J. Van de Voorde

Endothelium-dependent relaxation and hyperpolarization in aorta from control and renal hypertensive rats.

Endothelium-dependent relaxations are depressed in hypertension. In this study we investigated the possible involvement of endothelium-dependent smooth muscle hyperpolarization in this phenomenon. In isolated aortic segments from control rats, acetylcholine (10(-8)-10(-5) M) elicits relaxations after precontraction with norepinephrine (10(-7) M), and acetylcholine or carbachol (10(-5) M) induce smooth muscle hyperpolarization (10.6 +/- 0.9 mV). Both effects disappear after removal of the endothelium and are depressed by tetraethylammonium (3 x 10(-3) M), a rather nonspecific blocker of K+ channels, but not by glibenclamide (10(-5) M), a potent blocker of the ATP-regulated K+ channels, which has a marked effect on the relaxation induced by BRL 38227. The relaxation effect of acetylcholine is impaired in norepinephrine-contracted preparations from hypertensive rats but is not further depressed by tetraethylammonium. In aorta from hypertensive rats, hyperpolarization induced by carbachol was significantly reduced to a mean of only 21.8% of the values obtained in preparations from normotensive rats. From the relaxation-hyperpolarization relation obtained with BRL 38227 (opening K+ channels), it is derived that the endothelium-dependent hyperpolarization (approximately 10 mV) contributes for at least 20-30% of the maximal relaxation effect of acetylcholine on rat aorta. It is concluded that the diminished endothelium-dependent hyperpolarization may contribute to the depression of the endothelium-dependent relaxation in hypertension.

Release of endothelium-derived relaxing factor from human umbilical vessels.

The ability of human umbilical endothelial cells to release relaxing substance(s) in response to different agonists was investigated. Endothelium-denuded aortic rings of rats were used for the bioassay and tension recording. After precontraction, this preparation showed no response to histamine, acetylcholine, A 23187, or adenosine triphosphate while serotonin elicited further contraction. Superfusion of the precontracted preparations with the perfusate from umbilical veins and arteries stimulated with histamine (10(-7)-10(-5) M), A23187 (10(-7)-10(-6) M), or adenosine triphosphate (10(-5)-10(-4) M) elicited a relaxation. No relaxation was obtained with acetylcholine (10(-8)-10(-6) M) or serotonin (10(-8)-10(-6) M). The relaxation of bioassay aortic rings under the influence of the perfusate from histamine-stimulated umbilical vessels was inhibited by mepyramine (10(-5) M) but not by cimetidine (10(-4) M) suggesting the involvement of H1-receptors. The relaxation was also inhibited by increasing the transit time between the donor and the detector preparation, by methylene blue (5 X 10(-5) M), and by nordihydroguaiaretic acid (5 X 10(-5) M) but not by indomethacin (5 X 10(-5) M), and which have been reported for endothelium-derived relaxing factor. The involvement of umbilical endothelial cells in the relaxation response was further confirmed by studying precontracted, rubbed rat aortic rings seeded with cultured endothelial cells from human umbilical veins. Such preparations relaxed in response to histamine (10(-7)-10(-4) M) in contrast with the control preparations. No relaxations of these preparations were observed in response to acetylcholine (10(-9)-10(-6) M).(ABSTRACT TRUNCATED AT 250 WORDS)

The impaired renal vasodilator response attributed to endothelium-derived hyperpolarizing factor in streptozotocin – induced diabetic rats is restored by 5-methyltetrahydrofolate

