Cardiac and coronary prostaglandin synthesis and function

Study on the Active Constituents and Molecular Mechanism of Zhishi Xiebai Guizhi Decoction in the Treatment of CHD Based on UPLC-UESI-Q Exactive Focus, Gene Expression Profiling, Network Pharmacology, and Experimental Validation

As one of the most common clinical cardiovascular diseases (CVDs), coronary heart disease (CHD) is the most common cause of death in the world. It has been confirmed that Zhishi Xiebai Guizhi decoction (ZXGD), a classical prescription of the traditional Chinese medicine (TCM), has achieved certain effects in the treatment of CHD; however, the mechanism still remains controversial. In this paper, an integrated approach, including UPLC-UESI-Q Exactive Focus, gene expression profiling, network pharmacology, and experimental validation, was introduced to systematically investigate the mechanism of ZXGD in the treatment of CHD. First, UPLC-UESI-Q Exactive Focus was applied to identify the chemical compounds of ZXGD. Then, the targets of the components for ZXGD were predicted by MedChem Studio software embed in the integrative pharmacology-based research platform of TCM, and the differentially expressed genes (DEGs) of CHD were obtained by gene expression profiling in gene expression omnibus database. The common genes of the above two genes were obtained by Venn analysis as the targets of GXGD in treatment with CHD. Third, the core targets were screened out by protein-protein interaction network analysis, and the kyoto encyclopedia of genes and genomes pathway enrichment analysis was performed by the database for annotation, visualization, and integrated discovery bioinformatics resources. After that, the formula-herb-compound-target-pathway network was constructed to explore the mechanism of ZXGD in the treatment of CHD. Finally, molecular docking and the vitro experiment were carried out to validate some key targets. As a result, a total of 39 compounds, 12 core targets, and 4 pathways contributed to ZXGD for the treatment of CHD. This study preliminarily provided a foundation for the study on the mechanism against CHD for ZXGD and may be a reference for the compatibility mechanism and the extended application of TCM compound prescription.

Clopidogrel plus Aspirin Use is Associated with Worse Long-Term Outcomes, but Aspirin Use Alone is Safe in Patients with Vasospastic Angina: Results from the VA-Korea Registry, A Prospective Multi-Center Cohort

Anti-platelet agents are commonly used in vasospastic angina (VA) patients with comorbidity like coronary artery disease. However, long-term clinical outcomes in the use of aspirin, clopidogrel or the two agents together have rarely been investigated in VA patients. In a prospective study, we enrolled 2960 patients who received coronary angiography and ergonovine provocation test at 11 university hospitals in Korea. Among them, 1838 patients were diagnosed either with definite (n = 680) or intermediate (n = 1212) VA, using the criteria of chest pain, ECG changes and ergonovine provocation test results. They were analyzed according to their use of aspirin, clopidogrel or both, or no anti-platelet agent at all. The primary outcome was time to composite events of death from any cause, acute coronary syndrome (ACS) and symptomatic arrhythmia during a 3-year follow-up. A primary composite outcome was significantly more common in the aspirin plus clopidogrel group, at 10.8% (14/130), as compared with the non-antiplatelet group, at 4.4% (44/1011), (hazard ratio [HR] 2.41, 95% confidence interval [CI], 1.32–4.40, p = 0.004). With regard to the person-time event rate, similar results were shown, with the highest rate in the aspirin plus clopidogrel user at 4.72/1000 person months (95% CI, 2.79–7.96, log-rank test for primary outcome p = 0.016). The person-time event of the ACS rate was also highest in that group, at 2.81 (95% CI, 1.46–5.40, log-rank test for ACS p = 0.116). Kaplan-Meier survival analysis demonstrated poor prognosis in primary outcomes and ACS in aspirin plus clopidogrel users (log-rank test, p = 0.005 and p = 0.0392, respectively). Cox-proportional hazard regression analysis, adjusting for age, sex, history of coronary heart disease, hypertension, diabetes, presence or not of definite spasm, use of calcium channel blocker, demonstrated that the use of aspirin plus clopidogrel is an independent risk for the primary outcome (HR 2.01, CI: 1.07–3.81, p = 0.031). The aspirin-alone group had a similar primary and individual event rate compared to the no-antiplatelet agent group (HR 0.96, CI, 0.59–1.55, p = 0.872). Smokers using aspirin plus clopidogrel had poorer outcomes than non-smokers, with HR 6.36 (CI 2.31–17.54, p = 0.045 for interaction). In conclusion, among VA patients, aspirin plus clopidogrel use is associated with a poor clinical outcome at 3 years, especially in ACS. Aspirin alone appears to be safe for use in those patients.

Remodeling of Wall Mechanics and the Myogenic Mechanism of Rat Intramural Coronary Arterioles in Response to a Short-Term Daily Exercise Program: Role of Endothelial Factors

PURPOSE

Exercise elicits early adaptation of coronary vessels enabling the coronary circulation to respond adequately to higher flow demands. We hypothesized that short-term daily exercise induces biomechanical and functional remodeling of the coronary resistance arteries related to pressure.

METHODS

Male rats were subjected to a progressively increasing 4-week treadmill exercise program (over 60 min/day, 1 mph in the final step). In vitro pressure-diameter measurements were performed on coronary segments (119 ± 5 μm in diameter at 50 mm Hg) with microarteriography. The magnitude of the myogenic response and contribution of endogenous nitric oxide and prostanoid production to the wall mechanics and pressure-diameter relationship were assessed.

RESULTS

Arterioles isolated from exercised ani mals - compared to the sedentary group - had thicker walls, increased distensibility, and a decreased elastic modulus as a result of reduced wall stress in the low pressure range. The arterioles of exercised rats exhibited a more powerful myogenic response and less endogenous vasoconstrictor prostanoid modulation at higher pressures, while vasodilator nitric oxide modulation of diameter was augmented at low pressures (< 60 mm Hg).

CONCLUSIONS

A short-term daily exercise program induces remodeling of rat intramural coronary arterioles, likely resulting in a greater range of coronary autoregulatory function (constrictor and dilator reserves) and more effective protection against great changes in intraluminal pressure, contributing thereby to the optimization of coronary blood flow during exercise.

Clinical implications of low-dose aspirin on vasospastic angina patients without significant coronary artery stenosis; a propensity score-matched analysis

BACKGROUND

High-dose aspirin has been reported to exacerbate coronary artery spasm in patients with vasospastic angina. We investigated clinical implications of low-dose aspirin on vasospastic angina patients without significant coronary artery stenosis.

METHODS

We included patients without significant coronary artery stenosis on coronary angiography (CAG) and with positive results on intracoronary ergonovine provocation test between January 2003 and December 2014. A total of 777 patients were divided into two groups according to prescription of low-dose aspirin at discharge: aspirin group (n=321) and non-aspirin group (n=456). The major adverse cardiovascular events (MACE), defined as composite outcomes of cardiac death, acute myocardial infarction, revascularization, or rehospitalization requiring CAG or medication change due to recurrent angina were compared.

RESULTS

The aspirin group had significantly higher incidence of MACE (22.8% versus 12.1%; p=0.04) and had higher tendency for rehospitalization (20.6% versus 11.2%; p=0.08). All-cause mortality and cardiac death were similar between the two groups. After propensity score matching, the aspirin group had greater risk of MACE (hazard ratio [HR] 1.54; 95% confidence interval [CI], 1.04-2.28; p=0.037) and rehospitalization requiring CAG (HR, 1.33; 95% CI, 1.13-4.20; p=0.03), and a higher tendency for rehospitalization (HR, 1.40; 95% CI, 0.94-2.09; p=0.12).

CONCLUSION

In vasospastic angina without significant coronary artery stenosis, patients taking low-dose aspirin are at higher risk of MACE, driven primarily by tendency toward rehospitalization. Low-dose aspirin might be used with caution in vasospastic angina patients without significant coronary artery stenosis.

