (4%-10%), moderate (11%-30%), and severe ( greater than 30%) were assigned on the basis of electromagnetic flow. We attempted to obtain studies of varying degrees of AR in each animal. Mean regurgitant fraction for the three grades were 6.8 +/- 0.6% (n = 11), 22.0 +/- 2.4% (n = 7), and 40.4 +/- 2.5 (n = 20), respectively (each P less than 0.05). By color Doppler flow assessment, the ratio of regurgitant jet height to the left ventricular dimension at the junction of the left ventricular outflow tract and the aortic annulus (JH/LVOH) was measured in each study. AR was classified by Doppler as grade I (mild), 1%-24%; II (moderate), 25%-64%; and III (severe), greater than or equal to 65% jet height/left ventricular outflow tract height. Color Doppler flow correlated well with flowmeter assessment of regurgitant fraction. Color Doppler flow tests had a calculated sensitivity of 88%, specificity of 83%, and predictive value of 85% for significant (moderate + severe) aortic regurgitation. Our data support the concept that this method of color Doppler flow assessment provides a quantitative noninvasive evaluation of aortic regurgitation.

Effects of 5-lipoxygenase inhibition on cardiac anaphylaxis in isolated guinea pig hearts

Synthesis of the cardioactive peptidoleukotrienes depends on the activity of 5-lipoxygenase. It is unclear whether inhibition of endogenous leukotriene biosynthesis can alter vasoconstriction and negative inotropic effects associated with inflammatory states in the heart. In an attempt to study this problem, two 5-lipoxygenase inhibitors, the novel compound RG 6866, N-methyl-4-benzyloxyphenyl acetohydroxamic acid, and AA 861 have been examined in Langendorff-perfused guinea pig hearts undergoing cardiac anaphylaxis and compared to indomethacin and LY 171883, a cyclooxygenase inhibitor and a leukotriene antagonist, respectively. In paced hearts perfused at constant pressure, RG 6866 had no apparent direct effects, infused intracardially at 20 micrograms/min, about 3 mumol/l. LY 171883, but not RG 6866 or indomethacin, antagonized coronary vasoconstriction by exogenous leukotriene D4. When hearts were challenged with antigen (ovalbumin 1 mg i.c.) in the presence of antihistamines, a significant reduction in coronary flow occurred within 30 s which was maximal at 2-3 min, -48 +/- 3%, and persisted for at least 10 min. An initial positive intropic effect was followed by a 25% fall in developed pressure. Both 5-lipoxygenase inhibitors blocked effects of antigen challenge on coronary flow: RG 6866, -4 +/- 3%, AA 861, -11 +/- 3%; reduction at 2 min. The late negative inotropic effect was also blocked. The combined 5-lipoxygenase inhibitor/leukotriene antagonist, RG 5901, and the leukotriene antagonist, LY 171883, were also effective, but not indometacin. These results provide further evidence for the contribution of leukotrienes to cardiac anaphylaxis. More importantly, these findings suggest that 5-lipoxygenase inhibitors can be beneficial in situations where endogenous leukotrienes produce coronary vasoconstriction and myocardial depression.

Cardiovascular depression by verapamil: reversal by glucagon and interactions with propranolol

Verapamil-induced cardiovascular depression has been examined in dial-urethane-anesthetized open chest dogs. Verapamil was administered slowly intravenously until the mean arterial pressure was decreased by approximately 45 mm Hg. The dose of verapamil required to reach the hemodynamic endpoint was 1,495 +/- (SE) 165 micrograms/kg. In a second group, interactions between beta-adrenergic blockade, propranolol 1 mg/kg (i.v.), and verapamil were examined. Although propranolol alone had only minor hemodynamic effects, the cardiac depressant dose of verapamil was reduced significantly to 450 +/- 105 micrograms/kg. After cardiovascular depression with verapamil or verapamil plus propranolol, glucagon was administered to assess its inotropic activity using cumulative doses of 5, 15, and 45 micrograms/kg over 20 min. Glucagon produced a dose-dependent recovery of heart rate, mean arterial pressure, and PR interval. Depressed contractility assessed by peak positive dP/dt and right ventricular isometric contractile force also recovered after glucagon. These results suggest a significant interaction between the potency of verapamil as a myocardial depressant and the state of the myocardium as affected by beta-blockade. Cardiac depression by verapamil or verapamil in combination with propranolol was reversible by glucagon.

