Cardiovascular effects of dopamine and dobutamine in conscious pigs with chronic heart failure

OBJECTIVE

To test the hypothesis that the cardiovascular responses of dopamine and dobutamine might be affected by the cardiovascular conditions.

DESIGN

Prospective, controlled dose-response comparison of dopamine and dobutamine.

SETTING

Laboratory for Experimental Cardiology at a university.

SUBJECTS

Normal conscious pigs and conscious pigs with chronic left ventricular dysfunction induced by occlusion of a coronary artery 3 to 4 wks before measurements were obtained.

INTERVENTIONS

Intravenous infusions of dopamine and dobutamine at rates of 1 to 25 micrograms/kg/min.

MEASUREMENTS AND MAIN RESULTS

Left ventricular function was characterized by a lower cardiac output in the pigs with left ventricular dysfunction (23%), stroke volume (34%), and left ventricular pressure (15%), and a higher heart rate (16%), peripheral resistance (41%), and left ventricular end-diastolic pressure (96%) than the normal pigs. Dopamine increased cardiac output to the same extent in the animals with failure as in the normal animals; stroke volume increased only in the animals that had left ventricular dysfunction. The vasodilatory response to dopamine was also similar, but the increase in left ventricular pressure was attenuated similar, in the animals with left ventricular dysfunction, compared with normal animals. Dobutamine showed cardiovascular effects equivalent to dopamine. Left ventricular work, depressed at baseline, increased more rapidly during infusion of dopamine (or dobutamine) in the animals with heart failure than in normal animals.

CONCLUSIONS

Both dopamine and dobutamine increased cardiac output in conscious pigs with chronic heart failure. Unlike the response in normal conscious pigs, in which only heart rate increased, in animals with heart failure, these agents enhanced both stroke volume and heart rate.

Increased activity of the sarcoplasmic reticular calcium pump in porcine stunned myocardium

OBJECTIVE

The aim was to determine whether changes in sarcoplasmic reticular Ca2+ transport activity and the degree of phosphorylation of phospholamban of "stunned" myocardium are involved in the reversible depression of contractile function.

METHODS

In anaesthetised open chest swine, stunning was induced by subjecting the myocardium perfused by the left anterior descending coronary artery to two cycles of 10 min of occlusion and 30 min of reperfusion. Before and after stunning, systemic haemodynamic variables and regional myocardial function and perfusion were determined, while biopsies were taken for determination of the content of high energy phosphate compounds. Sarcoplasmic reticular function (ATP dependent Ca2+ transport and phosphorylation of phospholamban) of the stunned and control myocardium was determined at the end of the stunning protocol.

RESULTS

In the stunned myocardium the segment length shortening decreased from 17.4(SD 4.0)% to 3.5(4.4)%, while perfusion was 38% less than at baseline. ATP and total adenine nucleotide levels of the stunned myocardium were about 35% lower than in the control myocardium, but the energy charge was normal as creatine phosphate levels had increased by 66% over the content determined at baseline. Ca2+ uptake by the sarcoplasmic reticulum isolated from the stunned region was 17% (p < 0.05) higher than Ca2+ uptake from the control region [1240(303) and 1450(280) nmol.min-1.mg-1 protein, respectively]. In the presence of exogenous cyclic AMP dependent protein kinase the amount of 32P incorporated into phospholamban was similar for both myocardial regions.

CONCLUSIONS

In this model of stunned porcine myocardium, the phosphorylation state of phospholamban was unchanged, but Ca2+ uptake by the sarcoplasmic reticulum was slightly increased. The results indicate that a change in active Ca2+ transport by the sarcoplasmic reticulum is most likely not to be the principal cause of contractile dysfunction of stunned myocardium.

Altered coronary flow reserve in the hypertrophied heart: implications for therapy

Coronary flow reserve has been shown to be abnormally low in several models of left ventricular hypertrophy induced by long-standing pressure overload. Because the presence of hypertrophy is a risk factor for the development of subendocardial ischaemia and sudden death, efforts to restore alterations in flow reserve may prove beneficial. In the following review, we discuss potential mechanisms which might contribute to this abnormal vasodilator capacity in the hypertrophied heart, with particular emphasis on how chronic therapy may potentially reverse such abnormalities. In addition, we report how the acute administration of various classes of pharmacological agents can alter measurements of coronary flow reserve, as observed in our anaesthetised swine model. Such factors must be considered before interpreting any changes in coronary flow reserve in models of hypertrophy following chronic administration of drugs.

