Mechanisms of endothelium-dependent vascular smooth muscle relaxation

Inwardly rectifying potassium channels: their structure, function, and physiological roles

Inwardly rectifying K(+) (Kir) channels allow K(+) to move more easily into rather than out of the cell. They have diverse physiological functions depending on their type and their location. There are seven Kir channel subfamilies that can be classified into four functional groups: classical Kir channels (Kir2.x) are constitutively active, G protein-gated Kir channels (Kir3.x) are regulated by G protein-coupled receptors, ATP-sensitive K(+) channels (Kir6.x) are tightly linked to cellular metabolism, and K(+) transport channels (Kir1.x, Kir4.x, Kir5.x, and Kir7.x). Inward rectification results from pore block by intracellular substances such as Mg(2+) and polyamines. Kir channel activity can be modulated by ions, phospholipids, and binding proteins. The basic building block of a Kir channel is made up of two transmembrane helices with cytoplasmic NH(2) and COOH termini and an extracellular loop which folds back to form the pore-lining ion selectivity filter. In vivo, functional Kir channels are composed of four such subunits which are either homo- or heterotetramers. Gene targeting and genetic analysis have linked Kir channel dysfunction to diverse pathologies. The crystal structure of different Kir channels is opening the way to understanding the structure-function relationships of this simple but diverse ion channel family.

Role of phospholipase C and diacylglyceride lipase pathway in arachidonic acid release and acetylcholine-induced vascular relaxation in rabbit aorta

ACh stimulates arachidonic acid (AA) release from membrane phospholipids of vascular endothelial cells (ECs). In rabbit aorta, AA is metabolized through the 15-lipoxygenase pathway to form vasodilatory eicosanoids 15-hydroxy-11,12-epoxyeicosatrienoic acid (HEETA) and 11,12,15-trihydroxyeicosatrienoic acid (THETA). AA is released from phosphatidylcholine (PC) and phosphatidylethanolamine (PE) by phospholipase A2 (PLA2), or from phosphatidylinositol (PI) by phospholipase C (PLC) pathway. The diacylglycerol (DAG) lipase can convert DAG into 2-arachidonoylglycerol from which free AA can be released by monoacylglycerol (MAG) lipase or fatty acid amidohydrolase (FAAH). We used specific inhibitors to determine the involvement of the PLC pathway in ACh-induced AA release. In rabbit aortic rings precontracted by phenylephrine, ACh induced relaxation in the presence of indomethacin and N(omega)-nitro-L-arginine (L-NNA). These relaxations were blocked by the PLC inhibitor U-73122, DAG lipase inhibitor RHC-80267, and MAG lipase/FAAH inhibitor URB-532. Cultured rabbit aortic ECs were labeled with [14C]AA and stimulated with methacholine (10(-5) M). Free [14C]AA was released by methacholine. Methacholine decreased the [14C]AA content of PI, DAG, and MAG fractions but not PC or PE fractions. Methacholine-induced release of [14C]AA was blocked by U-73122, RHC-80267, and URB-532 but not by U-73343, an inactive analog of U-73122. The data suggested that ACh activates PLC, DAG lipase, and MAG lipase pathway to release AA from membrane lipids. This pathway is important in regulating vasodilatory eicosanoid synthesis and vascular relaxation in rabbit aorta.

Invited review: effects of flow on vascular endothelial intracellular calcium signaling of rat aortas ex vivo

To study the effects of flow on in situ endothelial intracellular calcium concentration ([Ca(2+)](i)) signaling, rat aortic rings were loaded with fura 2, mounted on a tissue flow chamber, and divided into control and flow-pretreated groups. The latter was perfused with buffer at a shear stress of 50 dyns/cm(2) for 1 h. Endothelial [Ca(2+)](i) responses to ACh or shear stresses were determined by ratio image analysis. Moreover, ACh-induced [Ca(2+)](i) elevation responses were measured in a calcium-free buffer, or in the presence of SKF-96365, to elucidate the role of calcium influx in the flow effects. Our results showed that 1) ACh increased endothelial [Ca(2+)](i) in a dose-dependent manner, and these responses were incremented by flow-pretreatment; 2) the differences in ACh-induced [Ca(2+)](i) elevation between control and flow-pretreated groups were abolished by SKF-96365 or by Ca(2+)-free buffer; and 3) in the presence of 10(-5) M ATP, shear stress induced dose-dependent [Ca(2+)](i) elevation responses that were not altered by flow-pretreatment. In conclusion, flow-pretreatment augments the ACh-induced endothelial calcium influx in rat aortas ex vivo.

The cardiac toxicity of anabolic steroids

Anabolic steroids are synthetic derivatives of testosterone that were developed as adjunct therapy for a variety of medical conditions. Today they are most commonly used to enhance athletic performance and muscular development. Both illicit and medically indicated anabolic steroid use have been temporally associated with many subsequent defects within each of the body systems. Testosterone is the preferred ligand of the human androgen receptor in the myocardium and directly modulates transcription, translation, and enzyme function. Consequent alterations of cellular pathology and organ physiology are similar to those seen with heart failure and cardiomyopathy. Hypertension, ventricular remodeling, myocardial ischemia, and sudden cardiac death have each been temporally and causally associated with anabolic steroid use in humans. These effects persist long after use has been discontinued and have significant impact on subsequent morbidity and mortality. The mechanisms of cardiac disease as a result of anabolic steroid use are discussed in this review.

The responsiveness of isolated human hand vein endothelial cells in normal pregnancy and in pre-eclampsia

1. Human hand vein endothelial cells were isolated from blood obtained by traumatic venepuncture. Cells were identified as endothelial by staining with endothelium-specific antibodies. The subject groups studied were (i) non-pregnant, (ii) pregnant (mean, 35 weeks gestation) and (iii) pre-eclamptic women (mean, 36 weeks gestation). 2. Fura-2 was used to measure agonist-induced responses in intracellular Ca2+ in single endothelial cells isolated and maintained in vitro. All of the cells examined responded to adenosine triphosphate (ATP) with a large transient increase in Ca2+ followed by a sustained plateau. 3. The responses to ATP were significantly larger in the cells from pregnant women than in those from non-pregnant and pre-eclamptic women, but no other differences were observed. The amplitudes of the responses to ATP were (means +/- s.e.m.) 0.56 +/- 0.04, 1.42 +/- 0.24 and 0.65 +/- 0.09 fura-2 ratio units for cells from non-pregnant, pregnant and pre-eclamptic subjects, respectively. 4. In cells isolated from non-pregnant subjects, the amplitude of the responses to carbachol, histamine and bradykinin were all smaller than those activated by ATP: 5.1, 13.9 and 4.4 %, respectively. Not all cells responded to these agonists: 25 % responded to carbachol, 70.5 % responded to histamine and 12.5 % responded to bradykinin. Sixty-five per cent of the cells from normotensive pregnant subjects responded to bradykinin compared with 25 % in the non-pregnant and 13.9 % in the pre-eclamptic subjects. 5. These data suggest that there may be differences in the responsiveness of venous endothelial cells in pregnancy and that pre-eclamptic cells behave differently.

A prostaglandin, not NO, mediates endothelium-dependent dilation in ventral aorta of shark (Squalus acanthias)

In mammals, the vascular endothelium releases a variety of paracrine factors, including the vasodilatory prostaglandin (PG)I2 and nitric oxide (NO), which is generally accepted as the major endothelium-derived relaxing factor (EDRF) in mammals. Current evidence for the vascular NO-EDRF system in fishes is contradictory. In addition, the role of PGs in the control of fish vascular tension is also unclear. We have utilized isolated rings of the ventral aorta of the spiny dogfish shark to examine the ability of various components of the NO system to dilate this vessel. Neither the NO precursor L-arginine, the NO donor sodium nitroprusside, nor NO itself dilated the rings. The Ca2+ ionophore A-23187 did produce an endothelium-dependent dilation that was not inhibited by the NO synthase inhibitor NG-nitro-L-arginine methyl ester but was inhibited by the cyclooxygenase inhibitor indomethacin, suggesting that PGs are involved. PGE1 and carbaprostacyclin, but not PGI2, produced concentration-dependent dilation, and intact aortic rings secreted five times as much PGI2 as PGE in both the unstimulated state and after stimulation with A-23187. Our data suggest strongly that a PG, most probably PGI2, is the EDRF in the ventral aorta of this shark species.