Examination of diltiazem for preservation of myocardial function after brief regional ischemia

Diltiazem (750 micrograms/kg plus 600 micrograms/kg/h X 1 h, i.v.) and vehicle were examined in open-chest anesthetized dogs subjected to 15 min of occlusion of the left circumflex coronary artery (LCCA). Regional segment lengths in myocardium supplied by the LCCA and by the left anterior descending coronary (LAD) were measured with piezoelectric crystals implanted in the subendocardium. Diltiazem decreased heart rate and mean arterial pressure, and increased coronary blood flow, determined with an electromagnetic flowmeter. Vehicle had no significant effects. Occlusion of the LCCA increased end diastolic segment length (EDL), and produced akinesis or paradoxical systolic lengthening: diltiazem -2.5 +/- 2.7% and vehicle 0.0 +/- 1.2% segmental shortening (SS). EDL and SS in the LAD zone showed small increases. After 15 min, the LCCA was reperfused and recovery of SS was followed for 3 h. Significantly greater recovery of SS was observed with diltiazem compared to vehicle throughout reperfusion: at 5 min, diltiazem 105 +/- 22% and vehicle 43 +/- 7% and at 180 min, diltiazem 73 +/- 0% and vehicle 33 +/- 8% of baseline SS. The LCCA and LAD zones both responded to isoproterenol 0.3 microgram/kg given 2.5 h after reperfusion. During the isoproterenol challenge SS for LCCA in the diltiazem group (122 +/- 21%) was not different than that of vehicle (99 +/- 15% of baseline). Calcium entry blockade with diltiazem resulted in improved myocardial function during reperfusion. The stunned myocardium showed significant stimulation of shortening by isoproterenol in both groups.

Evaluation of alpha-adrenergic cardiac stimulation in anesthetized dogs: can this play a role in propranolol insensitive cardiostimulatory effects of celiprolol

The role of alpha-adrenergic systems in modulating contractility and rate in the canine heart is not completely understood. This was evaluated by examining alpha-agonists and antagonists in ganglionic- and beta-blocked, anesthetized dogs. Also, partial agonist effects of the beta-blocker celiprolol in the ganglionic blocked dog are insensitive to propranolol and may be mediated via alpha-2 antagonism. Prazosin (0.3 mg/kg), yohimbine (0.3 mg/kg), celiprolol (3 mg/kg) and vehicle were administered to ganglionic-(mecamylamine 2 mg/kg) and beta-adrenergic-(propranolol 1 mg/kg + 0.3 mg/kg/hr) blocked dogs. Clonidine (0.3 and 3.0 micrograms/kg), phenylephrine (3 micrograms/kg) and norepinephrine (0.3 microgram/kg) produced significant increases in arterial pressure with minimal chronotropic or inotropic effects. Celiprolol produced sustained increases in heart rate and contractile force of 15 +/- 3 beats/min and 33 +/- 7 percent (X +/- SEM) without significant vascular alpha antagonism. Yohimbine, prazosin and vehicle were without significant chronotropic or inotropic effects. However, yohimbine and prazosin selectively reduced pressor responses to clonidine and phenylephrine, respectively. In further studies adding prazosin or phentolamine before treatment with celiprolol did not attenuate its effects on heart rate and contractility. These results do not support significant inotropic or chronotropic effects of alpha-adrenergic receptor modulation in anesthetized dogs. The cardiac stimulatory effects of celiprolol do not appear to be mediated via cardiac alpha receptors.

