[Situation of the envenomations by snakebites in Congo-Brazzaville: epidemiological, clinical and therapeutic approaches]. / Situation des envenimations par morsure de serpent au Congo-Brazzaville: approches épidémiologique, clinique et thérapeutique.

A retrospective study was carried out in six areas of Congo and in the town of Brazzaville for the period between 2000 and 2004 in order to evaluate the incidence, lethality, treatments and the used drugs in cases of snakebites. We associated a retrospective survey using health centre registers (11 centres) and a retrospective survey based on the staff statements of village communities (42) and private pharmacies and drug centrals. The questionnaire related to the snakebites (identification of victims, place of bite, symptoms and treatment) was used in communities. The total case fatality rate was relatively low (3,11%). The incidence of the estimated snakebites was higher in villages (221) than in health centres (165). But, lethality was equal in the two study clusters (6 cases versus 6 cases). There was no difference of cases rate between male and female subjects. Around urban areas, many victims consulted health centre and in rural area, many victims resorted systematically to traditional practitioners. In drug centrals and private pharmacies of Brazzaville, drugs against envenomations were proposed, respectively, by one and two structures. In health centres these drugs were not available. This evaluation could be underestimated as many victims consulted traditional practitioners. This explains why collecting data from health centre registers is not sufficient to evaluate the importance of envenomations in our study area.

P2u receptor-mediated release of endothelium-derived relaxing factor/nitric oxide and endothelium-derived hyperpolarizing factor from cerebrovascular endothelium in rats.

BACKGROUND AND PURPOSE: Stimulation of P2u purinoceptors by UTP on endothelium dilates the rat middle cerebral artery (MCA) through the release of endothelium-derived relaxing factor/nitric oxide (EDRF/NO) and an unknown relaxing factor. The purpose of this study was to determine whether this unknown relaxing factor is endothelium-derived hyperpolarizing factor (EDHF). METHODS: Rat MCAs were isolated, cannulated, pressurized, and luminally perfused. UTP was added to the luminal perfusate to elicit dilations. RESULTS: Resting outside diameter of the MCAs in one study was 209+/-7 micrometer (n=10). The MCAs showed concentration-dependent dilations with UTP administration. Inhibition of NO synthase with NG-nitro-L-arginine methyl ester (L-NAME) (1 micromol/L to 1 mmol/L) did not diminish the maximum response to UTP but did shift the concentration-response curve to the right. Scavenging NO with hemoglobin (1 or 10 micromol/L) or inhibition of guanylate cyclase with ODQ (1 or 10 micromol/L) had effects on the UTP-mediated dilations similar to those of L-NAME. In the presence of L-NAME, dilations induced by 10 micromol/L UTP were accompanied by 13+/-2 mV (P<0.009) hyperpolarization of the vascular smooth muscle membrane potential (-28+/-2 to -41+/-1 mV). Iberiotoxin (100 nmol/L), blocker of the large-conductance calcium-activated K channels, sometimes blocked the dilation, but its effects were variable. Charybdotoxin (100 nmol/L), also a blocker of the large-conductance calcium-activated K channels, abolished the L-NAME-insensitive component of the dilation to UTP. CONCLUSIONS: Stimulation of P2u purinoceptors on the endothelium of the rat MCA released EDHF, in addition to EDRF/NO, and dilated the rat MCA by opening an atypical calcium-activated K channel.

Potentiation of Ca2+ signaling in endothelial cells by 11,12-epoxyeicosatrienoic acid.

