Effects of a calcium-channel antagonist on large and small coronary arteries in conscious dogs

Unraveling the Gordian knot of coronary pressure-flow autoregulation

The coronary circulation has the inherent ability to maintain myocardial perfusion constant over a wide range of perfusion pressures. The phenomenon of pressure-flow autoregulation is crucial in response to flow-limiting atherosclerotic lesions which diminish coronary driving pressure and increase risk of myocardial ischemia and infarction. Despite well over half a century of devoted research, understanding of the mechanisms responsible for autoregulation remains one of the most fundamental and contested questions in the field today. The purpose of this review is to highlight current knowledge regarding the complex interrelationship between the pathways and mechanisms proposed to dictate the degree of coronary pressure-flow autoregulation. Our group recently likened the intertwined nature of the essential determinants of coronary flow control to the symbolically unsolvable "Gordian knot". To further efforts to unravel the autoregulatory "knot", we consider recent challenges to the local metabolic and myogenic hypotheses and the complicated dynamic structural and functional heterogeneity unique to the heart and coronary circulation. Additional consideration is given to interrogation of putative mediators, role of K+ and Ca2+ channels, and recent insights from computational modeling studies. Improved understanding of how specific vasoactive mediators, pathways, and underlying disease states influence coronary pressure-flow relations stands to significantly reduce morbidity and mortality for what remains the leading cause of death worldwide.

Role of potassium channels in coronary vasodilation

K+ channels in coronary arterial smooth muscle cells (CASMC) determine the resting membrane potential ( Em) and serve as targets of endogenous and therapeutic vasodilators. Em in CASMC is in the voltage range for activation of L-type Ca2+ channels; therefore, when K+ channel activity changes, Ca2+ influx and arterial tone change. This is why both Ca2+ channel blockers and K+ channel openers have such profound effects on coronary blood flow; the former directly inhibits Ca2+ influx through L-type Ca2+ channels, while the latter indirectly inhibits Ca2+ influx by hyperpolarizing Em and reducing Ca2+ channel activity. K+ channels in CASMC play important roles in vasodilation to endothelial, ischemic and metabolic stimuli. The purpose of this article is to review the types of K+ channels expressed in CASMC, discuss the regulation of their activity by physiological mechanisms and examine impairments related to cardiovascular disease.

Sodium-calcium exchange mediated contraction in left anterior descending and left ventricular branch arteries

We tested the hypothesis that the de-endothelialized artery rings from the left anterior descending (LAD) coronary artery and its left ventricular branch (LVB) differ in their contractile responses to Na⁺–Ca²⁺-exchanger (NCX) mediated Ca²⁺-entry, muscarinic receptor activation with carbachol, and sarco/endoplasmic reticulum Ca²⁺ pump (SERCA) inhibition with thapsigargin. In LVB, the force of contraction (in N/g tissue) produced by the NCX mediated Ca²⁺-entry (17.5 ± 1.4) and carbachol (18 ± 1.5) was only slightly smaller than that due to membrane depolarization with KCl (24.0 ± 1.0). In contrast, in LAD the force of contraction produced with NCX (8.7 ± 0.7) and carbachol (6.1 ± 1.1) was much smaller than with KCl (15.7 ± 0.7). Thapsigargin also contracted LVB with greater force than LAD. When isolated microsomes were used, the binding to the muscarinic receptor antagonist quinuclidinyl benzilate was greater in LVB than in LAD. Microsomes were also used for Western blots. The intensities of signals for both SERCA and NCX were greater in LVB than in LAD. These biochemical observations were consistent with the contractile experiments. Thus, it appears that the differences between LAD and the resistance arteries may begin as early as LVB.

Comparative Effects of Pranidipine with Amlodipine in Rats with Heart Failure

The aim of the present study was to compare the cardioprotective properties of long-acting calcium channel antagonist pranidipine with amlodipine in rat model of heart failure induced by autoimmune myocarditis. Twenty-eight days after immunization the surviving rats were randomized for the oral administration of low-dose amlodipine (1 mg/kg/day), high-dose amlodipine (5 mg/kg/day), pranidipine (0.3 mg/kg/day) or vehicle (0.5% methylcellulose). After oral administration for 1 month, the animals underwent echocardiography and hemodynamic analysis. Histopathology, immunohistochemistry, and Western immunoblotting were carried out in the heart samples. Both pranidipine and high-dose amlodipine increased survival rate. Although the heart rate did not differ among the four groups, left ventricular end-diastolic pressure was significantly decreased and +/-dP/dt was increased in the pranidipine- and high-dose amlodipine-treated rats, but not in low-dose amlodipine-treated rats. In comparison to amlodipine treatment, pranidipine treatment significantly reduced myocyte size and central venous pressure. Furthermore, both pranidipine and high-dose amlodipine treatment significantly reduced myocardial protein levels of atrial natriuretic peptide and inducible nitric oxide synthase, whereas pranidipine only significantly decreased tumor necrosis factor-alpha, and improved sarcoplasmic reticulum Ca2+ ATPase2 protein levels. We conclude that pranidipine ameliorates the progression of left ventricular dysfunction and cardiac remodeling in rats with heart failure after autoimmune myocarditis in a lower dose when compared to amlodipine and which may be a clinically potential therapeutic agent for the treatment of heart failure.

Effects of intravenous amlodipine on coronary hemodynamics in subjects with angiographically normal coronary arteries

The aim of the current study was to assess the ability of amlodipine to dilate the coronary vessels in subjects with angiographically normal coronary arteries and normal left ventricular function. Ten patients, six women and four men (mean age 48 +/- 14 years, range 25-67 years) were enrolled. Coronary flow velocity and coronary perfusion pressure were invasively measured at baseline, during intracoronary adenosine (1-mg bolus) and at 5, 15, and 30 min following IV amlodipine (10 or 20 mg). Quantitative coronary angiography was performed at baseline and at 5, 15, and 30 min after amlodipine. Coronary cross-sectional area and mean coronary flow velocity progressively increased after amlodipine administration, resulting in an average increase in coronary flow at 30 min of 76%. On an individual basis, all patients but one showed a consistent trend toward a progressive coronary vasodilator effect of amlodipine over time. The peak effect of amlodipine on baseline mean coronary flow velocity was 43 +/- 12% that of adenosine. This is the first clinical study demonstrating that the IV administration of amlodipine produces a powerful coronary vasodilatation in subjects with angiographically normal coronary arteries and normal ventricular function, besides its known systemic vasodilating effects. The coronary vasodilating properties of amlodipine are particularly expressed at the microcirculatory level.

Beneficial effects of therapy on the progression of structural remodeling during healing after reperfused and nonreperfused myocardial infarction: different effects on different parameters

BACKGROUND

Structural left ventricular remodeling after myocardial infarction is a complex process with several pathophysiologic descriptors that can be modified by pharmacotherapy. However, the possibility that different classes of antiremodeling agents might exert different effects on different remodeling parameters after reperfused and nonreperfused myocardial infarction has not been systematically studied.