Reduction of myocardial infarct size by neutrophil depletion: effect of duration of occlusion

Experiments were performed in the dog to examine the effects of neutropenia on ultimate infarct size resulting from short (90 minutes) or prolonged (4 hours) circumflex coronary artery occlusion. Sheep antiserum to canine neutrophils was used to produce neutropenia. Control animals received nonimmune serum. Neutrophil infiltration into myocardial infarcts was examined using histopathologic techniques and a semiquantitative scoring system. In 90-minute occlusions with 24-hour reperfusion, neutropenia was associated with the development of significantly smaller infarcts: normopenic group, 43.2% +/- 3.3% (n = 7) vs. neutropenic group, 26.6% +/- 3.7% (n = 10) of the area at risk, means +/- SEM. However, in 4-hour occlusion with 6-hour reperfusion experiments, the tendency of neutrophil depletion to reduce infarct size did not reach statistical significance (46.4% +/- 7.2% vs. 31.5% +/- 6.0% of the area at risk, normopenic vs. neutropenic) despite differences in neutrophil infiltration into the reperfused region. The observed differences in ultimate infarct size could not be attributed to differences in myocardial oxygen consumption. The results suggest that a significant amount of myocardial infarction induced by a limited duration of coronary artery occlusion followed by reperfusion is neutrophil dependent and appears to be less important in determining the fate of myocardium subjected to more prolonged periods of ischemia followed by reperfusion.

Enhanced relaxation response of canine coronary artery to isoproterenol and salbutamol after removal of endothelial cells

The importance of the endothelium for isoproterenol- and salbutamol-induced relaxation of canine coronary artery was examined. The relaxation effect of isoproterenol and salbutamol was significantly enhanced (P less than 0.05) upon removal of the coronary artery endothelium. In contrast, the relaxation effect of acetylcholine was completely abolished. These results indicate that canine coronary endothelium modulates beta-adrenoceptor-mediated relaxation, and that the role of the endothelium in agonist-induced relaxation of vascular smooth muscle appears to be heterogeneous.

Platelet depletion in experimental myocardial infarction

Accumulation of platelets in the microvasculature after acute myocardial ischemia may exacerbate tissue injury through the formation of microthrombi and by the release of vasoactive substances. To assess the role of platelets in myocardial ischemic injury and infarction, circulating platelets were reduced by 94 +/- 2% (mean +/- S.E.M.) with sheep antiserum to canine platelets. Regional myocardial ischemia was produced by occlusion of the left circumflex coronary artery (LCCA) for 90 min followed by reperfusion for 5 hours. Infarct size did not differ significantly between antiplatelet serum and nonimmune serum groups: 36 +/- 8 vs. 43 +/- 4% of the area at risk, determined by a post-mortem dual staining technique (p greater than 0.05). A second occlusion-reperfusion control group, sacrificed at 24 hours, did not differ from 5 hr reperfused groups with regard to infarct size. Coronary sinus thromboxane B2 (TXB2) concentrations were not altered significantly by platelet depletion. Histopathologic examination confirmed the presence of necrosis in the infarcted myocardium and revealed substantial leukocytic infiltration in both groups. The results suggest that circulating platelets are not required for the full expression of myocardial ischemic injury resulting from temporary coronary artery occlusion followed by reperfusion.

Protective effects of AICAriboside in the globally ischemic isolated cat heart

The effects of a purine precursor, AICAriboside (5-aminoimidazole-4-carboxamide riboside), on postischemic recovery of myocardial function and adenine nucleotides have been studied in the isolated blood-perfused cat heart. The isolated hearts received either AICAriboside or saline prior to 60 min of global ischemia and during 60 min of subsequent reperfusion. After 60 min of global ischemia and reperfusion, left ventricular function of the AICAriboside-treated hearts approached preischemic values, whereas contractile function of the saline-treated hearts remained depressed. At 60 min postischemia, recovery of left ventricular developed pressure (LVDP) was 62 +/- 10% for the saline-treated hearts as compared to 93 +/- 8% for the AICAriboside-treated hearts. Left ventricular compliance of the saline-treated hearts was decreased slightly at 60 min postischemia. In contrast, left ventricular compliance was increased in the isolated hearts which received AICAriboside. Myocardial ATP concentrations were decreased significantly at 60 min postischemia in both the saline-treated hearts and in the AICAriboside-treated hearts relative to nonischemic hearts. Similarly, total adenine nucleotides (TAN = ATP + ADP + AMP) were decreased significantly in both the saline-treated hearts and AICAriboside-treated hearts relative to nonischemic hearts. The present study demonstrates that AICAriboside protected globally ischemic hearts from the mechanical dysfunction associated with an ischemic insult but did not restore ATP or the total adenine nucleotide pool of the postischemic myocardium.