Incubation of endothelium with an increased epoxyeicosatrienoic acid (EET) concentration specifically augments the endothelium-dependent relaxation ascribed to endothelium-derived hyperpolarizing factor in porcine coronary arteries (Weintraub et al., Circ Res 1997;81:258-267). Experiments were designed to test whether such sustained increased levels of EETs in the environment of endothelial cells alters Ca2+ signaling. Changes in cytosolic Ca2+ were monitored in cultured porcine aortic endothelial cells (PAECs) and in the human endothelial EA.hy926 cell line after incubation (or not) with 5 microM 11,12-epoxyeicosatrienoic acid (EET). Although the mobilization of intracellular Ca2+ induced by 2 microM thapsigargin was not affected significantly, EET treatment augmented the capacitative Ca2+ entry evoked by the Ca(2+)-ATPase) inhibitor in both cell types. Similar observations were obtained by using histamine as a stimulant in EA.hy926 cells. As assessed in PAECs, 2 micrograms/ml triacsin C, a known inhibitor of the incorporation of EETs into phospholipids, did not significantly affect the potentiating action of EETs on Ca2+ signaling in response to thapsigargin. However, in solvent-control cells, triacsin C significantly reduced both the mobilization of Ca2+ from intracellular stores and the capacitative Ca2+ entry provoked by thapsigargin. Thus the EET-potentiating effect overcomes the inhibitory action of triacsin C on Ca2+ signaling in endothelial cells. Taken together, these results demonstrate that sustained increases in EETs may amplify Ca2+ signaling. However, contrary to the EET-induced augmentation of endothelium-dependent relaxation in the porcine coronary artery, resistance of this novel action of EETs to triacsin C suggests that the mechanism involved does not depend on incorporation into phospholipids.

Anandamide-induced mobilization of cytosolic Ca2+ in endothelial cells.

1. Experiments were designed to determine whether anandamide affects cytosolic Ca2+ concentrations in endothelial cells and, if so, whether CB1 cannabinoid receptors are involved. To this effect, human umbilical vein-derived EA.hy926 endothelial cells were loaded with fura-2 to monitor changes in cytosolic Ca2+ using conventional fluorescence spectrometry methods. 2. Anandamide induced an increase in Ca2+ in endothelial cells which, in contrast to histamine, developed slowly and was transient. Anandamide caused a concentration-dependent release of Ca2+ from intracellular stores without triggering capacitative Ca2+ entry, contrary to histamine or the endoplasmic reticulum Ca2+ -ATPase inhibitor thapsigargin. 3. Anandamide pretreatment slightly reduced the mobilization of Ca2+ from intracellular stores that was evoked by histamine. The mobilization of Ca2+ from intracellular stores evoked by anandamide was impaired by 10 mM caffeine. 4. Anandamide and histamine each significantly increased NO synthase activity in EA.hy926 cells, as determined by the enhanced conversion of L-[3H]-arginine to L-[3H]-citruline. 5. The CB1 cannabinoid receptor antagonist SR141716A (1 microM) only produced a marginal reduction of the mobilization of Ca2+ produced by 5 microM anandamide. However, at 5 microM SR141716A elicited the release of Ca2+ from intracellular stores. This concentration strongly impaired the mobilization of cytosolic Ca2+ evoked by either anandamide, histamine or thapsigargin. 6. Pretreatment of the cells with either 200 microM phenylmethylsulphonyl fluoride (to inhibit the conversion of anandamide into arachidonic acid) or 400 ng ml(-1) pertussis toxin (to uncouple CB1 cannabinoid receptors from Gi/o proteins) had no significant effect on the mobilization of cytosolic Ca2+ evoked by either anandamide, or histamine. 7. Taken together the results demonstrate that anandamide mobilizes Ca2+ from a caffeine-sensitive intracellular Ca2+ store that functionally overlaps in part with the internal stores mobilized by histamine. However, a classical CB1 cannabinoid receptor-mediated and pertussis toxin-sensitive mechanism does not mediate this novel effect of anandamide in endothelial cells. 8. The mobilization of cytosolic Ca2+ in endothelial cells may account for the endothelium-dependent and NO-mediated vasodilator actions of anandamide. Due to its non-specific inhibition of Ca2+ signalling in endothelial cells, SR141716A may not be used to assess the physiological involvement of endogenous cannabinoids to endothelium-dependent control of vascular smooth muscle tone.

Endothelial dysfunction: from physiology to therapy.