Single- and multiple-dose pharmacokinetics and tolerability of limaprost in healthy Chinese subjects

BACKGROUND AND OBJECTIVES

Limaprost, a prostaglandin E1 analogue, is used to treat various symptoms in patients with ischemic diseases. The present study was designed to determine the pharmacokinetics and tolerability of single and multiple oral doses of limaprost 5 μg tablets in healthy Chinese subjects.

METHODS

Single and multiple doses of 5-μg limaprost were orally administered to 12 healthy Chinese subjects. There was a 2-week washout period between single and multiple dosing. Blood samples were collected at various times. Indomethacin and aspirin were added to the blood samples to inhibit the endogenous release of prostaglandins during the sample processing. Plasma limaprost was measured by a two-dimensional liquid chromatography-tandem mass spectrometry method.

RESULTS

After single dosing, limaprost was rapidly absorbed (time to reach maximum plasma concentration [t max] = 22.50 min) and eliminated (elimination half-life [t ½] = 21.70 min), with the maximum plasma concentration (C max) being 2.56 pg/mL and area under the concentration-time curve (AUC) from time 0 to the last quantifiable time point (AUC0-t) being 70.68 pg·min/mL. There were significant inter-individual variations in the AUCs for both single- and multiple-dose regimens. The values of C max, AUC, t ½ and t max were not statistically different between single and multiple dosing. The accumulation factor R was 0.609 ± 0.432 (R < 1), indicating that there was no accumulation after multiple dosing. There were no statistically significant differences in pharmacokinetic parameters for both single and multiple dosing between female and male subjects. The drug was well tolerated, with no severe adverse events being observed.

CONCLUSIONS

Limaprost is rapidly absorbed after oral administration and is rapidly eliminated, with no accumulation after multiple dosing. The drug is well tolerated and no serious adverse events occurred.

How and why chemicals from tobacco smoke can induce a rise in blood pressure

The primary objective of this article is to analyze the role of tobacco smoke compounds able to damage the cardiovascular system and, in particular, to interfere with blood pressure. They are products of tobacco plant leaves, like nicotine, thiocyanate and aromatic amines, and a chemical derived from cigarette combustion, carbon monoxide. Of the other thousands of chemicals, there is no clear evidence of cardiovascular damage. Nicotine and its major metabolite, cotinine, usually increase blood pressure by a direct action and an action stimulating neuro-humoral metabolites of the body as well as sympathetic stimulation. An indirect mechanism of damage exerted by elevated carboxyhemoglobin concentrations is mediated by carbon monoxide, which, mainly induces arterial wall damage and, consequently, late rising in blood pressure by a toxic direct action on endothelial and blood cells. Thiocyanate, in turn, reinforces the hypoxic effects determined by carbon monoxide. Aromatic amines, depending on their chemical structure, may exert toxic effects on the cardiovascular system although they have little effect on blood pressure. A rise in blood pressure determined by smoking compounds is a consequence of both their direct toxicity and the characteristics of their chemical chains that are strongly reactive with a large number of molecules for their spatial shape. In addition, a rise in blood pressure has been documented in individuals smoking a cigarette, acutely and chronically, with irreversible artery wall alterations several years after beginning smoking. Since cigarette smoking has a worldwide diffusion, the evidence of this topic meets the interest of both the scientific community and those individuals aiming to control smoking.

Beneficial effects of prostaglandin E1 on myocardial energetics and pump performance in severe CHF

To provide more effective vasodilator agents for the therapy of severe left ventricular (LV) failure the cardiocirculatory actions of prostaglandin E1 (PGE1) were evaluated in nine coronary patients. PGE1 infusion modestly decreased mean systemic blood pressure (85 to 76 mm Hg, p less than 0.025) and LV filling pressure (19 to 15 mm Hg, p less than 0.01) while heart rate was unchanged (p less than 0.05). Simultaneously, PGE1 augmented cardiac index from 1.9 to 2.5 1/min/m2 (p less than 0.005), raised stroke index from 28 to 35 ml/beat m2 (p less than 0.01) and increased stroke work index from 26 to 30 g-m/m2 (p less than 0.02). Additionally, total systemic vascular resistance decreased from 1862 to 1282 dynes-sec-cm-5 (p less than 0.02) and double product of heart rate and systolic blood pressure diminished from 9492 to 8278 mm Hg (p less than 0.02) while the effective endocardial perfusion pressure was maintained (p less than 0.05). Concomitantly, forearm vascular resistance fell, forearm blood flow was raised, and forearm venous tone remained unchanged. Thus, our results demonstrate that PGE2 is a potent arteriolar vasodilator with markedly beneficial effects of myocardial energetics and on cardiac function in patients with severe ischemic congestive cardiac failure.

Regulation of Coronary Blood Flow During Exercise

Exercise is the most important physiological stimulus for increased myocardial oxygen demand. The requirement of exercising muscle for increased blood flow necessitates an increase in cardiac output that results in increases in the three main determinants of myocardial oxygen demand: heart rate, myocardial contractility, and ventricular work. The approximately sixfold increase in oxygen demands of the left ventricle during heavy exercise is met principally by augmenting coronary blood flow (∼5-fold), as hemoglobin concentration and oxygen extraction (which is already 70–80% at rest) increase only modestly in most species. In contrast, in the right ventricle, oxygen extraction is lower at rest and increases substantially during exercise, similar to skeletal muscle, suggesting fundamental differences in blood flow regulation between these two cardiac chambers. The increase in heart rate also increases the relative time spent in systole, thereby increasing the net extravascular compressive forces acting on the microvasculature within the wall of the left ventricle, in particular in its subendocardial layers. Hence, appropriate adjustment of coronary vascular resistance is critical for the cardiac response to exercise. Coronary resistance vessel tone results from the culmination of myriad vasodilator and vasoconstrictors influences, including neurohormones and endothelial and myocardial factors. Unraveling of the integrative mechanisms controlling coronary vasodilation in response to exercise has been difficult, in part due to the redundancies in coronary vasomotor control and differences between animal species. Exercise training is associated with adaptations in the coronary microvasculature including increased arteriolar densities and/or diameters, which provide a morphometric basis for the observed increase in peak coronary blood flow rates in exercise-trained animals. In larger animals trained by treadmill exercise, the formation of new capillaries maintains capillary density at a level commensurate with the degree of exercise-induced physiological myocardial hypertrophy. Nevertheless, training alters the distribution of coronary vascular resistance so that more capillaries are recruited, resulting in an increase in the permeability-surface area product without a change in capillary numerical density. Maintenance of α- and ß-adrenergic tone in the presence of lower circulating catecholamine levels appears to be due to increased receptor responsiveness to adrenergic stimulation. Exercise training also alters local control of coronary resistance vessels. Thus arterioles exhibit increased myogenic tone, likely due to a calcium-dependent protein kinase C signaling-mediated alteration in voltage-gated calcium channel activity in response to stretch. Conversely, training augments endothelium-dependent vasodilation throughout the coronary microcirculation. This enhanced responsiveness appears to result principally from an increased expression of nitric oxide (NO) synthase. Finally, physical conditioning decreases extravascular compressive forces at rest and at comparable levels of exercise, mainly because of a decrease in heart rate. Impedance to coronary inflow due to an epicardial coronary artery stenosis results in marked redistribution of myocardial blood flow during exercise away from the subendocardium towards the subepicardium. However, in contrast to the traditional view that myocardial ischemia causes maximal microvascular dilation, more recent studies have shown that the coronary microvessels retain some degree of vasodilator reserve during exercise-induced ischemia and remain responsive to vasoconstrictor stimuli. These observations have required reassessment of the principal sites of resistance to blood flow in the microcirculation. A significant fraction of resistance is located in small arteries that are outside the metabolic control of the myocardium but are sensitive to shear and nitrovasodilators. The coronary collateral system embodies a dynamic network of interarterial vessels that can undergo both long- and short-term adjustments that can modulate blood flow to the dependent myocardium. Long-term adjustments including recruitment and growth of collateral vessels in response to arterial occlusion are time dependent and determine the maximum blood flow rates available to the collateral-dependent vascular bed during exercise. Rapid short-term adjustments result from active vasomotor activity of the collateral vessels. Mature coronary collateral vessels are responsive to vasodilators such as nitroglycerin and atrial natriuretic peptide, and to vasoconstrictors such as vasopressin, angiotensin II, and the platelet products serotonin and thromboxane A2. During exercise, ß-adrenergic activity and endothelium-derived NO and prostanoids exert vasodilator influences on coronary collateral vessels. Importantly, alterations in collateral vasomotor tone, e.g., by exogenous vasopressin, inhibition of endogenous NO or prostanoid production, or increasing local adenosine production can modify collateral conductance, thereby influencing the blood supply to the dependent myocardium. In addition, vasomotor activity in the resistance vessels of the collateral perfused vascular bed can influence the volume and distribution of blood flow within the collateral zone. Finally, there is evidence that vasomotor control of resistance vessels in the normally perfused regions of collateralized hearts is altered, indicating that the vascular adaptations in hearts with a flow-limiting coronary obstruction occur at a global as well as a regional level. Exercise training does not stimulate growth of coronary collateral vessels in the normal heart. However, if exercise produces ischemia, which would be absent or minimal under resting conditions, there is evidence that collateral growth can be enhanced. In addition to ischemia, the pressure gradient between vascular beds, which is a determinant of the flow rate and therefore the shear stress on the collateral vessel endothelium, may also be important in stimulating growth of collateral vessels.

