Prostaglandins and the cardiovascular system

Competitive enzymatic interactions determine the relative amounts of prostaglandins E2 and D2

Prostaglandins (PGs) are a family of cellular messengers exerting diverse homeostatic and pathophysiologic effects. Recently, several studies reported significant increases of PGI(2) and PGF(2α) after the inhibition of microsomal PGE synthase-1 (mPGES-1) expression, which indicated that PGH(2) metabolism might be redistributed when the PGE(2) pathway is blocked. To address the determinants that govern the relative amounts of PGs, we developed an in vitro cell-free method, based on liquid chromatography-tandem mass spectrometry, to measure the exact amounts of these PGs formed in response to the addition of recombinant isomerases and their selective inhibitors. Our in vitro cell-free assay results were confirmed in cells using bone marrow-derived macrophage. Initially, we determined the in vitro stability of PGH(2) and noted that there was spontaneous nonenzymatic conversion to PGD(2) and PGE(2). mPGES-1 markedly increased the conversion to PGE(2) and decreased conversion to PGD(2). Reciprocally, the addition of hematopoietic or lipocalin PGD synthase resulted in a relative increase of PGD(2) and decrease of PGE(2). A detailed titration study showed that the ratio of PGE(2)/PGD(2) was closely correlated with the ratio of PGE synthase/PGD synthase. Our redistribution results also provide the foundation for understanding how PGH(2) metabolism is redistributed by the presence of distal isomerases or by blocking the major metabolic outlet, which could determine the relative benefits and risks resulting from interdiction in nonrated-limiting components of PG synthesis pathways.

Beneficial effect of beraprost sodium plus telmisartan in the prevention of arterial stiffness development in elderly patients with hypertension and cerebral infarction

Beraprost sodium (BPS, an analogue of prostacyclin) and telmisartan (TS, an angiotensin receptor blocker) have been reported to have a preventive effect on arterial stiffness in patients with cardiovascular diseases. The purpose of this study was to estimate the effects of a combined therapy using BPS and TS on arterial pulse wave velocity (PWV) values in elderly patients with hypertension and cerebral infarction. Over a 3-month period, 80 subjects with hypertension and histories of cerebral infarction received BPS only (120 microg/day p.o.), TS only (40 mg/day p.o.), both BPS and TS, or no medication at all (control). Arterial PWV and ankle brachial indices (ABI) were determined prior to and after 3 months of drug administration. During the follow-up, there were no significant changes in any of the parameters monitored with the exception of a significant decrease in systolic blood pressure in the BPS only, TS only, and BPS plus TS groups when compared to controls. The difference values for PWV in the control group, BPS only group, TS only group, and BPS plus TS group were +232.5, -114.6, -151.5, and -248.1 cm/s, respectively. The reduction values were significantly more pronounced in the BPS plus TS group than in the BPS only (P=0.037) and the TS only (P=0.022) groups. When BPS is combined with TS, an overall additive effect is seen in the improvement of PWV in Japanese patients with hypertension and cerebral infarction. This combination therapy is more beneficial than the corresponding monotherapies.

Transcriptional Control of COX-2 via C/EBPbeta

Cyclooxygenase-2 (COX-2) is a highly inducible enzyme exerting diverse actions on cell functions, including proliferation, migration, and DNA damage. Enhanced COX-2 expression may be protective, but excessive expression may be harmful, causing inflammation, atheromatous plaque instability, and intimal hyperplasia. COX-2 transcriptional activation by proinflammatory mediators has been extensively characterized. In this review, the role of C/EBP in regulating COX-2 transcription is highlighted. Recent advances in control of COX-2 transcription by aspirin and salicylate and by a cell cycle-dependent endogenous mechanism are described. The recent progress sheds light on the pathophysiological mechanisms of COX-2 and new transcription-based strategy for controlling COX-2 overexpression and COX-2-mediated cardiovascular diseases.

The prostacyclin analogue beraprost sodium prevents development of arterial stiffness in elderly patients with cerebral infarction

Prostacyclin (PGI(2)) inhibits platelet aggregation, smooth muscle cell proliferation, and vasoconstriction. Arterial stiffness assessed by pulse wave velocity (PWV) predicts mortality in various cardiovascular diseases. To study the preventive effects of a prostacyclin analogue, beraprost sodium, on arterial PWV values in elderly patients with cerebral infarction. Forty-four patients with a history of cerebral infarction received beraprost sodium (120 microg/day p.o.) or no beraprost sodium (control) for 3 months. Arterial PWV and ankle brachial indices (ABI) were determined prior to starting the medication and after 3 months of medication. Initially, there were no differences in age, blood pressure, and body mass index. Further, PWV or ABI did not differ between the beraprost sodium group (n = 22) and the control group (n = 22). After 3 months, PWV in beraprost sodium group was significantly reduced (-123 +/- 282) when compared with the control group (147 +/- 274)(P = 0.006). ABI was not significantly different when comparing the two groups at 3 months. Long-term administration of beraprost sodium prevents the decline in arterial biomechanics in elderly patients with cerebral infarction.