The endothelium controls the tone of the underlying vascular smooth muscle mainly through the production of vasodilator mediators. In some cases, this function is hampered by the release of constrictor substances. The endothelial mediators are also involved in the regulation by the endothelium of vascular architecture and the blood cell-vascular wall interactions. The endothelium-derived factors comprise nitric oxide (NO), prostacyclin, and a still unknown endothelium-derived hyperpolarizing factor(s) (EDHF). In most vascular diseases, the vasodilator function of the endothelium is attenuated. In advanced atherosclerotic lesions, endothelium-dependent vasodilatation may even be abolished. Various degrees and forms of endothelial dysfunction exist, including (1) the impairment of Galphai proteins, (2) less release of NO, prostacyclin and/or EDHF, (3) increased release of endoperoxides, (4) increased production of reactive oxygen species, (5) increased generation of endothelin-1, and (6) decreased sensitivity of the vascular smooth muscle to NO, prostacyclin and/or EDHF. The levels of bradykinin and angiotensin II within the vascular wall are controlled by angiotensin-converting enzyme (ACE). ACE degrades bradykinin and generates angiotensin II. Bradykinin stimulates endothelial cells to release vasodilators. The actions of the kinin are maintained despite endothelial dysfunction, except in very severe arterial lesions. Angiotensin II may be in part responsible for endothelial dysfunction because it induces resistance to the vasodilator action of NO. Thus, impairment of the generation of angiotensin II blocks the direct and indirect vasoconstrictor effect of the peptide. By potentiating bradykinin, ACE inhibitors promote the release of relaxing vasodilator mediators to restore vasodilator function, and to prevent platelet aggregation as well as the recruitment of leukocytes to the vascular wall.

Endothelium-derived hyperpolarizing factor(s): updating the unknown.

Endothelium-dependent hyperpolarization of vascular smooth muscle is a mechanism that contributes to the vasodilator response to shear stress and chemicals acting on endothelial receptors. The phenomenon is explained by the release from endothelial cells, of an endothelium-derived hyperpolarizing factor(s) (EDHF) (s), although its (their) exact nature is still controversial. Indeed, endothelial cells produce several substances that are capable of evoking hyperpolarization in vascular smooth muscle. However, which of these factors represents EDHF under physiological conditions remains unknown. The term EDHF should be reserved for a substance(s) that differs from both NO and prostaglandins. In this review Jean-Vivien Mombouli and Paul M. Vanhoutte consider the possible candidates for EDHF and the arguments that have lead to the proposal that these substances fulfil the functions of an endothelium-derived relaxing agent. The weaknesses of the available sudies are also discussed. The identification of EDHF would allow the understanding of its physiological role alongside other known endothelial mediators such as NO and prostacyclin. This could lead to the design of new therapies aimed at correcting the impairment of EDHF-mediated dilatation in a number of cardiovascular diseases.

ACE inhibition, endothelial function and coronary artery lesions. Role of kinins and nitric oxide.

In healthy coronary arteries, the endothelium plays an important role in the regulation of vascular smooth muscle growth and contractility. Furthermore, the endothelium inhibits overt platelet aggregation and prevents the adhesion of white blood cells to, and their infiltration into, the vascular wall. Among the mediators of these functions of endothelial cells, nitric oxide (NO) plays a central role. Moreover, the presence of local kinin-generating enzymatic systems associated with endothelial cells, vascular smooth muscle, platelets, neutrophils and monocytes suggests that bradykinin stimulates endothelial cells to release NO locally. The activation of endothelial cells by bradykinin is inhibited by kininase II, best known as angiotensin converting enzyme (ACE). Hence, ACE inhibitors, in addition to reducing the levels of angiotensin II (a potent stimulus to vascular smooth muscle growth and contraction), cause an amplification of the release of NO and other endothelial mediators that is induced by bradykinin. Independent risk factors for coronary artery disease such as hypertension, diabetes and hypercholesterolaemia reduce the NO-dependent regulation of vascular smooth muscle contractility and growth in otherwise normal coronary arteries. This endothelial dysfunction probably also affects the inhibitory role of NO with regard to platelet aggregation and monocyte infiltration into the vascular wall. In atherosclerotic vessels, the role of NO is severely reduced. In animal models, as well as in patients with coronary artery disease, endothelial dysfunction is improved by treatment with ACE inhibitors. Although in humans the mechanism of the restoration of endothelial function is not known, in animals endogenous kinins and NO are involved. However, it is clear that this process is multifactorial, and thus probably involves both the prevention of the deleterious actions of angiotensin II and the potentiation of bradykinin.