METHODS AND RESULTS

We measured detailed left ventricular remodeling parameters in vivo (echocardiograms) repeatedly over 6 weeks and ex vivo (planimetry) at 6 weeks after myocardial infarction in 36 dogs randomized (factorial design) after reperfused or nonreperfused myocardial infarction to 6 weeks of twice daily oral therapy with the calcium channel blocker amlodipine (5 mg), the angiotensin-converting enzyme inhibitor enalapril (5 mg) or placebo, and 18 matching sham or control animals. Compared to placebo and control groups over 6 weeks, both agents reduced left ventricular loading and limited overall remodeling in both reperfused and nonreperfused groups, but there were pertinent differences. Enalapril limited the increase in left ventricular asynergy in the reperfused group. Both enalapril and amlodipine limited infarct zone thinning in the nonreperfused groups but increased infarct zone thinning in the reperfused groups, despite preserved infarct zone collagen with amlodipine. Enalapril decreased left ventricular diastolic volume and mass more than amlodipine in the reperfused group and increased left ventricular ejection fraction in the nonreperfused group. Both agents limited regional and global shape deformation in reperfused and non-reperfused groups. Diastolic wall stress in the infarct zone decreased with amlodipine, and increased with enalapril and reperfusion.

CONCLUSIONS

Different antiremodeling therapies may exert different effects on different remodeling parameters during healing after reperfused myocardial infarction. Significant interactions occur during reperfusion. More than one variable may be needed for the comprehensive assessment of the antiremodeling efficacy of different therapies.

Calcium channel blockade limits cardiac remodeling and improves cardiac function in myocardial infarction-induced heart failure in rats

Calcium channel antagonists (CCAs) have been proposed to prevent cardiac events after myocardial infarction (MI). However, unwanted effects, such as negative inotropy, limit their use in many cases. The aim of this study was to compare the effects of long-term treatment with the CCAs, mibefradil, verapamil, and amlodipine, administered before and after chronic MI on myocardial remodeling and cardiac function. MI was induced by permanent ligation of the left coronary artery in male Wistar rats. Infarcted animals were treated with placebo, mibefradil (10 mg/kg/d po), verapamil (8 mg/kg bid po), or amlodipine (4 mg/kg/d po). Treatment was started 7 days before or 3 h after MI induction. Six weeks after MI, mean arterial blood pressure (MAP), heart rate (HR), left ventricular end diastolic pressure (LVEDP), and cardiac contractility (dP/dt(max)) were measured. Morphometric parameters such as infarct size (IS), left ventricular dilation (LVD), septal thickness (ST), and cardiac fibrosis were determined in picrosirius red-stained hearts. Six weeks after MI, MAP and dP/dt(max) were decreased, whereas LVEDP and HR were increased in placebo-treated controls. The hearts featured an IS of 45%, left ventricular dilation, cardiac fibrosis, and septal thinning. MAP of all CCA-treated animals was increased, whereas LVEDP was decreased and dP/dt(max) increased 7-day pre- and 3-h post-MI started in mibefradil- and amlodipine-treated animals, but not in verapamil-treated animals. In contrast to amlodipine treatment, before and after MI started mibefradil and verapamil treatment decreased HR. Pretreatment with all CCA reduced IS and increased ST, whereas only mibefradil and amlodipine pretreatment prevented LVD and cardiac fibrosis. After MI started treatment with mibefradil and amlodipine reduced IS and cardiac fibrosis, and increased ST. Long-term treatment with the CCAs mibefradil, verapamil, and amlodipine reduced myocardial remodeling and improved cardiac function in MI-induced heart failure in rats.

Effects of short-term administration of sublingual nifedipine on coronary arterial wall elastic properties: evaluation by intravascular ultrasound

Intravascular ultrasound is suited to measure coronary cross-sectional anatomy. Therefore the regional coronary wall elasticity was evaluated by examining the response to nifedipine. In 20 patients, coronary ostial pressure (P) and intravascular ultrasound images were simultaneously recorded before and after sublingual administration of 10 mg nifedipine. We identified the perimeter of the vessel wall, with normal or atherosclerotic plaque, on ultrasound image. At the atherosclerotic site, we measured segmental perimeter (S) for each normal or plaque segment. The ratio of the individual segment length (delta S/delta P) and cyclic variation of cross-sectional area (delta A/delta P) per mm Hg increase in P were calculated. Nifedipine decreased pressure (133/79-120/73 mm Hg) and increased heart rate (79-82 beats/min). After nifedipine, delta A/delta P increased from 8.5 +/- 10.2 x 10(-3) to 16.5 +/- 14.4 x 10(-3) mm2/mm Hg at 20 normal sites (p = 0.005) but was unchanged at 17 atherosclerotic sites (6.6 +/- 7.0 x 10(-3) to 6.7 +/- 7.1 x 10(-3) mm2/mm Hg). Nifedipine increased delta S/delta P in normal segments (4.5 +/- 8.7 x 10(-3) to 9.9 +/- 10.9 x 10(-3) mm/mm Hg; p = 0.02) but produced no change in segments with calcified or soft plaque (-1.1 +/- 0.3 x 10(-3) to 1.4 +/- 1.6 x 10(-3) mm/mm Hg and 5.0 +/- 3.6 x 10(-3) to 6.1 +/- 4.8 x 10(-3) mm/mm Hg, respectively). This study demonstrated that nifedipine increases regional coronary arterial elasticity at normal segments but not at that containing mildly atherosclerotic segment, and likely that the arterial wall function indicated by the response to nifedipine was impaired at an early stage of atherosclerosis.

Determination of the mean cross-sectional area of the thoracic aorta using a double indicator dilution technique

A double indicator dilution technique for determining the mean cross-sectional area (CSA) of a blood vessel in vivo is presented. Analogous to the thermodilution method, dilution of hypertonic saline was measured by an electrical conductance technique. Because the change in conductance rather than absolute conductance was used to calculate CSA, pulsatile changes in shear rate of blood and conductance of surrounding tissues had no effect on the data. To calculate CSA from an ion mass balance, cardiac output was needed and estimated from the thermodilution curve using the same "cold" (hypertonic) saline injection. The mean CSA, obtained from this double indicator dilution method (CSAGD), was compared with the CSA obtained from the intravascular ultrasound method (IVUS) in 44 paired observations in six piglets. The regression line is close to the line of identity (CSAGD = -1.83 + 1.06 . CSAIVUS, r = 0.96). The difference between both CSAs was independent of the diameter of the vessel, on average -0.99 mm2 +/- 2.64 mm2 (mean CSAGD = 46.84 +/- 8.21 mm2, mean CSAIVUS = 47.82 +/- 9.08 mm2) and not significant. The results show that the double indicator dilution method is a reliable technique for estimating the CSA of blood vessels in vivo.

Antiischemic effect of intracoronary diltiazem on myocardial ischemia during PTCA

To evaluate the effect of intracoronary diltiazem on myocardial ischemia during percutaneous transluminal coronary angioplasty (PTCA), 38 patients were randomly assigned to receive inactive placebo (n = 19; group C) or a low dose (1 mg, n = 10; group D1), or a high dose (2 or 3 mg, n = 9; group D2) of diltiazem in a double-blind manner. The agent was administered directly into the coronary artery via a balloon catheter following a control balloon inflation. Chest pain score (maximum, 10) and the magnitude of ischemic ST elevation on standard and intracoronary electrocardiograms (ECGs) during a balloon inflation were assessed in the control and posttreatment periods. After the administration of diltiazem, the chest pain score was significantly decreased in group D1 (control: 5.1 +/- 3.6, posttreatment: 3.8 +/- 3.1, P < 0.01) and group D2 (3.4 +/- 2.5 vs 2.5 +/- 2.0, P < 0.01), but not in group C (4.1 +/- 3.1 vs 3.7 +/- 3.3, difference not significant). The magnitude of ST elevation relative to the control on standard and intracoronary ECGs was significantly smaller in groups D1 and D2 than in group C (standard ECG; D1: 51.8 +/- 10.6% of control, D2: 41.6 +/- 28.7% vs C: 93.3 +/- 15.6% and intracoronary ECG; D1: 47.1 +/- 11.7% of control, D2: 27.5 +/- 26.9% vs C: 94.6 +/- 29.3%, all P < 0.01). Although systolic blood pressure decreased slightly in groups D1 and D2, there was no significant correlation between the change in ST elevation and the change in the rate-pressure product. Pretreatment with a small dose of intracoronary diltiazem attenuated myocardial ischemia during PTCA and this pretreatment may enable us to perform balloon inflation for a longer period.