The zone diet and athletic performance

The Zone diet is the latest eating regimen marketed to improve athletic performance by opposing traditional high carbohydrate sports diets. The 40/30/30 diet is centred primarily on protein intake (1.8 to 2.2 g/kg fat free mass; i.e. total bodyweight-fat weight) and promises a change in the body's insulin to glucagon ratio through its macronutrient alterations. Changes in the existing hormonal milieu are said to result in the production of more vasoactive eicosanoids, thus allowing greater oxygen delivery to exercising muscle. This favourable condition, known as the Zone, is anecdotally reported to benefit even the most elite endurance athletes. Applying the Zone's suggested protein needs and macronutrient distributions in practice, it is clear that it is a low carbohydrate diet by both relative and absolute standards, as well as calorie deficient by any standard. Reliable and abundant peer reviewed literature is in opposition to the suggestion that such a diet can support competitive athletic endeavours, much less improve them. The notion that a 40/30/30 diet can alter the pancreatic hormone response in favour of glucagon is also unfounded. The Zone is a mixed diet and not likely to affect pancreatic hormone release in the same way individual nutrients can. Although the postprandial insulin response is reduced when comparing a 40% with a 60% carbohydrate diet, it is still a sufficient stimulus to offset the lipolytic effects of glucagon. Many of the promised benefits of the Zone are based on selective information regarding hormonal influences on eicosanoid biology. Contradictory information is conveniently left out. The principle of vasodilating muscle arterioles by altering eicosanoid production is notably correct in theory. However, what little human evidence is available does not support any significant contribution of eicosanoids to active muscle vasodilation. In fact, the key eicosanoid reportedly produced in the Zone and responsible for improved muscle oxygenation is not found in skeletal muscle. Based on the best available scientific evidence, the Zone diet should be considered more ergolytic than ergogenic to performance.

Role of medial smooth muscle cell function in antithrombogenicity of vein grafts

OBJECTIVES

To determine the significance of prostaglandin I2 (PGI2) production by medial smooth muscle cells (SMCs), we assessed PGI2 production from denuded vein grafts and their antithrombogenicity.

MATERIALS AND METHODS

A total of 30 dogs were divided into two groups: in group I, 14 dogs (27 veins, 188 segments) were used to assay PGI2 production, which was measured as 6-keto-PGF1 alpha. In group II, 16 dogs were used for an implantation study and the thrombus-free surface (TFS) score was calculated 24 h after implantation. Both groups contained the following subgroups: subgroup A, freshly harvested veins; subgroup B, endothelial denuded veins; subgroup C, veins frozen and cryopreserved; subgroup D, veins treated with protease.

RESULTS

Values of 6-keto-PGF1 alpha (pg/mg/min) for basal and stimulated states in subgroup I-A through I-D were 58.0 +/- 8.9 and 530.6 +/- 74.7, 26.3 +/- 4.7 and 82.3 +/- 11.4, 17.9 +/- 1.3 and 39.4 +/- 3.3, and 13.3 +/- 1.8 and 32.2 +/- 6.2, respectively. The PGI2 production in subgroup I-A were significantly higher than those in the other three subgroups (p < 0.01 for basal and stimulated), while the production in subgroup I-B was also significantly higher than those in the remaining two (p < 0.05 for basal and stimulated). The TFS scores in subgroup II-A through II-D were 98 +/- 2%, 90 +/- 2%, 38 +/- 5%, and 15 +/- 7%, respectively, showing significantly superior antithrombogenicity in subgroup II-B, as well as in II-A, when compared with the remaining two (p = 0.014).

CONCLUSION

The amount of PGI2 generated by the medial SMCs may be sufficient for maintaining the antithrombogenicity of the endothelial denuded AVGs.

Prostacyclin and nitric oxide-related gene transfer in preventing arterial thrombosis and restenosis

Prostacyclin (PGI2) and nitric oxide (NO) are potent vascular mediators, playing key roles in protecting arterial wall from injury-induced lesions. The key enzyme that catalyzes PGI2 biosynthesis is cyclooxygenase (COX). COX-1 undergoes auto-inactivation, which severely limits PGI2 synthesis. Overexpression of COX-1 in cultured endothelial cells by COX-1 gene transfer was accompanied by a higher capacity for and sustained synthesis of PGI2. Adenovirus-mediated COX-1 gene transfer to angioplasty damaged carotid arteries in pigs augmented PGI2 synthesis and prevents thrombus formation. Transfer of endothelial NO synthase (eNOS) into angioplasty injured, carotid arteries was reported to suppress intimal hyperplasia in rats. Transfer of PGI2 and NO synthetic enzymes restores the vasoprotective properties and represents an exciting new strategy for treating arterial thrombotic disorders.