Vascular endothelium: vasoactive mediators.

In most blood vessels, the endothelium generates both vasodilator and growth-stabilizing mediators under normal physiological circumstances. The vasodilator influence of the endothelium modulates the vasoconstriction induced by adrenergic nerves, bloodborne substances, and local autacoids. Nitric oxide (NO) is a major endothelium-derived vasodilator, along with prostacyclin. A third substance called endothelium-derived hyperpolarizing factors (EDHF) mediates vasodilatation in certain conduit arteries and in most resistance vessels. EDHF may be a cytochrome P-450 metabolite of arachidonic acid. NO acts mostly through an elevation of cyclic guanosine monophosphate in vascular smooth muscle, whereas prostacyclin stimulates adenylate cyclase. The mode of action of EDHF involves the activation of K+ channels. The multiplicity of the factors released by the endothelium, as well as the complexity of the interactions among these factors and those with other nonendothelial mediators, determine the extent of vasomotor control exerted locally by the endothelium.

Endothelium-derived hyperpolarizing factor: a key mediator of the vasodilator action of bradykinin.

Bradykinin causes vasodilatation by stimulating the production of vasodilator prostanoids and nitric oxide (NO). However, there is an additional component that is mediated by a diffusible endothelium-derived hyperpolarizing factor (EDHF). The non-selective inhibitor of arachidonic acid metabolism eicosatetraynoic acid inhibits the EDHF-mediated component of the relaxation to bradykinin. Therefore, EDHF may be an archidonic acid metabolite. The diffusible nature of EDHF has been disputed because of the inability to consistently detect the factor using perfusion bioassay techniques. However, administration of the acyltransferase inhibitor thimerosal facilitates the release of EDHF by endothelial cells in culture. Further studies are warranted to identify EDHF and explore further its functions in vasomotion.

Bioassay of endothelium-derived hyperpolarizing factor.

Endothelium-derived hyperpolarizing factor (EDHF) mediates vasodilatation in certain blood vessels, together with prostacyclin and NO. However, its chemical nature is not known. A perfusion-superfusion cascade was developed to confirm the diffusible nature of EDHF. Canine carotid arteries with endothelium were used as donors of vasoactive substances, whereas rings of coronary artery without endothelium were used as detectors. Inhibitors of NO synthesis and cyclooxygenase were present throughout, to avoid interference from NO and prostanoids. Measurements of membrane potential and isometric tension, in coronary arteries without endothelium (used as detectors), demonstrated the release of EDHF from the carotid arteries, following treatment with 8-methoxypsoralen, bradykinin and thimerosal. The K+-channel blocker tetraethylammonium inhibited the action od EDHF in the detectors. Thus, these results demonstrate that endothelial cells release a diffusible activator of K+-channels in vascular smooth muscle.

Endothelium-dependent relaxation and hyperpolarization evoked by bradykinin in canine coronary arteries: enhancement by exercise-training.