Bioassay of prostacyclin and endothelium-derived relaxing factor (EDRF) from porcine aortic endothelial cells. 1985

A cascade superfusion technique has been developed for the differential bioassay of prostacyclin and endothelium-derived relaxing factor (EDRF) released from porcine aortic endothelial cells cultured on microcarriers, packed into a column and perfused.

Bradykinin (Bk; 20–100 Nm) released prostacyclin (9.6 ± 1.5 Nm per 10⁶ cells; mean ± s.e.mean, n = 9) and prostaglandin E₂ (PGE₂; 2.1 ± 0.6 Nm per 10° cells) from the column measured by relaxation of strips of bovine coronary artery (BCA) and rabbit mesenteric or coeliac artery, respectively. The presence of these prostanoids in the effluent was confirmed by specific radioimmunoassays.

A23187 (500–2000 Nm) also released both prostacyclin and PGE₂ from the cells. This release was long-lasting and not reproducible.

Bk (20–100 Nm) and A23187 (30–300 Nm) released EDRF from the column. This was detected in a cascade of four rabbit aortic strips (RbA), denuded of endothelium and contracted with U46619 or phenylephrine. The relaxation of the RbA strips caused by EDRF was progressively attenuated down the cascade (half-life < 7 s) and was not affected by indomethacin.

EDRF and prostacyclin could be differentially bioassayed in a cascade of alternating RbAs and BCAs as prostacyclin did not relax RbAs and the time delay to the BCAs destroys EDRF. EDRF could be bioassayed on its own when the endothelial cells were treated with indomethacin.

5-Hydroxytryptamine 0.2, noradrenaline 1.0, platelet-activating factor (Paf-acether) 1.0, formylmethionyl-leucyl-phenylalanine 1.0, acetylcholine 0.5, bethanecol 0.5, adenosine diphosphate 0.25 and angiotensin II 0.1 μm did not release either prostanoids or EDRF from the column.

Acetylcholine-induced vasoconstrictor response of coronary vessels in rats: a possible contribution of M2 muscarinic receptor activation

A mechanism by which acetylcholine (ACh) may elicit vasoconstrictor response in coronary vessels was studied in rat hearts perfused at a constant flow rate. In spontaneously beating hearts, bolus injections of ACh and carbachol (CCh) produced biphasic changes in coronary perfusion pressure (CPP): a transient increase at the initial period followed by a sustained decrease. In KCl-arrested hearts, ACh and CCh produced a monophasic increase in CPP, which was attenuated by either removal of endothelial cells by saponin or cyclooxygenase inhibition by diclofenac sodium. In the spontaneously beating heart, ACh-induced vasoconstriction was almost abolished by atropine (0.1 microM) and was markedly attenuated by an M2 antagonist, methoctramine (0.1 microM), but not by an M1 antagonist, pirenzepine (1 microM). Arecaidine propargyl ester (APE), an M2 agonist, produced coronary artery constriction which was attenuated by methoctramine (0.1 microM) but not by pirenzepine (0.1 microM) in both spontaneously beating and KCl-arrested hearts. McN-A-343, an M1 agonist, increased CPP in both beating and KCl-arrested hearts, but to a lesser degree than APE. These results suggest that the release of vasoconstrictor prostaglandins from endothelial cells contributes to the vasoconstrictor response to ACh in perfused rat coronary vessels, and the response to ACh appears to be mediated, in part, via the M2 subtype of muscarinic receptors.

Role of nitric oxide in the hypoxemia-induced renal dysfunction of the newborn rabbit

The current study was performed in 30 anesthetized and mechanically ventilated newborn rabbits to investigate the role of the endothelium-derived relaxing factor nitric oxide (NO) in the renal vasoconstriction observed during hypoxemia. Renal blood flow (RBF) and GFR were determined by the clearance of p-aminohippuric acid and inulin, respectively. In nine newborn rabbits (group 1), acute hypoxemia induced a significant decrease in RBF (-17 +/- 7%) and GFR (-11 +/- 6%). A second group of nine animals was used to determine the role of NO in regulating renal hemodynamics of the immature kidney in physiologic conditions. N omega-Nitro-L-arginine methyl ester (L-NAME), a NO synthesis inhibitor, significantly increased the renal vascular resistance by 31 +/- 9% and decreased RBF and GFR (-20 +/- 6% and -13 +/- 5%, respectively). Acute hypoxemia was induced in 12 additional newborn rabbits during L-NAME infusion (group 3) to define the role of NO in the renal vasoconstriction observed during hypoxemia. The changes in renal hemodynamics were greater in this group than in those induced by hypoxemia alone. The present results suggest that: 1) endogenous NO has a crucial role in maintaining basal renal perfusion, 2) the activity of NO synthase is maintained during acute hypoxemia, and 3) NO could blunt the effects of acute hypoxemia in the immature newborn rabbit kidney.

Endothelium-dependent and independent effects of garlic on rat aorta

Effects of garlic on isolated rat aorta were investigated by comparing with those of acetylcholine and L-arginine in the presence and absence of endothelium. For this purpose, certain linear and non-linear regression models were applied for concentration-response curves obtained by acetylcholine, L-arginine and garlic in the rat aorta. Garlic caused dose-dependent relaxations in isolated rat aorta which were attenuated by the removal of endothelium as in the case of acetylcholine. However, the relaxant responses to acetylcholine, L-arginine and garlic were not completely abolished by the endothelial denudation. Application of a number of regression models for the vasorelaxant effects of acetylcholine and garlic revealed that mechanism(s) of the effect of garlic may be different from that of acetylcholine. Furthermore, it was noted that L-arginine-induced relaxations, but not those induced by acetylcholine and garlic, are enhanced by a 2 or 4 h incubation period in the bathing medium. The findings obtained strongly suggested that the vasorelaxant effect of garlic is important in its hypotensive activity and mediated by the production of endothelium-and/or muscle-derived relaxing factors.

Chronic treatment with the anabolic steroid, nandrolone, inhibits vasodilator responses in rabbit aorta

The effect of chronic treatment of rabbits for 4, 8 and 12 weeks with the anabolic steroid, nandrolone, on vasodilator responses was studied in segments of different arteries. The treatment abolished endothelium-dependent relaxation caused by acetylcholine and the Ca(2+)-ionophore, A23187, in thoracic aorta, and reduced endothelium-independent relaxations induced by exogenous nitric oxide (NO) or sodium nitroprusside. The inhibitor of NO synthesis, NG-monomethyl-L-arginine, abolished vasodilator responses to acetylcholine and A23187. In contrast, relaxation induced by acetylcholine, NO or sodium nitroprusside in mesenteric and femoral arteries was unaltered by nandrolone treatment. Bioassay experiments using donor segments and endothelium-denuded bioassay rings from thoracic aorta show that acetylcholine, applied either through control or treated (12 weeks) donor segments, produced similar relaxation in bioassay rings from control rabbits, but this relaxation was markedly reduced in rings from treated rabbits. The increases of cyclic GMP levels induced by acetylcholine or sodium nitroprusside in segments from thoracic aorta were abolished by nandrolone treatment. These results suggest that the treatment with nandrolone reduces NO-mediated relaxation only in thoracic aorta by inhibition of guanylate cyclase, endothelial NO production and vasodilator machinery being unaltered.

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.