Negative inotropy of lidocaine: possible biochemical mechanisms

Previous studies have shown that lidocaine has a negative inotropic effect on the myocardium. This effect could be mediated by a decrease in O2 supply and/or utilization, or abnormalities in intracellular Ca2+ handling by the myocardium. To investigate which of these mechanisms are involved we studied nine open-chest anaesthetized pigs, which received an infusion of lidocaine (4-16 mg.min-1) in the left anterior descending coronary artery (LADCA), sufficient to induce a severe depression of the regional myocardial function. Biopsies for high energy phosphate levels were obtained from both the LADCA and control regions before and during the infusion. After measurements at peak lidocaine dose, the hearts were rapidly excised for harvesting of LADCA, and control region sarcoplasmic reticulum (SR) vesicles for in vitro measurements of Ca2+ uptake rate. During lidocaine infusion, coronary blood flow increased (23%), while ATP, Ca2+ uptake by the SR and percentage segment length shortening decreased by 20%, 19% and 30% respectively. However, O2 consumption in the LADCA region did not differ before or during lidocaine infusion (102 +/- 20 and 104 +/- 29 ml.min-1, respectively). Hence, lidocaine in doses sufficient to depress regional myocardial function does not decrease O2 supply, but decreases the efficiency of oxygen utilization. Although we cannot entirely rule out the possibility that blockade of fast sodium channels is a contributory factor, the observed decrease in the tissue level of ATP and the rate of Ca2+ uptake by the SR may be related to the negative inotropic action of lidocaine.(ABSTRACT TRUNCATED AT 250 WORDS)

Proto-oncogene expression in porcine myocardium subjected to ischemia and reperfusion

The molecular basis of myocardial adaptation to ischemia and reperfusion is poorly understood. It is thought that nuclear proto-oncogenes act as third messengers, converting cytoplasmic signal transduction into long-term changes of gene expression. We studied the expression of six nuclear proto-oncogenes (Egr-1, c-fos, fosB, c-jun, junB, and c-myc) in myocardium subjected to ischemia and reperfusion in anesthetized pigs. Stunning was achieved by two 10-minute left anterior descending coronary artery occlusions separated by 30 minutes of reperfusion. Hearts were excised after the first occlusion, after the first reperfusion, and at 30, 120, 150, and 210 minutes of reperfusion after the second occlusion. Total RNA was prepared from stunned as well as normally perfused myocardial tissue and subjected to Northern blotting. The response of the six nuclear proto-oncogenes varied.fosB gene expression was never detected. The c-myc gene was expressed, but its level was unchanged by ischemia. c-jun expression was slightly increased by ischemia (3.1 +/- 0.6-fold). The c-fos, Egr-1, and junB genes were highly induced, being fivefold to sevenfold higher in experimental than in control tissue. In three animals pretreated with the beta 1-antagonist metoprolol and then subjected to the above experimental protocol, the induction of proto-oncogenes was similar to that in nonblocked controls. Our results show that the myocardial adaptive response to ischemic stress includes the induction of at least four transcription factors that may be further operative in repair processes and angiogenesis.

Recruitment of myocardial work and metabolism in regionally stunned porcine myocardium

We characterized postischemic changes in myocardial metabolism and regional external work, as measured by the integral of left ventricular pressure-segment-length loops. In 12 anesthetized swine, the left anterior descending coronary artery (LAD) was occluded for 10 min and reperfused for 30 min for two successive cycles. Before ischemia, regional work was 16,920 +/- 5,630 mmHg-mm/min and after stunning, work was reduced to 50 +/- 14% (P < 0.05). At baseline, oxygen and lactate consumption were 4.80 +/- 1.40 and 1.02 +/- 0.46 mumol.min-1 x g-1, respectively, and after stunning they were reduced to 3.24 +/- 0.80 (P < 0.05) and 0.16 +/- 0.21 mumol.min-1 x g-1 (P < 0.05), respectively. The atria were then paced 50 beats/min higher than the reperfusion heart rate, during and without an infusion of dobutamine (2 micrograms.kg-1 x min-1). During dobutamine, both regional external work and oxygen consumption returned to 98% of preischemic values, but lactate utilization remained depressed. We conclude that regional external work and oxygen consumption remain coupled during inotropic stimulation after stunning, with a preferential shift toward nonlactate substrates.