Some adverse cardiodynamic effects of prostaglandin E2 in congestive heart failure

The cardiodynamic effects of prostaglandin E(2) (PGE(2)) were studied in both healthy sheep and in animals with congestive heart failure (CHF). Merino ewes were equipped surgically with high fidelity micromanometers and left ventricular pressures measured. Heart rate, left ventricular systolic and end-diastolic pressures, +dP/dt and T(ln) were calculated on a computer from the recorded pressure curves. The paired t-test was used to determine the statistical significance of the differences. PGE(2) (25 mu g/kg) significantly improved the cardiac contractility and relaxation rate of healthy sheep and significantly reduced the heart rate, while the loading conditions under which the heart operates were not significantly affected. In contrast to healthy sheep, PGE(2) significantly reduced the contractility and relaxation rate of sheep with congestive heart failure and significantly increased the preload while heart rate and afterload were significantly reduced. The study suggests that despite the promising vasodilatory, positive inotropic and relaxation rate actions of PGE(2) in normal hearts, PGE(2) might not be a suitable therapeutic agent for CHF, because of the worsening effect it has on the cardiodynamics and loading conditions of the failing heart.

Prevention of arterial thrombosis by adenovirus-mediated transfer of cyclooxygenase gene

BACKGROUND

Prostacyclin is an important vasoprotective molecule. It inhibits platelet aggregation, monocyte interaction with endothelium, and smooth muscle cell lipid accumulation. Vascular cyclooxygenase-1 (COX-1) is the rate-limiting step in prostacyclin synthesis. The objective of this study was to determine whether adenovirus-mediated transfer of COX-1 could restore COX-1 activity, augment prostacyclin synthesis, and prevent thrombus formation in a porcine carotid angioplasty model.

METHODS AND RESULTS

Human COX-1 cDNA driven by a cytomegalovirus promoter was constructed into a replication-defective adenovirus 5 vector by homologous recombination. Recombinant adenovirus without a foreign gene (Ad-RR) and buffer were included as controls. Recombinant Ad-LacZ was used for marking the transfected cells in vivo. In the in vitro experiments, cultured human endothelial cells (ECs) and porcine arterial smooth muscle cells (SMCs) were incubated with Ad-COX-1 for 2 hours and 6-keto-PGF(1 alpha) level and the transgene expression were determined 72 hours after infection. In the in vivo experiments, recombinant adenoviruses were directly instilled into angioplasty-injured porcine carotid arteries for 30 minutes. Cyclic flow changes were monitored for 10 days and thrombus formation was examined histologically thereafter. Transgene expression and prostaglandin I2 (PGI2) synthesis by the injured arteries were determined. Cultured ECs infected with Ad-COX-1 produced a fivefold to eightfold increase in PGI2, and the transgene expression in cultured porcine SMCs was demonstrated by Northern analysis. Direct administration of Ad-COX-1 at a dose of 3 x 10(10) pfu completely inhibited carotid cyclic flow changes and thrombus formation accompanied by a fourfold increase in PGI2 synthesis by the injured arteries 10 days after infection, whereas Ad-COX-1 at a lower dose, 5 x 10(9) pfu, had no antithrombotic effects when compared with Ad-RR vector and buffer controls.

CONCLUSIONS

Adenovirus-mediated transfer of COX-1 to angioplasty-injured carotid arteries was efficacious in augmenting PGI2 synthesis and was associated with an inhibition of thrombosis when a relatively high titer of adenovirus was instilled.

Papaverine injures the endothelium of the internal mammary artery

Intraluminal injection of papaverine may be employed to dilate the internal mammary artery for use as a coronary artery bypass graft. The biochemical and morphological consequences of exposing the endothelium of the internal mammary artery to papaverine have been investigated. Biochemical injury was assessed by measuring changes in basal and vortex-stimulated prostaglandin I2 production, and morphological damage by scanning electron microscopy. Segments of internal mammary artery from 10 patients were placed in one of three solutions; papaverine (1.5 mg/ml of normal saline), normal saline acidified to the pH of the papaverine solution, and normal saline alone. Basal production of prostaglandin I2 was similar in the three groups but vortex-stimulated production was significantly lower in segments stored in papaverine (18.3 pg/mg) and acidified saline (19.1 pg/mg) compared with that of saline alone (43.6 pg/mg). No consistent morphological difference was found by scanning electron microscopy. It was concluded that the low pH of the papaverine solution injured the endothelium of the internal mammary artery.

Distension produces medial but not endothelial damage in porcine internal mammary artery

The influence of intraluminal distension on porcine internal mammary artery was studied using adenosine 5'-triphosphate (ATP) concentration and prostacyclin production as biochemical markers of medial and endothelial functional integrity respectively. Distension reduced mean (95% confidence limits) tissue ATP concentrations from 459 (337-581) nmol/g wet weight to 314 (193-435) nmol/g wet weight (n = 10, P < 0.01). Stimulated prostacyclin production was similar in undistended (25.8(15.9-35.9) pg/min per mg wet weight) and distended arteries (33.2(21.4-45.1) pg/min per mg wet weight) (n = 8, not significant). The data demonstrate that distension of the internal mammary artery results in acute medial but not endothelial damage. Distension-induced medial damage is unlikely to be rapidly reversible and might have implications for the early and long-term function of the artery as a bypass graft.

