Prostacyclin and vascular function: implications for hypertension and atherosclerosis

Platelets in Renal Disease

Kidney disease is a major global health concern, affecting millions of people. Nephrologists have shown interest in platelets because of coagulation disorders caused by renal diseases. With a better understanding of platelets, it has been found that these anucleate and abundant blood cells not only play a role in hemostasis, but also have important functions in inflammation and immunity. Platelets are not only affected by kidney disease, but may also contribute to kidney disease progression by mediating inflammation and immune effects. This review summarizes the current evidence regarding platelet abnormalities in renal disease, and the multiple effects of platelets on kidney disease progression. The relationship between platelets and kidney disease is still being explored, and further research can provide mechanistic insights into the relationship between thrombosis, bleeding, and inflammation related to kidney disease, and elucidate targeted therapies for patients with kidney disease.

Extracellular histones disarrange vasoactive mediators release through a COX-NOS interaction in human endothelial cells

Extracellular histones are mediators of inflammation, tissue injury and organ dysfunction. Interactions between circulating histones and vascular endothelial cells are key events in histone-mediated pathologies. Our aim was to investigate the implication of extracellular histones in the production of the major vasoactive compounds released by human endothelial cells (HUVECs), prostanoids and nitric oxide (NO). HUVEC exposed to increasing concentrations of histones (0.001 to 100 μg/ml) for 4 hrs induced prostacyclin (PGI2) production in a dose-dependent manner and decreased thromboxane A2 (TXA2) release at 100 μg/ml. Extracellular histones raised cyclooxygenase-2 (COX-2) and prostacyclin synthase (PGIS) mRNA and protein expression, decreased COX-1 mRNA levels and did not change thromboxane A2 synthase (TXAS) expression. Moreover, extracellular histones decreased both, eNOS expression and NO production in HUVEC. The impaired NO production was related to COX-2 activity and superoxide production since was reversed after celecoxib (10 μmol/l) and tempol (100 μmol/l) treatments, respectively. In conclusion, our findings suggest that extracellular histones stimulate the release of endothelial-dependent mediators through an up-regulation in COX-2-PGIS-PGI2 pathway which involves a COX-2-dependent superoxide production that decreases the activity of eNOS and the NO production. These effects may contribute to the endothelial cell dysfunction observed in histone-mediated pathologies.

Prostacyclin signaling boosts NADPH oxidase 4 in the endothelium promoting cytoprotection and angiogenesis

AIMS

Prostacyclin (PGI2) that is released from the vascular endothelium plays an important role in vasodilatation and thrombo-resistance, and it has long been suspected to protect cell survival. How it does so has never been clear. Recently, it has been shown that the NADPH oxidase 4 (Nox4) improves endothelial cell functions and promotes angiogenesis in vivo, but it was not known how to boost Nox4 therapeutically to exploit its protective functions in the vasculature. Here, we identified such a stimulus.

RESULTS

The selective and stable prostacyclin receptor (IP-R) agonist cicaprost increases the expression of Nox4 in human endothelial cells of several types, including endothelial progenitor cells. The elevation of cellular cyclic-AMP increased Nox4 expression and H2O2 production and prevented endothelial cell apoptosis. We delineate the intracellular signaling that promotes cytoprotection: Cicaprost acts via the IP-R/protein kinase A (PKA)/cyclic adenosine monophosphate (cAMP) response element binding (CREB) protein pathway. Importantly, the up-regulation of Nox4 by cicaprost also enhanced endothelial cell proliferation, migration, and angiogenesis, with all effects being substantially decreased by Nox4 gene silencing. Finally, cicaprost enhanced the growth of blood vessels into subcutaneous sponges implanted in mice, an effect that was also blocked by Nox4 gene silencing.

INNOVATION

The prostacyclin analogue cicaprost induces Nox4 via IP receptor-cAMP/PKA/CREB pathway. The activation of this pathway protects endothelial cells and enhances pro-angiogenic activity both in vitro and in vivo.

CONCLUSION

Prostacyclin promotes the up-regulation of Nox4 in endothelial cells, which opens up a novel strategy that protects and enhances endothelial cell functions in cardiovascular disease, such as repair after myocardial infarction or other ischemic conditions.