Mechanism of the antiischemic effect of mibefradil, a selective T calcium channel blocker in dogs: comparison with amlodipine

Calcium channel blockers are active in variant angina principally by preventing coronary vasospasm. However, a direct antiischemic effect may also occur. In open-chest dogs, an attack of variant angina was mimicked by a 2-min critical coronary stenosis, and the following reversible myocardial ischemia was assessed by measuring the decrease of segmental shortening. We compared the antiischemic mechanism of mibefradil, a T and L calcium channel blocker, with that of amlodipine, a pure L channel blocker. Both drugs showed a similar relationship between the decrease of the rate-pressure product and the antiischemic effect, but only mibefradil reduced heart rate. Amlodipine and mibefradil at the highest doses tested (20 and 70 micrograms/kg/min, respectively) restored 68 +/- 8 and 76 +/- 5% of segmental shortening in the ischemic area, respectively, as compared with preischemic values. Matching blood pressure (by intraaortic balloon) or heart rate (by atrial pacing) to predrug values showed that the antiischemic effect was mainly afterload-dependent for amlodipine and heart rate-dependent for mibefradil. We conclude that in variant angina, in addition to their antivasospastic effects, calcium channel blockers may be antiischemic by a direct myocardial effect associated with a decrease of the rate pressure product. Blockade of the T channel does not seem to participate in the direct antiischemic effect of mibefradil but could explain the decrease of heart rate.

Xanthonolol: a calcium channel and beta-adrenoceptor blocker with vasodilating properties

1. Xanthonolol (0.1-5.0 mg/kg, i.v.) reduced the blood pressure, heart rate, and L-isoproterenol (0.05 microgram/kg, i.v.)-induced tachycardia in rats. 2. In the isolated guinea-pig right atrium, xanthonolol (10(-6)-3 x 10(-4) M) produced long-lasting negative, inhibited L-isoproterenol-induced positive chronotropic effects, prevented the rate-increasing effects of increased extracellular Ca2+ (3.0-9.0 mM), and inhibited Ca2+ (3.0-9.0 mM)-induced heart rate-increase. 3. In the isolated guinea-pig thoracic aorta, the contractions induced by CaCl2 (0.1-5.0 mM) were inhibited by xanthonolol (10(-6)-10(-4) M). 4. Xanthonolol is suggested to have a calcium channel and beta adrenergic blocking effect with vasodilating properties.

Effects of a new calcium antagonist, CD-832, on experimental coronary artery spasm in miniature pigs

The effects of a new calcium antagonist, CD-832, on experimental coronary artery spasms were studied in Göttingen miniature pigs. Pigs underwent endothelial denudation at the left anterior descending coronary artery using a balloon catheter. Changes in the diameter of the denuded and nondenuded site in response to an intracoronary administration of serotonin (10 micrograms/kg) or histamine (10 micrograms/kg) were assessed quantitatively by selective coronary arteriography 1 week after endothelial denudation. Percent reductions of the coronary artery diameter induced by serotonin or histamine in the denuded site were significantly greater than those in the nondenuded site (p < 0.01). Coronary artery spasm induced by serotonin or histamine in the denuded site was attenuated in a dose-dependent manner by intravenous infusion of CD-832 (10 and 30 micrograms/kg/min) or nifedipine (1 and 3 micrograms/kg/min). The degrees of inhibition of coronary artery spasm by CD-832 were similar to those produced by nifedipine. CD-832 and nifedipine at the high dose caused comparable increases in the basal coronary artery diameter. These results suggest that CD-832 may be a useful drug for the treatment of coronary artery spasm.

Coronary hemodynamics and coronary flow reserve after intracoronary diltiazem in humans

To analyze the effect of the calcium antagonist diltiazem on coronary hemodynamics, epicardial coronary artery diameter, coronary blood flow and coronary blood flow velocity were assessed at baseline and after a 0.5 mg intracoronary bolus of diltiazem in nonstenotic coronary arteries of awake humans. Patients (n = 20) were first randomized to pretreatment with either placebo (n = 10) or isosorbide dinitrate (0.5 microgram/kg/min infusion; n = 10), and coronary flow reserve was measured before and after administration of diltiazem. There were significant increases in epicardial coronary artery diameter (10%; p = 0.0001) and coronary blood flow (30%; p = 0.0001) in all patients after administration of diltiazem. Whereas basal coronary blood flow velocity increased only slightly (7%; p = not significant), there was a significant decrease in coronary flow reserve (10%; p = 0.004). Increases in coronary diameter and blood flow after diltiazem were comparable in patients pretreated with placebo or nitrates. However, the decrease in coronary flow reserve was significant only in patients pretreated with placebo (19%; p = 0.0008). This reduction in coronary flow reserve could be due to "raising the floor" (increased baseline coronary blood flow) or "lowering the ceiling" (reduction of maximal coronary blood flow).

Effect of a bradycardic agent on the isolated blood-perfused canine heart

Bradycardic agents could limit the consequences of myocardial ischemia via two mechanisms: by decreasing myocardial oxygen demand (MVO2) and by increasing diastolic coronary blood flow (CBF). We investigated whether the benzazepinone UL-FS 49 affects only sinus node cells or also smooth muscle and/or myocardial cells. To avoid confounding interactions with the periphery, we performed experiments on 11 isolated, blood-perfused canine hearts. Injection of UL-FS 49 (1 mg/kg i.c.) significantly reduced heart rate (HR) from 104 +/- 7 to 93 +/- 7 min-1 (mean +/- SEM) and increased stroke volume (n = 6: 9.8 +/- 1.1 vs. 13.2 +/- 1.6 ml), so that cardiac output remained unchanged (n = 6: 1.1 +/- 0.1 vs. 1.2 +/- 0.1 l/min). The contractile state, assessed by isovolumic peak systolic pressure, was unaltered by UL-FS 49 (n = 5: 72 +/- 6 vs. 72 +/- 6 mmHg). At a constant coronary arterial pressure (CAP) of 80 mmHg, mean CBF was slightly decreased (102 +/- 11 vs. 97 +/- 10 ml/[min.100 g]) by UL-FS 49, such that mean coronary resistance remained unchanged (0.9 +/- 0.1 vs 1.0 +/- 0.1 mmHg.min.100 g/ml). The slight decreases in arteriovenous oxygen content difference (n = 6: 6.6 +/- 0.7 vs. 6.5 +/- 0.7 ml/100 ml) and in CBF lead to a calculated, significant decrease in MVO2 (n = 6: 6.9 +/- 0.5 vs. 6.0 +/- 0.4 ml.100 g/min). In conclusion, UL-FS 49 at the dose used decreases MVO2 by reducing HR in isolated canine hearts. In the absence of negative inotropic and vasodilating effects, cardiac output is maintained via increased stroke volume, and CAP will likely be preserved in situ. Thus, this specific bradycardic agent could be useful in treating ischemic myocardial disease.