In vitro perfusion studies of resistance artery function in genetic hypertension

To examine the function of resistance-sized arteries in hypertension under in vitro conditions that approximate in vivo conditions as much as possible, we mounted segments of second-order mesenteric resistance arteries from spontaneously hypertensive rats (SHR) and Wistar-Kyoto normotensive control rats aged 12 to 13 weeks in a perfusion myograph and exposed them to conditions of constant flow and pressure. The endothelial integrity was validated both functionally and histologically. Vascular sensitivity to norepinephrine was examined when the hormone was applied either intraluminally or extraluminally and before and after removal of the endothelium. Both endothelium-dependent and -independent dilatation was assessed by the intraluminal application of acetylcholine and sodium nitroprusside, respectively. Sodium nitroprusside was applied to arteries after endothelium removal. Arterial responses were measured by changes in intraluminal diameter recorded with a video camera and imaging system. Vessels from SHR demonstrated depressed endothelium-dependent relaxation but similar endothelium-independent relaxation and greater sensitivity to norepinephrine with both intraluminal and extraluminal application. Removal of the endothelium abolished the differences in sensitivity to norepinephrine between the two strains. The results demonstrate that resistance arteries from SHR when examined under in vitro perfusion display enhanced sensitivity to norepinephrine due to depressed endothelium-dependent dilatation, and the data suggest that functional modifications in the endothelium may play an important role in hypertensive vascular disease.

Degradation of bradykinin by neutral endopeptidase (EC 3.4.24.11) in cultured human endothelial cells

The presence of neutral endopeptidase 24.11 was demonstrated in human umbilical vein endothelial cells by immunostaining. Enzymatic activity of neutral endopeptidase was determined as 0.167 +/- 0.02 mU/mg protein in the membrane fraction of human umbilical vein endothelial cells, using the fluorogenic peptide substrate, dansyl-D-Ala-Gly-Phe(pNO2)-Gly. No activity was found in the cytosolic fraction of endothelial cells. The role of this peptidase in the degradation of the endogenous vasodilator bradykinin was investigated by incubating human umbilical vein endothelial cell monolayers with bradykinin (10(-8) mol/l). The inhibitor of neutral endopeptidase, phosphoramidon (10(-8) mol/l), decreased the degradation of bradykinin in the supernatant of endothelial cells; the half-life of bradykinin was then increased from 29 +/- 1 to 46 +/- 2 minutes. The angiotensin-converting enzyme inhibitor, lisinopril (10(-8) mol/l), increased the half-life of bradykinin to 244 +/- 20 minutes; the combination of both inhibitors increased the half-life of bradykinin to 381 +/- 51 minutes. Inhibitors of aminopeptidase (amastatin) and carboxypeptidase (2-mercaptomethyl-3-guanidinoethyl-thiopropionic acid) caused no significant effect. The effect of phosphoramidon was small in comparison with that of lisinopril, but was pronounced in combination with lisinopril. Neutral endopeptidase activity is localized in the membranes of human endothelial cells and seems to be involved in the degradation of bradykinin by the vascular endothelium, particularly during angiotensin converting enzyme inhibition.

Hypoxia causes an abnormal contractile response in the atherosclerotic rabbit aorta. Implication of reduced nitric oxide and cGMP production

Both atherosclerotic lesions and hypoxia alter the contractile properties of the arterial wall and, in particular, may interfere with the relaxation mechanisms dependent or not on the endothelium. The present study was designed to test the effect of severe hypoxia on the contractile behavior of the atherosclerotic rabbit aorta. Segments of aortas obtained from control, cholesterol-fed, or Watanabe hereditary hyperlipidemic rabbits were mounted in organ chambers for isometric tension recording. A change of the bath PO2 from "normoxic" conditions (95% O2-5% CO2) to "hypoxic" conditions (95% N2-5% CO2) caused relaxation in the precontracted control aortas (by approximately 85%) but a transient contraction (approximately 20% of the maximal contraction obtained with 30 mM KCl) followed by a relaxation in the precontracted atherosclerotic aortas. Both types of responses were observed in aortas contracted with aggregating platelets, 5-hydroxytryptamine (5-HT), norepinephrine, endothelin, and prostaglandin F2 alpha. The hypoxic contractions in atherosclerosis were not dependent on the presence of an intact endothelium. They could not be antagonized by blockers of alpha-adrenoceptors, 5-HT2 receptors, histamine receptors, thromboxane receptors, and muscarinic cholinoreceptors. Inhibitors of cyclooxygenase, lipoxygenase, Na+, K(+)-ATPase, and free radical scavengers or an activator of endothelium-derived relaxing factor did not significantly affect the hypoxic contraction; the absence of effect of some inhibitors of protein synthesis seems to rule out the involvement of endothelin, angiotensin II, and bradykinin. The hypoxic contraction was not influenced by omission of Ca2+ from the medium or by inhibition of Ca2+ influx but was prevented by blockade of intracellular Ca2+. The inhibitor of nitric oxide synthase (nitro-L-arginine, 100 microM) and the guanylyl cyclase inhibitor (methylene blue, 10 microM) both enhanced the initial contractile responses to 5-HT to a similar extent as hypoxia and completely prevented the hypoxic contraction in the atherosclerotic tissues. The cyclic nucleotide analogues 8-bromo-cGMP and dibutyryl cAMP also inhibited the hypoxic contraction in the atherosclerotic aorta. The cGMP levels were markedly decreased and the cAMP levels were moderately decreased in the aortas of the cholesterol-fed rabbits as compared with the control aortas. Hypoxia further decreased cGMP but not the cAMP levels in atherosclerotic aortas with and without endothelium. Our data thus demonstrate the occurrence of an unusual vasoconstrictor response in atherosclerotic arteries; this constrictor response depends on the availability of intracellular Ca2+ and seems to be due to the further inhibition of an already impaired cGMP production.(ABSTRACT TRUNCATED AT 400 WORDS)

Electrical properties of resting and acetylcholine-stimulated endothelium in intact rat aorta

1. The passive electrical properties and the effects of acetylcholine on the membrane potential of the endothelium of intact rat aorta were investigated using the whole cell mode of the patch clamp technique. 2. Unstimulated endothelium had a membrane potential of -58 +/- 8 mV (S.E.M., n = 193; range -47 to -76 mV). The input resistance was 43 +/- 13 M omega (S.E.M., n = 8; range 26-64 M omega). KCl and BaCl2, but not tetraethylammonium (2 mM), 4-aminopyridine (5 mM) or 4,4'-diisothiocyanatostilbene-2,2'-disulphonic acid (DIDS; 100 microM) depolarized the endothelium. 3. Acetylcholine (0.2-4 microM) evoked in most preparations a biphasic response with a transient hyperpolarization to a value close to the K+ reversal potential, followed by depolarization beyond the resting potential. In 46% of recordings, the depolarization was followed by oscillations in membrane potential. The duration of the hyperpolarization and magnitude of the depolarization was similar in all recordings from a given aorta, but varied greatly between different preparations. 4. Hyperpolarization of the endothelium below the K+ reversal potential reversed the direction of the first phase of the acetylcholine-evoked response, which was unaffected by tetraethylammonium, 4-aminopyridine, or DIDS. 5. The removal of extracellular Ca2+ evoked a depolarization of the endothelium from -61 +/- 3 to -34 +/- 3 mV (S.E.M., n = 9) over 2-15 min. Restoration of external Ca2+ evoked a transient hyperpolarization. 6. ACh applied in nominally Ca(2+)-free medium shortly after Ca2+ removal evoked only a transient hyperpolarization. After the establishment of a stable membrane potential in Ca(2+)-free medium, acetylcholine was without effect. 7. NiCl2 (2 mM) evoked a small depolarization of the endothelium (6 +/- 2 mV; S.E.M., n = 7). The subsequent removal of Ni2+ evoked a transient hyperpolarization. 8. In the presence of Ni2+, acetylcholine evoked a short-lived hyperpolarization. Both the application of Ni2+ and the removal of extracellular Ca2+ immediately blocked oscillations in membrane potential evoked by acetylcholine. 9. The blockers of voltage-operated Ca2+ channels, nifedipine (1-10 microM) and verapamil (20 microM) were without effect on the biphasic acetylcholine-evoked responses. 10. In preparations in which acetylcholine evoked large (20-45 mV) oscillations in membrane potential, depolarization of the endothelium alone, by current injection or application of KCl, did not evoke oscillations. 11. The activator of protein kinase C, phorbol 12, 13-dibutyrate (200 nM) depolarized and greatly increased the input resistance of the endothelium, presumably due to an effect on gap junctions.(ABSTRACT TRUNCATED AT 400 WORDS)