Synthesis and evaluation of N-acylsulfonamide and N-acylsulfonylurea prodrugs of a prostacyclin receptor agonist

N-Acylsulfonamide and N-acylsulfonylurea derivatives of the carboxylic acid prostacyclin receptor agonist 1 were synthesized and their potential as prodrug forms of the carboxylic acid was evaluated in vitro and in vivo. These compounds were converted to the active compound 1 by hepatic microsomes from rats, dogs, monkeys, and humans, and some of the compounds were shown to yield sustained plasma concentrations of 1 when they were orally administered to monkeys. These types of analogues, including NS-304 (2a), are potentially useful prodrugs of 1.

Replacing the cyclohexene-linker of FR181157 leading to novel IP receptor agonists: Orally active prostacyclin mimetics. Part 6

The synthesis and biological activity of novel derivatives of our previously reported IP receptor agonist FR181157 is described. SAR studies to replace the cyclohexene-linker of FR181157 led to the discovery of compound 1i (FR207845) as a potent non-prostanoid PGI2 mimetic with good oral bioavailability.

Discovery of new diphenyloxazole derivatives containing a pyrrolidine ring: orally active prostacyclin mimetics. Part 2

Synthetic and biological evaluation of novel diphenyloxazole derivatives containing a pyrrolidine ring, as a prostacyclin mimetic without the PG skeleton, are described. Asymmetric reduction of a ketone using a chiral Ru complex and reductive amination by NaBH(4) produces four isomers of the tetrahydronaphthalene ring and the pyrrolidine ring with high stereoselectivity. FR193262 (4), (R,R)-diphenyloxazolyl pyrrolidine derivative, displays high potency and agonist efficacy at the IP receptor and has good bioavailability in rats and dogs.

Discovery of diphenylcarbamate derivatives as highly potent and selective IP receptor agonists: orally active prostacyclin mimetics. Part 3

The new classes of diphenylcarbamate derivatives with a tetrahydronaphthalene skeleton as highly potent and selective IP agonists have been discovered. The optimized diphenylcarbamate type compound FK-788: (R)-4 exhibited potent antiaggregative potency with an IC50 of 18 nM and high binding affinity for the human recombinant IP receptor with K(i) values of 20 nM and selectivity for human IP over all other members of the human prostanoid receptor family. Compound (R)-4 was shown to exhibit good pharmacokinetic properties in rats and dogs, and also good bioavailability in healthy volunteers.

Activation of IP prostanoid receptors prevents cardiomyocyte hypertrophy via cAMP-dependent signaling

The antihypertrophic action of angiotensin-converting enzyme inhibitors in the heart results partly from local potentiation of bradykinin. We have demonstrated that the antihypertrophic action of bradykinin is mediated by the release of nitric oxide from endothelium and elevation of cardiomyocyte cGMP. Whether other paracrine factors derived from the coronary endothelium, such as prostacyclin (PGI2), may act to prevent hypertrophy has not been explored. In the vasculature, activation by PGI2 of IP and EP1 prostanoid receptors elicits vasodilatation (via cAMP-dependent signaling) and vasoconstriction, respectively. The present objective was to determine whether IP prostanoid receptor activation has antihypertrophic actions in adult rat cardiomyocytes (ARCM). The selective IP agonist cicaprost (1 microM) virtually abolished the increase in [3H]phenylalanine incorporation (a marker of hypertrophy) induced either by endothelin-1 (ET-1; 60 nM, n = 10, P < 0.005) or by angiotensin II (1 microM, n = 6, P < 0.005). Cicaprost also inhibited ET-1 induction of c-fos mRNA expression, an additional marker of hypertrophy in ARCM (n = 5, P < 0.005). In the absence of hypertrophic stimuli, cicaprost alone did not significantly influence either marker. The antihypertrophic actions of cicaprost were mimicked by the dual IP/EP1 agonist iloprost (1 microM) in the presence of the EP1 antagonist AH-6809 (3 microM). Furthermore, cicaprost modestly but significantly increased cardiomyocyte cAMP content by 13 +/- 6% (P < 0.05, n = 4), and the antihypertrophic effect of cicaprost was lost in the presence of the cAMP-dependent protein kinase inhibitor H-89 (1 microM, n = 5, P < 0.05). However, ET-1 also induced increases in the activity of the intracellular growth signals ERK1 (by 3-fold) and ERK2 (by 5-fold) in ARCM, and these were not inhibited by cicaprost (P < 0.01, n = 5). Activation of IP receptors thus represents a novel approach to prevention of hypertrophy, and this effect is linked to cAMP-dependent signaling.