Prevention of alpha-adrenergic coronary constriction by calcium-antagonists

This manuscript reviews the experimental evidence for a functional antagonism of Ca-antagonists against alpha-adrenoceptor-mediated increases in coronary vasomotor tone. In studies on anesthetized dogs, intravenous nifedipine effectively prevented the alpha 1-adrenoceptor-mediated increase in epicardial coronary resistance, as well as the increase in end-diastolic resistance mediated by both alpha 1- and alpha 2-adrenoceptors during cardiac sympathetic nerve stimulation. Both intracoronary and intravenous administration of nifedipine also prevented the alpha 2-adrenoceptor-mediated increase in coronary resistance distal to severe stenoses, as well as the resulting ischemic dysfunction and net lactate production during cardiac sympathetic nerve stimulation. Felodipine was equally effective as nifedipine in preventing an alpha 2-adrenoceptor-mediated increase in coronary resistance and the resulting contractile dysfunction distal to severe coronary stenoses. alpha 1- and alpha 2-Adrenergic coronary constriction also contribute to the severity of myocardial ischemia in conscious dogs during treadmill exercise. Again, nifedipine improved regional myocardial blood flow and attenuated regional contractile dysfunction during exercise-induced ischemia in conscious dogs with a chronic coronary stenosis. This beneficial effect of nifedipine was attributed to a recruitment of coronary dilator reserve and not to a reduction in heart rate or afterload. In conclusion, there is solid experimental evidence for a functional antagonism of Ca-antagonists against alpha-adrenergic coronary constriction and its contribution to myocardial ischemia.

Decreased lymphocyte blastogenesis, IL2 production and NK activity following nifedipine administration to healthy humans

The effects of a single oral dose of nifedipine on part of the immune response in healthy humans has been investigated in terms of two different immune functions: T lymphocyte proliferation and NK activity. Both functions are known to require calcium ions. Ten healthy subjects were bled before and 30 min, and 4 and 24 h after receiving 10 mg nifedipine. Lymphocyte proliferation, both in mitogen-activated lymphocyte cultures, and in autologous and allogeneic mixed lymphocyte reactions, was significantly reduced (up to 48%) 30 min after drug administration and reverted to normal 4 h later. The inhibition could be attributed to reduction in IL2 production by the T cells isolated 30 min following the administration of nifedipine, since they normally express IL2-receptors. The addition of recombinant IL2 of 200 U.ml-1 to the cell cultures restored their responsiveness. NK activity was significantly reduced 30 min and 4 h after drug administration and returned to normal at the 24th h. This function was also restored by the addition of IL2. The data suggest that calcium channel blockers may inhibit, at least transiently, lymphocyte functions in vivo.

Individualized antianginal therapy guided by systemic arterial pressure

All antianginal drugs except nitrates are also first-line antihypertensive drugs. Their antianginal efficacy has not been evaluated in relation to pretreatment blood pressure. They may aggravate ischemia due to excessive reduction in blood pressure. Until the results of direct comparative studies are available, it is advisable to start treatment of angina pectoris in normotensive and hypotensive patients with other drugs that do not primarily decrease blood pressure. Nitrates are a reasonable choice.

Pharmacology of acute effort angina

From the pharmacologic point of view, each of the major types of antianginal agents--calcium antagonists, beta-blockers, and nitrates--seem to act at least in part by an improvement of the myocardial blood supply. The recently elucidated mechanism of action of nitrates, acting on a common pathway with the endothelium-derived relaxation factor (EDRF), suggests an important role for guanylate cyclase and cyclic GMP in maintaining coronary artery patency in patients with coronary atheroma. The efficacy of calcium antagonists, even in effort-induced angina, is in accord with a current hypothesis that physical exercise in the presence of coronary stenosis can cause relative coronary vasoconstriction, or at the least, failure of full dilation. Therefore, calcium antagonists all act, at least in part, on the "supply" side of the supply-demand equation. Beta-adrenergic blockers appear to have as their major mode of action a reduction of heart rate, which not only reduces the oxygen demand but, through an anti-ischemic effect, also appears to improve the endocardial blood supply (in relation to the heart rate). Thus beta-blockade indirectly enhances the supply side of the equation. The intriguing situation arises whereby all three major types of antianginal compounds may also act by a common mechanism of anginal relief, namely, improvement in the coronary blood supply, in addition to the diverse mechanisms specific to each type of compound. That conclusion does not mean the the "demand" side of the equation can be ignored. Rather, the critical importance of a reduced myocardial blood supply in the production of anginal syndromes is highlighted.

Coronary collateral reserve during exercise induced ischemia in swine

We determined coronary collateral vasodilator reserve during exercise-induced ischemia in 17 mini-swine. We induced coronary collateral development in the left circumflex bed by placing an ameroid occluder on that artery. Four weeks later we studied the animals at rest and during exercise (EX) eliciting heart rates (HR) of 240 and 265 beats/min. We measured myocardial blood flow with microspheres and myocardial function by wall thickness sonomicrometry gauges. At matched exercise HRs we treated the animals with nifedipine (10 micrograms/kg IV) (EXN 10), nifedipine (100 micrograms/kg IV), (EXN 100), and adenosine infusion (1.2 mg/min/kg) EXAD. EXN 10 did not significantly alter hemodynamics compared to EX but EXN 100 and EXAD both decreased blood pressure significantly (p less than 0.05). Ischemic endocardial/nonischemic endocardial flow ratios and collateral resistance served as indices of vasodilator reserve. In the ischemic zone exercise reduced vasodilator reserve to 24 +/- 3% in the endocardium and 64 +/- 7% in the epicardium. Neither EXN 10 nor EXAD improved exercise-induced ischemia measured either as flow or function. However EXN 100 improved function during exercise-induced ischemia without improving coronary collateral flow. We conclude there is no additional coronary flow reserve during exercise-induced ischemia in the collateral dependent bed of the pig a few days after occlusion that can be recruited. Large doses of nifedipine improve function by direct action on the myocardium or by reducing afterload. The lack of development and deep myocardial distribution of the coronary collateral vessels in the pig may be an important factor of why these nifedipine responses differ from those reported in species which have primarily large epicardial coronary collaterals.