The effects of orally administered atenolol on the coronary hemodynamics and prostaglandin metabolism in angina pectoris patients

The effects of oral atenolol on coronary hemodynamics and prostaglandin metabolism have been investigated in 8 chronic stable angina pectoris patients who underwent the supine bicycle ergometer. At rest, atenolol taken orally reduced the pressure-rate product significantly (P < 0.05) but did not significantly affect the coronary sinus blood flow or the coronary sinus pressure. During exercise, atenolol also reduced the pressure-rate product significantly (P < 0.05) but did not significantly affect the coronary sinus blood flow, the coronary sinus pressure, or the coronary vascular resistance. Atenolol also did not significantly affect the thromboxane B2/6-keto prostaglandin F1 alpha ratio in the arterial blood before and after exercise but did reduce this ratio in the coronary sinus blood by 15% from 1.9 +/- 1.1 to 1.5 +/- 0.46 (P < 0.10) after exercise. These results indicate that atenolol taken orally does not significantly depress the coronary hemodynamics. However, the effects of atenolol on the prostaglandin metabolism could not be clearly determined.

Transduction of arginine vasopressin signal in skeletal myogenic cells

Arginine vasopressin (AVP) induced concentration-dependent (10(-9) to 10(-6) M) stimulation of inositol phosphate production and a biphasic increment of cytosolic free Ca2+ concentration ([Ca2+]i) in skeletal myogenic cells in culture. These effects were almost completely abolished when the cells were pretreated with the AVP antagonist [deamino-Pen1,Val4,D-Arg8]-vasopressin before stimulation with AVP, thus confirming a V1 receptor-mediated effect. Inositol 1,4,5-trisphosphate production was maximally stimulated within 2-3 s of treatment with AVP, immediately followed by release of Ca2+ from intracellular deposits. Both effects were inhibited by treatment with 12-O-tetradecanoyl phorbol 13-acetate (TPA). Such effect of TPA was reversed by the protein kinase C inhibitor staurosporine. Vasopressin also regulated the intracellular pH of responsive cells with mechanisms involving both Na+ and anion transport across the plasma membrane. However, unlike in other cell types, AVP stimulated the Na(+)-H+ antiport only simultaneously with a dramatic cell acidification or after treatment with TPA. Response to AVP was observed in L6 and L5 and, to a lesser extent, in chick embryo myogenic cells, regardless of the stage of differentiation (myoblast or myotube). Comparison of different subclones of the L6 cell line demonstrated that the responsiveness to AVP correlated positively with their myogenic potential.

Marathon run stimulates more prostacyclin than thromboxane synthesis and differently in men and women

To study the effect of strenuous physical exercise on the balance between vasodilatory and antiaggregatory prostacyclin (PGI2) and its endogenous antagonist thromboxane A2 (TxA2), we measured the urinary output of two metabolites of PGI2 (6-keto-prostaglandin F1 alfa, 6-keto, and 2,3-dinor-6-keto), as well as two metabolites of TxA2 (thromboxane B2, TxB2, and 2,3-dinor-TxB2) ten days before, during and one, three and five days after a marathon run by 15 women and ten men. The basal urinary outputs of women and men were similar. In women, 6-keto excretion increased 10-fold (p < 0.001) and in men 30-fold (p < 0.05) during the run, and 2,3-dinor-6-keto increased 2-fold in women (p < 0.05) and 7-fold in men (p < 0.05). During the run, TxB2 output increased only in women (3-fold, p < 0.05) and 2,3-dinor-TxB2 only in men (4-fold, p < 0.05). The marathon-induced changes lasted maximally one day. The greater PGI2-than TxA2-stimulation during marathon run may be involved with the favorable effects on the cardiovascular system of physical exercise.

Cyclosporin reduces renal prostanoid excretion in type 1 diabetic patients

Prostacyclin and thromboxane A2 are important regulators of kidney blood flow. To examine whether changes in their metabolism could be involved in the nephrotoxicity of cyclosporin, we determined urinary excretion of 6-keto PGF1a and dinor-6-keto PGF1a (prostacyclin metabolites) and dinor-TxB2 (thromboxane metabolite) in five newly diagnosed type 1 diabetic patients during and after stopping cyclosporin therapy. In the resting state, cyclosporin had no effect on prostanoid excretion. In response to exercise, urinary excretion of 6-keto PGF1a was reduced by 50% (P less than 0.02), dinor-6-keto PGF1a by 15% (P less than 0.05) and dinor-TxB2 by 45% (P less than 0.02), while albumin excretion increased 4.5-fold (P less than 0.05) during cyclosporin therapy. Simultaneously, there was a rise in serum creatinine concentration, and renal biopsy specimens obtained from three patients showed periglomerular and interstitial fibrosis and tubular atrophy. After the discontinuation of cyclosporin therapy, serum creatinine concentrations returned to normal, histological changes improved and there was an associated rise in urinary prostanoid excretion. These data suggest that a reduction in renal prostanoid synthesis by cyclosporin may diminish renal blood flow and function, and lead to histological changes in the kidney.