Experimental coronary artery thrombosis in the absence of thromboxane A2 synthesis: evidence for alternate pathways for coronary thrombosis

The actions of the thromboxane synthetase inhibitor, U-63557A, were evaluated in vivo in anesthetized open-chest dogs by inducing left circumflex coronary artery (LCCA) thrombosis with low amperage electrical stimulation (100 microA for 6 h) of the intimal surface of the vessel, and ex vivo by assessing platelet aggregation and TXB2 production. U-63557A, 10 mg/kg + 5 mg/kg/h i.v., reduced ex vivo platelet aggregation in response to arachidonic acid (0.65 mM) by 93 +/- 2% (p less than 0.05, means +/- SEM), whereas the concurrent formation of TXB2 was decreased by 78 +/- 8% (p less than 0.05). TXB2 concentration also was reduced significantly in vivo as measured from coronary sinus blood samples; however, 6-keto-PGF1 alpha concentration was unchanged from predrug values. Despite the significant inhibition of platelet aggregation and TXB2 production, thrombus mass was not reduced: control, 32.0 +/- 5.9 mg (n = 7); U-63557A, 30.8 +/- 12.0 mg (n = 5, p = NS). These results suggest that U-63557A effectively inhibits TXA2 synthetase, but lacks antithrombotic activity in our experimental model. Therefore, substances other than TXA2 may be capable of mediating occlusive coronary artery thrombosis.

Beneficial effects of nafazatrom on ischemic reperfused myocardium

The effect of nafazatrom, a new antithrombotic agent, was studied in a canine model of regional myocardial ischemia. Nafazatrom was administered 1 mg/kg intravenously every 6 h for 48 h. After 24 h of drug or placebo administration, animals underwent 90 min of occlusion of the proximal left circumflex coronary artery followed by gradual reperfusion over a period of 30 min. Twenty-four hours later, the animals were sacrificed and infarct size was determined by histochemical staining with triphenyltetrazolium chloride. Nafazatrom-treated animals had a significant reduction in infarct size expressed as a percent of the anatomical area at risk for infarction: 21 +/- 5% in the treated group vs. 41 +/- 5% in the control group (X +/- S.E.M., P less than 0.05). Histological examination confirmed the gross results of postmortem histochemical staining. Salvage of ischemically jeopardized tissue appeared to be unrelated to myocardial oxygen demand as there were no hemodynamic differences between groups. The beneficial effects of nafazatrom are presumably related to a limitation of autolytic processes on the heart during and after ischemia as a result of the drug's ability to inhibit lipoxygenase and to prevent the enzymatic degradation of prostacyclin.

Canine myocardial reperfusion injury. Its reduction by the combined administration of superoxide dismutase and catalase

Therapy directed against the toxic effects of reactive oxygen species may reduce the final extent of ischemic injury in otherwise viable tissue irreversibly injured by the abrupt reoxygenation of reperfusion. In four groups of dogs, superoxide dismutase plus catalase (groups I-III) or saline (controls) (group IV) was infused into the left atrium. Group I received the infusion for 2 hours, beginning 15 minutes before occlusion of the left circumflex coronary artery (90 minutes) and ending 15 minutes after reperfusion. Group II received the infusion for 1 hour starting 15 minutes before reperfusion. Group III received the infusion for 1 hour beginning 40 minutes after reperfusion. Dogs were killed the next day, and infarct size was determined by dissection and weighing, and confirmed histologically. Infarct size expressed as percent of the anatomic area at risk was: group I, 19.4 +/- 5.0; group II, 21.8 +/- 3.3; group III, 47.6 +/- 10.3; group IV, 43.6 +/- 3.5 (mean +/- SEM). Analysis of variance followed by Duncan's multiple range test showed that ultimate infarct size as assessed in groups I and II differed significantly (P less than 0.05) from that observed in the control animals in group IV, whereas infarct size between groups III and IV did not differ significantly (P greater than 0.05). The percent of left ventricle at risk did not differ between the four groups. The beneficial effects of superoxide dismutase plus catalase could not be explained by hemodynamic differences. Similar protection of jeopardized myocardium in groups I and II suggest that potentially viable tissue is salvaged by scavenging free radicals during early reperfusion.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of BW755C in an occlusion-reperfusion model of ischemic myocardial injury