Basal release of nitric oxide from aortic rings is greater in female rabbits than in male rabbits: implications for atherosclerosis

Estradiol is known to exert a protective effect against the development of atherosclerosis, but the mechanism of this hormonal action is unknown. One of the early events in the development of atherosclerosis is the adhesion of macrophages to endothelial cells, and nitric oxide (NO) inhibits this process. We show that basal release of NO is greater with endothelium-intact aortic rings from female rabbits than those from males. Oophorectomy diminishes both circulating estradiol concentration and basal release of NO to levels seen in male rabbits. These data establish that basal NO release from endothelium-intact aortic rings depends on circulating estradiol concentration and offer an explanation for the protective effect of estradiol against the development of atherosclerosis.

A possible mechanism of endothelium-dependent relaxation induced by pirarubicin and carbachol in rat isolated aorta

The mechanism of endothelium-dependent relaxation induced by pirarubicin, (2''R)-4'-O-tetrahydropyranyladriamycin, THP, or carbachol was investigated in the rat isolated aorta. The relaxant effect of THP (1.5 x 10(-6)-4.5 x 10(-5) M) or carbachol (10(-8)-10(-4) M) on the aorta with endothelium was decreased by lowering Ca2+ in the medium. The relaxation induced by THP was not inhibited by pretreatment with verapamil (10(-6)-10(-5) M), and that induced by carbachol was only partially inhibited. However, on replacement of all but 20 mM Na+ with either Li+ or choline, the THP- or carbachol-induced relaxation was inhibited. Furthermore, the relaxing effect of THP or carbachol was inhibited by pretreatment with amiloride (10(-4)-3 x 10(-4) M), with ouabain (10(-4)-10(-3) M), or with K(+)-depletion. These results suggest that the THP- or carbachol-induced relaxation depending on endothelium was affected by modifying the calcium ion concentration, and that a Na(+)-Ca2+ exchange process is involved.

Nitrergic transmission: nitric oxide as a mediator of non-adrenergic, non-cholinergic neuro-effector transmission

1. The possibility that transmission at some non-adrenergic, non-cholinergic (NANC) neuro-effector junctions is mediated by nitric oxide (NO) arose from the discoveries that NO mediated the effects of nitrovasodilator drugs and that endothelium-derived relaxing factor (EDRF) was NO or a NO-yielding substance. 2. NO donated by nitrovasodilator drugs or formed by endothelial cells activates soluble guanylate cyclase in smooth muscle and the consequent increase in cyclic guanosine monophosphate (cGMP) results in relaxation. The relaxations produced by stimulation of some NANC nerves are also due to a rise in cGMP. 3. The biosynthesis of NO by oxidation of a terminal guanidino nitrogen of L-arginine is inhibited by some NG-substituted analogues of L-arginine. These substances block EDRF formation by NO synthase and endothelium-dependent vasodilatation, and the blockade is overcome by L-arginine 4. NANC relaxations in some tissues are blocked by NG-substituted analogues of L-arginine and restored by L-arginine. Other agents that affect endothelium-dependent vasodilator responses produce corresponding changes in responses to stimulation of these NANC nerves. Such observations indicate that transmission is mediated by NO: we have termed this mode of transmission nitrergic. 5. There is evidence for nitrergic innervation of smooth muscle in the gastrointestinal tract, genito-urinary system, trachea and some blood vessels (penile and cerebral arteries). 6. The recognition of a mediator role for NO in neurotransmission calls for reconsideration of previously accepted generalizations about mechanisms of transmission. 7. Studies on nitrergic transmission will provide new insights into physiological control mechanisms and pathophysiological processes and may lead to new therapeutic developments.

Differential muscarinic receptor mRNA expression by freshly isolated and cultured bovine aortic endothelial cells

Endothelial cells, either in vivo or freshly isolated, respond when exposed to muscarinic agonists with an increase in cytosolic free calcium concentration ([Ca2+]i) and release of endothelium-derived relaxing factor (EDRF). When placed in culture, however, endothelial cells rapidly lose these responses, which may be related to changes in muscarinic receptor expression. Northern blot analysis of poly(A) + RNA from freshly isolated or cultured bovine aortic endothelial cells was used to address this problem. Through the use of specific cDNA probes complementary to the nonconserved regions of the m1, m2, m3, m4, and m5 muscarinic receptors, mRNA transcripts for the m1 (3.9 kb), m2 (3.8 kb), and m3 (3.1 kb) receptor subtypes were identified in freshly isolated endothelial cells, whereas m1 and m3 transcripts were identified in aortic smooth muscle. In contrast, cultured endothelial cells contained mRNA for only the m2 receptor subtype. Transcripts for the m4 or m5 receptors were not detected in either freshly isolated or cultured endothelial cells. Since m1 and m3 receptor subtypes are coupled to phospholipase C, activation of which is required for EDRF release, these observations may explain the failure of muscarinic agonists to elicit a rise in [Ca2+]i and EDRF release from cultured endothelial cells.

Endothelium-Derived Nitric Oxide and Cyclooxygenase Products Modulate Corpus Cavernosum Smooth Muscle Tone

Relaxation of penile corpus cavernosum smooth muscle is controlled by nerve and endothelium derived substances. In this study, endothelium-dependent relaxation of corporal smooth muscle was characterized and the role of arachidonic acid products of cyclooxygenase in endothelium-dependent relaxation was examined. Endothelium removal from rabbit corpora was performed by infusion with 3-[(3-cholamidopropyl)-dimethylammonio]-1-propane sulfonate and was confirmed by transmission electron microscopy. Strips of human and rabbit corporal tissues were studied in the organ chambers for isometric tension measurement. The accumulation of cyclic guanosine monophosphate (cGMP) and the release of eicosanoids from corporal tissue was measured by radioimmunoassay and correlated to smooth muscle relaxation. Our study showed that relaxation of corpus cavernosum tissue to acetylcholine, bradykinin and substance P was endothelium-dependent; potentiated by indomethacin; and inhibited by NG-monomethyl-L-arginine, methylene blue or LY83583. Relaxation to papaverine and sodium nitroprusside was endothelium-independent, and unaffected by NG-monomethyl-L-arginine. Relaxation to vasoactive intestinal polypeptide was partially endothelium-dependent; potentiated by indomethacin; attenuated by NG-monomethyl-L-arginine or methylene blue. The tissue level of cGMP was enhanced by acetylcholine and nitric oxide. Methylene blue inhibited both basal and drug-stimulated levels of cGMP. The release of eicosanoids was enhanced by acetylcholine and blocked by indomethacin. In conclusion, nitric oxide or a closely related substance accounts for the activity of endothelium-derived relaxing factor in the corporal tissue. Inhibition of the release of eicosanoids potentiates the relaxing effect of nitric oxide. Nitric oxide increases tissue cGMP which appears to modulate corporal smooth muscle relaxation.