Prostacyclin attenuates in the rabbit hippocampus early consequences of transient complete cerebral ischemia

The effects of prostacyclin (PGI2) on ischemic changes of extracellular calcium concentration (CaE+2) and the blood-brain barrier (BBB) permeability were studied by microdialysis of the rabbit hippocampus. This was combined with morphological and neurophysiological observations. Complete cerebral ischemia lasting 15 min was produced by ligation of the brachiocephalic trunk, the left subclavian and both internal thoracic arteries. PGI2 was infused continuously i.v. in the last 3 min of ischemia and for 40 min after it, at a rate of 2 micrograms/kg/min. Control rabbits were submitted to untreated 15-min complete cerebral ischemia. The animals treated with PGI2 were found to have recovered bioelectric activity of the cortex and hippocampus in half the time that it took the untreated group. Application of PGI2 reduced by 60% the depth of ischemia-evoked drop of CaE+2 without acceleration of recovery during recirculation. The postischemic increase of BBB permeability to fluorescein was diminished. The number of morphologically changed neurons in the hippocampus of PGI2-treated animals was significantly lower than in the untreated group.

Increased hydrolysis of cholesteryl ester with prostacyclin is potentiated by high density lipoprotein through the prostacyclin stabilization

Prostacyclin (PGI2) has been reported to stimulate activities of acid cholesteryl ester hydrolase (ACEH; EC 3.1.1.13) and neutral cholesteryl ester hydrolase (NCEH; EC 3.1.1.13) in the smooth muscle cells leading to a decrease in intracellular cholesteryl ester. Recently, we have found that the half-life of PGI2 was prolonged through stabilization by HDL. HDL is known to have anti-atherogenic properties, although its precise mechanism has not been fully clarified. We therefore hypothesized that HDL can exert anti-atherogenic action by augmenting PGI2-stimulated increases in the activities of ACEH and NCEH. After incubation with PGI2 and HDL, a cell homogenate was made from which the activities of ACEH and NCEH were assessed. HDL significantly augmented the PGI2-induced increase in the activities of both enzymes. This effect of HDL was abolished in the absence of PGI2. Elevated intracellular levels of cyclic AMP were maintained for longer periods by HDL. The increase in both intracellular cyclic AMP levels and enzyme activities disappeared in the presence of an inhibitor of adenylate cyclase, 2'5'-dideoxyadenosine. Radiolabeled smooth muscle cells demonstrated a significant loss in total cholesterol and cholesteryl ester after treatment with PGI2 and HDL, due to the increase in cholesteryl ester hydrolytic activities. These data suggest that HDL enhanced the PGI2-stimulated hydrolysis of cholesteryl ester and augmented the PGI2-induced reduction of cellular cholesteryl ester content by stabilizing PGI2.

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.

Effect of prostacyclin on coronary occlusion in acute myocardial infarction

Prostacyclin is a powerful inhibitor of platelet aggregation and induces relaxation of vascular smooth muscle. We have studied the coronary effects of high local concentrations of prostacyclin in 17 patients during the early stages of acute myocardial infarction. We infused graded concentrations of intracoronary prostacyclin and compared the effects to those of intracoronary isosorbide dinitrate before and after an intracoronary infusion of streptokinase. Considerable dilation of the infarct-related stenosis may follow local infusions of prostacyclin in some patients. In general, however, dilation of the infarct-related stenosis or coronary recanalization did not result from infusion of prostacyclin.

Serum prostacyclin stabilizing factor is identical to apolipoprotein A-I (Apo A-I). A novel function of Apo A-I

Serum PGI2 stabilizing factor (PSF) was purified from human serum to a single protein with a molecular weight of 28,000 D by SDS-PAGE. Analyses of NH2-terminal sequence (32 residues), COOH-terminal sequence (3 residues) and the composition of amino acids disclosed its homology with human apolipoprotein A-I (Apo A-I), a major apolipoprotein of HDL. Apolipoprotein A-II, C-I, C-II, C-III, D and E, as well as LDL, and VLDL did not possess this activity. The alpha-helix structure of Apo A-I is necessary for the binding of PGI2. HDL and nascent HDL reconstituted from Apo A-I and phospholipid significantly prolonged the half-life of PGI2. PGI2 stabilization by HDL and Apo A-I may be an important protective action against the accumulation of platelet thrombi at sites of vascular damage. The beneficial effect of HDL in the prevention of coronary artery disease may be partly due to this action.

Plasma thromboxane and prostacyclin metabolite ratio in atherosclerosis and diabetes mellitus

Thromboxane and prostacyclin metabolite determinations (radioimmunoassay) were performed in obliterative atherosclerosis and in diabetes mellitus with microangiopathy. The shift of these metabolites to the thromboxane side could have been documented in both diseases. This phenomenon calls attention to an increased platelet activation and endothelial cell damage. In a third group patients received aspirin (500 mg on alternative days) which caused a marked inhibition of both thromboxane and prostacyclin production, measured this way. The possible role of altered balance of these two prostanoids in atherogenesis and diabetic angiopathy is discussed.