Platelets, atherosclerosis and the endothelium: new therapeutic targets?

One of the major causes of morbidity and mortality in the developed world is atherosclerosis. Recent research has suggested that the interaction of platelets with the endothelium is important in both the progression of atherosclerosis and the development of the acute complications of the disease. Both of these cells secrete various signalling molecules and express adhesion molecules, which can influence the development of pathological states. Certainly, there may be a vicious cycle in which platelet activation promotes atherosclerosis; a process involving inflammation and the activation of many other cell types (for example, leukocytes and smooth muscle cells), which causes further platelet activation. Therefore, intense effort has been made to develop therapeutic agents that can modulate the function of these cells, with the ultimate aim to retard (or even reverse) the progression of atheroma growth.

A simple stereoselective synthesis and biological evaluation of FR181157: orally active prostacyclin mimetic

Synthetic method of a novel prostaglandin (PG) mimetic: FR181175 without PG skeleton are described. The key to success is creation of a chiral epoxide using Sharpless AD reaction with high ee yield. FR181157 shows high potency and agonist efficacy at the IP receptor and has good bioavailability.

Cyclooxygenase-2-dependent prostacyclin formation is regulated by low density lipoprotein cholesterol in vitro

Reduction of plasma low density lipoprotein (LDL) levels is associated with a reduced risk of myocardial infarction, stroke, and death. Some of this clinical benefit may be derived from an improvement in endothelium-dependent vasodilation. In the present study, we examined the effects of LDL reduction on cyclooxygenase (COX) activity and prostacyclin (PGI2) production. Human umbilical vein endothelial cells exposed to reduced concentrations of LDL demonstrated increased PGI2 production in a dose-dependent manner (from 0.75+/-0.2 to 2.6+/-0.2 ng/mL, P<0.0001). This alteration in PGI2 production did not result from LDL-induced changes in PGI2 synthase expression. However, selective inhibition of COX-2, but not COX-1, blocked PGI2 production under low cholesterol conditions. Addition of exogenous cholesterol induces dose-dependent reductions in endothelial COX-2 expression as measured by reverse transcription-polymerase chain reaction and by Western blotting. Pretreatment of cells with actinomycin D, a transcription inhibitor, reduced COX-2-derived PGI2 production by 45.9% (from 0.55+/-0.09 to 0.25+/-0.08 ng/mL). Taken together, these observations indicate that endothelial PGI2 production is regulated by cholesterol at the transcriptional level and that cholesterol-sensitive transcriptional pathways that regulate COX-2 expression are present in vascular tissue.

Nitric oxide in atherosclerosis: vascular protector or villain?

1. Nitric oxide (NO) has important roles in physiological vasodilatation, cytotoxicity and vascular disease. Nitric oxide and prostacyclin (PGI2), both released from the endothelium, act synergistically to inhibit platelet aggregation and adhesion. These autacoids also inhibit the adhesion and migration of leucocytes and, in some arteries, they synergize in terms of vasodilation. 2. The development of atherosclerosis and hyperlipaemia per se is accompanied by impairment of endothelium-dependent vasodilation. 3. Atherosclerosis is associated with marked changes in the activity of isoforms of NO synthase (NOS) in the artery wall, including increased expression of the NOS2 (inducible) isoform in complex human lesions as well as in the neointima of experimental animal models. 4. Failure of NO release from the endothelium with normal physiological stimuli, which has been attributed to a defect in the operation of the endothelial NOS (NOS3), provides conditions propitious for leucocyte adhesion, vasospasm, thrombosis and, in addition, may promote increased proliferation of intimal cells. 5. Nitric oxide and superoxide anions generated by inflammatory cells in atherosclerosis react to form cytodestructive peroxynitrite radicals, potentially causing injury to the endothelium and myocytes, and this may be a factor in apoptosis of cells leading to plaque rupture. 6. We have been able to reverse these NO defects with therapeutic agents, including angiotensin-converting enzyme inhibitors, antagonists of platelet-activating factor and NO donor compounds, all offering promise in protecting against some manifestations of vascular disease.