Endothelium-derived relaxing factor: basic review and clinical implications

EDRF is a potent, endogenous vasodilator that is produced and released from endothelial cells and subsequently causes the relaxation of VSM through the activation of soluble guanylate cyclase and an increase in VSM cyclic GMP. Structurally, EDRF is likely to be NO or a related nitrogen oxide-containing compound. It is synthesized in endothelial and other cell types from L-arginine by a calcium-calmodulin and NADPH-dependent enzyme. Its action is very similar to the nitrovasodilators that act directly on VSM. EDRF is present in all vascular beds, large and small vessels, and in a wide range of species. Its role in human vascular physiology and pathophysiology is just beginning to be understood. EDRF is a potent endogenous vasodilator and inhibitor of platelet aggregation and adhesion. Its activity is impaired in hypertension and atherosclerosis, and its absence due to endothelial damage may play a role in cerebral and coronary vasospasm. It is a mediator of flow-dependent vasodilation, and its inhibition by hypoxia may contribute to the hypoxic pulmonary vasoconstrictor response. Endothelial cell damage and impairment of EDRF production may also contribute to acute and chronic pulmonary hypertension. A further understanding of the chemical nature and synthetic pathways of EDRF should lead to the production of analogs and antagonists, which may play an important role in future treatments for atherosclerosis, myocardial infarction, angina, hypertension, and other vascular diseases. The recent realization that EDRF serves as the second messenger for guanylate cyclase activation and cyclic GMP production in a variety of cell types outside of the cardiovascular system, including renal and respiratory epithelium, cerebellar neurons, macrophages, and adrenocytes, suggests even broader implications. The importance of EDRF to the anesthesiologist may go beyond an understanding of its role in cardiovascular physiological and pathophysiological states. Initial studies have shown that the endothelium may play a role in mediating the vascular actions of anesthetics, and that anesthetics can inhibit the production, release, or action of EDRF. How are these interactions mediated? Are there significant differences between anesthetics with regard to their effects on EDRF? Is there a clinically significant effect of anesthetics on basal activity of EDRF, or only in response to exogenous stimulation? Conversely, it is important to determine if alterations in endothelial cell function by various disease states such as hypertension, atherosclerosis, adult respiratory distress syndrome, cerebral vasospasm, and others cause changes in the vascular actions of anesthetics. The potential interactions of anesthetics with EDRF production and action in cell types other than the endothelium have not yet been explored.(ABSTRACT TRUNCATED AT 400 WORDS)

Does EDRF/NO regulate its own release by increasing endothelial cyclic GMP?

EDRF/NO released from bovine aortic endothelial cells was measured by transferring conditioned medium to rat fetal lung fibroblasts (RFL-6 cells). These cells contain considerable amounts of soluble guanylyl cyclase. The increase in cyclic GMP in these cells provided a sensitive bioassay for EDRF/NO activity. Bovine aortic endothelial cells released a material that markedly enhanced cyclic GMP in RFL-6 cells. The synthesis of this substance could be stimulated with bradykinin (10 nM) or Ca2+ ionophore A23187 (1 microM) and was completely prevented by treatment of the endothelial cells with the EDRF/NO synthesis inhibitor, NG-L-arginine (100 microM), or incubation of the RFL-6 detector cells with the inhibitor of soluble guanylyl cyclase, methylene blue (10 microM). The release of EDRF/NO by bradykinin and A23187 was accompanied by an about two-fold increase in the cyclic GMP content in the producing endothelial cells. Incubation of bovine aortic endothelial cells with atrial natriuretic peptide (0.1 microM) or sodium nitroprusside (10 microM) enhanced their cyclic GMP content 6.5-fold and 4.1-fold, respectively. These increases in endothelial cyclic GMP levels had no effect on basal or bradykinin- and A23187-stimulated release of EDRF/NO. We conclude that cyclic GMP does not feed back on EDRF/NO formation or release in bovine aortic endothelial cells.

Neurokinin A induces expression of the c-fos, c-jun, and c-myc genes in rat smooth muscle cells

Neurokinin A, a member of the tachykinin family of neuropeptides, has been identified as a mitogen for cultured smooth muscle cells. Tachykinin-induced DNA synthesis has previously been shown to be mediated by a receptor-specific mechanism and to correlate with accumulation of phosphatidylinositol 4,5-bisphosphate breakdown products. In the present experiments, we have studied intracellular pH and expression of the proto-oncogenes c-myc, c-jun and c-fos in smooth muscle cells exposed to mitogenic concentrations of neurokinin A. Growth-arrested smooth muscle cells stimulated with neurokinin A responded with an amiloride-sensitive intracellular alkalinization, indicating Na+/H+ antiport activation. c-myc and c-jun mRNA expression was only slightly elevated by neurokinin A, while c-fos expression underwent a more pronounced increase. Maximal levels of c-fos transcripts were found after 15 min and 30 min following neurokinin A stimulation. The results demonstrate that neuropeptides may influence proto-oncogene expression in smooth muscle cells and suggest a mechanism by which peripheral neurons may modulate differentiation and growth of these cells.

Mono-L-arginine-containing compounds dilate piglet pial arterioles via an endothelium-derived relaxing factor-like substance

We determined the effects of mono-L-arginine-containing compounds on pial arterioles of anesthetized piglets. A closed cranial window was implanted, and the diameter of one pial arteriole was determined by intravital microscopy. Diameter was determined during application of artificial cerebrospinal fluid containing no drugs and during application of 10(-5), 10(-4), 10(-3), and 10(-2) M L-arginine (ARG), L-arginine ethyl ester (AEE), N alpha-benzoyl-L-arginine (NBA), N alpha-benzoyl-L-arginine ester ethyl (BAEE), and L-citrulline (CIT). Initial diameters were 100-200 microns. All of these compounds dilated arterioles, but the threshold concentration needed to elicit dilation varied: 10(-5) M for NBA (n = 5), 10(-3) M for AEE (n = 9) and BAEE (n = 6), and 10(-2) M for ARG (n = 6) and CIT (n = 4). Maximal responses were 15 +/- 8% for CIT, 17 +/- 4% for ARG, 19 +/- 8% for BAEE, 28 +/- 5% for NBA, and 27 +/- 6% for AEE. Indomethacin pretreatment (5 mg/kg i.v.) did not change arteriolar responses to AEE, NBA, and BAEE. However, coadministration of methylene blue (0.5 x 10(-4) M or 0.5 x 10(-3) M) abolished dilation to 10(-3) M AEE or BAEE and attenuated dilation to 10(-5) M NBA. In addition, coadministration of hemoglobin (0.4 x 10(-4) M) abolished dilation to AEE, BAEE, or NBA. Last, intravenous (5 mg/kg) and coadministration (10(-3) M) of NG-methyl-L-arginine blocked dilation to NBA or AEE. We conclude that mono-L-arginine-containing compounds produce pial arteriolar dilation in piglets, possibly involving an endothelium-derived relaxing factor.

Evidence for muscarinic receptors in endothelial cells from combined functional and binding studies

The aim of this study was to characterize muscarinic receptors of the bovine coronary artery by means of a combination of mechanical relaxation and contraction responses and radioligand binding data. Fresh helical strips of bovine coronary artery with intact endothelium relaxed in response to low concentrations (0.03-1 microM) of acetylcholine (ACh) and contracted at higher concentrations while endothelium-denuded strips only contracted. The ED50 for relaxation was 0.13 microM and that for contraction 1.8 microM (without endothelium); in the presence of endothelium, contraction dose-response curves were shifted to the right and the maximum contraction was reduced. In order to determine the location of the receptors mediating vasorelaxation, apparent affinity constants (KA) of ACh for relaxant and contractile effects were determined by irreversible blockade of a fraction of receptors with propyl benzilylcholine mustard (PBCM). The affinity constants (KA) were 0.22 microM for relaxation and 13 microM (with endothelium) and 20 microM (without endothelium) for contraction. In competition binding experiments against the muscarinic antagonist, [3H]N-methylscopolamine ([3H]NMS), the apparent affinity (KI) of ACh for binding sites in homogenates of endothelium-free coronary artery was 16 microM which was not different from the affinity constant determined in functional contraction experiments. Thus, the affinity constant of ACh determined for relaxation responses with endothelium-preserved vessels had no correlate in the binding affinity as determined with endothelium-free arteries. These findings indicate that bovine coronary arteries are relaxed by ACh through muscarinic receptors located on the endothelium whereas contractions are mediated by receptors on smooth muscle cells.