5-Hydroxytryptamine-induced increase in left ventricular dP/dtmax does not suggest the presence of ventricular 5-HT4 receptors in the pig

Although 5-hydroxytryptamine (5-HT) increases porcine atrial force and rate via 5-HT4 receptors, its effect on left ventricular contractility is not known. Therefore, using the maximum rate of rise of left ventricular pressure (LVdP/dtmax) as an index of cardiac contractility, we have attempted to analyze the possible role of ventricular 5-HT4 receptors in the anaesthetized pig. The full agonists at 5-HT4 receptors, 5-HT and 5-methoxytryptamine (each 3, 10 and 30 micrograms.kg-1), and the beta-adrenoceptor agonist, isoprenaline (0.01, 0.03 and 0.1 micrograms.kg-1), increased heart rate, LVdP/dtmax and cardiac output. For a given degree of tachycardia, the increase in LVdP/dtmax by isoprenaline was substantially more than that observed with either 5-HT or 5-methoxytryptamine. The 5-HT4 receptor partial agonist, renzapride (3, 10, 30, 100 and 300 micrograms.kg-1), also increased heart rate and LVdP/dtmax dose-dependently. When the heart was paced at 150 beats.min-1, increases in LVdP/dtmax as well as cardiac output (except with the highest doses) by 5-HT, 5-methoxytryptamine and isoprenaline were clearly attenuated. However, the magnitude of attenuation of LVdP/dtmax responses by cardiac pacing was more marked in the case of 5-HT and 5-methoxytryptamine than with isoprenaline. The effects of renzapride (300 micrograms.kg-1) and tropisetron (0.3 and 3 mg.kg-1) on increases in heart rate and LVdP/dtmax by 5-HT, 5-methoxytryptamine and isoprenaline were also studied.(ABSTRACT TRUNCATED AT 250 WORDS)

L-propionylcarnitine and myocardial performance in stunned porcine myocardium

Recently, we showed that L-propionylcarnitine did not affect recovery of regional contractile function of porcine myocardium subjected to 1 h of low-flow ischemia followed by 2 hr of reperfusion. In that study, ischemia may have been too severe and/or the duration of reperfusion too short to detect a beneficial effect of the compound. Therefore, in the present study we investigated the effects of saline (control group; n = 14) or pretreatment with L-propionyl-carnitine (3 days of 50 mg/kg p.o. b.i.d. + 50 mg/kg i.v. prior to the experiment; n = 13) on recovery of regional contractile function of the myocardium in open-chest anesthetized pigs, subjected to two cycles of 10 min of left anterior descending coronary artery (LADCA) occlusion, each followed by 30 min of reperfusion. In the control animals, at the end of the second reperfusion period, systemic vascular resistance had increased by 18%, which, however, was not observed in the L-propionylcarnitine-treated pigs. In the control group, during the first occlusion, systolic segment length shortening (SSLS) of the LADCA-perfused area decreased from 18.5 +/- 5.5% to -3.7 = 3.2%. After 30 min of reperfusion, SSLS of the LADCA-perfused area had only partially recovered to 6.2 +/- 5.9%. During the second occlusion-reperfusion cycle similar values for SSLS were observed. In the treated animals, SSLS of the LADCA-perfused area was slightly improved after the second occlusion-reperfusion cycle (p = 0.056). This effect did not result in an overall improvement in cardiac pump function.(ABSTRACT TRUNCATED AT 250 WORDS)

Differential cardiovascular and neuroendocrine effects of epinine and dopamine in conscious pigs before and after adrenoceptor blockade