Interrelationships between prostacyclin and thromboxane A2

Prostacyclin is a product of arachidonic acid metabolism generated by the vessel wall of all mammalian species studied including man. Prostacyclin is a potent vasodilator and the most potent inhibitor of platelet aggregation so far described. It inhibits platelet aggregation through stimulation of adenylate cyclase leading to an increase in cyclic AMP in the platelets. The enzyme which synthesizes prostacyclin is mainly localized in the endothelial layer of the vascular wall. Prostacyclin can also be a circulating hormone constantly released by the pulmonary circulation. On the basis of these observations we proposed that platelet aggregability in vivo is controlled via a prostacyclin mechanism. In contrast to the vessel wall, in blood platelets arachidonic acid is converted by the enzyme thromboxane synthetase to a potent vasoconstrictor and proaggregating substance, thromboxane A2. Therefore arachidonic acid is metabolized in the vessel wall and the platelets to potent substances with opposing biological activities. The balance between the activities of these substances is important in the homeostatic interaction of the platelets and the vessel wall. The different ways of interfering with this balance and its impact in the development of thrombosis and atherosclerosis are discussed. The balance between thromboxane A2 and prostacyclin might be important in the control of the pulmonary circulation. This possibility is discussed in the light of the present evidence.

Nitric Oxide and Prostaglandins Modulate Pressure-Induced Myogenic Responses of Intramural Coronary Arterioles

The myogenic response, an active constriction and dilation of vessels to changes in intravascular pressure, can play an important role in the regulation of coronary blood flow. The characteristics of the myogenic response and its modulation by endothelium-derived factors are organ and location specific and have not been studied extensively in intramural coronary arterioles. Thus, distal intramural branches (approximately 100 and approximately 170 microm active and passive diameter, respectively) of the left anterior descending coronary artery of rats were isolated and cannulated. Step increases in intraluminal pressure from 0 to 40 mm Hg elicited increases in diameter, whereas further increases in pressure from 50 to 150 mm Hg resulted in constrictions. In control, the pressure-induced myogenic tone of coronary arterioles was 67.3 +/- 2.7% of passive diameter (PD, obtained in Ca2+-free solution) at 60 mm Hg. Nomega-nitro-L-arginine (L-NNA, 10(-5) M), an inhibitor of nitric oxide synthase, reduced the initial arteriolar diameter (by 44.8 +/- 5.1 microm at 2 mm Hg, P < 0.05) and significantly mitigated increases in diameter to lower pressures and constrictions to higher pressures (41.1 +/- 5.6% of PD at 60 mm Hg). Administration of adenosine restored the initial diameter in the presence of l-NNA, but the increase in diameter to lower pressures and the decrease in diameter to higher pressures observed under control conditions remained greatly inhibited. Inhibition of prostaglandin synthesis, or PGH2/TxA2 receptors significantly reduced the constrictions to higher pressures as compared with control (indomethacin: from 57.9 +/- 4.8% of PD to 67.0 +/- 4.7% of PD at 150 mm Hg). Thus, because in isolated intramural coronary arterioles of rats a negative slope for the pressure-diameter curve develops only in the presence of nitric oxide and constrictor prostaglandins, they seem to be essential for the normal development of the myogenic response.

Decreased phospholipid polyunsaturated fatty acid content and superoxide dismutase activity in cardiac muscle of malignant hyperthermia-susceptible swine

Homogenates of cardiac left ventricle from malignant hyperthermia-susceptible (MHS) pigs produced a circa 72% more pentane than those from malignant hyperthermia-resistant (MHR) animals, indicating enhanced peroxidation of n-6 fatty acids. This is consistent with the observed circa 70% decrease in total phospholipid polyunsaturated fatty acids (PUFA) in MHS compared with MHR tissue, a decrease mainly due to the quantitatively greater loss of n-6 PUFA. Although the percentage loss of n-3 PUFA was greater than that of n-6 PUFA (90% vs 60%), absolute amounts were insufficient to register as ethane production. Three-fold greater phospholipid content of MHS compared with MHR ventricles indicates reduced neutral lipid content probably due to increased catecholamine stimulation. These findings were associated with a small but significant decrease in superoxide dismutase activity in MHS tissues.

Effect of diltiazem on silent ischemic episodes, plasma bradykinin and prostaglandin metabolism

Plasma bradykinin and prostaglandin metabolism are related to the anginal pain modulating system in patients with ischemic heart disease. We carried out a placebo controlled single blind test of diltiazem (30 mg three times a day) in 15 patients with chronic stable angina. The effect of diltiazem was evaluated by exercise treadmill testing and 48-h ambulatory electrocardiographic monitoring. Plasma bradykinin, thromboxane B2, and 6-keto-prostaglandin F1 alpha levels were determined by radioimmunoassay prior to and during diltiazem therapy. Diltiazem significantly increased the exercise time and reduced episodes of angina. Diltiazem, however, did not appreciably improve either the frequency of silent myocardial ischemic episodes or the total duration of the silent myocardial ischemic episodes. Diltiazem also tended to decrease plasma bradykinin, thromboxane B2, and 6-keto-prostaglandin F1 alpha levels. When ischemic episodes on ambulatory electrocardiographic monitoring are categorized according to heart rate change at the onset of episode (type A, preceded by heart rate increase > or = 5 beats/min; type B, no preceding heart rate increase), diltiazem was only effective on type A ischemic episodes as well as on symptomatic ischemia. Further, bradykinin was significantly decreased by diltiazem only in patients with exercise-induced silent ischemia or no exercise-induced ischemia, while the thromboxane B2/6-keto-prostaglandin F1 alpha ratio was unaffected by the administration of diltiazem. Thus, silent and symptomatic ischemia may be associated with different bradykinin and prostaglandin responses.

Effect of cyclooxygenase blockade on blood flow through well-developed coronary collateral vessels

Collateral vessels that develop after coronary artery occlusion demonstrate perivascular inflammation, subintimal hyperplasia, and endothelial proliferation. This study was performed to test the hypothesis that these abnormalities are associated with evidence for increased production of vasodilator prostaglandins. Eight dogs were studied 4-6 months after occlusion of the anterior descending coronary artery had been performed to stimulate collateral vessel growth. At the time of study, the anterior descending coronary artery was cannulated at the site of occlusion to allow measurement of retrograde blood flow as an index of interarterial collateral flow. Injection of radioactive microspheres during the retrograde flow collection allowed determination of continuing tissue flow in the collateral-dependent zone as an index of intramural microvascular collateral flow. Retrograde and tissue flows were measured before and 20 minutes after 5 mg/kg i.v. indomethacin, a dose that caused 95 +/- 3% inhibition of the coronary vasodilation in response to a 500 micrograms intracoronary bolus of arachidonic acid. Heart rate and mean aortic pressure were not significantly altered by indomethacin, and blood flow to the normally perfused myocardial region was not changed by administration of indomethacin. However, indomethacin caused a 40 +/- 7% decrease in retrograde flow (p less than 0.01), and microvascular collateral flow to the dependent myocardium decreased by 20 +/- 10% (p less than 0.05). These data indicate that, unlike the normal coronary circulation, well-developed coronary collateral vessels are under the tonic influence of vasodilator prostaglandins.