Paracrine regulation of cardiac myocytes in normal and septic heart

A paracrine pathway for the regulation of cardiac contractile function by nonmuscle cells is documented in the heart. Coronary and endocardial endothelium release several diffusible agents, such as prostaglandins, endothelin-1, and nitric oxide, with an action on cardiac myocyte function. Cardiac diseases involving an immune or inflammatory mechanism, such as endotoxic shock, are now seen as conditions in which cross-talk between different cell types in the heart is clearly implicated. The potential biological relevance of inducible nitric oxide synthase in the myocardium, and the subsequent production of nitric oxide has been proposed as a mechanism of the cardiac depression observed in septic shock. In addition to cardiac myocytes, activated microvascular endothelial cells and cardiac endothelial cells may contribute to nitric oxide generation and, ultimately, to the depression of myocardial contractile activity during sepsis. This article reviews the local intercellular communication between cardiac myocytes and endothelial cells in the normal heart and discusses some of the mechanisms potentially claimed to depress heart function in sepsis.

Long-term effects of cicletanine on secondary pulmonary hypertension

Cicletanine, a furopyridine-derivative drug, was shown to enhance the production of endogenous prostacyclin. The potent vasodilating properties of prostacyclin are used to treat severe primary pulmonary hypertension. Prostacyclin has a short half-life and can be administered only as an i.v. infusion. The aim of this study was to evaluate the effects of cicletanine on pulmonary artery hypertension (PAH) resulting from chronic obstructive lung disease (COLD). In a double-blind controlled study, we evaluated the effects of short- and long-term administration of cicletanine (50 mg daily, orally) on hemodynamics and blood gases of patients with PAH resulting from COLD. The initial dose of 50 mg of cicletanine had no effect. A significant decrease in the mean pulmonary artery pressure (15%) and in total pulmonary resistance (20%) was observed after 3 or 12 months of treatment in the cicletanine group (11 patients), when compared with placebo (12 patients). PaO2 decreased slightly in the cicletanine group, but the difference from the control group was not significant. These results suggest that long-term treatment with cicletanine can induce effective pulmonary vasodilation in patients with PAH caused by COLD and that this is probably responsible for a small venous admixture.

The cardiac endothelium: cardioactive mediators

Endothelial cells within the heart release a number of substances that modulate myocardial contractile function. These agents include nitric oxide, endothelin, prostanoids, adenylpurines, and other substances that have so far been characterized only in bioassay studies. A notable feature of many of these agents is that they influence contractile behavior predominantly by modifying cardiac myofilament properties rather than altering cytosolic Ca2+ transients. A consequence of this subcellular action is often a disproportionate effect on myocardial relaxation and diastolic tone. The paracrine modulation of cardiac myocyte function by endothelial cell factors is likely to be an important mechanism contributing to the overall regulation of cardiac contractile function, both physiologically and in pathological states.

Nitric oxide in coronary artery disease: roles in atherosclerosis, myocardial reperfusion and heart failure

