Failure of a slow channel calcium antagonist, verapamil, to retard atherosclerosis in the Watanabe heritable hyperlipidemic rabbit: an animal model of familial hypercholesterolemia.

Verapamil and other slow channel calcium antagonists have been reported to retard atherosclerosis in rabbits fed a high cholesterol diet. Because atherosclerosis in such a model may differ significantly from human atherosclerosis, experiments were conducted to prevent atherosclerosis with verapamil in the Watanabe heritable hyperlipidemic (WHHL) rabbit, which is a genetic, metabolic and pathologic model of homozygous familial hypercholesterolemia. At 2 months of age, 23 WHHL rabbits were divided into two groups since earlier studies showed no macroscopic atherosclerosis at 2 months. Group A (n = 11) was fed standard rabbit chow for 6 months. Group B (n = 12) received oral verapamil (46 mg/kg per day) absorbed in the identical chow as fed to Group A and subcutaneous verapamil (0.25 mg/kg twice daily 6 days a week). In Group B, mean serum verapamil concentrations (+/- SEM) averaged 16.9 +/- 1.9 ng/ml at 3 hours after subcutaneous injection. Sex ratios and serum cholesterol concentrations were the same in both groups. The percent of aortic surface area with visible plaque in Group A versus B was 49 +/- 7 versus 43 +/- 7%, respectively, of the entire aorta, and 61 +/- 5 versus 65 +/- 5%, respectively, of the proximal 3 cm of aorta (p = NS). Thus, verapamil did not suppress atherosclerosis in WHHL rabbits at serum drug levels greater than those reported to be effective in other models.

Effects of fluorocarbons with and without oxygen supplementation on cardiac hemodynamics and energetics.

Because of uncertainty about the mechanism by which fluorocarbons ameliorate myocardial ischemia, the effects of a fluorocarbon emulsion, perfluorodecalin and perfluorotripropylamine (Fluosol-DA 20% TM) with and without 100% O2 inhalation, on cardiac hemodynamics and energetics were studied in the anesthetized dog. Left ventricular (LV) intramural partial pressure of oxygen (PmO2) was measured by mass spectrometry before and after intravenous infusion of Fluosol-DA 20% (40 ml/kg), and was compared with measurements made in another group of dogs receiving the volume expander dextran (36 ml/kg). Both groups of dogs were then ventilated with 100% O2 and repeat measurements were performed. In the 11 animals receiving fluorocarbons, there were increases in left atrial pressure, LV myocardial blood flow, and LV myocardial O2 consumption (MVO2) compatible with volume expansion. After 100% O2, LV MVO2 decreased to control values, while PmO2 increased to 127 +/- 48 mm Hg (p less than 0.001). There were no significant changes in heart rate, arterial pressure or first derivative of LV pressure (dP/dt) during the study. In 10 dogs treated with dextran there was no change in heart rate or dP/dt, but arterial and left atrial pressures were higher after dextran infusion and remained elevated after 100% O2 inhalation. LV MVO2 increased with volume expansion, and remained increased after 100% O2. PmO2 (66 +/- 18 mm Hg) after 100% O2 was lower (p less than 0.02) than in the fluorocarbon-treated dogs after O2 inhalation.(ABSTRACT TRUNCATED AT 250 WORDS)

Acute hemodynamic and electrophysiologic effects of propranolol in patients receiving diltiazem.

Because the combined use of a beta-adrenergic blocking agent and a calcium antagonist may be beneficial in some patients with severe angina, the acute hemodynamic and electrophysiologic effects of intravenous propranolol in the presence and absence of oral diltiazem treatment was studied. In 22 patients (11 men, 11 women, mean age 50 years), 12 receiving diltiazem (mean 243 mg/day, range 180 to 360) and 10 not receiving diltiazem, hemodynamic and electrophysiologic variables were measured before and 5 minutes after intravenous propranolol (0.1 mg/kg). Cardiac index (by thermodilution) and left ventricular (LV) peak dP/dt fell and LV end-diastolic pressure increased similarly in both groups. Mean systemic arterial pressure was unchanged. Coronary sinus blood flow (by thermodilution) decreased slightly in patients receiving diltiazem and was unchanged in those not receiving it. Propranolol caused a similar reduction in heart rate and increase in atrio-His conduction in both groups. Thus, when intravenous propranolol is given to patients with normal or only mildly depressed LV systolic function, the hemodynamic and electrophysiologic effects are similar in those receiving and not receiving oral diltiazem.