Effects of prostaglandin E1 in postoperative surgical patients with circulatory deficiency

Hemodynamic and oxygen transport effects of PGE1 were observed in the early postoperative period before development of ARDS in two series of general surgical patients with circulatory deficiencies. The first was a series of 19 studies in 18 patients, the second was a placebo-controlled series of 20 patients (ten received PGE1 and ten received a placebo). In the first series, PGE1 was given as a trial of therapy after fluid therapy to pulmonary wedge pressures greater than 15 mm Hg failed to correct satisfactorily circulatory and metabolic functions. There were two deaths in the placebo group and none in the PGE1 group. Previous studies indicated that PGE1 disaggregates platelets and reduces local vasoconstriction in pulmonary circulation; this study suggests that PGE1 improves tissue perfusion of systemic circulation. After fluid therapy to PAOP greater than 15 mm Hg fails to restore circulatory function to optimal values. PGE1 should be considered as ancillary therapy in critically ill postoperative patients.

Defective coronary prostaglandin modulation in anginal patients

In order to investigate whether coronary vasodilating prostaglandins (PGI2 and PGE2) have a role in the pathophysiology of myocardial ischemia, 26 patients with angina pectoris and 23 control subjects (nonischemic patients) were studied by assessing coronary hemodynamics and prostaglandin formation in relation to sympathetic stimulation. Following a cold pressor test (CPT), coronary prostaglandin output markedly increased (p less than 0.001) and coronary vascular resistance (CVR) decreased (p less than 0.001) in all control subjects. In contrast, in anginal patients prostaglandins in the coronary sinus were undetectable and after CPT prostaglandin output did not increase, whereas CVR paradoxically increased (p less than 0.001). In control subjects the inhibition of coronary prostaglandin formation (by ketoprofen [1 mg/kg intravenously] or by aspirin [15 mg/kg intravenously]) caused a paradoxical increase of CVR following CPT (p less than 0.001). In anginal patients the inhibition of prostaglandins further exaggerated the increase of CVR after CPT (p less than 0.001). These results indicate that coronary vasodilating prostaglandin PGI2 and PGE2 play a role in modulating coronary vascular response to sympathetic stimulation induced by CPT. Their defective production in anginal patients may be responsible for the paradoxical increase in CVR following sympathetic stimulation.

Physiologic role of coronary PGI2 and PGE2 in modulating coronary vascular response to sympathetic stimulation

To investigate a physiologic role of coronary prostacyclin (PGI2) and prostaglandin E2 (PGE2) 30 patients who were not affected by coronary heart disease were evaluated for coronary hemodynamics and coronary PGI2 and PGE2 production. Inhibition of coronary prostaglandin biosynthesis by ketoprofen (1 mg/kg) or aspirin (15 mg/kg) administered intravenously did not significantly change coronary hemodynamics in resting conditions. In all patients cold pressor tests induced significant increases in coronary blood flow (p less than 0.001) and decreases in coronary vascular resistance (p less than 0.001) without changes in cardiac oxygen extraction and with consequent increases in calculated myocardial oxygen consumption. Simultaneously, a marked increase in coronary PGI2 (as 6-keto-PGF1 alpha) and PGE2 formation was observed (p less than 0.001). Both ketoprofen (1 mg/kg) and aspirin (15 mg/kg) administration completely abolished PGI2 and PGE2 formation that was induced by cold pressor test and caused a paradoxical increase in coronary vascular resistance (ketoprofen: p less than 0.02; aspirin: p less than 0.05). The results of this study support a physiologic role for the coronary prostaglandins in modulating coronary vascular response to sympathetic stimulation in nonischemic patients.

Attenuation of reactive hyperemia caused by aspirin in canine coronary artery

Effects of intracoronary aspirin on coronary blood flow and reactive hyperemia were evaluated in closed-chest, anesthetized dogs. In 18 dogs the left circumflex coronary artery was cannulated and perfused by arterial blood at a constant pressure. Coronary blood flow was measured by an electromagnetic flowmeter. Intracoronary aspirin at doses of 5, 10, and 20 mg reduced coronary blood flow in a dose-dependent manner. Injection of aspirin at doses of 10 to 25 mg also inhibited reactive hyperemia following the coronary occlusion for fifteen seconds. The mean peak flow ratio was reduced from 2.13 +/- 0.42 to 1.75 +/- 0.35 (p less than 0.005). The increment of coronary blood flow provoked by intracoronary arachidonic acid at doses of 150 to 300 micrograms was almost entirely inhibited by the pretreatment of the coronary artery with aspirin. The authors conclude that aspirin increases coronary arterial resistance in a dose-dependent manner and also restricts the maximal dilating capacity, possibly by inhibition of prostacyclin synthesis.

Arachidonate metabolism in cultured fibroblasts derived from normal and infarcted canine heart

Metabolites of arachidonic acid (eicosanoids) may have an important role in the healing process after myocardial infarction. We examined the ability of cardiac fibroblasts from normal and from healing infarcted ventricle to metabolize arachidonate. We induced myocardial infarction in dogs and then allowed them to recover for 1 week, at which time they were killed, and the heart was removed. Fibroblasts were harvested from normal and from the healing, infarcted areas of the left ventricle. The cells from each source were morphologically indistinguishable. There were 347 +/- 102-fold more fibroblasts cultured from the infarcted area than from the normal area. Interestingly, the infarct-derived cells had a slower doubling time (37.4 +/- 3.7 hours) than the normal cells (22.0 +/- 3.6 hours). The uptake of exogenous arachidonate and its distribution in complex lipids was the same in the cells from each area. When stimulated with the calcium ionophore, free exogenous arachidonate, bradykinin, or histamine the cells produced prostaglandin E2 and prostaglandin I2. In each case the infarct-derived cells produced from twofold to fivefold more prostaglandin than the normal cells. We also found that prostaglandin synthesis was highly dependent on the growth state of the cells with a marked decrease a confluence. Finally, in experiments designed to mimic the early state of infarction, we confirmed that isolated cardiac myocytes release arachidonate and showed that normal fibroblasts can incorporate it. The production of eicosanoids by cardiac fibroblasts may be substantial during the healing of myocardial infarction due to their dramatic proliferation and the increased prostaglandin production per cell.

Prostaglandin E1 attenuates postischemic contractile dysfunction after brief coronary occlusion and reperfusion

We have previously demonstrated that administration of the prostacyclin analogue iloprost improved postischemic functional recovery in reversibly injured ischemic-reperfused myocardium. The present study investigated the effects of administering an endogenous vasodilator prostanoid, prostaglandin E1 (PGE1), in the stunned myocardium (15 minutes of coronary artery occlusion and 3 hours of reperfusion) of anesthetized dogs. The percentage of regional myocardial segment shortening (%SS) after administration of PGE1 by two routes, intravenously (1 microgram/kg/min) or intraatrially (0.1 microgram/kg/min), to avoid pulmonary metabolism, 15 minutes before and throughout the period of occlusion, was compared to %SS in a control group treated with saline solution. Nearly equivalent reductions in mean arterial pressure during occlusion compared to pretreatment control (PTC) values were produced by intravenous (33%) or intraatrial (25%) PGE1. There was no difference in transmural myocardial blood flow (radioactive microsphere technique) in the ischemic region between the PGE1-treated and control groups at any time. Although there were no differences in %SS in the nonischemic region between groups throughout the experiment, postischemic recovery of segment function in the ischemic-reperfused area was significantly improved (p less than 0.05) at all times during reperfusion by intravenous PGE1 (%SS of PTC: 30 minutes = 65 +/- 8; 3 hours = 58 +/- 7) or intraatrial PGE1 (%SS of PTC: 30 minutes = 57 +/- 12; 3 hours = 50 +/- 4) compared to the control group (%SS of PTC: 30 minutes = 25 +/- 13; 3 hours = 10 +/- 13). Thus treatment with PGE1 attenuates postischemic contractile dysfunction in the stunned myocardium.2+ both.