Nitric oxide (NO), derived from the vascular endothelium or other cells of the cardiovascular system, has an important role in physiological regulation of blood flow and has pathophysiological functions in cardiovascular disease. The mechanisms and enzymes involved in the biosynthesis of NO and biological actions of NO, including vasodilatation, cytotoxicity and inflammation, are briefly reviewed. These reactions involving NO cause pathological disturbances of arterial function, coronary blood flow regulation, and may contribute to cardiac myocyte dysfunction. NO and prostacyclin (PGI2), which is also released from the endothelium, act synergistically to inhibit platelet aggregation and adhesion, and in some arteries these mediators also synergise in terms of vasodilatation. In addition, NO is capable of hyperpolarizing vascular smooth muscle, but activation of the endothelium may cause hyperpolarization and may thus promote vasodilatation by an additional mechanism. After myocardial ischemia and reperfusion, production of NO and superoxide radicals represent important mechanisms of cytotoxicity, causing injury to the coronary endothelium and myocytes and compromising ventricular contractile function. Moreover, upon reperfusion endothelium-dependent vasodilatation is impaired and the coronary arteries constrict, leading to irregular myocardial perfusion. This is a consequence of the accumulation of activated leucocytes that we found to generate endogenous inhibitors of NO. These factors have yet to be fully characterised, but clearly they may have a role in irregularities of myocardial reperfusion and cellular injury. Chronic heart failure is associated both with impairment of endothelium-dependent vasodilatation and with excess production of NO via the inducible NO synthase (iNOS), although it is unclear whether the latter assists or compromises ventricular contractile performance under these conditions. Disturbances in the activity of isoforms of NO synthase in the artery wall also accompany the development of atherosclerosis, providing conditions propitious for vasospasm and thrombosis, and perhaps contributing to cell proliferation. Reversing these NO defects with therapeutic agents including angiotensin converting enzyme (ACE) inhibitors offers promise in protecting against some manifestations of vascular disease.

Endothelial stimulation of sodium pump in cultured vascular smooth muscle

We studied vascular sodium pump activity and its regulation by vasoactive agents and endothelium in cultured aortic vascular smooth muscle cells from normotensive Wistar-Kyoto rats (WKY) and spontaneously hypertensive rats (SHR). Baseline sodium pump activity (ouabain-inhibitable 86Rb+ uptake) was similar in cells from both rat strains. Angiotensin II and endothelin-1 increased ouabain-inhibitable 86Rb+ uptake more in SHR than WKY cells, whereas no effects were obtained with sodium nitroprusside, 8-bromo-cGMP, or iloprost. We examined the influence of endothelium on vascular sodium pump activity either by coculturing smooth muscle and endothelial cells or by using conditioned medium. Both coculture for 24 hours with endothelial cells and treatment with conditioned medium increased smooth muscle cell sodium pump activity, this effect being higher in SHR cells. These results suggest that the endothelium may modulate sodium pump activity in the underlying smooth muscle by releasing a diffusible compound, which is more active on SHR smooth muscle. The conditioned medium obtained in the presence of inhibitors of angiotensin-converting enzyme, endothelin-1-converting enzyme, cyclooxygenase, lipoxygenase, and nitric oxide synthase had no effect on the ability of conditioned medium to increase sodium pump activity, suggesting that angiotensin II, endothelin-1, eicosanoids, and nitric oxide are not involved in this stimulatory effect. The nature of the possible endothelial factor involved is still unknown, but it possesses a molecular weight between 25 and 50 kD, is heat stable, and is sensitive to trypsin treatment. We propose it could be a growth factor.

Endogenous nitric oxide in cardiovascular disease and transplantation

Nitric oxide (NO), derived from the vascular endothelium and other cells of the cardiovascular system, has important roles in physiological regulation of blood flow and may have pathophysiological functions in cardiovascular disease. The mechanisms involved in NO-induced vasodilatation and cytotoxicity are briefly reviewed in the context of inflammatory reactions and cardiovascular function. Although NO can hyperpolarize vascular smooth muscle, activation of the endothelium can induce hyperpolarization and vasodilatation by other means. Endogenous inhibitors of NO generated by leucocytes may compromise blood flow distribution after ischaemia and reperfusion injury. Chronic heart failure is associated simultaneously with impairment of endothelium-dependent vasodilatation and with excess production of NO via the inducible NO synthase (iNOS), although it is unclear whether the latter ameliorates or exacerbates ventricular dysfunction. Excess NO production is also one of the earliest signs of transplant rejection, and suppression of iNOS expression by immunosuppressant drugs such as cyclosporin A might be one means by which these drugs protect allografts. Disturbances in the activity of NOS isoforms in the artery wall also accompany the development of atherosclerosis, providing conditions propitious for vasospasm and thrombosis. Reversing the NO defects with therapeutic agents, including angiotensin converting enzyme (ACE) inhibitors, offers promise in protecting against some manifestations of vascular disease.