1. The effects of epinine or dopamine (both 1-10 micrograms kg-1 min-1) on systemic haemodynamics and plasma concentrations of catecholamines and prolactin were studied in conscious pigs before and after combined non-selective alpha- and beta-adrenoceptor blockade. 2. The plasma concentrations of the two compounds did not differ from each other over the entire dose-range. 3. Epinine increased aortic blood flow (AoBF, 24 +/- 6%), which was due to an increase in heart rate (HR) for doses less than 10 micrograms kg-1 min-1. At 10 micrograms kg-1 min-1, HR decreased slightly (10 +/- 3%, as compared to the value obtained at 5 micrograms kg-1 min-1) and stroke volume increased up to 15% (P < 0.05). Mean arterial pressure (MAP, 99 +/- 3 mmHg at baseline) decreased dose-dependently (14 +/- 2%, P < 0.05) up to the infusion rate of 5 micrograms kg-1 min-1, but increased by 4.0 +/- 1.8 mmHg during infusion of 10 micrograms kg-1 min-1. Systemic vascular resistance (SVR) decreased up to 23 +/- 3% for doses less than 10 micrograms kg-1 min-1, but did not change further during infusion of the highest dose. LVdP/dtmax increased during the two highest infusion rates up to 22 +/- 6% (P < 0.05). After the infusion was stopped there was an abrupt increase in HR (18 +/- 4%, P < 0.05) and a further decrease in SVR before all parameters returned to baseline.4. Dopamine caused increases in AoBF (27 +/- 3%) similar to epinine, the only difference being that HR continued to increase (32 +/- 5%) and MAP (13 +/- 3%) and SVR continued to decrease (31 +/- 3%) over the entire dose-range. The increase in LVdP/dt,,,, at the highest dose (48 +/- 4%, P <0.05) was more pronounced than with epinine.5. Adrenoceptor blockade inhibited all epinine-induced changes, but did not affect the dopamineinduced changes in AoBF, SVR and MAP, but attenuated the increases in HR and LVdP/dtmax.6. Noradrenaline (NA) and adrenaline (Ad) concentrations did not change during infusion of epinine or dopamine, but NA increased by 50% within 2.5 min after stopping the infusion of epinine. After adrenoceptor blockade NA and Ad concentrations did not change during infusion of dopamine, which contrasted with a decrease of 55 +/- 5% (P<0.05) in NA during infusion of epinine.7. Prolactin concentrations decreased gradually from 480 +/- 40 pg ml-' to 270 +/- 50 pg ml1' (P<0.05) during infusion of epinine, but did not change significantly during dopamine infusion.8. The differential effects of epinine and dopamine on MAP, SVR, plasma NA (before and after adrenoceptor blockade) and prolactin, leads us to conclude that in conscious pigs, epinine is a more potent a, P2 and D2-receptor agonist, but a weaker D,-receptor agonist than dopamine.

In-vivo validation of on-line and off-line geometric coronary measurements using insertion of stenosis phantoms in porcine coronary arteries

Geometric coronary artery measurements with the Phillips Digital Cardiac Imaging System (DCI) and the Cardiovascular Angiography Analysis System (CAAS) were validated using percutaneous insertion of radiolucent stenosis phantoms in swine coronary arteries. Angiographic visualization of the stenosis lumens (phi 0.5, 0.7, 1.0, 1.4, 1.9 mm) was simultaneously recorded on DCI and cinefilm. The acquisition systems were calibrated by either the diameter of the guiding catheter (catheter CAL) or the isocenter method (isocenter CAL). Minimal luminal diameters (MLD) obtained with CAAS and DCI on 20 corresponding cineframes were compared with the true phantom diameters (PD). The accuracy of MLD measurements with the CAAS using isocenter CAL was -0.07mm, the precision 0.21 mm (r = 0.91; y = 0.30 + 0.79x; SEE = 0.19), with catheter CAL the accuracy was 0.09 mm, the precision 0.23 mm (r = 0.89; y = 0.19 + 0.74x; SEE = 0.19). The accuracy of MLD measurements using the DCI with isocenter CAL was 0.08 mm, the precision 0.15 min (r = 0.96; y = 0.08 + 0.86x; SEE = 0.14), with catheter CAL the accuracy was 0.18 mm, the precision 0.21 mm (r = 0.92; y = 0.09 + 0.76x; SEE = 0.17). DCI underestimated PD with isocenter CAL (p less than 0.05) and with catheter CAL (p less than 0.001). MLD can be measured with high accuracy, both applying on-line digital as well as off-line cineangiographic analysis. The results of digital measurements demonstrate high reliability of the new digital software package.

Development of a polymer endovascular prosthesis and its implantation in porcine arteries