Plasmenylethanolamine is the major storage depot for arachidonic acid in rabbit vascular smooth muscle and is rapidly hydrolyzed after angiotensin II stimulation

The present study demonstrates that rabbit aortic intimal smooth muscle cells contain the majority of their endogenous arachidonic acid mass in plasmenylethanolamine molecular species. To demonstrate the potential significance of these plasmenylethanolamines as substrates for the smooth muscle cell phospholipases that are activated during agonist stimulation, aortic rings were prelabeled with [3H]arachidonic acid and stimulated with angiotensin II. Although the specific activities of the choline and inositol glycerophospholipid pools were similar after the labeling interval, ethanolamine glycerophospholipids had a specific activity of only 20% of the specific activity of choline and inositol glycerophospholipids. Despite the marked disparity in the specific activities of these three phospholipid classes, angiotensin II stimulation resulted in similar fractional losses (35-41%) of [3H]arachidonic acid from vascular smooth muscle choline, ethanolamine, and inositol glycerophospholipid classes. Reverse-phase HPLC demonstrated that greater than 60% of the [3H]arachidonic acid released from ethanolamine glycerophospholipids after angiotensin II stimulation originated from plasmenylethanolamine molecular species. Taken together, the results demonstrate that the major phospholipid storage depot for arachidonic acid in vascular smooth muscle cells are plasmenylethanolamine molecular species which are important substrates for the phospholipase(s) that are activated during agonist stimulation.

Intracoronary infusion of prostaglandin I2 attenuates arterial baroreflex control of heart rate in conscious dogs

Prostaglandin I2 (PGI2) is known to stimulate ventricular C fiber receptors resulting in a Bezold-Jarisch-like reflex. Also, cardiac receptor stimulation is known to interact with the expression of arterial baroreflexes. Therefore, experiments were performed to determine the effects of left circumflex coronary artery infusion of PGI2 on the baroreflex control of heart rate in conscious instrumented dogs. Dogs were instrumented chronically with an aortic catheter for the measurement of mean aortic pressure, hydraulic occluder cuffs on the descending aorta and inferior vena cava, a left ventricular catheter for the measurement of left ventricular pressure and heart rate, and a nonocclusive catheter in the left circumflex coronary artery. At the time of experimentation, arterial pressure was altered randomly in steps by partially inflating the occluders. Mean arterial pressure-heart curves (baroreflex curves) were constructed by fitting the data to a logistic curve by nonlinear regression. PGI2 infused into the left circumflex coronary artery at doses of 10, 20, and 50 ng/kg/min caused significant (p less than 0.05) inhibition of the maximum heart rate, heart rate range, and maximum slope of the curve compared to the control baroreflex curve obtained during intracoronary infusion of PGI2 vehicle. PGI2 had no significant effect on the minimum heart rate during hypertension. Since PGI2 is known to stimulate left ventricular receptors, these effects were most likely produced via stimulation of cardiac receptors. In additional experiments using beta 1-blockade with metoprolol or cholinergic blockade with atropine methyl bromide, it was shown that PGI2 attenuates baroreflex-mediated tachycardia by preventing parasympathetic withdrawal completely and by attenuating sympathetic stimulation by approximately 50%.(ABSTRACT TRUNCATED AT 250 WORDS)

Increased prostacyclin and thromboxane A2 biosynthesis in atherosclerosis

It has been proposed that atherosclerotic arteries produce less prostacyclin (PGI2) than nonatherosclerotic arteries do, thereby predisposing arteries to vasospasm and thrombosis in vivo. We reexamined this concept by measuring spontaneous as well as arachidonate-induced PGI2 biosynthesis in aortic segments from nonatherosclerotic and cholesterol-fed atherosclerotic New Zealand White rabbits. Thromboxane A2 (TXA2) generation was also measured. Formation of PGI2, as well as TXA2, as measured by radioimmunoassay (RIA) of their metabolites, was increased in atherosclerotic aortic segments relative to nonatherosclerotic segments (P less than or equal to 0.05) at 0, 5, 10, 15, and 30 min of incubation with arachidonate. Pretreatment of arterial segments with indomethacin inhibited PGI2 as well as TXA2 formation, whereas pretreatment with the selective TXA2 inhibitor OKY-046 inhibited only TXA2 release, thus confirming the identity of icosanoids. To confirm the RIA data, aortic segments were incubated with [14C]arachidonate prior to stimulation with unlabeled arachidonate. The uptake of arachidonate was similar, but the release of incorporated [14C]arachidonate was significantly (P less than or equal to 0.05) greater in atherosclerotic segments than in nonatherosclerotic ones. Conversions of released [14C]arachidonate to 6-keto[14C]prostaglandin F1 alpha and [14C]thromboxane B2 were similar in the two types of aortic segments. Thus, synthesis of PGI2 as well as TXA2 is increased in atherosclerosis, and this alteration in arachidonate metabolism is related to increased release of arachidonate.

Impact of smoking on heart attacks, strokes, blood pressure control, drug dose, and quality of life aspects in the International Prospective Primary Prevention Study in Hypertension

Effects of smoking are highlighted in a posthoc analysis of this randomized, double-blind International Prospective Primary Prevention Study in Hypertension (IPPPSH). At the time of entry, 37% of the men and 23% of the women were smoking cigarettes, and only 537 patients changed their smoking status during the trial. In men and women, smoking doubled cardiac and cerebrovascular event rates. Nonsmoking men had fewer myocardial infarctions and sudden deaths when treated with oxprenolol. Smoking status did not affect in-study blood pressure control, the type of drugs, or the combinations used, but smokers were given higher doses of oxprenolol. For a given blood pressure during antihypertensive treatment, rates for cardiac and cerebrovascular events were higher in smokers. Heart rates were higher in both oxprenolol and non-beta-blocker-treated smokers. Smoking dose dependently increased hematocrit level. Among physician-elicited symptoms, dyspnea and cold extremities were more frequent in smokers, whereas dyspnea, headaches, impotence, dizziness, and anxiety states were common, with unsatisfactory blood pressure control (diastolic blood pressure greater than 95 mm Hg). Quality of life may be more jeopardized by smoking, poor blood pressure control, or diuretic use than by beta-blocker-based therapy. In the IPPPSH, the patient who smoked had double the cardiovascular complication rates without cardiac benefit from the beta-blocker despite higher doses given; the higher heart rate and hematocrit level may have been contributing factors.

Constriction of cat coronary arteries by synthetic thromboxane A2 and its antagonism

Synthetic thromboxane A2 (TxA2S) induced rapid, concentration-dependent constriction of isolated perfused cat coronary arteries. Its potency was approximately 30 times that of the prostaglandin endoperoxide, PGH2. Pinane thromboxane A2 (PTA2), BM-13.505 and SQ-29,548, compounds previously shown to antagonize the effects of stable prostaglandin endoperoxide analogs, inhibited the constriction induced by TxA2S in a concentration-dependent fashion. These experiments provide further evidence that the oxetane structure proposed for TxA2 is correct and show that compounds that inhibit the effects of prostaglandin endoperoxides also antagonize the effects of TxA2.