Blood vessel structure and function: a brief update on recent advances

This article briefly reviews recent advances in knowledge of the histology and function of blood vessels. It focuses upon the multifunctional roles of endothelium and smooth muscle cells. Particular reference is made to the synthesis of a number of factors now known to be involved in maintenance of the integrity of the vessel wall and the initiation of arterial disease. The cells of the vascular wall are much more versatile and dynamic than previously thought.

Effects of clenbuterol treatment on the responses to vasodilators in urethane-anaesthetized rats

Seven or 14 days of treatment with the beta 2-adrenoceptor agonist clenbuterol, 0.3 mg kg-1, s.c., twice daily, increased the basal mean blood pressure in normotensive urethane-anaesthetized rats. The elevated pressure values were maintained until 48 h after the end of the 14 day treatment. Clenbuterol treatment decreased the vasodilatory responses to the beta-adrenoceptor agonist isoprenaline and adenosine, agents which act through an increase in intracellular cyclic AMP. Decreased responses were maintained until 48 h after a 14 day treatment with clenbuterol. On the other hand, its administration to rats for 14 days did not modify the vasodilator responses to acetylcholine or sodium nitroprusside, two agents that exert their effects by enhancing cyclic GMP. The increase in mean blood pressure in urethane-anaesthetized rats after clenbuterol treatment may be a consequence of a reduced vasodilator beta 2-adrenoceptor-mediated response to circulating catecholamines.

The salvage of rabbit ischaemic epigastric free flaps using the vasodilator calcitonin gene-related peptide

The rabbit epigastric free flap, subjected to 21 hours of warm (25 degrees C) ischaemia, was used as an experimental model to test the ability of two endothelium-dependent vasodilators, calcitonin gene-related peptide (CGRP) and carbamyl beta-methylcholine chloride (MCh, bethanechol chloride, the stable acetylcholine analogue) to improve flap viability. After the period of ischaemia, flaps were infused intra-arterially with either Hanks balanced salt solution (controls), CGRP or MCh for 30 minutes, and received additional intravenous boluses of these drugs at 2 and 32 minutes after revascularisation. The area of flap surviving improved significantly (p less than 0.025) from 39.9% (n = 18) for controls to 70.2% (n = 14) for CGRP treatment at 2 micrograms/kg, but was unchanged at 47.1% (n = 14) for MCh treatment at 50 micrograms/kg. Both CGRP and MCh significantly increased blood flow (p less than 0.05) resulting in 34% lower peripheral resistances compared with controls. These results suggest that CGRP has considerable clinical potential for the salvage of ischaemic flaps. CGRP must have several, as yet undefined, beneficial effects on the ischaemic tissue, since MCh invoked a vasodilatory response but failed to salvage ischaemic flaps.

Endothelium-dependent mechanical properties of the carotid artery in WKY and SHR. Role of angiotensin converting enzyme inhibition

An experimental model of in situ isolated carotid arteries has been used to evaluate the static mechanical properties of the arterial wall in 12-week-old Wistar-Kyoto rats (WKY) and spontaneously hypertensive rats (SHR). The effects of endothelium removal and of local incubation with the converting enzyme inhibitor lisinopril (ICI Pharma 209000) on the carotid compliance (CC) were compared with the effects of total abolition of the vascular smooth muscle tone by potassium cyanide. CC measured for pressures ranging from 50 to 175 mm Hg had maximal values (0.22 +/- 0.07 microliter/mm Hg and 0.13 +/- 0.03 microliter/mm Hg, respectively, for WKY and SHR, p less than 0.001) for pressure values close to the operating pressures in both groups. Maximal values of CC were increased by 35% and 45% in WKY and SHR, respectively, after potassium cyanide poisoning (p less than 0.01). The endothelium removal induced a significant increase in CC compared with their control values (+37%, p less than 0.01, and +25%, p less than 0.01, respectively, in WKY and SHR). CC measured after endothelium removal did not significantly differ from its values measured after potassium cyanide poisoning in normotensive animals. In contrast, in hypertensive animals, CC was significantly lower after endothelium, removal than after potassium cyanide poisoning (p less than 0.01). In the presence of intact endothelium, local incubation with converting enzyme inhibitor increased CC by 23% (p less than 0.05) in WKY rats and by 14% (p less than 0.01) in SHR. In contrast, after endothelium removal, converting enzyme inhibitors did not significantly increase further CC in either strain.(ABSTRACT TRUNCATED AT 250 WORDS)

Role of endothelium-formed nitric oxide on vascular responses

1. Endothelial cells of blood vessels generate factors which can modulate underlying smooth muscle tone, inducing vasorelaxation, (endothelium-derived relaxing factor, EDRF, and endothelium-derived hyperpolarizing factor) and/or vasoconstriction (endothelium-derived contracting factors, EDCFs, including the peptide endothelin). 2. EDRF is nitric oxide (NO) or a RNO compound from which this oxide is released. Its half-life is very short (6-50 sec), and it produces rapid vasodilations and inhibits platelet aggregation. 3. NO is formed from the terminal guanidino of L-arginine, but not of D-arginine. NO effects and NO formation are inhibited by NG-monomethyl-L-arginine (L-NMMA), but not by D-NMMA. These inhibitory effects are blocked by L-arginine. 4. Removal of endothelium or pathological situations that can induce endothelial dysfunction (atherosclerosis, diabetes, hypertension or subarachnoid hemorrhage) cause increases on the vascular contractility elicited by agonists (noradrenaline, serotonin, EDCFs, etc.). These findings suggest that EDRF produces a physiological inhibitory modulation of vascular smooth muscle tone and its alteration produces or facilitates the development of diseases such as hypertension or coronary and cerebral vasospasm.

Endothelium-derived contractile factors

1. Vascular endothelium releases different substances (endothelium-derived contractile factors, EDCFs), which mediate vasoconstrictor responses induced by several agents. 2. Clear differences have been reported in endothelium-dependent contractions, which suggest at least three distinct EDCFs, named EDCF1, EDCF2 and EDCF3, respectively. 3. EDCF1 is a cyclooxygenase metabolite(s) of arachidonic acid. EDCF2 is a polypeptide released from cultured endothelial cells. It has been isolated and identified as a 21-amino acid peptide called endothelin, which is described as the most potent vasoconstrictor agent known to date. EDCF3 is an unidentified contractile factor(s), which is neither EDCF1 nor EDCF2. 4. The physiological role of these endothelial contractile factors is not yet clear. However, they have been implicated in the local mechanisms involved in blood flow regulation, as well as in some pathological conditions, such as hypertension or cerebral vasospasm.

Effect of calcium on endothelium-derived relaxing factor formation and cGMP levels in endothelial cells

Various stimulants of the release of EDRF (endothelium-derived relaxing factor) increased intracellular cGMP levels in bovine aortic endothelial cells. ATP was the most effective compound tested, increasing cGMP 7-fold, followed by the calcium ionophore, A23187 (4.8-fold), and bradykinin (4.0-fold). The EC50 values were similar to those obtained when EDRF release was measured with the bioassay technique, which suggests a stimulation of endothelial guanylate cyclase by EDRF. The direct acting stimulants of soluble guanylate cyclase, sodium nitroprusside and SIN-1 (3-morpholino-sydnonimine), also increased the cGMP content of endothelial cells by 9.4 and 7.2 times, respectively. The effects of both groups of stimulants on cGMP levels were antagonized by the lipoxygenase inhibitor, nordihydroguaiaretic acid, and by the radical scavenger, phenylbutylnitrone, whereas gossypol or canavanine only antagonized the EDRF-induced effect on endothelial cGMP levels. Bradykinin, ATP and A23187 also increased the uptake of 45CaCl2 into endothelial cells but since the complete removal of extracellular Ca2+ or blockade of Ca2+ transport by LaCl3 did not affect the ability of these compounds to elevate cGMP levels, the formation of EDRF appears not to be triggered by an influx of extracellular calcium. This study provides evidence that EDRF stimulators enhance cGMP levels in endothelial cells, probably due to a direct activation of guanylate cyclase by EDRF.