Mechanisms of vasoconstriction induced by 9,11-epithio-11,12-methano-thromboxane A2 in the rabbit coronary artery

The vasoconstrictor effects of 9,11-epithio-11,12-methano-thromboxane A2 (STA2) on smooth muscle strips of the rabbit coronary artery have been investigated in vitro. Right coronary artery (RCA) was more responsive to STA2 than either the left anterior descending or the circumflex coronary artery. On endothelium-denuded RCA strips, the sensitivity and responsiveness to STA2 were greater than observed on intact muscle strips. A thromboxane(Tx)-antagonist, (9,11), (11,12)-dideoxa-9 alpha, 11 alpha-dimethylmethano-11,12-methano-13,14-dihydro-13-aza-14-oxo-15 - cyclopenthyl-16,17,18,19,20-pethanol-15-epi-TxA2 (ONO-3708), inhibited the STA2-induced contraction, whereas atropine or prazosin had no effect. Nifedipine partly inhibited the STA2-induced contraction, one half of which was still evoked in Ca2+-free solution. When acetylcholine was applied prior to the application of STA2 in Ca2+-free solution, the STA2-vasoconstriction disappeared. In saponin-treated chemically skinned muscle strips, STA2 itself had no effect on either the pCa-tension relation or on the release of Ca2+ from intracellular stores. However, inositol 1,4,5-trisphosphate released Ca2+ from such stores, and 12-o-tetradecanoyl phorbol-13-acetate (TPA) and 1,2-diolein, activators of protein kinase C, enhanced the contraction induced by 0.3 microM Ca2+. It is concluded that STA2 acts on the TxA2 receptor and produces contraction due to an increase in both voltage- and agonist(receptor)-dependent Ca2+ influx. STA2 also releases Ca2+ from ACh- and caffeine-sensitive storage sites.

Converting enzyme inhibitors (captopril, enalapril, perindopril) prevent early-post infarction ventricular fibrillation in the anaesthetized rat

The angiotensin-converting enzyme inhibitors, captopril, enalapril and perindopril, exert antiarrhythmic effects on early post-infarction arrhythmias in anaesthetized rats. These studies support the hypothesis that converting enzyme inhibitors could have a "cardioprotective" effect, but the doses used are probably "high" in relation to those therapeutically applicable to man.

Selective thromboxane A2 synthetase inhibition in vasospastic angina pectoris

To investigate whether thromboxane A2 is responsible for the initiation of vasospastic angina pectoris, thromboxane B2 levels were measured in the great cardiac vein and the arterial blood of 12 patients with clinically and angiographically proved vasospastic angina and therapeutic trials were performed with selective thromboxane A2 synthetase inhibitor OKY-046, an imidazole derivative. During ergonovine-provoked (11 cases) and spontaneous (1 case) anginal attacks, great cardiac vein thromboxane B2 increased from 121 +/- 27 to 430 +/- 382 pg/ml (p less than 0.05, n = 12), arterial thromboxane B2 increased from 93 +/- 18 to 122 +/- 33 pg/ml (NS, n = 12) and thromboxane B2 production increased from 3.18 +/- 1.88 to 25.16 +/- 22.32 ng/min (p less than 0.05, n = 6). Subsequently, OKY-046, 400 mg/day orally, was administered to 7 of the 12 patients, while a continuous electrocardiogram was recorded on a dual channel Holter monitor during a 3 day placebo period and the 3 day OKY-046 regimen. Although peripheral plasma thromboxane B2 levels decreased significantly from 98 +/- 15 to 12 +/- 8 and 28 +/- 10 pg/ml (1 and 6 hours after ingestion, respectively) (p less than 0.05 for both), 6-keto-prostaglandin F1 alpha production in serum increased significantly from 0.48 +/- 0.22 to 2.3 +/- 0.72 (1 hour) and 1.8 +/- 0.46 ng/ml (6 hours) (p less than 0.05 for both) during OKY-046 administration.(ABSTRACT TRUNCATED AT 250 WORDS)

Prostacyclin and variant angina

Plasma levels of thromboxane B2 (TXB2) and 6-keto PGF1 alpha in the blood samples taken at the coronary sinus and ascending aorta from twenty-one Japanese patients with variant angina and twenty with effort angina were measured by radioimmunoassay, the objective being to search for the contribution of prostanoids in coronary spasm. The data were compared with data on thirteen subjects free from coronary artery diseases. In coronary sinus blood, plasma TXB2 in patients with effort angina exhibited statistically significant high levels, as compared with data in the controls. These with variant angina also had high levels, albeit without a statistically significant difference. Eight patients with variant angina and for whom the coronary angiogram showed more than 50% of narrowing had statistically significant high levels of TXB2, and the other thirteen with variant angina and normal coronaries or less than 50% of narrowing had the same plasma levels of TXB2 as the controls. In contrast to TXB2, the plasma levels of 6-keto PGF1 alpha in both coronary sinus and aortic blood of patients with variant angina were very low, as compared with normal controls. Statistically significant low levels of 6-keto PGF1 alpha were noted in the coronary sinus blood of patients with variant angina with normal coronaries and in the aortic blood of those with variant angina, as compared with data on the normal controls. Neither ergonovine test nor spontaneous attacks in patients with variant angina revealed characteristic changes in levels of TXB2 and 6-keto PGF1 alpha in the coronary sinus. These data suggest that high levels of TXB2 in patients with atherosclerotic coronaries may be one factor leading to spasm, while low levels of PGI2 may be a contributing factor.