A polyethylene-terephthalate braided mesh stent has been developed for application in the (coronary) arterial tree. In vitro measurements showed that the radial pressure delivered by this device was in the same range as that of a stainless steel stent. Hysteresis-like behavior, however, occurred after constraining the polyester stent for a period of only 15 minutes on a delivery system for percutaneous implantation. This implies that the polymer stent must be mounted on this delivery system immediately before the placement procedure, and that either a diameter in the unconstrained condition must be selected, which is considerably larger than the diameter of the target vessel, or stent expansion has to be enhanced by balloon expansion. Taking into account the results obtained during the in vitro studies, we investigated the angiographic patency and histologic features after implantation of this polyester stent in peripheral arteries of pigs. In four animals eight stents were placed. Except for heparin during the implantation procedure only, antithrombotic or antiplatelet drugs were not administered. After 4 weeks repeat angiography was performed. Angiography revealed that five of the six correctly placed stents were patent. At autopsy, two additional patent stents proved to be located in the aortic bifurcation, probably due to failure of the delivery system. Quantitative assessment showed that the mean luminal diameters of the site of stent placement were 3.3 +/- 0.2 mm before, 3.2 +/- 0.2 mm immediately after, and 3.1 +/- 0.3 mm at 4 weeks after implantation. Histology demonstrated an inflammatory reaction of variable severity around the stent fibers. Quantitative histologic measurements showed that the thickness of the neointima was 114 +/- 38 mum after 4 weeks. In conclusion, polyester stents can be constructed with mechanical properties similar to stainless steel stents. Hysteresis-like behavior of polyester stents, however, influences the selection of the nominal stent diameter as well as the forces exerted to the vessel wall. After implantation in porcine peripheral arteries, five of six correctly placed stents were patent at 4 weeks. The extent of neointimal proliferation was similar to that observed after placement of metal stents in swine, despite the presence of a more pronounced inflammatory reaction.

Cardiovascular effects of the novel potassium channel opener bimakalim in conscious pigs after myocardial infarction: a comparative study with nicorandil

The benzopyran-derivative bimakalim is an ATP-dependent potassium channel activator that has been shown to be a potent arterial vasodilator in anesthetized pigs. In the present study we evaluated the cardiovascular profile of bimakalim in normal conscious animals and conscious animals with chronic left ventricular dysfunction and compared the results to those obtained with nicorandil. In normal conscious pigs, bimakalim (37.5-300 ng/kg/min, n = 6) and nicorandil (10-80 micrograms/kg/min, n = 8) increased cardiac output from 2.7 +/- 0.1 l/min to 3.8 +/- 0.2 l/min and from 2.7 +/- 0.1 l/min to 3.9 +/- 0.3 l/min (both p less than .05) due to increases in heart rate (up to 62 +/- 14% and 74 +/- 9%, respectively, both p less than .05). The mean arterial blood pressure decreased gradually from 104 +/- 4 mmHg to 91 +/- 5 mmHg with bimakalim and from 98 +/- 3 mmHg to 84 +/- 5 mmHg with nicorandil (both p less than .05), due to similar decreases in systemic vascular resistance. LVdP/dtmax also increased with both drugs (up to 48 +/- 11% and 69 +/- 7%, respectively, p less than .05), but left ventricular end-diastolic pressure remained unchanged with bimakalim, while it gradually decreased from 9 +/- 1 mmHg to 5 +/- 1 mmHg (p less than .05) with nicorandil. In pigs with a 3- to 4-week-old myocardial infarction, the vasodilator responses to bimakalim (n = 8) and nicorandil (n = 9) were not affected, but the increases in heart rate and LVdP/dtmax were attenuated compared to the effects in the normal animals.(ABSTRACT TRUNCATED AT 250 WORDS)

Metabolism of angiotensin I by different tissues in the intact animal

To quantify regional conversion of angiotensin (ANG) I to ANG II and its degradation to peptides other than ANG II, monoiodinated 125I-labeled ANG I was given to anesthetized pigs by constant infusion into the left cardiac ventricle. At steady state, blood samples were taken from the aorta and various regional veins. Distribution volume of ANG I appeared to be 24% of body weight. After angiotensin-converting enzyme (ACE) inhibitor treatment, fractional ANG I metabolism (fraction of arterially delivered ANG I that was metabolized during a single passage of blood) was 10% in the lungs (conversion 4%), compared with 56% in the combined systemic vascular beds (conversion 1%). Fractional ANG I metabolism during ACE inhibition was 93% in the kidney; 50-70% in myocardium, skeletal muscle, head, and skin; 21% in the left cardiac cavity; and 14% in the right cardiac cavity. Without ACE inhibition, fractional ANG I metabolism was 29% in the lungs (conversion 25%); 49% in the combined systemic vascular beds (conversion 10%); 38% in the left cardiac cavity (conversion 11%); and 14% in the right cardiac cavity (conversion 0%). It may thus be concluded that 1) extrapulmonary vascular beds make an important contribution to the conversion of circulating ANG I and 2) there is rapid extrapulmonary ANG I degradation that does not depend on ANG I-II conversion.