Adjunctive therapy in thrombolysis for acute myocardial infarction.

The value of prompt coronary reperfusion utilizing thrombolytic therapy during acute myocardial infarction has been well established. However, new data indicates that although rapid reperfusion is imperative, this positive effect may, in fact, be partially or totally negated if patency is not sustained and complete. The following manuscript discusses the role of adjunctive agents in thrombolysis that are essential in preventing coronary reocclusion. It is this important function that serves to prevent recurrent ischemia and reinfarction, thereby improving resultant left ventricular function. This, in turn, should have a positive effect on post-thrombolytic mortality. The data presented in this paper supports high dose, titrated intravenous heparin and aspirin as required adjunctive therapy to thrombolytic treatment in the setting of acute myocardial infarction.

Effects of the selective thromboxane synthetase inhibitor dazoxiben on variations in cyclic blood flow in stenosed canine coronary arteries.

Recent studies suggest that platelet activation and subsequent thromboxane (TX) A2 release play important roles in certain coronary syndromes. To further test this possibility, we examined the ability of a selective TXA2-synthetase inhibitor, dazoxiben (UK-37-248), to abolish cyclic flow reductions (CFRs) that occur in experimentally stenosed canine coronary arteries. CFRs, which are characterized by progressive declines in coronary blood flow and interrupted by sudden and usually spontaneous restorations of flow, were produced by placing hard plastic cylindrical constrictors (5 mm long X 4.5 mm outer diameter) on the proximal left anterior descending or circumflex coronary artery in open-chest, anesthetized dogs. Coronary blood flow was measured with pulsed Doppler flow probes placed proximal to the constrictors and regional myocardial blood flow with 15 micron radiolabeled microspheres. CFRs were observed for 1 hr, during which coronary blood flow was monitored continuously. Regional myocardial blood flow was measured before constriction, when coronary blood flow appeared to be at its nadir, and after spontaneous restorations of flow. After 1 hr dazoxiben (2.5 mg/kg iv) or an equal volume of saline was given and coronary blood flow was monitored for another hour. Dazoxiben abolished CFRs completely in 18 of 28 dogs and significantly reduced their frequency in the dogs receiving the drug (10.1 +/- 0.8 vs 3.2 +/- 1.0 per hour [+/- SE]; p less than .001, n = 28). The frequency and magnitude of variations in cyclic blood flow were unchanged after saline (8.8 +/- 0.8 vs 9.0 +/- 1.0 per hour; p = NS, n = 13). The lowest levels of coronary blood flow before and after dazoxiben were 8.6 +/- 2.2% and 48.8 +/- 5.4% of control, respectively (p less than .001, n = 28), whereas this parameter remained unchanged after saline (18.7 +/- 5.7% vs 13.4 +/- 4.1%, respectively; n = 13). The levels of TXB2 and 6-keto-prostaglandin (PG) F1 alpha (stable breakdown products of TXA2 and prostacyclin, respectively) were measured in blood collected from aortic and distal coronary arterial catheters before coronary constriction (control), during CFRs, and after administration of dazoxiben. TXB2 levels measured distal to the stenosis were increased fivefold during CFRs (352 +/- 126 vs 71 +/- 18 pg/ml plasma; p less than .03) and were reduced to preconstriction (control) levels by dazoxiben (57 +/- 12 pg/ml). Aortic TXB2 levels almost doubled with CFRs and also returned to control levels after dazoxiben.(ABSTRACT TRUNCATED AT 400 WORDS)

Effect of diltiazem and propranolol on left ventricular segmental relaxation during temporary coronary arterial occlusion and one month reperfusion in conscious dogs.