Effects of acute pressure overload on prostacyclin release and myocardial blood flow in canine hearts: inhibition of prostacyclin synthesis with 15-hydroperoxy-eicosatetraenoic acid

This study was undertaken to evaluate the effects of acute pressure overload on prostacyclin (PGI2) release and the influences of 15-hydroperoxy-eicosatetraenoic acid (15-HPETE), an inhibitor of PGI2 synthetase, and indomethacin, an inhibitor of cyclo-oxygenase, in canine hearts. Gradual stenosis of the ascending aorta was performed in 24 anesthetized open-chest dogs. The mongrel dogs were divided into three groups, which received indomethacin, 15-HPETE, and no drug. Changes in the hemodynamics, regional myocardial blood flow (MBF) by the method of H2 gas clearance, and plasma immunoreactive 6-keto-prostaglandin (PG) F1 alpha level in the descending aorta (AO) and great cardiac vein (GCV) were measured. Five minutes after aortic stenosis, the plasma immunoreactive 6-keto-PGF1 alpha level in the GCV and MBF increased from 162 +/- 23 to 289 +/- 37 pg/ml and from 87 +/- 5 to 107 +/- 8 ml/min/100 g, respectively, and the calculated coronary vascular resistance (CVR) decreased significantly from 0.93 +/- 0.08 to 0.77 +/- 0.08 mmHg/ml/min/100 g. These significant changes persisted thereafter. Continuous infusion of 15-HPETE (66 pg/kg/min) into the coronary artery simultaneously prevented significant changes in MBF and the plasma immunoreactive 6-keto-PGF1 alpha level in the GCV and CVR. Intravenous infusion of indomethacin (5 mg/kg), on the other hand, induced a significant decrease in the plasma immunoreactive 6-keto-PGF1 alpha level in both the GCV and AO; significant changes in MBF 5 to 15 min after aortic stenosis and CVR were not affected. From these results, it is suggested that PGI2 plays an important role in the regulation of coronary blood flow in canine hearts with acute pressure overload.(ABSTRACT TRUNCATED AT 250 WORDS)

Molsidomine: alternative approaches to treat myocardial ischemia

The long-acting antianginal drug molsidomine has been shown experimentally to reduce myocardial infarct size when administered prior to or after cardiac insult. This is due to several drug actions. Dilation of postcapillary capacitance vessels diminishes venous return, preload, heart dimensions, and myocardial oxygen consumption. Relaxation of stenosed conductive coronary arteries increases the perfusion of myocardial areas at risk of infarction due to enhanced collateral circulation. Increased regional blood supply nourishes predominantly subendocardial cardiac muscles as a result of reduction of extravascular coronary pressure, and resistance. The stable heart rate and cardiac contractility favor improved heart performance. The inhibition of platelet aggregation in vivo by molsidomine or its active metabolites, SIN-1 and SIN-1A, is linked to the stimulation of prostacyclin synthesis, inhibition of thromboxane release with induction of thrombosis and vasoconstriction, and enhanced concentrations of cyclic guanosine monophosphate. Dilation of coronary arteries after intracoronary administration of SIN-1, with inhibition of platelet aggregation by restrained release of adenosine diphosphate and stabilization of platelet membranes, facilitates the recanalization of stenosed arteries and reduces coronary muscle tone at the site of thrombosis. Activation of the human fibrinolytic system and drug-induced release of a plasminogen activator favor dysaggregatory effects. The drug's inhibiting actions on lipoxygenase products of arachidonate (e.g., 12-hydroperoxy-eicosatetraenoic acid and leukotrienes) may shift prostaglandin catabolism to cyclooxygenase products (e.g., prostacyclin) that protect against the expansion of ischemia and the induction of coronary spasm. Experimentally, the hemodynamic effectiveness of molsidomine can be antagonized by catecholamines (afterload effects) and dihydroergotamine (preload and afterload effects) respectively. Further clinical investigations will clarify the application of these mechanisms for the therapeutic success of the drug in human myocardial infarction.

Regulation of large coronary arteries

The majority of studies on the control of coronary artery vasoactivity have examined changes in coronary blood flow and coronary vascular resistance, indices that primarily reflect regulation of small arterioles and precapillary vessels. With the emergence of coronary artery vasospasm as a significant cause of angina pectoris, myocardial infarction, and sudden death, the control of large coronary artery caliber has assumed more significance. It is clear that resistance coronary vessels and large coronary arteries differ in response to both pharmacologic and physiologic stimuli. Vasodilation of large coronary arteries may occur by direct action of agents on the arterial smooth muscle or by the indirect action of receptor occupation, changes in blood flow, or liberation of endothelial factors. These indirect factors appear to contribute also to responses to agents that constrict coronary smooth muscle directly or through the autonomic nervous system. Furthermore, the mechanisms responsible for control of large coronary vessels in the normal circulation are likely to be profoundly different from those in the presence of diseased vessels. For example, several factors associated with coronary artery disease--elevated plasma cholesterol levels, endothelial disruption, atherosclerosis, vascular stenosis, and aggregated platelets--all have important actions on the control of large coronary arteries.

Intracoronary prostaglandin E1 plus streptokinase in acute myocardial infarction

Fourteen patients with acute myocardial infarction (duration of chest pain 5 +/- 2 hours) received intracoronary infusion of prostaglandin E1 (PGE1) and streptokinase. Intracoronary PGE1 was followed by intracoronary streptokinase in 10 patients (group A), with successful recanalization in all patients. Of 4 patients in whom recanalization failed with intracoronary streptokinase given first (group B), 2 had successful recanalization after addition of intracoronary PGE1. Immediately after successful recanalization, left ventricular ejection fraction increased from 50 +/- 9% to 62 +/- 10% (p less than 0.0008), left ventricular end-diastolic pressure decreased from 20 +/- 10 to 16 +/- 10 mm Hg (p less than 0.05) and stroke volume index increased from 34 +/- 10 to 44 +/- 12 ml/m2 (p less than 0.02). Infarct segment shortening improved from 9 +/- 5 to 18 +/- 4% (p less than 0.0002). Transient hypotension in 1 patient was the only complication. Follow-up catheterization in recanalized patients at 2 to 10 days showed maintained improvement in left ventricular global and infarct segment function. Reocclusion occurred in 1 patient. Thus, intracoronary infusion of PGE1 was effective in establishing reperfusion in all patients when followed by streptokinase and was associated with immediately improved left ventricular global and regional function. PGE1 deserves further evaluation in acute myocardial infarction.

Coronary artery thrombosis and elevated urine immunoreactive thromboxane B2

Immunoreactive thromboxane B2 (i-TXB2) was measured by radio-immunoassay (RIA) in urines collected over eight hours on the day of admission in 25 patients who were admitted with the diagnosis of myocardial infarction. In 16 of the patients myocardial infarction was confirmed by ECG and plasma enzymes. Another patient presented with pulmonary embolism and the remaining eight patients had angina pectoris. A further eight hour urine collection was obtained 24 hours later from eleven of the sixteen patients with myocardial infarction. In these eleven patients myocardial infarction was associated with five fold higher urine i-TXB2 (2.72 +/- 0.48 ng/ml) at the day of admission when compared to patients admitted under the same diagnosis but found to have angina only (0.51 +/- 0.08 ng/ml, p less than 0.001). In patients with myocardial infarction the urine i-TXB2 values were reduced 24 hours later (1.58 +/- 0.27 ng/ml, p less than 0.01). One patient was followed with urine i-TXB2 from three days prior to diagnosis of myocardial infarction and to one day prior to a second infarction. In this patient i-TXB2 was highest three days prior to infarction. We conclude that this early elevation of urine i-TXB2 three days prior to diagnosis of infarction and the increased i-TXB2 in patients with myocardial infarction when compared to patients with angina suggest thromboxane is probably released from activated platelets prior to infarction. We suggest that urine i-TXB2 may be of value in the differential diagnosis between myocardial infarction and angina.

Left ventricular receptors: physiological controllers or pathological curiosities?