Double-blind controlled trial of the therapeutic effects of prostacyclin in patients with completed ischaemic stroke

In a pilot study, 26 patients with acute completed strokes (48 hours to 5 days after cerebral infarction) were randomly assigned to the prostacyclin (PGI2) or placebo groups. PGI2 sodium salt (Epoprostenol, Wellcome Research Laboratories and Upjohn Company) or its solvent (glycine buffer) were infused into the subclavian vein for six-hour periods in five courses separated by six-hour intervals. Prostacyclin was administered at a rate of 2.5-5.0 ng/kg/min. A significant alleviation of neurological deficits occurred 6 and 54 hours after the treatment in patients receiving prostacyclin. This improvement lost its statistical significance at the end of a two-week observation period. It is concluded that further modified controlled studies are required to evaluate the therapeutic usefulness of PGI2 in the treatment of patients with cerebral ischaemia.

[Eicosanoids and phospholipases]

Prostaglandins, thromboxanes, and leukotrienes have been implicated to play an important role in physiology as well as in a growing list of pathophysiologic conditions. These oxidation products of 8.11.14-eicosatrienoic-, 5.8.11.14.-eicosatetraenoic-, and 5.8.11.14.17.-pentaenoic acids have been collectively designated eicosanoids. Many clinically important diseases are associated with altered eicosanoid biosynthesis. Furthermore, a series of hormones are known to induce acutely formation of eicosanoids, suggesting a crucial role in a multitude of tissue responses including phenomena such as secretion, platelet aggregation, chemotaxis, and smooth muscle contraction. The major precursor for the eicosanoids seems to be 5.8.11.14.-eicosatetraenoic acid or arachidonic acid. Virtually all of arachidonic acid however is present in esterified form in complex glycerolipids. Since cyclooxygenase and the lipoxygenases utilize arachidonic acid in its free form, a set of acylhydrolases is required to liberate arachidonic acid from membrane lipids before eicosanoid formation can occur. It became only recently apparent that a minor acidic phospholipid, phosphatidylinositol, comprising only 5%-10% of the phospholipid mass in mammalian cells, plays an important role in arachidonic acid metabolism. Phosphatidylinositol--after phosphorylation to phosphatidylinositolphosphate and phosphatidylinositolbisphosphate--appears to be hydrolyzed by specific phospholipases C generating 1-stearoyl-2-arachidonoyl-diglyceride. Diglyceride serves as substrate for diglyceride lipase to form monoglyceride and free fatty acid. Alternatively diglyceride is phosphorylated by diglyceride kinase yielding phosphatidic acid, which is believed to be reincorporated into phosphatidylinositol. In addition to phosphatidylinositol phosphatidylcholine, phosphatidylethanolamine and phosphatidic acid may contribute to arachidonic acid release. These phospholipids are substrates for phospholipases A2 generating free arachidonic acid and the respective lysophospholipid. Understanding of the biochemistry of arachidonic acid liberation may be critical in developing strategies of pharmacological intervention in a variety of pathological conditions.

Effect of high dose aspirin on coronary hemodynamics during pacing-induced myocardial ischemia

The effects of aspirin on coronary hemodynamics and transcardiac concentrations of thromboxane B2 (the stable metabolite of thromboxane A2) were determined at rest and during pacing-induced myocardial ischemia in 11 patients with coronary disease. Control coronary sinus pacing increased both arterial thromboxane B2 (331 +/- 70 to 623 +/- 132 pg/ml, p less than 0.02) and coronary sinus thromboxane B2 (184 +/- 3 to 403 +/- 156 pg/ml, p less than 0.05), but positive transmyocardial gradients developed in only three patients. After 650 mg of oral aspirin, more than 90% inhibition of in vitro thromboxane B2 production was demonstrated and circulating thromboxane B2 was undetectable at rest and during pacing in all patients. Despite these changes in thromboxane B2 concentrations, coronary blood flow was unchanged by aspirin at rest (107 +/- 14 versus 112 +/- 13 ml/min, p = NS) and during pacing (189 +/- 29 versus 181 +/- 25 ml/min, p = NS). Myocardial lactate extraction was also unchanged at rest (24 +/- 7 versus 19 +/- 5%, p = NS) and during pacing (5 +/- 6 versus 9 +/- 5%, p = NS). No change occurred in the anginal threshold. Thus, aspirin does not have the vasoconstrictive properties that have been reported with another cyclo-oxygenase inhibitor, indomethacin. These findings also suggest that thromboxane A2 production does not play a major role in the pathogenesis of stress-induced ischemia. Nonetheless, intracoronary thromboxane A2 production in some patients may potentiate platelet activation and coronary thrombosis. Such patients may benefit from long-term aspirin therapy and can be treated with aspirin without risk of adverse coronary hemodynamic effects.