Using sonar microcrystals implanted in conscious dogs, we have characterized left ventricular segmental relaxation (LVSR) by measuring the mean rate to half end-diastolic thinning (RHEDT) and the late diastolic thinning fraction (TF). In protocol 1 (five nonischemic dogs), RHEDT correlated with changes in left ventricular dP/dt (r = .87) and systemic arterial pressure (r = -.80) but not with alterations in heart rate. Only systemic arterial pressure importantly influenced TF (r = -.65). In protocol 2 (21 dogs), LVSR paralleled net systolic segmental wall thickness (NET) during both 2 and 4 hr of coronary occlusion followed by 1 month reperfusion. Both LVSR and NET remained depressed during 2 and 4 hr of coronary occlusion and through 24 hr of reperfusion, but both also gradually improved afterwards. In protocol 3, 31 dogs underwent 4 hr of coronary occlusion with 1 month of reperfusion. Among these animals, 11 dogs (group S4) received saline after 1 hr of occlusion, nine dogs (group P4) received propranolol, and 11 dogs (group D4) received diltiazem. Drug therapy was stopped at 2 hr of reperfusion. In segments with mildly and moderately depressed NET, LVSR was significantly increased in group D4 vs group S4 animals during the diltiazem infusion. Expressed as mean percentage of control value +/- SEM, RHEDT of moderately dysfunctional segments in group D4 compared with group S4 measured 53 +/- 10% vs 25 +/- 5%, respectively, at 2 hr of occlusion of the left anterior descending coronary artery (p = .03), 76 +/- 17% vs 28 +/- 8%, respectively, at 4 hr of occlusion (p = .01), and 74 +/- 11% vs 33 +/- 10%, respectively, at 1 hr of reperfusion (p less than .05). The differences in TF at these same time points were 106 +/- 10% vs 70 +/- 9% (p less than .03), 105 +/- 7% vs 65 +/- 16% (p less than .02), and 106 +/- 11% vs 74 +/- 13% (p less than .05), respectively. The improvement in LVSR occurred independently of changes in NET. The values of LVSR in the diltiazem-treated dogs fell to the levels of groups S4 and P4 within 24 hr of stopping the intervention. Propranolol did not significantly alter LVSR over the short or long term. The increase in LVSR during administration of diltiazem did not appear to be mediated by changes in contractility or regional myocardial blood flow, but were probably mediated in part by afterload reduction and possibly by a reduction in calcium entry into ischemic myocardium.

The effects of alpha 2-adrenergic and serotonergic receptor antagonists on cyclic blood flow alterations in stenosed canine coronary arteries.

Platelets possess alpha 2-adrenergic and serotonergic (5-hydroxytryptamine) receptors which are thought to mediate the in vitro proaggregatory effects of epinephrine and serotonin, respectively. However, their importance in platelet aggregation in vivo is uncertain. In the present study, we evaluate the ability of yohimbine and ketanserin, relatively selective alpha 2-adrenergic and serotonin antagonists, respectively, to alter cyclic flow reductions in stenosed coronary arteries in open-chest, anesthetized dogs. These cyclic flow reductions, characterized by progressive declines in coronary blood flow interrupted by abrupt and, often spontaneous, restorations of flow, were produced by cylindrical constrictors placed on the left anterior descending coronary artery. A pulsed Doppler flow probe, placed proximal to the constrictor, was used to measure coronary blood flow. Regional myocardial blood flow was measured with 15-micron radiolabeled microspheres before coronary constriction and when coronary blood flow appeared to be at its nadir and zenith during cyclic flow reductions. After the cyclic flow reductions had been observed for 1 hour, yohimbine (1-2 mg/kg), ketanserin (0.25 or 0.5 mg/kg), or saline was given, and coronary blood flow and hemodynamics were monitored for another hour. The frequency of cyclic flow reductions and the mean of the three lowest nadirs of coronary blood flow (mean +/- SE) were compared between the first and second hours. Ketanserin, at doses of 0.25 and 0.50 mg/kg, virtually abolished cyclic flow reductions in all dogs tested. Yohimbine [1 mg/kg ( n = 14)] was partially effective in reducing the frequency (9.6 vs. 5.5 cyclic flow reductions/hr) and severity of cyclic flow reductions (nadirs of coronary blood flow = 6.2 +/- 2.4 vs. 20.9 +/- 6.1% of control). A higher dose of yohimbine [2 mg/kg (n = 7)] was no more effective. The frequency (9.3 +/- 0.9 vs. 9.3 +/- 1.0 CFR/hr) and severity (17.4 +/- 5.4 vs. 12.4 +/- 3.9% of control coronary blood flow) of cyclic flow reductions were not changed by saline. The relatively selective alpha 1-adrenergic antagonist, prazosin (0.01 mg/kg, iv), and the beta-adrenergic antagonist, propranolol (1-2 mg/kg, iv), did not affect the frequency or severity of cyclic flow reductions. Thus, the abilities of yohimbine to inhibit and ketanserin to abolish cyclic flow reductions in stenosed canine coronary arteries suggest that serotonin and, possibly, alpha 2-adrenergic agonists may influence cyclic flow alterations importantly in this model.