Comparative acute effects of adenosine and prostacyclin in primary pulmonary hypertension

Vasodilators have been a main focus of therapy for primary pulmonary hypertension. Adenosine and prostacyclin have been shown to reduce pulmonary vascular resistance acutely in these patients. In order to compare the acute hemodynamic effects of adenosine and prostacyclin, ten patients with severe primary pulmonary hypertension, unresponsive to medical therapy, were studied. After baseline hemodynamics were obtained, an adenosine infusion, 50 to 100 ng/kg/min, was begun and titrated to the maximum tolerated dose. Hemodynamics were allowed to return to baseline, and thereafter, a prostacyclin infusion was begun at 2 ng/kg/min, and titrated to the maximum tolerated dose. Overall, adenosine (200 +/- 53 ng/kg/min) produced a 33 +/- 18% (p < 0.001) fall in pulmonary vascular resistance and a 52 +/- 25% (p < 0.001) increase in cardiac output with no effect on pulmonary or systemic arterial pressures. Prostacyclin (8 +/- 4 ng/kg/min) caused a 22 +/- 18% (p < 0.01) fall in pulmonary vascular resistance and a 25 +/- 26% (p < 0.05) increase in cardiac output with a 14 +/- 6% (p < 0.001) decrease in systemic arterial pressure, but no change in pulmonary arterial pressure. The effects of adenosine and prostacyclin on pulmonary vascular resistance were similar (r = 0.70, r2 = 0.49, p = 0.02). Adenosine and prostacyclin have similar hemodynamic effects acutely in primary pulmonary hypertension. Adenosine may be useful as a test of the potential for long-term prostacyclin therapy in patients with primary pulmonary hypertension.

EDRF(NO)-Mediated Modulation of Collagen-Induced Platelet Accumulation in Rat Pulmonary Microcirculation

Endothelium-derived relaxing factor (EDRF) or nitric oxide (NO) biosynthesis from L-arginine occurs in the endothelium and platelets and may modulate platelet function and contribute to thromboresistance in the vessel wall. A rat model was used to evaluate selective accumulation of (III)In-labeled platelets in the pulmonary microcirculation following the administration of collagen, adenosine 5'-diphosphate (ADP) or thrombin. Platelet aggregation was monitored continuously over the thorax using a microcomputer-based system. Sodium nitroprusside, a stimulator of soluble guanylate cyclase and zaprinast, a phosphodiesterase V inhibitor, both known to cause accumulation of cyclic guanosine monophosphate, exhibited moderate inhibitory activity, which was shared by L-arginine. N(G)-monomethyl-L-arginine (L-NMMA; 1 mg/kg/min), an inhibitor of EDRF(NO), potentiated the aggregatory response to collagen at an intravenous dose of 100 &mgr;g/kg but not at one of 30 &mgr;g/kg. D-NMMA had no such effect. The augmenting effect of L-NMMA was abolished by L-arginine. N(G)-nitro-L-arginine methyl ester (L-NAME; 0.1 mg/kg/min) also markedly augmented the collagen-induced platelet response, and, at higher doses, all treated animals died upon collagen challenge. Both L-NMMA and L-NAME did not affect the responses to ADP and thrombin. The results suggest that in the intact vascular system, basal releae of EDRF(NO) is not critically involved in modulation of platelet function but becomes a significant factor when platelets are exposed to great amounts of collagen fibrils. Copyright 1994 S. Karger AG, Basel

17 beta-Estradiol inhibits flow- and acute hypoxia-induced prostacyclin release from perfused endocardial endothelial cells

BACKGROUND

Because of the marked difference in the incidence and severity of cardiovascular diseases between men and premenopausal women, several groups have studied the effect of sex steroids, particularly estrogen, on vascular endothelial prostacyclin (PGI2) release. No previous studies have addressed the effect of estrogen on endocardial endothelial cells (EECs), which are involved in the modulation of the myocardium and potentially in downstream pulmonary and systemic vascular tone. Furthermore, all previous studies of estrogen effects on cultured endothelial cell function have used cells grown under standard static cell culture conditions, thereby ignoring the contribution of flow, the ubiquitous environmental endothelial stimulus.