Prostacyclin for ischemic ulcers in peripheral arterial disease. A random assignment, placebo controlled study

A 72 h infusion of prostacyclin or placebo was given into femoral artery as a treatment for ischemic ulcers in 30 patients with peripheral arterial disease. Patients were well matched for age, sex, type and localization of disease, rest pain, number and area of ulcers, calf blood flow and previous sympathectomies. They had no diabetes mellitus, gangrene or marked aorto-iliac involvement. Six weeks after the infusion there was a significant difference in ulcer area between the two groups (p less than 0.02, t unpaired test): mean ulcer area decreased (p less than 0.02, t paired test) in the prostacyclin-treated group, but not in the placebo group (p greater than 0.05, t paired test). Thus, intra-arterial infusion of prostacyclin promotes healing of ischemic ulcers in non-diabetic patients with peripheral arterial disease without gangrene.

Decreased serum levels of a factor stimulating prostacyclin synthesis in acute myocardial infarction

To investigate the role of a factor in serum stimulating prostacyclin synthesis in acute myocardial infarction, we compared the activities of the factor among 7 patients with acute myocardial infarction (2.5 +/- 0.8 hrs and 80 +/- 17 hrs after the onset of symptoms), 12 patients with angina pectoris, and 7 normal subjects. In this study, we found that in patients with acute myocardial infarction, this activity is much lower immediately after infarction (2.5 +/- 0.8 hrs) than 80 +/- 17 hrs later, or in patients with stable angina pectoris, or in healthy volunteers. Since prostacyclin is antiaggregating and vasodilating, the deficiency in this ability during the very early phase of acute myocardial infarction may be related to the development of the thrombosis of acute myocardial infarction.

Treatment with prostacyclin of various forms of spontaneous angina pectoris not responding to placebo

We studied the effects of prostacyclin on the frequency, duration and severity of ischemic attacks in spontaneous angina. Twenty-seven patients who did not respond to 48 hours infusion of placebo, received after a two-day observation period, 48 hours infusion of prostacyclin at an average rate of 4.0 ng/kg/min. Prostacyclin decreased number of ischemic attacks in only one of four patients with Prinzmetal angina, and was without any effect in five other patients whose attacks were associated with increase in blood pressure and heart rate. However, in 12 of 18 patients with coronary atherosclerosis, whose attacks were characterized by ST-segment depression without increase in heart rate or blood pressure, and often occurred at night, prostacyclin consistently diminished both frequency of anginal attacks and nitroglycerin consumption. This improvement lasted from 10 days to 3 months. Healing of endothelial damage by prostacyclin could explain the favorable therapeutic response in this subset of patients with spontaneous angina.

Intravenous infusion of a selective inhibitor of thromboxane A2 synthetase in man: influence on thromboxane B2 and 6-keto-prostaglandin F1 alpha levels and platelet aggregation

The effect of the selective thromboxane A2 synthetase inhibitor OKY-1581, a pyridine derivative [sodium (E)-3-(4-(3-pyridylmethyl)phenyl)-2-methyl-2-propenoate], on thromboxane B2 and 6-keto-prostaglandin F1 alpha levels and platelet aggregation was studied in human volunteers. To clarify its effectiveness as an enzyme inhibitor, OKY-1581, at doses of 17, 83, 167, 417, 833, and 1667 micrograms/kg (n = 5 for each group), was injected intravenously, or was infused (10 micrograms/kg/min; n = 5) over 3 hr on 3 successive days. OKY-1580 (OKY-1581 free acid) was rapidly converted to its main beta-oxidized product, OKY-1565, and its reduced form, OKY-1558. During the study, plasma thromboxane B2 levels, inhibition of thromboxane B2 production in serum, and inhibition of rabbit platelet thromboxane A2 synthetase were monitored continuously. Twenty-five minutes after the injection of the above doses, plasma thromboxane B2 levels decreased by 4 +/- 7%, 40 +/- 14%, 57 +/- 7%, 68 +/- 6%, 93 +/- 5%, and 96 +/- 5% (mean +/- SD), respectively. Thromboxane B2 production in serum was decreased by 2 +/- 8%, 70 +/- 10%, 75 +/- 8%, 81 +/- 10%, and 96 +/- 8%, respectively, and rabbit platelet thromboxane A2 synthetase by 2 +/- 7%, 52 +/- 8%, 79 +/- 10%, 80 +/- 9%, 96 +/- 8%, and 95 +/- 7%. These parameters returned to the control levels 24 hr after the injection.(ABSTRACT TRUNCATED AT 250 WORDS)

Beneficial effects of nafazatrom on ischemic reperfused myocardium

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