Aims/hypothesis. Endothelial dysfunction contributes to the development of diabetic vascular complications. A better understanding of the pathophysiology of endothelial dysfunction in diabetes could lead to new approaches to prevent microvascular disease. Methods. Endothelium-dependent and endothelium-independent vasodilator responses were investigated in the renal microcirculation of streptozotocin-induced diabetic rats. We measured renal blood flow changes with an electromagnetic flow probe. In addition, the responses of the different segments of the renal microcirculation were evaluated with videomicroscopy using the hydronephrotic kidney technique. Because endothelial cells release different relaxing factors (nitric oxide, prostacyclin and an unidentified endothelium-derived hyperpolarizing factor), responses to acetylcholine were measured before and after treatment with the nitric oxide synthase inhibitor l-NG-nitroarginine methylester HCI (l-NAME) and the cyclooxygenase inhibitor indomethacin. We evaluated with the effect of 5-methyltetrahydrofolate, the active form of folate, on the responses. Results. The l-NAME- and indomethacin-resistant vasodilation to intra-renal acetylcholine was significantly reduced in the diabetic compared with control rats, suggesting impaired endothelium-derived hyperpolarizing factor-mediated vasodilation. The responses to the nitric oxide donor (Z)-1-[-2-(aminoethyl)-N-(2-ammonioethyl)amino]diazen-1-ium-1,2-diolate (DETA-NONOate) and to the K+-channel opener pinacidil were similar in diabetics and controls, indicating intact endothelium-independent vasodilator mechanisms. The contribution of endothelium-derived hyperpolarizing factor to vasodilation induced by acetylcholine was greatest in the smallest arterioles. In diabetic rats, the response to acetylcholine was increasingly impared as vessel size decreased. Defective vasodilation in diabetic kidneys was rapidly normalized by 5-methyltetrahydrofolate. Conclusion-interpretation. Endothelium-derived hyperpolarizing factor-mediated vasodilation is impaired in the renal microcirculation of diabetic rats, in particular in the smallest arteries. Treatment with folate restores the impaired endothelial function in diabetes. [Diabetologia (2000) 43: 1116–1125]

CONTRIBUTION OF NITRIC-OXIDE TO THE ENDOTHELIUM-DEPENDENT HYPERPOLARIZATION IN RAT AORTA.

1. The effect of endogenous and exogenous nitric oxide on the membrane potential (Em) of smooth muscle cells of the thoracic aorta of rats was investigated. 2. In tissues with intact endothelium, application of ACh or carbachol generated a change of the membrane potential consisting of an initial hyperpolarization by 10‐12 mV, followed by a partial recovery toward a level which was at 10 min still 6‐8 mV more negative than in control conditions. 3. Application of NG‐nitro‐L‐arginine methylester (L‐NAME), an inhibitor of endogenous NO production, had no significant effect on the resting membrane potential. The initial peak endothelium‐dependent hyperpolarization elicited by ACh or carbachol was not significantly diminished. However, the recovery was more accentuated. Similarly, NG‐monomethyl‐L‐arginine (L‐NMMA) significantly diminished the second component of the endothelium‐dependent hyperpolarization without affecting the magnitude of the first transient peak Em change. 4. Nitroglycerin produced a small sustained hyperpolarization of 1‐2 mV, and the NO donor SIN‐1, the active metabolite of molsidomine, similarly increased Em by about 1 mV. Infusion of high doses of acidified NaNO2 solution caused a hyperpolarization smaller than that evoked by ACh or carbachol. 5. 8‐Bromo‐cyclic GMP caused little change of membrane potential. In the presence of 8‐Br‐cGMP, ACh evoked a membrane electrical response similar to that observed in the absence of the nucleotide. 6. It is concluded that, in the rat aorta, the initial peak endothelium‐dependent hyperpolarization observed under the influence of ACh or carbachol is not directly related to the synthesis of NO.(ABSTRACT TRUNCATED AT 250 WORDS)

Depressed endothelium-dependent relaxation in hypertension: relation to increased blood pressure and reversibility

Endothelium-dependent relaxation effects have been reported to be impaired in thoracic aorta from genetic and experimentally induced hypertensive rats. This study extends these observations to carotid artery and abdominal aorta from renovascular hypertensive rats. It was also found that rats with coarctation of aorta show depressed endothelium-dependent relaxation responses in thoracic aorta above the stenosis (high pressure region) while no depressed responses are observed in abdominal aorta below the stenosis (normal pressure region). Reversibility of the depression of endothelium-dependent relaxation was investigated on aorta from renovascular hypertensive rats in which blood pressure was normalized by removal of the stenotic kidney three months after induction of hypertension. Endothelium-dependent responses were restored partially after 1–2 weeks and completely after two months of normalization of blood pressure. These results indicate that the increased blood pressure is indeed the causative factor responsible for the impaired endothelium-dependent relaxations in arteries from experimental hypertensive rats, a phenomenon which is reversible, at least in our experimental conditions.

Treatment of erectile dysfunction: new targets and strategies from recent research.

In recent years, research on penile erection has increasingly been centered on the molecular mechanisms involved. Major progress has been made in the field and at present a whole number of neurotransmitters, chemical effectors, growth factors, second-messenger molecules, ions, intercellular proteins, and hormones have been characterized as components of the complex process of erection. This knowledge has led to the discovery of several new therapeutic targets and multiple medical approaches for the treatment of erectile dysfunction (ED). This review focuses on the progress made in this field within the last few years.