Prevention of coronary vasoconstriction by diltiazem during dynamic exercise in patients with coronary artery disease

Whether exercise-induced vasoconstriction of coronary artery stenoses is modified by the administration of calcium antagonists was examined in 14 patients with classic angina pectoris. In this group the effect of intracoronary diltiazem (2 to 3 mg) on luminal area was evaluated in normal and stenotic segments of epicardial coronary arteries during symptom-limited supine exercise. The luminal area of a normal and a stenotic coronary artery segment was determined by quantitative coronary arteriography with a computer-assisted system. Patients were studied at rest, 6 min after 2 to 3 mg of intracoronary diltiazem, during supine bicycle exercise (96 W) and 5 min after sublingual administration of 1.6 mg nitroglycerin. Heart rate, mean pulmonary and aortic pressure as well as the percent change of both normal and stenotic luminal area were determined. Intracoronary administration of diltiazem was associated with mild dilation of both normal (19%, p less than 0.01) and stenotic coronary luminal area (11%, p less than 0.05). During subsequent exercise, luminal area of the stenotic vessel segment increased by 23% (p less than 0.001) and that of the normal vessel segment by 24% (p less than 0.001), whereas in a previously reported control group, luminal area of the stenotic vessel segment decreased by 29% during exercise. After sublingual administration of nitroglycerin, the luminal area of both the normal and the stenotic vessel segment increased further by 19% (p less than 0.01) and 22% (p less than 0.01), respectively, compared with the values after intracoronary administration of diltiazem.(ABSTRACT TRUNCATED AT 250 WORDS)

Combined effects of calcium antagonists and nitroglycerin on large coronary artery diameter

Nitroglycerin and calcium antagonists are direct dilators of large coronary arteries. Their amelioration of myocardial ischemia may be in part related to their dilating action on coronary stenoses. The present study was done to determine if the effects of calcium antagonists and nitroglycerin on large coronary arterial diameter are additive. External circumflex coronary arterial diameter was measured by sonomicrometry in 16 awake, instrumented dogs. Intravenous nifedipine (mean dose 30 +/- 4 micrograms/kg) caused dilation of the circumflex coronary artery (4.01 +/- 0.13 to 4.10 +/- 0.12 mm, p less than 0.05). The addition of intravenous nitroglycerin (10 to 20 micrograms/kg) caused further coronary arterial dilation (4.10 +/- 0.12 to 4.13 +/- 0.12 mm, p less than 0.05). Intravenous verapamil (mean dose 520 +/- 77 micrograms/kg) also caused dilation of the circumflex coronary artery (4.14 +/- 0.35 to 4.26 +/- 0.35 mm, p less than 0.05). The addition of intravenous nitroglycerin caused further dilation (4.26 +/- 0.35 to 4.31 +/- 0.35 mm, p less than 0.05). Intravenous diltiazem (mean dose 640 +/- 140 micrograms/kg) caused circumflex coronary arterial dilation in four of the five dogs studied (mean change 4.14 +/- 0.36 to 4.21 +/- 0.33 mm). The addition of intravenous nitroglycerin caused further circumflex coronary dilation (4.21 +/- 0.33 to 4.26 +/- 0.33 mm, p less than 0.05). Therefore, the effects of nitroglycerin and each of these three calcium antagonists on large coronary diameter are additive, with the combination of nitroglycerin and the calcium antagonist causing more large coronary dilation than the calcium antagonist alone.

Interdependence of pharmacologically-induced and endothelium-mediated coronary vasodilation in antianginal therapy

Recent advances in the understanding of vascular physiology have furnished new aspects in the treatment of angina pectoris by various vasodilators. Upon stimulation by various factors (viscous drag from increased flow, pulsatile stretch, ADP/ATP, norepinephrine, serotonin), the coronary endothelium releases a vasodilator called endothelium-derived relaxant factor (EDRF). This factor has recently been shown to probably be nitric oxide (NO), which is identical to the active compound of nitroglycerin. EDRF (NO) dilates both large epicardial arteries and also coronary resistance vessels. It also has a strong platelet antiaggregant effect. The predominant effect of Ca2+ antagonists is on resistance vessels, increasing myocardial perfusion and viscous drag acting upon the endothelial lining. This, in turn, stimulates EDRF (NO) release in epicardial arteries and dilation. This additional nitrate-like effect augments the direct vasodilator effect of Ca2+ antagonists. Lack of normal endothelial function results in diminished capacity to dilate, and sometimes even in a shift from dilator to constrictor effects, paralleled by an increased tendency for platelet adhesion, activation, and thrombosis, which is still enhanced when plasma low density lipoprotein (LDL) is augmented. EDRF release, vasodilator capacity, and antiaggregant effects are reduced when LDL is high. Nitrates have a direct, endothelium-independent dilator effect, particularly on large coronary arteries, which seems even more pronounced when the endothelium is absent, but only when the vessel segment is still compliant. Therefore nitrates may particularly be effective in vessels with deficient EDRF release.

Delayed myocardial ischemia following the cessation of sympathetic stimulation

A phenomenon entitled "delayed myocardial ischemia" has been described, in which there is a significant degree of coronary malperfusion following the cessation of behavioral stress. The primary objective of the present study was to develop a model for the delayed ischemic response in anesthetized animals to gain insights into the underlying mechanisms. In 15 morphine and chloralose-anesthetized dogs, a moderate degree of stenosis was applied to the left circumflex coronary artery by means of a toroidal balloon occluder. The pulsed Doppler technique was used to monitor coronary flow. After baseline data were obtained, the left stellate ganglion was stimulated for 30 seconds. Heart rate increased (63%), as did systemic blood pressure (41%) and flow in the left circumflex artery (47%). These parameters rapidly returned to control levels when stimulation was terminated. Forty-five to 90 seconds later, coronary flow decreased by 65% and coronary vascular resistance increased by 45%. These hemodynamic changes were accompanied by ECG abnormalities indicative of regional myocardial ischemia. The delayed ischemic response could be prevented by pretreatment with either nifedipine (20 micrograms/kg) or prazosin (0.3 mg/kg). These data indicate that the primary mechanism for the delayed ischemic response is alpha-adrenergically mediated contraction of the smooth muscle in the coronary artery wall.

Total ischemic burden: effect of vasoactive agents

Treatment of the total ischemic burden is dependent on adequate documentation of both painful and painless episodes of myocardial ischemia, an understanding of the pathophysiologic mechanisms involved, and knowledge of prognosis for affected patients. Because a vasoconstrictive component appears to be an important element in the genesis of many episodes of myocardial ischemia, those vasoactive drugs that produce increased flow in the coronary circulation should be clinically useful. Nitrates and calcium blockers--especially nifedipine--have been found to be particularly valuable in this regard in both experimental and clinical trials.

Comparative effects of intracoronary vasodilators on restoring coronary perfusion during flow-reducing coronary stenosis in the dog

The effects of intracoronary injection of nitroglycerin, adenosine, nifedipine and prostacyclin on restoring coronary perfusion during flow-reducing partial coronary obstruction in anesthetized dogs were studied. Coronary obstruction was obtained by inflation of an intraluminal balloon to decrease coronary blood flow and rate of rise in left ventricular pressure (dP/dt) by approximately 30 to 40 and 10%, respectively. Nitroglycerin (0.01 to 10 micrograms/kg per min) increased coronary blood flow and distal coronary pressure and decreased stenosis resistance associated with improved left ventricular dP/dt depending on its dose. In contrast, adenosine (0.3 to 1.0 micrograms/kg per min) decreased coronary blood flow and distal coronary pressure and intensified stenosis resistance associated with depression of left ventricular dP/dt. Nifedipine and prostacyclin caused divergent effects on the coronary circulation related to each dose. Nifedipine (0.01 and 0.1 micrograms/kg per min) and prostacyclin (0.01 micrograms/kg per min) increased coronary blood flow and distal coronary pressure and reduced stenosis resistance. Nifedipine (1.0 micrograms/kg per min) and prostacyclin (0.3 micrograms/kg per min) did not increase coronary blood flow, but reduced distal coronary pressure and intensified stenosis resistance. Thus, the vasodilators produced different effects on restoration of coronary perfusion during pliable severe coronary stenosis. Nitroglycerin and lower doses of nifedipine and prostacyclin improved coronary perfusion due to selective or preferential dilation of large coronary arteries. Adenosine and higher doses of nifedipine and prostacyclin had deleterious effects on the coronary circulation due to potent arteriolar vasodilation.