METHODS AND RESULTS

The effect of 17 beta-estradiol pretreatment (100 ng/mL, 72 hours) on cultured sheep EEC PGI2 release in response to multiple physiologically relevant stimuli was studied. EECs were grown in six-well plates (static conditions) or on microcarrier beads and perfused at a constant flow with normoxic (PO2 = 150 mm Hg, PCO2 = 35 mm Hg) or hypoxic (PO2 = 35 mm Hg, PCO2 = 35 mm Hg) Krebs solution. The stable metabolite of PGI2, 6-keto-PGF1 alpha, was determined in samples from both static and perfusion experiments by direct radioimmunoassay. 17 beta-Estradiol pretreatment did not alter basal or stimulated (arachidonic acid, 1 mumol/L, 10 mumol/L; A23187, 10 mumol/L; and bradykinin, 1 mumol/L) PGI2 release in static conditions. Untreated and acutely treated (100 ng/mL added to perfusate) EECs responded to flow with a time-dependent increase in PGI2 release that plateaued between 60 and 100 minutes. In contrast, 17 beta-estradiol-pretreated, perfused EECs did not increase PGI2 release over time. During perfusion, acute hypoxia increased PGI2 release: 140 +/- 65 (normoxia) to 296 +/- 113 pg (hypoxia) 6-keto-PGF1 alpha/mg per minute. 17 beta-Estradiol inhibited hypoxia-induced PGI2 release: 296 +/- 113 pg (untreated EECs, hypoxia) versus 159 +/- 60 pg (17 beta-estradiol pretreated, hypoxia) 6-keto-PGF1 alpha/mg per minute.

CONCLUSIONS

This study demonstrates for the first time an inhibitory effect of 17 beta-estradiol on flow- and acute hypoxia-induced increase in PGI2 release from perfused EECs in the absence of any effect on pharmacologically stimulated PGI2 release from static cultures. These effects of 17 beta-estradiol may explain in part the well-recognized gender and estrogen effects in cardiovascular diseases and highlight the importance of flow in studies of endothelial cell function.

Review of postoperative pharmacological infusions in ischemic skin flaps

No single drug has yet been found which can overcome the inflammatory and microvascular changes which occur in a skin flap after ischemia-reperfusion. Nevertheless, the continued failure of approximately 7% of all free flap transfers clinically suggests that there may be a place for pharmacological intervention at the time of threatened flap failure. To date, plastic and reconstructive microsurgeons have been reluctant to use drugs because of the mass of conflicting evidence emanating from the plastic surgery literature. However, scientists and surgeons now have a clearer understanding of the problems arising in ischemia-reperfusion. Multi-acting drugs which can inhibit most of the important inflammatory changes would be the ideal. This review considers some of the historical developments in the pharmacological treatment of ischemic flaps in the past decade and looks to the future when pharmacological infusions may be part of the routine for salvaging failing skin flaps.

Effect of aspirin on conformation and dynamics of membrane proteins in platelets and erythrocytes

The effect of the chemical modifications induced by aspirin (acetylsalicylic acid), acetyl chloride or salicylate on platelet membranes and erythrocyte ghosts has been investigated by means of fluorescence quenching and ESR spectroscopy in relation to our earlier findings of acetylation-induced reduction of platelet and erythrocyte membrane lipid fluidity. Only aspirin was found to induce disorders in the lipid-protein matrix and membrane protein conformation. The apparent distance separating the membrane tryptophan and bound 1-anilino-8-naphthalenesulphonate (ANS) molecules was decreased after aspirin action in both platelet and erythrocyte membranes. This resulted in a significant increase in the maximum energy transfer efficiency. The decrease in the ratio of the amplitudes of low-field peaks of weakly to strongly immobilized fractions of maleimide spin label (4-maleimido-2,2,6-6-tetramethylpiperidine-1-oxyl) and the rise in the relative rotational correlation time of iodoacetamide spin label [4-(2-iodoacetamido)-2,2,6,6-tetramethylpiperidine-1-oxyl] indicate that aspirin effectively immobilizes membrane proteins in the plane of the lipid bilayer, whereas neither acetyl chloride or salicylate gave rise to detectable effects. We conclude that aspirin-induced alterations in membrane protein structure induce a reorganization of lipid assembly as well as rearrangements in the membrane protein pattern, and consequently alterations in lipid-protein interactions. Thus, the interaction of aspirin with platelet and erythrocyte membranes may induce local conformational changes in membranes, which are discussed in connection with impairment of platelet function. A new mode of protein chemical modification by aspirin is suggested which involves the generation of reactive salicylic residue during the fast degradation of aspirin under physiological conditions.