Production of angiotensins I and II at tissue sites in intact pigs

To estimate the contribution of angiotensin (ANG) I and II production at tissue sites to the circulating levels, ANG I and II and their radiolabeled counterparts were measured in arterial and venous plasma across various vascular beds during constant infusion of 125I-ANG I into the left cardiac ventricle of anesthetized pigs. In the combined systemic vascular beds, ANG I production was closely correlated with plasma renin activity (PRA) and ANG II production was greater than in the lungs. In the lungs virtually no ANG I but 31% of ANG II in venous plasma was derived from de novo production, which could be fully accounted for by conversion of circulating ANG I. In myocardium, head, skin, skeletal muscle, and kidney, respectively, 40, 58, 55, 67, and 94% of venous ANG I, and 32, 49, 40, 59, and 85% of venous ANG II were derived from de novo production. In these extrapulmonary beds part of de novo produced ANG I and II appeared not to be generated, respectively, by PRA and by conversion of circulating ANG I. These results indicate that production of ANG I at tissue sites contributes to its circulating level and that some circulating ANG II may not be derived from circulating ANG I.

Pressure-maximal coronary flow relationship in regionally stunned porcine myocardium

In view of variable results on maximal coronary blood flow in stunned myocardium, we studied the pressure-maximal coronary flow (PMCF) relationship in stunned myocardium in 12 anesthetized swine by using intracoronary adenosine (20 micrograms/kg). Subendocardial systolic segment shortening (SS) measured with sonomicrometry was 19 +/- 5% (means +/- SD) at baseline and 7 +/- 6% (P less than 0.01) at 30 min of reperfusion after 15 min of low-flow ischemia, at which time postsystolic shortening was present. Myocardial stunning increased the slope of the PMCF regression line (alpha PMCF) from 3.34 +/- 1.03 to 3.89 +/- 1.33 ml.min-1.mmHg-1 (P less than 0.01). Atrial pacing at 40 beats/min above spontaneous heart rate (n = 6) further reduced subendocardial SS to 6 +/- 6% (P less than 0.05). Dobutamine (4 micrograms.kg-1.min-1; n = 6) increased subendocardial SS to 13 +/- 5% (P less than 0.05) and abolished postsystolic shortening. Both interventions left alpha PMCF unchanged. In conclusion, myocardial stunning was associated with an increase in alpha PMCF that most likely resulted from the decreased contractile function. The absence of an effect of dobutamine may be due to its predominant action on diastolic function.

Coronary vasodilatory action of elgodipine in coronary artery disease

The effects of intravenous elgodipine, a new second-generation dihydropyridine calcium antagonist, on hemodynamics and coronary artery diameter were investigated in 15 patients undergoing cardiac catheterization for suspected coronary artery disease. Despite a significant decrease in systemic blood pressure, elgodipine infused at a rate of 1.5 micrograms/kg/min over a period of 10 minutes did not affect heart rate and left ventricular end-diastolic pressure. The contractile responses during isovolumic contraction showed a slight but significant increase in maximum velocity (56 +/- 10 to 60 +/- 10 seconds-1; p less than 0.005), whereas the time constant of early relaxation was shortened from 49 +/- 11 to 44 +/- 9 ms (p less than 0.05). Coronary sinus and great cardiac vein flow increased significantly by 15 and 26%, respectively. As mean aortic pressure decreased, a significant decrease in coronary sinus (-27%) and great cardiac vein (-28%) resistance was observed, while the calculated myocardial oxygen consumption remained unchanged. In all, 69 coronary segments (including 13 stenotic segments) were analyzed quantitatively using computer-assisted quantitative coronary angiography. A significant increase in mean coronary artery diameter (2.27 +/- 0.53 to 2.48 +/- 0.53 mm; p less than 0.000001), as well as in obstruction diameter, (1.08 +/- 0.29 to 1.36 +/- 0.32 mm; p less than 0.02), was observed. The results demonstrate that elgodipine, in the route and dose described, induces significant vasodilatation of both coronary resistance and epicardial conductance vessels, without adverse effects on heart rate, myocardial oxygen demand and contractile indexes.