1. Kinins, which are produced locally in arterial walls, stimulate the release of endothelium-derived vasodilator substances. Therefore, they may participate in the metabolic adaptation to chronic exercise that occurs in the coronary circulation. Experiments were designed to compare the reactivity to bradykinin in coronary arteries isolated from sedentary and exercised-trained dogs (for 8-10 weeks). 2. The organ chambers used in this study were designed for measurement of isometric tension and cell membrane potential with glass microelectrodes. Rings of canine isolated coronary arteries with endothelium were suspended in the organ chambers filled with modified Krebs-Ringer bicarbonate solution (37 degrees C, gassed with 5% CO2 in 95 O2), and were all treated with indomethacin to prevent interference from prostaglandins. 3. Bradykinin evoked concentration-dependent relaxations of the coronary arteries. However, the kinin was significantly less potent in relaxing coronary arteries from the sedentary dogs than those from the trained ones. 4. In the presence of NG-nitro-L-arginine (an inhibitor of nitric oxide synthases), concentration-relaxation curves to bradykinin were shifted to the right in both types of preparations. Nonetheless, the peptide was still significantly more potent in arteries from exercise-trained animals. 5. In the electrophysiological experiments, concentration-hyperpolarization curves to bradykinin obtained in arteries from sedentary dogs were also significantly to the right of those in vessels from exercise-trained animals. Thus, in arteries from exercised animals, bradykinin more potently evoked the release of both nitric oxide (NO) and endothelium-derived hyperpolarizing factor (EDHF). 7. The angiotensin converting enzyme (ACE)-inhibitor, perindoprilat, shifted to the left the concentration-relaxation curves to bradykinin obtained under control conditions and in the presence of NG-nitro-L-arginine. The concentration-hyperpolarization curves to bradykinin were also shifted to the left by perindoprilat. The shift induced by the ACE-inhibitor in either type of preparation was not significantly different. 8. These findings demonstrate that exercise-training augments the sensitivity of the coronary artery of the dog to the endothelium-dependent effects of bradykinin. This sensitization to bradykinin may reflect an increased role of both NO and EDHF, and is not the consequence of differences in ACE activity in the receptor compartment.

Endothelium-derived relaxing factors and converting enzyme inhibition.

Endothelial cells can produce at least 3 substances which cause relaxation of vascular smooth muscle: (1) endothelium-derived nitric oxide (NO, which is secreted not only toward the underlying vascular smooth muscle but also into the blood vessel lumen). NO also has a physiological role at the interface between the endothelial cells and the blood content; in particular, NO inhibits the adhesion of platelets and leukocytes to the endothelium. (2) Endothelium-derived hyperpolarizing factor, presumably a labile metabolite of arachidonic acid formed through the P-450 pathway, which appears to act on smooth muscle by being one of the few physiologic openers of the potassium channels. (3) Prostacyclin, which can be considered as an endothelium-derived relaxing substance, given its vasodilator activity and its primarily endothelial origin. One of the main factors modulating the release of these EDRFs is the shear stress of blood on the arterial wall, which explains why flow-induced vasodilation is endothelium-dependent in the intact organism. The peptide bradykinin is a potent stimulus for EDRF release. The normal lifespan of an adult human endothelial cell is some 30 years, after which aging takes its toll and the cells must be replaced. The regenerated cells lose some of their ability to release EDRF, in particular in response to platelet aggregation and thrombin. Finally, in hypertension and atherosclerosis, a decrease in endothelium-dependent relaxation is obvious in response to a variety of stimuli. All converting enzyme inhibitors tested so far share a potentiating effect on endothelium-dependent relaxation to bradykinin, and augmented local production of bradykinin may help to explain the acute vasodilator properties of these compounds.

Endothelium-derived hyperpolarizing factor(s) and the potentiation of kinins by converting enzyme inhibitors.

Inhibitors of angiotensin converting-enzyme (ACE) enhance the endothelium-dependent relaxation to bradykinin and cause the accumulation of kinins in the vascular wall. Bradykinin elicits the production of vasodilator prostanoids and nitric oxide by endothelial cells. However, there is an additional component to the dilator actions of bradykinin, which is mediated by a diffusible endothelium-derived hyperpolarizing factor (EDHF). The knowledge gathered on the nature of EDHF and its mechanism of action are reviewed briefly. EDHF causes hyperpolarization and relaxation of arterial smooth muscle by activating K(+)-channel, the nature of which varies between species. During the inhibition of both cyclooxygenase and nitric oxide synthase, concentration-response relationships of the hyperpolarization and relaxation elicited by bradykinin overlap in canine coronary arteries. Both effects are enhanced equally by the ACE inhibitor perindoprilat. They are inhibited by membrane depolarization that is obtained by raising the extracellular concentrations of potassium ions. Likewise, in the human coronary artery, the hyperpolarization elicited by bradykinin, which is also mediated by EDHF, is augmented in the presence of perindoprilat and prevented by potassium-induced depolarization. In this blood vessel, contrary to the canine coronary artery, the EDHF-mediated responses occur at concentrations comparable to those initiating the nitric oxide-dependent component. Therefore, the increased production of EDHF, which is induced by kinins, may contribute to the cardiovascular effects of perindoprilat, together with an enhanced production of nitric oxide and vasodilator prostanoids.

cGMP mediates the desensitization to bradykinin in isolated canine coronary arteries.