Effect of nifedipine on the myocardial and vascular response to myocardial ischemia

Nifedipine reduces reactive hyperemia following brief coronary artery occlusions. To determine whether this is related to improvement in collateral blood flow to ischemic myocardium or alterations in myocardial oxygen consumption, ten chloralose anesthetized dogs were instrumented with coronary sinus catheters, circumflex artery flowmeters, and ultrasonic microcrystals for measurement of myocardial segment shortening. Myocardial oxygen consumption and circumflex coronary artery flow were determined at rest and during incremental infusions of isoproterenol. Myocardial blood flow measured with microspheres and segmental function were assessed during and following 30- and 60-second coronary artery occlusions. Thirty minutes after the intravenous administration of nifedipine, 10 micrograms/kg iv, all measurements were repeated. Nifedipine did not alter myocardial oxygen consumption or the relationship between oxygen consumption and circumflex coronary artery flow either at rest or during isoproterenol infusion. Following 60-second coronary occlusions, nifedipine reduced peak circumflex coronary artery flow (176 +/- 99 vs. 128 +/- 68 cc/min) and reactive hyperemia debt repayment (221 +/- 84 vs. 158 +/- 66%; p less than 0.01). Nifedipine did not alter flow to ischemic segments during coronary artery occlusions (0.16 +/- 0.10 vs. 0.19 +/- 0.13 ml/min/g mean transmural flow). Furthermore, nifedipine did not affect the severity of ischemic segment dysfunction, nor the rate of recovery of ischemic segment function following release of coronary artery occlusion. We conclude that the reduction in reactive hyperemia induced by nifedipine was not related to alterations in the severity of hypoperfusion in ischemic areas, or alterations in myocardial oxygen consumption. Reductions in reactive hyperemia produced by nifedipine did not impair recovery of mechanical function in postischemic myocardium.

The effects of nisoldipine (Bay K 5552) on cardiovascular performance and regional blood flow in pentobarbital-anaesthetized pigs with or without beta-adrenoceptor blockade

The effects of the 1,4-dihydropyridine derivative nisoldipine, infused intravenously (i.v.) at 3 different rates (0.25, 0.5 and 1.0 microgram kg-1 min-1), were studied in anaesthetized pigs on cardiovascular performance with or without beta-adrenoceptor blockade produced by propranolol. Nisoldipine caused dose-dependent decreases in arterial blood pressure (30%), systemic vascular resistance (30%) and left ventricular filling pressure (15%), but raised heart rate (25%) and LV dP/dt max (20%). Cardiac output was not significantly affected. Transmural myocardial blood flow and vascular conductances increased dose-dependently after nisoldipine. The elevation in blood flow to the left ventricle favoured epicardial layers. Endocardial blood flow showed small increases as the changes in conductance of the endocardial layer more than compensated for the loss in perfusion pressure. The endo-epi blood flow ratio decreased from 1.16 +/- 0.05 to 0.70 +/- 0.01. Myocardial O2-consumption was unaltered as the decrease in arterial-coronary venous O2-content difference (30%) was balanced by the increase in transmural blood flow. Nisoldipine increased blood flow to skeletal muscle (500%), stomach (50%) and adrenals (25%), but decreased that to the liver (50%), spleen (25%) and kidneys (25%). No changes were noticed in the small intestine, skin and brain. In spite of differential effects on blood flow, vascular conductance in all organs and tissues, with the exception of the liver, increased. After beta-adrenoceptor blockade the responses of mean arterial blood pressure, cardiac output and systemic vascular resistance to nisoldipine remained virtually unchanged, but the elevations in heart rate and LV dP/dt max were abolished, as was the decrease in left ventricular filling pressure. A higher dose of nisoldipine was required after beta-adrenoceptor blockade to elicit significant vasodilatation in the epi- and endocardial layers. However, the reduction in endo-epi blood flow ratio by nisoldipine was not affected by propranolol. Myocardial O2-consumption tended to decrease as the diminution in the arterial-coronary venous O2-content difference (30%) slightly exceeded the increase of left ventricular blood flow (30%). Except for the brain and liver, effects of nisoldipine on regional vascular conductances were attenuated after beta-adrenoceptor blockade.

Effect of calcium entry blockers and adenosine on the relaxation of large and small coronary arteries

The mechanism(s) by which adenosine causes dilation of the vascular smooth muscle is not properly understood. Several mechanisms including the inhibition of calcium influx and intracellular translocation have been suggested for its action. This study is an attempt to further elucidate the site of action of adenosine in relation to calcium by making use of calcium entry blockers. Large (1 +/- 0.2 mm, o.d.) and small (0.5 +/- 0.2 mm, o.d.) branches of bovine left anterior descending coronary artery (LADCA) contracted with 50 mM K+ were used as a model for these studies. Concentration-response curves for various calcium entry blockers were obtained and the order of potency was found to be: D-600 greater than nifedipine greater than verapamil greater than diltiazem greater than lidoflazine for large branches and nifedipine greater than D-600 greater than verapamil greater than lidoflazine greater than diltiazem for small branches of LADCA. The concentration-response relationship for adenosine (10(-6)-10(-4) M) in the presence and absence of these drugs (10(-9)-10(-7) M) was unchanged. 8-phenyltheophylline (2 X 10(-5) M), an adenosine receptor antagonist was without an effect on the relaxations induced by various calcium entry blockers, however, it antagonized the relaxing response to adenosine. Lidoflazine at concentrations of 7 X 10(-7) M and 2 X 10(-7) M potentiated the effect of adenosine in relaxing the large and small LADCA, respectively. In summary, the data show an increased sensitivity of small coronary vessels to nifedipine, D-600 and lidoflazine. The data further suggest a different site of action for adenosine and calcium entry blockers.

Left ventricular dysfunction induced by cold exposure in patients with systemic sclerosis

Raynaud's phenomenon and cardiac abnormalities are frequent in patients with systemic sclerosis. Radionuclide ventriculograms were obtained in 16 patients with Raynaud's phenomenon and systemic sclerosis or the related CREST syndrome and in 11 normal volunteers in order to evaluate changes in left ventricular function that might be induced by exposure to cold. Left ventricular regional wall motion abnormalities developed in nine of 16 patients during cooling compared with only one of 11 control subjects, despite a comparable rise in mean arterial pressure (p less than 0.02). The abnormalities occurred in seven of 11 patients with systemic sclerosis, one of four with CREST syndrome, and one with Raynaud's disease. To test the potential protective effect of nifedipine, radionuclide ventriculograms were then obtained during cooling after sublingual nifedipine (20 mg). Only five of 13 patients had wall motion abnormalities, and the severity of the abnormalities was significantly less than during the first cooling period (p = 0.03). Five of eight patients who had cold-induced wall motion abnormalities during the first cooling period had none after nifedipine, whereas two other patients demonstrated small abnormalities only during the second cooling period after treatment with nifedipine. It is concluded that cold induces segmental myocardial dysfunction in patients with systemic sclerosis and that nifedipine may blunt the severity of this abnormal response.