BW755C is a new antiinflammatory agent which predominantly inhibits lipoxygenase over cyclooxygenase. Effects of BW755C have been examined in a canine, occlusion-reperfusion, model of ischemic myocardial injury. In pentobarbital anesthetized open-chest dogs, the proximal left circumflex coronary artery (LCX) was occluded for 90 minutes and slowly reperfused using a micrometer-driven occluder. Thirty minutes before occlusion, animals randomly received BW755C, 3 mg/kg (n = 7), or 10 mg/kg (n = 8), or saline (n = 16) by intravenous infusion. The thoracotomy was closed and the animals subsequently were killed at 24 hours. Infarct size and anatomic area dependent on the occluded LCX were determined by a dual staining technique using triphenyltetrazolium and Evan's blue. Both doses of BW755C significantly reduced the ultimate extent of irreversible myocardial ischemic injury, whether results were expressed as grams of infarcted tissue or as percent of risk region infarcted. No difference in risk region size was observed between groups. No effects of BW755C on heart rate, arterial pressure, or left circumflex flow were observed. BW755C (10 mg/kg) did not significantly inhibit ex vivo platelet aggregation in response to collagen, adenosine diphosphate, or arachidonic acid. These results suggest that inhibition of lipoxygenase may reduce the extent of ischemic damage to the heart.

Effect of zomepirac on experimental coronary artery thrombosis and ischemic myocardial injury in the conscious dog

The nonsteroidal anti-inflammatory agent, zomepirac, was evaluated for its in vivo antithrombotic effects in conscious canines by inducing left circumflex (LCX) coronary artery thrombosis with low-amperage electrical stimulation (50 muA for 24 h) of the intimal surface of the vessel. Zomepirac, 10 mg/kg i.v., given at 0 and 12 h, prevented occlusive coronary artery thrombosis (seven of 10 controls developed occlusive thrombi, compared to one of eight zomepirac-treated animals; p = 0.02). LCX thrombus mass also was reduced by zomepirac (control: 24.0 +/- 4.0 mg; zomepirac: 10.2 +/- 2.4 mg, p less than 0.05; means +/- SEM). Left ventricular infarct mass due to occlusive LCX coronary artery thrombosis was likewise reduced. In a separate series of experiments, zomepirac (10 mg/kg i.v.), given 30 min before occlusion, failed to limit the extent of irreversible myocardial injury after temporary (90 min) LCX coronary artery occlusion in the canine. Infarct size, as a percent of the area at risk of infarction, averaged 47.8 +/- 3.9% in controls, and 40.4 +/- 7.5% in zomepirac-treated animals (means +/- SEM). No difference in the mass of myocardium at risk of infarction was observed between the two groups. In this latter study, zomepirac produced no significant hemodynamic effects. Ex vivo platelet aggregation in response to collagen and arachidonic acid was decreased significantly by zomepirac, but aggregation to ADP was unaffected. These results suggest that zomepirac possesses anti-thrombotic properties, but lacks intrinsic cardioprotective effects. Therefore, zomepirac may be of potential value in the prevention of coronary artery thrombosis owing to its ability to modify platelet reactivity.