Mechanically and chemically sensitive receptors in the ventricle have been described histologically and electrophysiologically. Early experiments documented the hypotension and bradycardia that resulted from the intracoronary administration of one of the veratrum alkaloids (the Bezold-Jarisch reflex). Mechanical distension of the ventricles also results in a reflex decrease in heart rate and a reduction in peripheral resistance. Skeletal muscle and coronary vascular resistance appear to be most prominently affected by stimulation of ventricular receptors. Coronary ischemia has also been shown to evoke reflex effects which are attributable to stimulation of ventricular receptors. The resultant bradycardia can be especially ominous in acute myocardial infarction. Changes in myocardial inotropic state have been shown to alter ventricular receptor discharge in experimental animals. This stimulus may evoke reflex changes in peripheral hemodynamics. A variety of humoral substances can alter ventricular receptor discharge and evoke Bezold-Jarisch like responses. These include bradykinin and prostaglandins. PGI2, when given intracoronary in small doses or intravenously in larger doses will lower blood pressure while inhibiting the baroreflex induced tachycardia. It has also been shown in some experiments that PGI2 and arachidonic acid can evoke overt bradycardia and hypotension via a reflex mechanism. The role of prostaglandins in cardiovascular reflex control may be important in pathophysiologic states such as coronary ischemia and heart failure. Ventricular receptors can interact centrally with the arterial baroreceptors to attenuate the baroreflex control of both heart rate and peripheral resistance. Finally, the stimulation of ventricular receptors can alter a variety of humoral substances which are important regulators of cardiovascular and fluid volume homeostasis. These include vasopressin, renin and catecholamines. Those studies which have been done within the last 10 years or so, especially in unanesthetized animals, have demonstrated that the Bezold-Jarisch reflex is more important to cardiovascular control than previously thought. Future work will be necessary to determine the precise role ventricular receptors play in various pathological situations.

Impaired cardiac PGI2 and PGE2 biosynthesis in patients with angina pectoris

Thirty-four patients with unstable angina and 14 patients with stable effort angina were investigated for cardiac prostacyclin and prostaglandin E2 (PGE2) biosynthesis, under resting conditions and after cold pressor testing. Twenty-seven patients undergoing cardiac catheterization and coronary angiography for congenital or acquired heart diseases other than coronary artery disease were studied as a control group. Prostacyclin (as 6-keto-PGF1 alpha) and PGE2 were measured by specific radioimmunoassay of blood from the coronary sinus and aorta. During resting conditions no significant differences in plasma 6-keto-PGF1 alpha and PGE2 concentrations were found between coronary sinus and aortic blood, and no transcardiac gradient existed either in control subjects or in patients with stable and unstable angina, respectively. In control subjects cold pressor testing induced a significant increase in 6-keto-PGF1 alpha and PGE2 levels in blood from the different sampling sites, and a significant transcardiac gradient occurred (+11.2 +/- 6.4 pg/ml for 6-keto-PGF1 alpha and +5.1 +/- 3.4 pg/ml for PGE2). However, in angina patients no significant increase in 6-keto-PGF1 alpha and PGE2 plasma levels was found and no transcardiac gradient was formed after cold pressor testing. These results indicate impaired cardiac prostacyclin and PGE2 biosynthesis both in patients with stable and unstable effort angina.

Prostacyclin reduction of regional ischemic injury in the canine myocardium

The effect of prostacyclin (PGI2) on the myocardium of the awake dog subjected to coronary artery occlusion was examined. Animals were randomly administered PGI2 200 ng/kg/min (n = 6), PGI2 100 ng/kg/min (n = 6), or the vehicle control (n = 6), beginning 30 min prior to coronary artery occlusion. Radiolabeled microspheres (15 microns) were used to measure myocardial blood flow. The myocardial region at risk was determined by fluorescein injection, and infarct size was assessed by triphenyl tetrazolium staining. Segmental myocardial function was evaluated from the systolic ejection shortening (SES) by subendocardial ultrasonic dimension crystals in normal, ischemic, and border zones. PGI2 200 ng/kg/min produced significant decreases in aortic pressure and systemic vascular resistance. PGI2 100 ng/kg/min, which achieves 95% platelet inhibition, had no significant hemodynamic effects. Animals receiving PGI2 200 ng/kg/min had significantly higher blood flow to the ischemic region, better border zones SES, and a smaller infarct. PGI2 ameliorates myocardial injury and reduces functional impairment produced by ischemia in doses that elicit vasodilation. This beneficial effect of PGI2 does not appear to be mediated solely by an antiplatelet mechanism.

Action and localization of vasoactive intestinal peptide in the coronary circulation: evidence for nonadrenergic, noncholinergic coronary regulation

Vasoactive intestinal polypeptide, a neurotransmitter peptide detected in animal and human hearts, has been found in nerves of coronary arteries. To determine the amount and distribution of vasoactive intestinal polypeptide in the large coronary vessels and its possible participation in coronary vasoregulation, two groups of animals were studied. In the first group, 11 anesthetized dogs were sacrificed to collect three (1 cm) segments along the circumflex and left anterior descending coronary arteries. These segments represented proximal (I), middle (II) and distal (III) portions of the two arteries. Concentrations (ng/g) of vasoactive intestinal polypeptide-like immunoreactive substance were determined by radioimmunoassay. Vasoactive intestinal polypeptide-like immunoreactivity was present in the left anterior descending (I = 7.28 +/- 1.65, II = 3.74 +/- 0.57, III = 2.29 +/- 0.53) and circumflex (I = 4.16 +/- 1.52, II = 4.58 +/- 1.13, III = 4.00 +/- 0.81) coronary arteries. The difference in vasoactive intestinal polypeptide-like immunoreactivity among epicardial segments of the anterior descending artery was significant, but there was no significant difference among segments of the circumflex coronary artery. In the second group (eight closed chest anesthetized dogs), the effects of vasoactive intestinal polypeptide intracoronary infusion on epicardial coronary constriction were examined at rest and with the artery constricted by serotonin. Left anterior descending (segments I, II and III) artery responses (% area change) to vasoactive intestinal polypeptide and vasoactive intestinal polypeptide plus serotonin were examined using quantitative coronary angiography. Vasoactive intestinal polypeptide infusion resulted in significant vasodilation in all the segments (I, II and III) of the left anterior descending artery.(ABSTRACT TRUNCATED AT 250 WORDS)

Lack of production of thromboxane A2 by the sheep heart following coronary occlusion

Blood pressure, heart rate and ECG were monitored continuously and coronary venous blood samples assayed for thromboxane B2. Arterio-coronary venous lactic acid differences were estimated. In anaesthetized sheep, 60 sec occlusions of the left circumflex coronary artery caused hypotension with little change in heart rate. Five minute occlusions produced similar changes accompanied by cardiac arrhythmias and a larger fall in blood pressure. In conscious sheep heart rate rose and blood pressure was maintained. ECG and lactic acid changes indicated severe myocardial ischaemia but not change in thromboxane release was detected. The apparent lack of involvement of thromboxane may reflect a relative inability of sheep platelets to produce this substance or a failure to provide an adequate stimulus for synthesis.

Anti-ischemic actions of a new thromboxane receptor antagonist during acute myocardial ischemia in cats

Thromboxane A2 (TxA2) production increases significantly during acute myocardial ischemia. Since TxA2 induces platelet aggregation, coronary vasoconstriction, and has a direct cytolytic effect, thromboxane receptor antagonism would be expected to be beneficial in acute myocardial ischemia. Thirty minutes after ligation of the left anterior descending coronary artery (LAD) in anesthetized cats, the TxA2 receptor antagonist BM-13,177 or its vehicle was given as a bolus injection at 20 mg/kg, followed by continuous infusion of 20 mg/kg/hr for 4.5 hours. ST segment elevation declined significantly (p less than 0.02) after BM-13,177 treatment, suggesting a reduction in cellular ischemia. The loss in myocardial creatine kinase (CK) activity and in free amino-nitrogen concentration in the ischemic area was also significantly reduced (p less than 0.01). No significant changes in blood pressure or heart rate were seen with BM-13,177 during myocardial ischemia or in nonischemic control cats. Blood levels of BM-13,177 were sufficient to inhibit ex vivo platelet aggregation induced by the prostaglandin endoperoxide analog, U-46,619. Data from isolated cat coronary arteries suggest that BM-13, 177 antagonizes the thromboxane/endoperoxide receptor in coronary vascular smooth muscle. These experiments indicate that TxA2 plays a significant role in propagating the extension of ischemic damage, and that thromboxane receptor antagonism is an effective means of reducing the damage provoked by TxA2 in acute myocardial ischemia.