Effect of epinine on systemic hemodynamics and regional blood flow in conscious pigs

Intravenous (i.v.) infusions (1, 2.5, 5, and 10 micrograms/kg/min for 10 min) were used to evaluate the cardiovascular effects of epinine (N-methyl-dopamine) in 8 conscious pigs. Epinine is a nonselective and nonspecific dopamine (DA) agonist, that also stimulates alpha- and beta-adrenoceptors. Epinine (1-5 microgram/kg/min) increased cardiac output (CO) by up to 15 +/- 5% (p less than 0.05), owing to an increase in heart rate (HR, 24 +/- 6%), but an increase in stroke volume (SV, 16 +/- 4%) caused the further increase in CO at 10 micrograms/kg/min. Mean arterial blood pressure decreased gradually from 100 +/- 5 mm Hg to 84 +/- 4 mm Hg during infusions up to 5 microgram/kg/min, but increased to 89 +/- 4 mm Hg during infusion of 10 micrograms/kg/min (p less than 0.05). Systemic vascular resistance had decreased from 36.5 +/- 2.8 to 27.5 +/- 3.0 mm Hg/L/min after infusion of 5 micrograms/kg/min but did not change further during infusion of 10 micrograms/kg/min. LV dP/dtmax increased only at 10 micrograms/kg/min. Myocardial blood flow did not change at any dose, owing to metabolically regulated coronary vasodilatation (myocardial work did not change). Flow to the adrenals (up to 110 +/- 37%) and the spleen (up to 95 +/- 13%) increased dose dependently. Cerebral blood flow increased only at the highest dose (15 +/- 5%, p less than 0.05); flow to the kidneys, liver, small intestine, and skeletal muscle did not change. Flow decreased to the stomach (21 +/- 5%) and skin (for doses less than 2.5 micrograms/kg/min).(ABSTRACT TRUNCATED AT 250 WORDS)

The selective bradycardic effects of zatebradine (UL-FS 49) do not adversely affect left ventricular function in conscious pigs with chronic coronary artery occlusion

This study was designed to test whether the selective bradycardic effects of zatebradine (UL-FS 49) were altered in the setting of chronic mild left ventricular dysfunction secondary to a myocardial infarction. We therefore administered four doses of UL-FS 49 at 15-min intervals (cumulative doses of 10, 30, 100, and 300 micrograms/kg) to eight normal conscious pigs and to seven pigs in which the left circumflex coronary artery was occluded 3 weeks previously. Left ventricular dysfunction in this second group of animals was manifested by an increase in left ventricular end-diastolic pressure (LVEDP, 11 +/- 2 mmHg vs. 7 +/- 1 mmHg, respectively; p less than 0.05) and a decrease in LVdP/dtmax (3020 +/- 210 mmHg vs. 3720 +/- 210 mmHg, respectively; p less than 0.05). The results showed that UL-FS 49 was equally effective in reducing heart rate in both groups of animals [from 126 +/- 4 to 95 +/- 2 beats/min and from 140 +/- 5 to 98 +/- 6 beats/min for the normal animals and for the animals with a chronic myocardial infarction (MI), respectively]. The duration of left ventricular systole was not affected, but the duration of diastole was prolonged from 290 +/- 10 msec to 420 +/- 20 msec in the normal animals and from 250 +/- 10 msec to 430 +/- 30 msec in the animals with MI (both p less than 0.05). Up to 100 micrograms/kg UL-FS 49 did not affect arterial blood pressure, whereas LVdP/dtmax and cardiac output decreased by less than 10% in either group.(ABSTRACT TRUNCATED AT 250 WORDS)

Catecholamines and regional hemodynamics during isovolemic hemodilution in anesthetized pigs

The effects of stepwise isovolemic hemodilution on systemic and regional hemodynamics, oxygen flux, and circulating catecholamines were studied in six pigs anesthetized with midazolam and fentanyl. Reduction of the hematocrit from 28 to 9% resulted in doubling of the cardiac output, mainly due to an increase in stroke volume. Regional blood flows, measured using the radioactive microsphere technique, showed an increase in blood flow to all organs except liver (hepatic artery fraction) and adrenals, with a redistribution of cardiac output in favor of heart and brain (increase in blood flow 420 and 170%, respectively). Oxygen flux to most organs did not decrease until hematocrit decreased to 9%, while total body oxygen consumption was well maintained. Left ventricular oxygen consumption increased, but because left ventricular blood flow also increased, left ventricular extraction ratio did not increase. Circulating catecholamines did not play any role in these regulatory mechanisms.

Can myocardial contrast echo determine coronary flow reserve?