Effects of lodoxamide on ischemic reperfused myocardium

The beneficial effects of lodoxamide tromethamine (U42585E) have been examined in a canine model of myocardial ischemic injury. Lodoxamide was infused 20 mg/kg/h i.v. starting 30 min before occlusion of the proximal left circumflex coronary artery (LCX) and continuing through 90 min of ischemia. Lodoxamide produced a significant reduction in ultimate infarct size measured at 24 h by postmortem tetrazolium perfusion staining. Infarct size expressed as a percent of the anatomical area at risk was 21.7 +/- 2.7 in the treated group vs. 47.0 +/- 3.1 in the control group (mean +/- SEM). No significant difference in area at risk was observed between treated and control groups. Salvage occurred primarily in subepicardial and midmyocardial tissue without apparent lateral protection. Histological examination confirmed gross results of postmortem staining. The protection appeared to be unrelated to myocardial oxygen demand since no hemodynamic differences between groups were observed at the time of occlusion of throughout the 24-h experimental course. Concurrent studies of ex vivo platelet aggregation showed no effect of lodoxamide on adenosine diphosphate (ADP), collagen, and arachidonic acid-induced aggregation. In vivo antithrombotic effects were evaluated in four conscious dogs by inducing LCX thrombosis with low-amperage stimulation (50 microA for 24 h) of the intimal surface. Occlusive thrombi occurred in all four dogs and were similar to controls. These results suggest that lodoxamide reduces myocardial ischemic injury by a mechanism unrelated to oxygen demand or antiplatelet effects.

Comparison of isoproterenol, salbutamol and tazolol as lipolytic agents with isolated rodent adipocytes

Cranial nuclear magnetic resonance (NMR) scans were performed on 13 healthy volunteers and 140 patients with a broad spectrum of neurologic disease and compared with x-ray computed tomography (CT) scans. The NMR scans included a variety of sequences reflecting proton density, blood flow, T₁, and T₂ as well as transverse, sagittal, and coronal images. White matter, gray matter, and cerebrospinal fluid were clearly distinguished in the normal brain with inversion-recovery (IR) sequences, and normal progressive myelination was demonstrated in infants and children.

Acute hemorrhages displayed short T₁ values, but other pathologic processes such as infarction, infection, demyelination, edema, and malignancy were associated with long T₁ values. Cysts had very long T₁ values (about that of cerebrospinal fluid). Spinecho (SE) sequences showed increased values of T₂ in a variety of conditions and highlighted lesions against the relatively featureless background of the remaining brain. With inversion-recovery scans, different stages of infarction were recognized in the hemispheres. NMR was more useful than CT in demonstrating brainstem infarction.

The white matter lesions in demyelinating diseases were well demonstrated with NMR scans. Many more lesions were observed in multiple sclerosis with NMR than with CT. Benign tumors were well seen and usually had shorter T₁ values than malignant tumors. Mass effects from tumors were generally better demonstrated with NMR than with CT, including more subtle mass effects such as displacement of the external capsule. Abnormalities were seen in diseases of the basal ganglia, including marked atrophy of the head of the caudate nucleus in Huntington chorea.

Advantages of NMR imaging include the high level of gray–white matter contrast, lack of bone artifact, variety of possible sequences, transverse, sagittal, and coronal imaging, sensitivity to pathologic change, and lack of known hazard. Disadvantages include lack of bone detail, limited spatial resolution, lack of contrast agent s, and cost. Promising directions for future clinical research include developmental neurology, tissue characterization with T₁ and T₂, assessment of blood flow, and the development of contrast agents. Much more detailed evaluation will be required, but NMR seems to be a potentially important addition to existing techniques of neurologic diagnosis.

Protective effects of diltiazem during myocardial ischemia in isolated cat hearts