The relaxation to bradykinin in canine coronary arteries is mediated by endothelium-derived nitric oxide (NO) and hyperpolarizing factor (EDHF). Desensitization to the kinin was induced by incubation of canine coronary arteries with endothelium with 10(-8) M bradykinin for 30 min. After washout, tissues were contracted with prostaglandin F2 alpha, and concentration-relaxation curves to bradykinin were obtained in control and desensitized arteries treated with indomethacin. After desensitization, there was a shift to the right of the concentration-relaxation curves to bradykinin. However, the elevation in guanosine 3',5'-cyclic monophosphate (cGMP) levels evoked by bradykinin was similar in both groups of tissues. The curves to bradykinin obtained in the presence of NG-nitro-L-arginine (an NO synthase inhibitor) were depressed, whereas those obtained in arteries contracted with potassium (to eliminate the EDHF-mediated relaxation) were not affected by the desensitization. Addition of NG-nitro-L-arginine, oxyhemoglobin, or methylene blue before the desensitization procedure preserved, whereas 3-morpholinosydnonimine (SIN-1, a donor of NO) and 8-bromoguanosine 3',5'-cyclic monophosphate impaired, the EDHF-mediated relaxation to bradykinin. Thus the selective impairment of the EDHF-dependent relaxation to bradykinin may be mediated by NO, acting mainly through increased production of cGMP.

Kinins and endothelial control of vascular smooth muscle.

Plasma and vascular kinins stimulate the production of endothelium-derived nitric oxide, prostacyclin and hyperpolarizing factor (which regulates the function of vascular smooth muscle), and endothelial interactions with blood cells. The role of kinins in vasomotion is determined by the rate of production of the peptides by kininogenases and their degradation by kininases, in particular angiotensin-converting enzyme (ACE). Acute increases in plasma kinin levels during exercise or myocardial ischemia indicate that the metabolism of the peptides is fine tuned to the systemic or local metabolic demands. The release of endothelial vasodilators is impaired (or counterbalanced by the release of chemical or functional antagonists) in atherosclerosis, hypertension, diabetes, subarachidonic hemorrhage, and following postischemic injury. ACE-inhibitors potentiate the action of kinins and normalize endothelial function. In septic shock, hypotension triggered by overproduction of kinins leads to cardiovascular impairment and end-organ damage. Thus the balance in the metabolism of kinins modulates the control of blood flow by the endothelium.

The endothelium and vascular effects of the ACE inhibitor trandolaprilat.

Experiments were designed to study the effects of trandolaprilat on endothelium-dependent responses in isolated blood vessels. Rings of either femoral or left circumflex coronary arteries of the dog or thoracic aortas of normotensive rats were suspended in organ chambers for isometric tension recording. During contractions induced by prostaglandin F2 alpha, trandolaprilat did not cause direct endothelium-dependent or -independent relaxation. However, when given to preparations incubated with angiotensin I or bradykinin, the compound evoked significant endothelium-dependent relaxation. By contrast, trandolaprilat failed to cause any change in tension when given in the presence of acetylcholine (ACh). In rings of femoral arteries, trandolaprilat potentiated the endothelium-dependent relaxation evoked by bradykinin and adenosine diphosphate; it did not modify the endothelium-dependent relaxations induced by ACh, substance P, or thrombin. In rings of femoral arteries without endothelium, trandolaprilat augmented relaxation induced by adenosine diphosphate (ADP) but not by adenosine. In perfused coronary arteries with but not those without endothelium, trandolaprilat caused relaxation in the absence of exogenous bradykinin (or ADP). These experiments suggest that trandolaprilat does not directly release endothelium-derived relaxing factor from the endothelial cells, does not interfere with the ability of the endothelium to release endothelium-derived relaxing factor, augments the endothelium-dependent responses to bradykinin (given exogenously or produced locally) and angiotensin I by direct interaction with converting enzyme, and potentiates the relaxation induced by ADP by augmenting its direct effect on vascular smooth muscle.