OBJECTIVE

The aim was to evaluate the applicability of myocardial contrast echocardiography in the measurement of coronary flow reserve.

METHODS

Eleven anaesthetised open chest pigs were studied, in which coronary atherosclerosis had been induced by abrasion of the left anterior descending coronary artery at one month, followed by an atherogenic diet for eight months. Coronary flow reserve was determined by electromagnetic flow measurement and contrast echocardiography before and after partial occlusion of the left anterior descending coronary artery, using papaverine as a coronary vasodilator. Coronary blood flow was reduced by tightening a clamp placed around the coronary artery. Systemic haemodynamics and myocardial wall thickness (epicardial ultrasound 5 MHz transducer) were recorded simultaneously. Echocardiograms were recorded on VHS tape and analysed by digitised videodensitometry off line for construction of the time v videointensity curve (time-intensity curves). From these curves washout time (T50), area under the curve, peak contrast intensity, and time to peak intensity were calculated.

RESULTS

Following papaverine, coronary blood flow increased significantly from 47 (SD 23) ml.min-1 at baseline to 88(39) ml.min-1 (p less than 0.05). During the stenosis, flow decreased to 19(16) ml.min-1 (p less than 0.01), and increased to 38(29) ml.min-1 (p less than 0.05 v stenosis) after administration of papaverine. Correlations between coronary blood flow and indices calculated from the quantitative videodensitometric analysis were poor, varying between r = 0.03 for area at control flow to r = 0.62 for T50 during stenosis. The same was true for coronary flow reserve: r = 0.09 for peak to r = 0.75 (p less than 0.05) for time to peak without the stenosis.

CONCLUSIONS

Current limitations in injection, imaging, and analysis techniques cause variability in data from time-intensity curves, which precludes accurate quantification of coronary flow (reserve) by myocardial contrast echocardiography.

Effect of antiischemic therapy on coronary flow reserve and the pressure-maximal coronary flow relationship in anesthetized swine

The effect of nifedipine (0.5, 1.0, and 2.0 micrograms/kg/min), metoprolol (0.1, 0.5, and 1.0 mg/kg), the beta 1-selective adrenoceptor partial agonist epanolol (10, 50, and 200 micrograms/kg), or equivalent volumes of isotonic saline (n = 6, in each group), on coronary blood flow capacity were studied in anesthetized swine. Intracoronary bolus injections of adenosine (20 micrograms/kg/0.2 ml) were administered without and during three levels of coronary stenosis, prior to and following each dose of drug, to obtain maximal coronary blood flows at different perfusion pressures in the autoregulatory range. Coronary perfusion pressures were varied by partial inflation of a balloon around the left anterior descending coronary artery. Special care was taken that the stenoses not lead to myocardial ischemia. Three indices of coronary blood flow capacity were used: absolute coronary flow reserve (ACFR, the ratio of maximal to resting coronary blood flow), the slope and the extrapolated pressure at zero flow (Pzf) of the pressure-maximal coronary flow (PMCF) relationship, and relative coronary flow reserve (RCFR, the ratio of maximal coronary blood flow with a stenosis to maximal coronary blood flow without a stenosis) at two of the three levels of stenosis. Nifedipine decreased ACFR from 4.5 +/- 1.9 to 1.9 +/- 0.3 (mean +/- SD; p less than 0.05), reflecting in part the increase in resting coronary blood flow. The nifedipine-induced changes in maximal coronary blood flow were not only due to a drop in perfusion pressure, as the slope of the PMCF relationship decreased from 2.27 +/- 0.49 ml/(min.mm Hg) to 1.54 +/- 0.51 ml/(min.mm Hg) (p less than 0.05), and Pzf decreased from 30 +/- 4 mm Hg to 20 +/- 7 mm Hg (p less than 0.05). Consequently, calculated maximal coronary blood flow was attenuated from 114 +/- 31 ml/min to 93 +/- 37 ml/min at 80 mm Hg, but was enhanced from 23 +/- 13 to 37 +/- 24 ml/min at 40 mm Hg coronary perfusion pressure. In concert with the change in the PMCF relationship, RCFR at equivalent severe stenosis increased from 0.33 +/- 0.06 to 0.47 +/- 0.10 (p less than 0.05). No changes were observed with metoprolol, epanolol, or saline. The effect of nifedipine on the PMCF relationship not only provides a mechanism for the drug's antiischemic action, but should also be considered in the interpretation of coronary flow reserve measurements in patients on nifedipine treatment.