Endotheiium-dependent and independent relaxation effects on aorta preparations of renal hypertensive rats

AbstractThe important role of the endothelium in the effects of many vasodilating substances has been amply demonstrated (for review: Furchgott, 1983). Thus, acetylcholine and histamine produce relaxation of pre-contracted (norepinephrine 107 M) rat aorta preparations only in the presence of intact endothelial structures (Van DE Voorde & Leusen, 1983). In a previous study we demonstrated that these endotheiium-dependent responses were much less pronounced in aorta rings of renal hypertensive rats than in aorta preparations of normotensive rats (Van DE Voorde et al., 1984). Impaired relaxation responses were also reported (Cohen & Berkowitz, 1976) to substances which are thought to act directly on the smooth muscle cells (e.g. isoproterenol, nitroglycerine). Microscopic examination of the hypertensive preparations revealed, however, important histologic changes not only in the muscular cell layer of the vessel wall but also in the intima. These observations led us to investigate whether the impaired relaxa...

Regionally different influence of contractile agonists on isolated rat airway segments

Rats are increasingly used to study airway inflammation and bronchial responsiveness. Relative little is known on the contribution of small airways in this animal model. We therefore compared the responsiveness to various inflammatory agents of isolated trachea, main bronchi (using classic organ bath) and isolated bronchioles (using small myograph) from Wistar and Fisher 344 rats. The largest contraction was elicited on all preparations by carbachol. Histamine elicited a (small) contraction only on bronchioles. The contractions elicited by serotonin, bradykinin, and the thromboxane A2-mimetic U-46619 were always relatively larger in bronchioles than in trachea and main bronchi. The sensitivities to carbachol and serotonin were smaller in bronchioles. The tachykinins substance P and neurokinin A elicited no substantial contraction on bronchioles or main bronchi. Trachea of Fisher 344 but not of Wistar rats showed a small contraction. No other differences were found between preparations from Wistar and Fisher 344 rats. It is concluded that rat trachea, main bronchi and small bronchioles show regional and strain-dependent variations in their responsiveness to contractile agents.

Influence of prostaglandin-synthesis inhibitors on carbachol-and histamine-induced vasodilatation in perfused rat hindquarters

abstractIn perfused rat hindquarters, in which vascular tone was maintained by norepinephrine, carbachol-induced dilatations were blocked by atropine (10−7 M), while histamine dilatations were inhibited as well by mepyramine (10−6 M) as by cimetidine (10−5 M) indicating a histamine effect through both H1- and H2-receptors. This double-receptor histamine effect was confirmed by the observation that speccific H1- and H2-receptor agonists, respectively PEA (2-pyridyl-ethylaminedihydrochloride) and dimaprit also produced a vasodilation.Carbachol- and histamine-induced dilatations were also inhibited by ETYA (5,8, 11,14-eicosatetraynoic acid) and quinacrine but not by indomethacin. The inhibition of the histamine vasodilatation appeared to rest on an interference with the H1-receptor mechanism. It is concluded that metabolites of arachidonic acid possibly mediate the dilating effect of carbachol, acting through muscarine receptors, and of histamine, acting through H1-receptors.

Endothelium-dependent relaxation effects in aorta from hypertensive rats

AbstractSince the original observations by Furchgott & Zawadzki(1980), it has been repeatedly demonstrated that the endothelium has an important role in the effects of many vasodilating substances (for review: Furchgott, 1983). In a previous study we showed that histamine and acetylcholine produce relaxations of pre-contracted rat aorta preparations on the condition that intact endothelial cells are present. Using a “sandwich” technique, it was demonstrated that both agonists induce the generation of (a) mediator(s) in the endothelium, which leads to relaxation of the vascular smooth muscle cells (Furchgott & Zawadzki, 1980; Van de Voorde & Leusen, 1983). Endothelial changes have been implicated in several vascular diseases of major clinical importance (Chand & Altura, 1981). One of these, hypertension, is known to induce endothelial damages (Hazama et al., 1978) and replication (Schwartz & Benditt, 1977; Daniel et al., 1982), intimal thickening (Still, 1968) and changes in arachidonate metabolism (Rioux ...