Improved myocardial oxygen utilization by diltiazem in patients

Calcium entry blocking drugs produce different effects on systemic and coronary hemodynamics and myocardial oxygen extraction. To examine the effects on myocardial oxygen extraction, intravenous diltiazem (100 micrograms/kg bolus with a continuous 10 micrograms/kg/min infusion) was administered to 11 patients at rest and during controlled heart rates (100 +/- 5 and 120 +/- 5 bpm). At rest, diltiazem decreased mean arterial pressure from 109 +/- 13 to 99 +/- 14 mm Hg (p less than 0.01), increased heart rate from 64 + 12 to 74 +/- 14 bpm (p less than 0.01), and decreased coronary sinus resistance (1.02 +/- .41 to 0.87 +/- .40 U, p less than 0.05). Myocardial oxygen extraction was significantly reduced since coronary sinus oxygen content increased (6.0 +/- 0.9 to 7.8 +/- 1.2 ml/dl, p less than 0.01) and the arterial-coronary sinus oxygen difference decreased (12.0 +/- 1.7 to 10.6 +/- 1.6 ml/dl, p less than 0.01). Similar changes occurred with heart rate held constant. There were no significant changes in absolute coronary sinus blood flow, calculated myocardial oxygen consumption, or left ventricular dP/dt. Diltiazem decreases mean arterial pressure while reducing both myocardial oxygen extraction and coronary arterial resistance, suggesting that a principal mechanism of a beneficial effect upon the coronary circulation appears to be an improvement in myocardial oxygen extraction relative to myocardial oxygen demand.

Coronary and peripheral vascular resistance in the anaesthetized diabetic sheep

To determine whether vascular resistance was altered in diabetes, the vascular resistance in both the peripheral arterial bed and the circumflex coronary artery was compared in six normal and five diabetic adult sheep, under pentobarbitone anaesthesia. Diabetes induced by alloxan significantly increased blood glucose (15.6 mmol/l, s.e.m. = 2.8, vs 5.5 mmol/l, s.e.m. = 0.6; P greater than 0.001) compared with controls. Systolic blood pressure was lower in diabetics (92 mmHg, s.e.m. = 12, vs 123 mmHg, s.e.m. = 5; P less than 0.025) as was diastolic blood pressure (73 mmHg, s.e.m. = 15, vs 104 mmHg, s.e.m. = 4; P greater than 0.05). Basal peripheral resistance was lower in diabetics than controls (36.0 mmHg.min/l, s.e.m. = 7.9, vs 42.3 mmHg.min/l, s.e.m. = 2.8), but not significantly so. Methoxamine markedly increased peripheral vascular resistance in both groups, but did not change coronary vascular resistance, due to autoregulation. The dose-response curves of peripheral or coronary arteries to methoxamine showed no significant difference between diabetic and control sheep. Dose-response curves for isoprenaline and noradrenaline infusion suggested there may be altered beta-receptor sensitivity in diabetes. In conclusion, there are marked differences in the vascular beds of diabetic and normal sheep under basal conditions. In contrast to previous studies, alpha-adrenoceptors are not different in diabetics, but further studies in unanaesthetized animals are indicated, as beta-receptor sensitivity may be altered in diabetes.

The effects of nifedipine on the systemic and coronary vascular beds of the sheep: a potential method for induction of ischaemia

Nifedipine has been reported to aggravate symptoms of ischaemic heart disease in some patients. To investigate the possible reasons for this, vascular resistance changes in the systemic and coronary beds of sheep were compared with and without coronary artery stenoses. In six anaesthetized sheep, the dose-response curve comparing vascular resistance to nifedipine dose showed greater sensitivity than that reported for either dogs or humans. The coronary vascular bed was more reactive than the systemic vascular bed but this difference did not reach a level of statistical significance. With fixed non-elastic proximal coronary artery stenoses, the relationship of both coronary flow and coronary resistance to a standard dose of nifedipine (5 micrograms/kg) was indirectly related to the degree of stenosis. With stenosis reducing flow at rest by 50% or more, nifedipine usually produced a reduction in coronary flow in the stenosed artery and associated ST elevation, consistent with severe ischaemia in the distribution of the coronary. This effect is related to the reduction in perfusion pressure.

Regional coronary vasoconstriction after combined beta-adrenergic and calcium channel blockade in patients with coronary artery disease

The beta-adrenergic and calcium channel blocking drugs, which individually and combined have proven efficacious in the treatment of angina pectoris, appear to have opposing effects on coronary artery vasomotion. Previous studies have shown that beta-adrenergic blockade may potentiate and calcium channel blockade reverse coronary vasoconstriction during adrenergic cold stimulation in patients with coronary artery disease. To assess the coronary hemodynamic effects of combined drug therapy, thermodilution coronary sinus and great cardiac vein flow and mean arterial pressure were measured during serial cold pressor testing, both before and after 0.1 mg/kg of intravenous propranolol and again after the addition of 10 mg of sublingual nifedipine in 21 patients (9 without [group A1] and 12 with [group A2] greater than 50% narrowing of the left anterior descending coronary artery). In an additional 15 patients (6 patients without [group B1] and 9 with [group B2] left anterior descending artery stenosis), serial cold pressor testing was performed reversing the drug order. Despite significant increases in mean arterial pressure (p less than 0.01) during cold pressor testing, coronary sinus resistance responses after propranolol plus nifedipine were not statistically significant for any group. However, regional coronary resistance responses differed between patients with and without left anterior descending artery stenosis. In group A1, great cardiac vein resistance was unchanged after propranolol plus nifedipine. In group A2, great cardiac vein flow decreased significantly after propranolol plus nifedipine from 8 +/- 17 to -4 +/- 12% (p less than 0.01 versus control), and great cardiac vein resistance increased from 4 +/- 21 to 15 +/- 19% (p less than 0.01 versus control). A similar significant response was observed for groups B1 and B2. Regional coronary vasoconstriction during adrenergic stimulation after combined drug therapy was only observed in patients with significant left anterior descending artery stenosis. These data suggest that in some patients with severe coronary artery disease, combined beta-adrenergic and calcium channel blockade modified regional coronary responses to adrenergic stimulation with an inhomogeneous distribution of blood flow to potentially ischemic regions without affecting total coronary blood flow. These data also imply that an improvement in anginal symptoms after combined drug therapy may be due primarily to mechanisms that reduce myocardial oxygen demand rather than to improved myocardial oxygen supply.

Effect of nifedipine on coronary hemodynamics in patients with left anterior descending coronary occlusion

The mechanisms responsible for the beneficial effects of calcium channel antagonists in patients with effort angina were investigated by studying the coronary hemodynamic responses of the anterior left ventricular region before and after administration of nifedipine in 13 patients whose left anterior descending coronary artery was filled by flow from collateral vessels. Nifedipine was given bucally in a dose (10 or 20 mg) that decreased aortic pressure 5 mm Hg or more. Nifedipine increased collateral flow (regional thermodilution) in only three patients (p = NS), but consistently decreased coronary resistance in the left ventricular anterior region (p less than 0.05). Anterior region myocardial oxygen consumption did not change after nifedipine administration. Lactate metabolism was evaluated in eight patients: values were abnormal in four patients before nifedipine; after nifedipine, values remained abnormal in three of these patients and became abnormal in one other. During atrial pacing stress, angina occurred in all patients before nifedipine and at the same or lower heart rate in nine patients after nifedipine. After nifedipine administered at the same rate that induced angina during the control period, collateral flow and myocardial oxygen consumption were usually lower (both p less than 0.05), but anterior region coronary resistance was unchanged compared with control values. Lactate metabolism was not usually improved. Thus, although nifedipine maintained collateral flow while aortic pressure decreased, no consistent beneficial effect on pacing-induced angina was seen.