The protective effects of diltiazem, a calcium channel blocker, were studied in isolated, blood-perfused cat hearts subjected to 60 or 90 min of global ischemia, followed by reperfusion of 60 or 120 min, respectively. Ischemia-induced alterations of left ventricular (LV) developed pressure (DP) and compliance, measured with an intraventricular fluid-filled latex balloon, were correlated with respiratory activity in vitro of mitochondria isolated from ischemic-reperfused LV myocardium. Nontreated isolated hearts sustained severe declines of LVDP as a result of 60 (-50 +/- 8%) and 90 min (-83 +/- 7%) of ischemia, whereas diltiazem-treated hearts demonstrated only minor losses of LVDP (-17 +/- 8 and -26 +/- 2%). Diltiazem prevented losses of compliance caused by 60 or 90 min of ischemia, which were severe in nontreated hearts after the latter period of ischemia. The progressive deterioration of mechanical function observed in nontreated hearts was paralleled by depressed mitochondrial oxygen consumption and respiratory control. The respiratory activity of mitochondria isolated from cat heart mitochondria. Diltiazem also prevented significant elevations of tissue and mitochondria Ca++ content, reflecting inhibition of Ca++ influx during ischemia and reperfusion. Also, recovery of ATP levels was greater after 60 min each of ischemia and reperfusion in diltiazem-treated hearts. Thus, diltiazem exerts direct, cardioprotective effects during myocardial ischemia, presumably by inhibiting transmembrane Ca++ fluxes.

Comparison of two dihydropyridine calcium antagonists on coronary collateral blood flow in acute myocardial ischemia

Effects of two dihydropyridine calcium antagonists on regional myocardial blood flow produced by acute ligation of the left anterior descending coronary artery were examined in the pentobarbital-anesthetized open-chest dog. Equivalent hypotensive doses of nifedipine (1.25 and 2.5 microgram/kg/min) and FR 7534 (5 and 10 micrograms/kg/min) produced similar decreases in mean arterial pressure and myocardial oxygen consumption and increases in coronary blood flow, dp/dt and contractile force in the intact nonischemic dog heart. Heart rate was unaffected. Nifedipine was 4 times as potent as FR 7534. Effects on ischemic myocardial blood flow measured with radioactive microspheres were examined with the same doses and also at controlled mean arterial pressure by use of methoxamine. Despite significant hypotension, nifedipine maintained and FR 7534 increased ischemic blood flow. When perfusion pressure was controlled, both compounds produced significant increases in transmural blood flow to the ischemic region. The increase produced by FR 7534 was significantly greater. Both nifedipine and, to a lesser extent, FR 7534 decreased the subendocardial to subepicardial blood flow ratio in the nonischemic myocardium without altering that of the ischemic myocardium. Drug-induced increases in ischemic blood flow were positively correlated with initial flow rate. The results indicate that both dihydropyridine calcium antagonists are capable of improving the oxygen supply-demand relationship during ischemia by reducing overall myocardial oxygen demand by increasing collateral blood flow.

Comparative effects of a new calcium antagonist, FR 7534, nitroglycerin, and dipyridamole on regional myocardial blood flow and cardiac contractility during partial coronary artery occlusion in the dog

The present study was designed to determine the effects of three different types of coronary vasodilators--FR 7534 (a new calcium antagonist), nitroglycerin, and dipyridamole--on the transmural blood flow and contractile function in the normal and ischemic myocardium of anesthetized dogs. Radioactive microspheres (15 muc) and Walton-Brodie strain gauge arches were used to measure tissue blood flow and contractile force, respectively. During 5 min intravenous infusions of nitroglycerin (5 microgram/kg/min) or dipyridamole (50 microgram/kg/min), which produced approximately 20% reductions in mean aortic pressure, blood flow and contractile force in ischemic myocardium decreased significantly. Under similar conditions, FR 7534 (10 microgram/kg/min) produced a significant decrease in ischemic contractile force, but tissue blood flow to the ischemic area did not change. In contrast, when mean aortic pressure was controlled by administration of methoxamine, nitroglycerin produced significant increases in ischemic blood flow (42%) and contractile force (47%), whereas dipyridamole produced significant decreases (41 and 32%, respectively). On the other hand, FR 7534 plus methoxamine produced a significant increase in ischemic blood flow (70%); however, ischemic contractile force did not change. These results demonstrate FR 7534 to affect the oxygen supply-demand balance in ischemic myocardium favorably by maintaining blood flow and depressing contractility during hypotension or by increasing flow during controlled systemic pressure.