Potentiation by trandolaprilat of the endothelium-dependent hyperpolarization induced by bradykinin.

In canine coronary arteries, bradykinin evokes endothelium-dependent relaxations that are mediated by nitric oxide (NO) and endothelium-derived hyperpolarizing factor (EDHF). The converting-enzyme inhibitor trandolaprilat potentiates the endothelium-dependent relaxations evoked by bradykinin in this tissue. The present experiments were designed to determine whether or not facilitated release of EDHF contributes to the augmented response to bradykinin in the presence of trandolaprilat. Organ-chamber studies were performed to measure changes in isometric tension in rings of canine coronary arteries. In the presence of nitro-L-arginine, an inhibitor of NO synthase, trandolaprilat augmented the endothelium-dependent relaxations evoked by bradykinin. These relaxations were not inhibited by the K(+)-channel inhibitors tetraethylammonium, 4-aminopyridine, or glibenclamide, but were abolished in high-potassium solution. The membrane potential in individual smooth-muscle cells of coronary artery was measured by means of glass microelectrodes. Trandolaprilat potentiated the endothelium-dependent hyperpolarizations evoked by a subthreshold concentration of bradykinin, and these endothelium-dependent hyperpolarizations were inhibited by high-potassium solution. These experiments demonstrate that EDHF contributes to the relaxation evoked by bradykinin in the canine coronary artery and that trandolaprilat potentiates the release of this factor. This effect of trandolaprilat may contribute to its vasodilator properties.

Role of extracellular calcium and calcium channels in the response of human placental venous smooth muscle to endothelin-1.

OBJECTIVE: Our purpose was to evaluate the role of calcium and calcium channels in endothelin-1-induced contraction of the smooth muscle of human placental veins. STUDY DESIGN: Placentas were collected after vaginal delivery at term. After their removal from the chorionic plate, placental veins were divided into rings that were suspended in organ chambers and stretched to optimal tension. In the first part of the study, vessels from six women were initially suspended in calcium-poor modified Krebs-Ringer solution. They were then treated with either EGTA [ethylene glycol-bis(beta-aminoethyl ether)N,N,N',N'-tetraacetic acid; calcium chelator, 0.5 mmol/L] or calcium chloride 2.5 mmol/L (control). Endothelin-1 was then added cumulatively (10(-10) to 10(-7) mol/L), and the resulting changes in isometric tensions were recorded. In the second part of the study vessels from six other women were treated with either (1) normal modified Krebs-Ringers solution (control), (2) calcium-poor modified Krebs-Ringers solution, or (3) nicardipine (dihydropyridine calcium channel inhibitor, 10(-7) mol/L) in separate organ chambers. Endothelin-1 was then added cumulatively. RESULTS: Endothelin-1 produced concentration-dependent contractions in placental veins, with maximal tension reached at 10(-7) mol/L. Substitution of calcium-poor for standard Krebs-Ringers solution in the organ chamber abolished contractions to low endothelin-1 concentrations (< or = 10(-9) mol/L, p < 0.001) but did not affect the contractile response to higher concentrations. EGTA abolished contractions to all concentrations tested (p < 0.02). Nicardipine significantly, but incompletely, inhibited the contractile responses to all endothelin-1 concentrations tested (p < 0.05). CONCLUSIONS: Endothelin-1 induces contraction of the smooth muscle of human placental veins, which requires the influx of extracellular calcium. Dihydropyridine-sensitive calcium channels represent a major route of entry, but other pathways participate. The fetal effects of nifedipine and other calcium-channel blockers deserve specific evaluation in intrauterine growth retardation and other pregnancies complicated by elevated fetal levels of endothelin-1.