Effect of seeding time and density on endothelial cell attachment to damaged vascular surfaces

An in vitro model to facilitate the study of endothelial cell seeding of damaged vascular surfaces has been developed. This may have applications in the study of endothelial seeding of angioplasty and endarterectomy sites. Using this model, the optimum endothelial seeding time for attachment to damaged vascular surfaces should not exceed 30 min and, to achieve confluent cell attachment, a seeding density > 5 x 10(5) cells/cm2 should be used.

Endothelial cell seeding of damaged native vascular surfaces: prostacyclin production

Endothelial cell seeding has been successful in reducing the thrombogenicity of prosthetic vascular grafts in animal and clinical studies. The reduction in thrombogenicity may be attributed to the intrinsic properties of endothelial cells themselves, and their ability to produce anti-thrombogenic mediators such as prostacyclin, and endothelium-derived relaxing factor. Endothelial seeding of damaged vascular surfaces produced during percutaneous transluminal angioplasty and endarterectomy is an attractive possibility due to the excellent attachment characteristics of the sub-endothelial tissue exposed during these procedures. The ability of endothelial seeded damaged vascular surfaces to produce prostacyclin was measured in an in vitro model of vascular injury. Endothelial-seeded damaged surfaces produced significantly higher prostacyclin release than did vessels damaged by balloon dilatation (265.5 pg cm-2 min-1 and 87.5 pg cm-2 min-1 respectively). This study provides evidence that endothelial seeding of damaged native vascular surfaces is technically feasible and that seeding may reduce the thrombogenicity of vascular surfaces following balloon dilatation.

The influence of endocardial endothelium on myocardial contraction

A novel unidentified agent, provisionally named 'endocardin', has been shown to be released from endocardial endothelium. Endocardin has a unique prolonging effect on myocardial contraction. In contrast, endothelium-derived relaxing factor released from endocardial endothelium has the opposite effect of abbreviating contraction. Jerry Smith and colleagues discuss the mechanisms of action of these agents and their possible physiology and pathophysiology.

Mechanisms and pathology of monocrotaline pulmonary toxicity

Monocrotaline (MCT) is an 11-membered macrocyclic pyrrolizidine alkaloid (PA) that causes a pulmonary vascular syndrome in rats characterized by proliferative pulmonary vasculitis, pulmonary hypertension, and cor pulmonale. Current hypotheses of the pathogenesis of MCT-induced pneumotoxicity suggest that MCT is activated to a reactive metabolite(s) in the liver and is then transported by red blood cells (RBCs) to the lung, where it initiates endothelial injury. While several lines of evidence support the requirement of hepatic metabolism for pneumotoxicity, the mechanism and relative importance of RBC transport remain undetermined. The endothelial injury does not appear to be acute cell death but rather a delayed functional alteration that leads to disease of the pulmonary arterial walls by unknown mechanisms. The selectivity of MCT for the lung, as opposed to that of other primarily hepatotoxic PAs, appears likely to be a consequence of the differences in hepatic metabolism and blood kinetics of MCT. A likely candidate for a reactive metabolite of MCT is the dehydrogenation product monocrotaline pyrrole (MCTP). Secondary or phase II metabolism of MCT through glutathione (GSH) conjugation has been characterized recently and appears to represent a detoxification pathway. The role of inflammation in the progression of MCT-induced pulmonary vascular disease is uncertain. Both perivascular inflammation and platelet activation have been proposed as processes contributing to the response of the vascular media. This review presents the experimental evidence supporting these hypotheses and outlines additional questions that arise from them.