Improvement in ischemic myocardial blood flow following a new calcium antagonist

The effect of FR 7534, a new dihydropyridine CA2+ antagonist, nitroglycerin, and dipyridamole have been compared on coronary collateral function in pentobarbital-anesthetized open-chest dogs following acute ligation of the left anterior descending coronary artery. Measurements of tissue blood flow using radioactive microspheres were made 60 min postligation after low and high doses of each drug and at the higher dose with methoxamine added to to return mean aortic pressure. FR 7534 treatment increased subepicardial, subendocardial, and transmural tissue flow by 100% in the central ischemic zone when perfusion pressure was controlled by methoxamine. Nitroglycerin also increased ischemic tissue flow, but to a lesser degree, 18% transmurally. Dipyridamole produced no significant change. Tissue flow in normal myocardium was similarly increased by FR 7534 and dipyridamole but slightly reduced by nitroglycerin. FR 7534 and nitroglycerin also increased retrograde coronary pressure when aortic presure was maintained constant. FR 7534, but not nitroglycerin, increased ischemic contractile force. In this model, FR 7534 may produce greater effects than nitroglycerin in increasing blood supply to ischemic myocardium delivered by endogenous collaterals especially when aortic perfusion pressure was controlled.

Effect of aging and cellularity on lipolysis in isolated mouse fat cells

The effects of age and cellularity on lipolysis have been investigated in isolated epididymal fat cells from both Swiss albino mice and Sprague-Dawley rats. No significant lipolytic response to glucagon could be demonstrated with adipocytes from either young or old mice, while glycerol output was increased by this hormone with fat cells from young rats. Larger adipocytes from older mice showed significantly greater isoproterenol-stimulated lipolysis than those from younger animals if the glycerol output was expressed on a per cell basis. However, the lipolytic response per cell appeared to be equivalent in young and old rat adipocytes with either isoproterenol or ACTH-(1-24). In a complete aging study, relationships between body weight, epididymal fat pad weight and cellularity were examined covering the life span of the mouse. ACTH-(1-24)- and dibutyryl cyclic AMP-stimulated lipolysis increased with age and cell size but fell at senescence when adipocyte size diminished. Although an effect of aging per se cannot be ruled out with the experimental techniques used in the present study, a dominant influence of adipocyte size on the lipolytic process was demonstrated.

Effect of FR 7534, a new calcium antagonist, on myocardial oxygen demand

The actions of FR 7534, a new calcium antagonist, nitroglycerin, and dipyridamole on myocardial oxygen demand have been compared. Six anaesthetized dogs received two infusion levels of each drug which produced equivalent arterial hypotension. All three compounds reduced the tension-time index (TTI). FR 7534 and nitroglycerin but not dipyridamole produced significant decreases in myocardial oxygen consumption (MVO2). FR 7534 demonstrated oxygen-sparing actions comparable to nitroglycerin. FR 7534 may prove beneficial in alleviating myocardial ischemia.

Influence of genetic obesity in mice on the lipolytic response of isolated adipocytes to isoproterenol and ACTH-(1-24)

The lipolytic response of isolated adipocytes from genetic obese (C57/BL/64 ob/ob) and lean (C57BL/6J +/?) mice to ACTH-(1-24), isoproterenol and glucagon has been studied. The mean cell idameter of adipocytes form ob/ob mice was approximately twice that of lean controls. The adipocytes from obese mice contained on the average approximately six times the amount of triacylglycerol present in the smaller lean mouse adipocyte. Lipolysis was calculated both on a per cell basis (10(5) cells) and per mu mole of triacylglycerol and when expressed on a cell number basis, the larger adipocytes from obese mice showed an ACTH-(1-24) stimulated glycerol release which was quantitatively similar to that of smaller adipocytes from lean mice. When expressed per mu mole of triacylglycerol, the smaller cells from lean animals appeared to be dramatically more responsive to either isoproterenol or ACTH-(1-24). On either basis, ACTH-(1-24) stimulated glycerol release from obese mouse cells was greater than the isoproterenol response. The obese mouse of adipocyte showed selective loss of response to isoproterenol compared to its lean control.