Delayed effects of early infarct-limiting therapies on healing after myocardial infarction

The effect of early infarct-limiting therapy on the hydroxypyroline (OHP, a marker of collagen) content and topography of 7-day-old infarcts was studied in 76 conscious dogs (69 ligated; seven sham operated). Two hours after their left anterior descending coronary arteries were occluded, 69 dogs were randomly assigned to receive 6 hr intravenous infusions of saline (controls; n = 29), low-dose nitroglycerin (NG; n = 13), prostacyclin (PGI2; n = 14), or ibuprofen (IBU; n = 13). Regional OHP (mg/g dry weight) was measured by spectrophotometry, and size of infarction and topography were determined by computerized planimetry. Infarct size was less in the NG, PGI2, and IBU groups compared with that in the saline group, both when measured as a percent of the arteriographic occluded bed (p less than .001) and as a percent of the left ventricle (p less than .005). For each treatment group (1) the level of OHP was higher (p less than .001) in the region of infarction (saline group, 9.9 +/- 0.7 mg/g; NG group, 14.9 +/- 1.9 mg/g; PGI2 group, 12.9 +/- 0.9 mg/g; IBU group, 10.6 +/- 1.4 mg/g) than in normal zones (4.4 +/- 0.2 mg/g), with more (p less than .05) OHP in border than center regions, and (2) the total OHP in the infarct zone was linearly related to size of infarction as a percent of the left ventricle (r = .89 to .94). However, the slopes of regressions for the NG, PGI2, and IBU groups were greater (p less than .001) than the slope for the saline group.(ABSTRACT TRUNCATED AT 250 WORDS)

Does prostacyclin (PGI2) cardioplegic infusion improve myocardial protection after ischemic arrest?

To determine whether prostacyclin (PGI2) plays a beneficial role in the blood-perfused heart undergoing global ischemia, 20 isolated canine hearts were studied after sustaining one hour of cardioplegic arrest under moderate hypothermia (27 degrees to 28 degrees C). Left ventricular function (peak systolic pressure, rate of rise of left ventricular pressure [dP/dt], and compliance change in left ventricular volume), myocardial edema, coronary blood flow, and oxygen content were measured during the preischemic period and at 15 and 30 minutes during reperfusion. Results showed an improved hemodynamic recovery (peak systolic pressure, p = 0.018 at 30 minutes; dP/dt, p = 0.020 at 15 minutes) in the group of hearts treated with PGI2 infusion compared with controls. There was no difference in ventricular compliance or myocardial edema between the two groups. This benefit was attributed to a significant increase in myocardial blood flow (p = 0.028 at 15 minutes) and oxygen delivery (p = 0.021 at 15 minutes) during the reperfusion period with PGI2. These data suggest a potential clinical role for PGI2 when applied to the globally ischemic heart in the improvement of myocardial resuscitation during the early reperfusion period.

Spontaneous and cold pressor test-induced prostaglandin biosynthesis by human heart

To investigate prostaglandin biosynthesis by the heart, 21 patients undergoing cardiac catheterization and coronary angiography for congenital or acquired heart diseases other than coronary artery disease were investigated. Prostacyclin (as 6-keto-PGF1 alpha), PGE2, PGF2 alpha and TxA2 (as TxB2) were measured by specific radioimmunoassay in blood from coronary sinus, aorta, and a peripheral vein under resting conditions and following cold pressor test (CPT). PGF2 alpha was always found undetectable. In resting conditions, no significant differences in plasma 6-keto-PGF1 alpha, PGE2, or TxB2 concentrations were found among coronary sinus, aorta, and peripheral venous blood and no transcardiac gradient existed (mean: +0.4 +/- 1.2 pg/ml for 6-keto-PGF1 alpha, +0.1 +/- 0.6 pg/ml for PGE2, and -0.4 +/- 9.9 pg/ml for TxB2). CPT was able to induce a significant increase in 6-keto-PGF1 alpha and PGE2 concentration in blood from the different sampling sites and a significant transcardiac gradient was found following CPT (+11.6 +/- 7.4 pg/ml for 6-keto-PGF1 alpha (p less than 0.01) and +5.2 +/- 3.6 pg/ml for PGE2 (p less than 0.001). TxB2 levels significantly increased in peripheral venous blood (from 18.3 +/- 6.2 to 29.2 +/- 20.3 pg/ml, p less than 0.05), but they did not increase either in coronary sinus (from 21.9 +/- 9.7 to 22.9 +/- 9.8 pg/ml) or in aorta (from 22.3 +/- 4.7 to 19.1 +/- 6.5 pg/ml). Present results indicate that a cardiocoronary prostacyclin and PGE2 synthesis is inappreciable under resting conditions but it becomes remarkable following sympathetic stimulation. On the contrary, no TxA2 cardiocoronary biosynthesis seems to occur in patients free from coronary artery disease.

Abnormal cardiocoronary thromboxane A2 production in patients with unstable angina

Thromboxane B2 (TXB2), the stable metabolite of thromboxane A2 (TXA2), was measured in the coronary sinus and in aortic blood before and after cold pressor test (CPT) in 21 patients suffering from ischemic heart disease (7 affected by stable effort angina and 14 by unstable angina) and in 12 patients not suffering from myocardial ischemia (control group) during coronary angiography. Aspirin (10 mg/kg intravenously) was administered before catheterization in order to prevent platelet and leukocyte TXA2 formation. Control subjects and patients with effort angina had TXB2 resting levels lower than unstable angina patients without a transcardiac gradient which, on the contrary, was found in unstable angina patients. Only in these patients CPT resulted in a significant TXB2 increase more marked in the coronary sinus (from 50.0 +/- 18.9 pg/ml to 73.0 +/- 35.1 pg/ml, p less than 0.001) than in the aorta (from 33.4 +/- 17.1 pg/ml to 42.6 +/- 24.0 pg/ml, p less than 0.05), so that the transcardiac TXB2 gradient significantly increased. In all but two unstable angina patients, TXB2 elevation was not associated with a fall of cardiac lactate extraction. The resting and CPT-induced TXB2 gradients were unrelated to the presence and severity of coronary angiographic lesions. These results indicate that unstable angina patients show an abnormal cardiocoronary capacity to synthesize TXA2, which seems not to be elicited by the occurrence of myocardial ischemia.

Suppression of cholesteryl ester accumulation in cultured human monocyte-derived macrophages by lipoxygenase inhibitors

Atherosclerotic lesions and xanthomas are characterized by the occurrence of cholesteryl ester (CE)-laden foam cells, which partly originate from macrophages. Little is known about the role of cyclo-oxygenase or lipoxygenase metabolites of arachidonic acid in the development of foam cells. In this study we investigated the influence of prostaglandins and inhibitors of the cyclo-oxygenase or the lipoxygenase pathway on CE accumulation in cultured human monocyte-derived macrophages. Accumulation of CE was achieved by incubation of the cells with acetylated low density lipoprotein (AcLDL). The stable prostacyclin analogue ZK 36 374 and prostaglandin E2 showed no effect on cellular CE storage. Similarly, the cyclo-oxygenase inhibitor indomethacin failed to influence AcLDL-induced CE accumulation. By contrast, however, the inhibitors of lipoxygenase activity nordihydroguaiaretic acid (NDGA) and BW 755 C markedly suppressed the accumulation of CE in monocyte-derived macrophages. The inhibitory effect of NDGA was dose-dependent. Incubation of the cells with the anti-oxidant vitamin E gave no significant reduction of CE accumulation. Our results indicate that inhibition of the lipoxygenase pathway of arachidonic acid metabolism in cultured monocyte-derived macrophages effectively decreases the rate of experimentally-induced CE accumulation.