Alterations in contrast medium-induced coronary reactive hyperemia after bepridil in patients with coronary artery disease

The acute effects of an intravenous infusion of bepridil (BEP) (4 mg . kg-1) on left ventricular (LV) hemodynamics, coronary sinus blood flow (CSBF), and myocardial metabolism were studied in eight patients with coronary artery disease. In contrast with data previously reported with calcium channel blockers, BEP induced an elevation in LV end-diastolic pressure from 12.0 +/- 7.1 to 20.1 +/- 7.2 mm Hg (mean +/- SD, p less than 0.001) and a fall in LV dp/dt max from 1339 +/- 302 to 1177 +/- 251 mm Hg . sec-1 (p less than 0.01). This significant alteration in LV function is likely to be explained by the lack of effect on heart rate and aortic pressure observed after an acute intravenous infusion of BEP. Myocardial oxygen consumption (MVO2) increased from 448 +/- 272 to 498 +/- 273 mumol . min-1/100 g LV (p less than 0.05) as did CSBF from 79.5 +/- 42.7 to 92.1 +/- 45.1 ml X min-1/100 g LV (p less than 0.01). Lactate extraction fell from 0.33 +/- 0.17 to 0.15 +/- 0.17 (p less than 0.05). A contrast medium-induced coronary reactive hyperemia (HPR) evidenced an increased hyperemic volume from 9.5 +/- 3.6 to 12.1 +/- 4.5 ml/100 g LV (p less than 0.01) and HPR duration from 23.3 +/- 6.9 to 32.3 +/- 15.4 sec (p less than 0.05) after BEP. However, the peak/resting CSBF ratio was blunted after BEP from 1.74 +/- 0.18 to 1.61 +/- 0.12 (p less than 0.05), evidencing a net effect of BEP on HPR.(ABSTRACT TRUNCATED AT 250 WORDS)

Criteria for successful coronary angioplasty as assessed by alterations in coronary vasodilatory reserve

Currently, the success of coronary angioplasty is defined by anatomic criteria. Because of the known limitations of coronary arteriography, the translesional pressure gradient and coronary vasodilatory reserve were studied in 15 patients undergoing coronary angioplasty with the intent of defining a physiologically successful result. Coronary vasodilatory reserve was measured by a digital radiographic technique that has been previously validated against directly measured coronary sinus flow (r = 0.90, p less than 0.0001). A significant reduction in luminal stenosis from 71 +/- 12 to 34 +/- 11% (p less than 0.001) was accompanied by a reduction in translesional gradient from 47 +/- 19 to 21 +/- 12 mm Hg (p less than 0.001) and an increase in coronary vasodilatory reserve from 1.03 +/- 0.15 to 1.29 +/- 0.13 (p less than 0.001). There was a significant correlation between changes in luminal stenosis and changes in translesional gradient (r = 0.61, p less than 0.05), although a change of 20% or less in luminal diameter was accompanied by no change in pressure gradient. A more significant relation between changes in gradient and in coronary hyperemic reserve existed (r = 0.77, p less than 0.005). The relation was accurate even for small changes in gradient. Because saphenous vein bypass grafts have been shown to increase coronary vasodilatory reserve to at least 1.20, it is proposed that this physiologic criterion be used to define the success of revascularization by angioplasty. In patients in whom this value was achieved, translesional gradient was invariably 25% or less of ostial pressure and 20 mm Hg or less.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of nifedipine on myocardial blood flow during exercise in dogs with chronic coronary artery occlusion

The effect of nifedipine, 0.010 mg/kg intravenously, on myocardial blood flow was studied in 15 dogs 4 weeks after placement of an Ameroid constrictor on either the left circumflex or left anterior descending coronary artery to produce total coronary occlusion. Myocardial blood flow was measured with radionuclide-labeled microspheres at rest and during two levels of treadmill exercise to achieve a heart rate of 190 (light exercise) and 230 (heavy exercise) beats/min. During control conditions, increasing exercise resulted in a progressive increase in myocardial blood flow in normally perfused areas, but was associated with worsening subendocardial hypoperfusion in collateral-dependent areas. Nifedipine administration resulted in a transient reduction of arterial pressure and an increase in heart rate. To determine whether nifedipine exerted significant persistent effects on the coronary collateral circulation, measurements of myocardial blood flow were repeated beginning 30 minutes after nifedipine administration, at a time when heart rate and arterial pressure had returned to control levels. In normally perfused areas, nifedipine did not significantly alter myocardial blood flow at rest, but increased mean myocardial blood flow from 2.06 +/- 0.15 to 2.40 +/- 0.20 ml/min per g during light exercise (p less than 0.01), while blood flow during heavy exercise was not significantly altered. In collateral-dependent myocardial areas, the volume and transmural distribution of myocardial blood flow were not significantly altered after nifedipine administration either at rest or during exercise. These results fail to demonstrate persistent vasodilation of the coronary collateral vessels after the systemic hemodynamic effects of nifedipine have subsided.

Transmural gradient of coronary blood flow following dihydropyridine calcium antagonists and other vasodilator drugs

The effects of the dihydropyridine calcium antagonists, nifedipine, nitrendipine and FR 7534 on the transmural distribution of coronary blood flow (endo/epi) were compared to the structurally unrelated calcium antagonists, verapamil and diltiazem and to the non-calcium antagonist vasodilator drugs, chromonar and dipyridamole in anesthetized dogs. The increase in transmural blood flow produced by diltiazem, verapamil, chromonar and dipyridamole was equally distributed between subendocardium and subepicardium (no change in endo/epi). On the other hand, the increase in myocardial blood flow produced by the dihydropyridine calcium antagonists nifedipine, nitrendipine and FR 7534 was relatively selective for subepicardial regions resulting in a significant and dose-related decrease in endo/epi. This unusual effect of the dihydropyridine calcium antagonists to produce a redistribution of flow within normal myocardium was not shared by the non-dihydropyridine calcium antagonists or non-calcium antagonist vasodilators studied. The redistribution of flow was not related to changes in heart rate, aortic blood pressure or to the level of total coronary blood flow. Such an effect may be related to the distribution of dihydropyridine receptors across the left ventricular wall, antagonism of the action of adenosine, or changes in regional intramyocardial tissue pressure and extravascular resistance.

Pathogenesis of angina pectoris and role of nitrates in relief of myocardial ischemia

The pathophysiologic mechanism of angina of effort has been understood for one and three-quarter centuries. However, the mechanisms underlying angina at rest are still largely unknown. Coronary spasm, whatever its mechanism, clearly causes Prinzmetal's variant angina. However, evidence that spasm is the cause of all angina at rest is wanting. Rather than spasm, it is suggested that most attacks may be the result of normal fluctuations in the tone of conductive coronary arteries in the presence of critical levels of organic obstruction. The nitrates both relieve coronary spasm and diminish normal coronary tone. They also affect the systemic circulation, so as to favorably influence the level of energy demand.