Regulation of Na-K-Cl cotransport in endothelial cells by atrial natriuretic factor

Many vasoactive agents have been shown to bind to specific receptors on endothelial cells. Among these is atrial natriuretic factor (ANF). Binding of ANF to endothelial cells has been demonstrated to induce elevation of intracellular guanosine 3',5'-cyclic monophosphate (cGMP). Other vasoactive agents have been shown to cause elevation of intracellular adenosine 3',5'-cyclic monophosphate (cAMP), Ca, and diacylglycerol. However, the endothelial cell response that occurs subsequent to elevation of cGMP or other second messengers is not well understood. Recently, endothelial cells have been shown to possess a Na-K-Cl cotransport system that is stimulated by vasopressin and bradykinin and inhibited by isoproterenol. Thus it is possible that modulation of Na-K-Cl cotransport may play a role in the endothelial cell response to second messengers that are elevated by ANF and other vasoactive agents. This possibility was examined in the present study by evaluating the effects of a variety of vasoactive agents and their second messengers on endothelial cell Na-K-Cl cotransport. Cotransport was assessed as bumetanide-sensitive K influx in cultured bovine aortic endothelial cells. A number of agents were found to reduce Na-K-Cl cotransport, including ANF, acetylcholine, histamine, and norepinephrine. Cotransport was found to be stimulated by angiotensin II, as well as vasopressin and bradykinin. Na-K-Cl cotransport was also inhibited by elevation of intracellular cGMP or cAMP or by treatment of the cells with phorbol ester to activate protein kinase C. However, A23187-induced elevation of intracellular Ca caused stimulation of Na-K-Cl cotransport.(ABSTRACT TRUNCATED AT 250 WORDS)

Mechanism of action of EDRF on pressurized arteries: effect on K+ conductance

Experiments were performed to study the cellular mechanism of endothelium-derived relaxing factor (EDRF) on vascular smooth muscle. Rat femoral arteries were cannulated and pressurized to 100 mm Hg. Vascular smooth muscle membrane potential (Em) and diameter responses to perfusion with 5 x 10(-6) M acetylcholine (ACh) were measured in vessels precontracted with 5 x 10(-6) M norepinephrine (NE). Hyperpolarization (-35 +/- 1.2 to -66 +/- 2.0 mV) and dilation were observed during ACh administration. Both responses were abolished on removal of the endothelium with collagenase. A bioassay was developed in which two vessel segments from the same artery were connected in series. The downstream vessel was deendothelialized while the endothelium of the upstream vessel remained intact. The protocol used was the same as in the first set of measurements. Hyperpolarization and dilation were observed in both vessels during ACh perfusion. However, when the direction of the perfusate flow in the bioassay system was reversed so that the deendothelialized vessel was upstream, only the "endothelium-intact" vessel demonstrated vascular smooth muscle hyperpolarization. To examine the ionic mechanism underlying the hyperpolarization presumably by released EDRF, the Em was measured as a function of increasing extracellular potassium ([K+]o). In the presence of ACh (but not NE) the maximum depolarization produced by a decade increase of [K+]o (10-100 mM) was 50 mV. In the deendothelialized vessel, this depolarization was decreased significantly to 39 mV. Addition to the superfusate of 10 mM tetraethylammonium, a K+ channel blocker, significantly reduced the hyperpolarization caused by ACh-induced EDRF release.(ABSTRACT TRUNCATED AT 250 WORDS)

Culture of human corpus cavernosum endothelium

A method for culturing endothelial cells (HCC-EC) from surgical specimens of human corpus cavernosum has been developed. The approach involves selective endothelial outgrowth from explants and may be generally applicable to tissues whose endothelium is not amenable to isolation by routine mechanical or enzymatic methods. The tissue is minced into pieces which are placed onto gelatin- or fibronectin-coated tissue culture plastic, and grown in medium suitable for microvascular endothelial cell growth (Carson and Haudenschild, In Vitro 22:344-354, 1986). By Days 5 to 7 EC colonies are found. Within a day or two after the appearance of the EC colonies, a non-EC cell type appears and, if undisturbed, quickly overgrows the EC. An exploitable temporal separation between the emergence of EC and non-EC is obtained when both conditioned medium (from bovine aortic endothelium) and retinal extract are present during the outgrowth period. Explants are removed by pipetting at the first sign of the emergence of the non-EC cell type. Once isolated, HCC-EC do not require conditioned medium but do require either retinal extract or acidic fibroblast growth factor for survival and growth. Approximately 60% of the first passage cultures are at least 80% EC as judged by DiI-Ac-LDL labeling. One corpus (0.3 x 0.3 x 0.5 cm) usually produces 120 cm2 of primary culture within 2 wk. These EC form contact-inhibited monolayers and stain positively for Factor VIII. They have a doubling time at 6th passage of 48 h and a plateau density of 5 to 7 x 10(4) cells/cm2. The availability of such cultures should facilitate the study of endothelium-mediated responses which play an important role in the erectile function of human penile corpus cavernosum.

Impaired canine coronary vasodilator response to acetylcholine and bradykinin after occlusion-reperfusion

Previous studies indicate impairment of coronary arterial ring relaxation in response to acetylcholine (ACh) following coronary reperfusion, mediated via loss of endothelium-derived relaxing factor (EDRF). To examine if coronary vasodilator reserve is reduced following coronary occlusion-reperfusion in intact animals, 16 open-chest mongrel dogs were subjected to 1 hour of total left circumflex (Cx) coronary artery occlusion followed by reperfusion for 1 hour. Prior to Cx occlusion, coronary blood flow increased and vascular resistance decreased (both p less than or equal to 0.01) in response to ACh and bradykinin (BK). Following reperfusion, increase in Cx coronary flow in response to both vasodilators was significantly (p less than or equal to 0.01) impaired. Myocardial histology showed extensive neutrophil infiltration and capillary plugging by neutrophils in the Cx compared with the left anterior descending coronary artery-supplied myocardium. Myocardial myeloperoxidase activity was also increased in the Cx compared with the left anterior descending region (p less than or equal to 0.02). Pretreatment of four dogs with indomethacin partially reduced the vasodilator response to BK but not to ACh. However, indomethacin did not affect reperfusion-induced attenuation of BK or ACh's coronary vasodilator effects. To determine if calcium blocker verapamil would modify reperfusion-induced impairment in coronary vasodilator reserve, six dogs were treated with verapamil. Although verapamil enhanced coronary vasodilator effects of ACh and BK, it did not modify reperfusion-induced attenuation of coronary vasodilator reserve. Myocardial neutrophil accumulation and myeloperoxidase activity was also similar in control, indomethacin, and verapamil-treated dogs. These observations suggest that coronary reperfusion impairs coronary vasodilator reserve in intact dogs. This impairment is not modified by prostaglandin inhibition or by calcium blockade. Besides loss of EDRF, capillary plugging by neutrophils may contribute to the altered coronary flow reserve observed in the immediate post-reperfusion period. Furthermore, indomethacin or verapamil are not effective in modifying the reperfusion-related impairment of coronary vasodilator reserve.

Augmentation of hypoxic pulmonary vasoconstriction in the isolated perfused rat lung by in vitro antagonists of endothelium-dependent relaxation

The role of the endothelium in hypoxic constriction of the intact pulmonary vascular bed has not been clearly elucidated. To test for a possible role for endothelium-derived relaxing factor(s) (EDRF) in the hypoxic pressor response, isolated, whole blood-perfused rat lungs from male Sprague-Dawley rats treated with meclofenamate were prepared. Three protocols were performed, including: (a) normal saline (control); (b) the putative EDRF inhibitors, eicosatetraynoic acid (ETYA, 1 X 10(-4) M) or nordihydroguaiaretic acid (NDGA, 1 X 10(-4) M) versus vehicle DMSO; and (c) the putative EDRF inhibitor hydroquinone (HQ, 1 X 10(-4) M) versus vehicle ethyl alcohol (ETOH). The pulmonary pressor response to angiotensin II (Ang II, 0.25 micrograms) injections alternated with 6-min periods of hypoxic ventilation (3% O2, 5% CO2) was measured before and after the administration of saline, inhibitors, or vehicles. The administration of the EDRF inhibitors ETYA, NDGA, and HQ resulted in a marked accentuation of the hypoxic pressor response that was not seen in the controls (P less than 0.05). In separate experiments, lungs precontracted with norepinephrine (1 X 10(-6) M) were pretreated with edrophonium (1 X 10(-4) M) and then observed for endothelium-dependent vasodilator responses to acetylcholine at increasing doses (1 X 10(-7)-1 X 10(-4) M). Administration of ETYA, NDGA, or HQ abrogated the observed vasodilatation to acetylcholine, which was not seen with vehicles alone (P less than 0.01). These studies suggest an important role for the endothelium in pulmonary vascular responsiveness to alveolar hypoxia through possible release of a relaxing factor(s) that attenuates the degree of pulmonary arterial constriction.

External ATP triggers a biphasic activation process of a calcium-dependent K+ channel in cultured bovine aortic endothelial cells

We have used the patch-clamp method in order to investigate the single-channel events underlying the effect of external ATP on the potassium permeability of bovine aortic endothelial cells (BAE). The results obtained from cell-attached and inside-out experiments led first to conclude that BAE cells possess an inward rectifying potassium channel activated by internal calcium at micromolar concentrations. The channel conductance for inward currents was estimated at 40 pS in symmetrical 200 mM KCl and the open-channel probability was found to be voltage insensitive within the membrane voltage range -50 to -100 mV. Based on results obtained in the cell-attached configuration, it could next be established that external ATP and ADP at micromolar concentrations could trigger, via the stimulation of P2 purinergic receptors, a time variable activation process of the observed calcium-dependent potassium channel. This activation process was found to occur in a biphasic manner with an initial phase independent of the presence of calcium in the cell bathing medium. The second phase which could be blocked by calcium channel blockers such as Co2+ or La3+ required, however, the presence of external calcium and could be abolished by depolarizing the cells using high K+ external solutions. Another important aspect related to this phenomenon was the observation that removing ATP from the external medium during the second phase led to a complete abolition of the associated calcium-dependent potassium channel activation process. It is suggested from these results that the action of ATP on the potassium permeability of BAE cells is related to a second messenger mediated release of calcium from internal calcium stores coupled to an ATP-dependent calcium influx abolished at depolarizing voltages.

Endothelium-dependent modulation of the pressor activity of arginine vasopressin in the isolated superior mesenteric arterial bed of the rat

1. Pressor responses to arginine vasopressin (AVP) were determined in the rat isolated superior mesenteric arterial bed perfused with Krebs-Henseleit solution and compared with those to noradrenaline. 2. In control preparations the maximum pressor response to the peptide was 34 +/- 3 mmHg and the ED50 was 21 +/- 4 mu (n = 11). The maximal pressor response to noradrenaline (30 micrograms) was 100 +/- 6 mmHg (n = 8). After removal of the functional endothelium with the detergent CHAPS, the maximum pressor response to AVP increased to 64 +/- 4 mmHg and the ED50 decreased to 7.7 +/- 2.0 mu (n = 11) but the response to 10 micrograms noradrenaline was unaffected. 3. Nordihydroguaiaretic acid (2.5 microM) significantly increased the maximum pressor response to AVP from 41 +/- 2 mmHg to 86 +/- 8 mmHg (n = 9); the ED50 was unchanged. Methylene blue (50 microM) also increased the maximum response from 41 +/- 3 mmHg to 87 +/- 13 mmHg (n = 8) without affecting the ED50. Neither treatment significantly affected the response to 10 micrograms noradrenaline. 4. Neither indomethacin (10 microM) nor BW755C (10 microM) had significant effects upon either the maximal response or ED50 for AVP nor did they affect the response to 10 micrograms noradrenaline. 5. In 6 preparations SKF-525A significantly increased both the ED50, from 9.8 +/- 2.1 to 22 +/- 2 mu, and the maximum response, from 36 +/- 2 to 70 +/- 3 mmHg. 6. It is concluded that the pressor response to AVP in this vascular bed is modulated, in the presence of functional endothelium, by the simultaneous release of endothelium-derived relaxing factor.

An autoradiographic study of muscarinic cholinoceptors in blood vessels: no localization on vascular endothelium

In vitro labelling and autoradiographic techniques were used to examine the localization of [3H]quinuclidinyl benzilate ([3H]QNB) and [125I]4-iodo-QNB ([125I]4IQNB) to slide-mounted sections of rabbit aorta and pulmonary artery, cat aorta, pulmonary and superior mesenteric arteries. These vessels all respond to acetylcholine (ACh) with endothelium-dependent relaxation, yet there was no evidence for endothelium-related binding of either [3H]QNB or [125I]4IQNB. Muscarinic receptors were localized over the medial smooth muscle and, in the rabbit pulmonary artery, the density of binding increased towards the adventitia. Binding of either radioligand to sections of rabbit pulmonary artery was not affected by the muscarinic M1 receptor antagonist pirenzepine (20 nM) but was markedly reduced by the muscarinic M2 antagonist 4DAMP (4-diphenylacetoxy-N-methyl-piperidine methobromide) (1 nM). This study provides evidence for muscarinic receptors located directly on smooth muscle cells, indicating that endothelium-dependent relaxation to ACh results from an indirect mechanism involving smooth muscle muscarinic receptors.

Release of arachidonic acid from vascular endothelial cells: fatty acyl specificity is observed with receptor-mediated agonists and with the calcium ionophore A23187 but not with melittin

Vascular endothelial cells respond to a variety of physiological and pharmacological stimuli by releasing free arachidonic acid from membrane phospholipids, thus initiating synthesis of prostacyclin. Previous work in our laboratory has demonstrated that the thrombin-stimulated deacylation is specific for arachidonate and structurally similar polyunsaturated fatty acids that contain a delta-5 double bond. We now report that histamine, bradykinin, and the calcium ionophore A23187 exhibit the same fatty acid specificity as does thrombin. Experiments with both human umbilical vein and calf pulmonary artery endothelial cells indicate that these agonists stimulate the release of previously incorporated [14C]arachidonate but not 8,11,14-[14C]eicosatrienoate or [14C]docosatetraenoate. By contrast, melittin stimulates the release of 8,11,14-eicosatrienoate, docosatetraenoate, and oleate as well as arachidonate. These results suggest that histamine, bradykinin, and A23187 activate a common calcium-dependent phospholipase A2. Melittin appears either to alter the substrate specificity of the receptor-linked phospholipase A2 activity or to activate additional enzymes as well.

Pharmacology of penile erection in humans

The pharmacologic aspects of erection, including neuropharmacology and erectile responses to exogenous agents, are reviewed. The pharmacology of erection is complex and still incompletely understood. Older evidence suggesting acetylcholine as the primary neurotransmitter has been shown to be insufficient. Our recent experiments utilizing strips of human corpus cavernosum indicate the need to consider the roles of other erectogenic substances, such as vasoactive intestinal polypeptide, endothelium-derived relaxation factor (EDRF), and prostaglandins. From the results of these studies, three stages in the development of an erection are postulated: (1) withdrawal of alpha-adrenergic neuromuscular activity, (2) inhibition of alpha-adrenergic neuromuscular activity by endogenous substances such as prostaglandin E1 and vasoactive intestinal polypeptide, and (3) activation of NANC neurotransmission and direct relaxation of smooth muscle by endogenous substances such as EDRF.