Endothelin binding to cultured calf adrenal zona glomerulosa cells and stimulation of aldosterone secretion.

Endothelins are a group of potent vasoconstrictors whose structure was deduced from genomic DNA. ET-1 was first isolated from culture supernatants from porcine endothelial cells and ET-3 was identified from a rat DNA library. We report on the binding of 125I-ET-1 to zona glomerulosa cells in culture and on its ability to stimulate aldosterone secretion. Cultured calf adrenal zona glomerulosa cells have saturable, high affinity [Kd = 1.00 +/- 0.17 X 10(-10) M (SEM)] receptors which bind ET-1 in a temperature and time dependent manner. Binding was specific and angiotensin II, vasopressin, ANP, BNP, apamin, calcium channel agonists or antagonists did not interact with the receptor. ET-3 displaced 125I-ET-1 from the receptor with a relative potency of 0.39 +/- 0.1% (SEM) that of ET-1. ET-1 incubated with cultured glomerulosa cells stimulated aldosterone secretion in a dose dependent manner but it was less potent than angiotensin II. ET-3 had less than 1% the relative potency of ET-1 stimulating aldosterone secretion. This data suggest that ET-1 is an independent stimulator of aldosterone secretion and we are speculating that it might be important in those situations, like in malignant hypertension, where endothelial damage might result in increased ET-1 production.

Immunoreactive endothelin in rat kidney inner medulla: marked decrease in spontaneously hypertensive rats.

Using a specific and sensitive radioimmunoassay for endothelin, the regional distribution and molecular form of endothelin was investigated in rat tissue. The highest concentration was observed in the inner medulla of the kidney (8.7 +/- 2.2 pg/mg wet weight). On two kinds of reverse phase high performance liquid chromatography, immunoreactive endothelin in the inner medulla of the kidney was separated into two peaks at positions where authentic porcine/human and putative rat/human endothelin eluted. Furthermore, the concentration of immunoreactive endothelin in the inner medulla of the kidney was remarkably decreased in spontaneously hypertensive rats (SHR) compared with normotensive control Wistar Kyoto rats (WKY) but no difference was observed in lung immunoreactive endothelin.

A novel peptide vasoconstrictor, endothelin, is produced by vascular endothelium and modulates smooth muscle Ca2+ channels.

Since the discovery of endothelium-dependent vasodilation, vascular endothelium has been recognized as an important functional unit contributing to the regulation of vascular tonus. Recent purification, structure determination and molecular cloning of a novel peptidergic vasoconstrictor, endothelin, from the culture supernatant of porcine aortic endothelial cells has further substantiated this concept. Starting from a large quantity of serum-fee endothelial cell-conditioned medium, endothelin was purified to homogeneity after three steps of high performance liquid chromatography by collecting active fractions and constricting porcine coronary artery strips. A peptide sequence analysis showed that endothelin was a previously unknown 21-residue peptide with two intrachain disulphide bonds. The EC50 of endothelin for contraction of porcine coronary artery was 4.0 x 10(-10) mol/l, indicating that endothelin is one of the most potent vasoconstrictors known. The pharmacological and structural properties of endothelin suggest that the peptide acts by activating voltage-dependent Ca2+ channels in vascular smooth muscle cells. Cloning and sequence analysis of complementary (c)DNA encoding porcine and human endothelin precursors showed that endothelin was produced de novo in endothelial cells from an approximately 200-residue prepropeptide through an unusual proteolytic processing by a putative 'endothelin-converting enzyme'. Northern blot analysis showed that preproendothelin messenger (m)RNA was expressed not only in cultured endothelial cells but also in fresh intimal tissue from porcine aorta, and that mRNA can be induced markedly in response to several vasoactive agents in cultured endothelial cells, suggesting the existence of a novel endothelium-mediated cardiovascular control system.

Interaction between myocardial depressant factor and vasoactive mediators with ischemia and shock.

A variety of endogenously formed vasoconstrictor substances circulate in the blood and act as mediators in ischemia and shock states. These humoral substances are chemically diverse and include peptides, lipids, and aromatic amines. One of the novel peptides, myocardial depressant factor (MDF) and several interesting lipids, including thromboxane A2 (TxA2), leukotriene D4 (LTD4), and platelet-activating factor (PAF) are very potent substances having a broad profile of pathophysiological actions. Some of the effects of MDF include myocardial depression, constriction of splanchnic vessels, and impairment of phagocytosis. TxA2 primarily constricts blood vessels, aggregates platelets, and increases membrane permeability. LTD4 is a potent vasoconstrictor and bronchoconstrictor and promotes leakage of fluid out of blood vessels. PAF activates platelets, depresses cardiac function, constricts airways, and enhances fluid leakage from the intravascular compartment. Thus vasoconstriction is common to all these mediators. Moreover, these vasoactive substances have common mechanisms of release and interact to exacerbate ischemia and contribute to the pathogenesis of a variety of shock states. New pharmacological approaches to blocking the formation and action of these mediators have provided interesting insights into the pathophysiology of shock.

Activation of the central vasopressin system: a common pathway for several centrally acting pressor agents.

Hypertonic saline (HS) and angiotensin II (ANG II) administered centrally or peripherally produce a forebrain-mediated central nervous system-(CNS) dependent pressor action. Although the majority of these effects are due to increased central sympathetic drive and inhibition of the cardiac baroreceptor reflex, evidence from peripheral infusions of vasopressin (Vp) receptor antagonists have suggested that part of the blood pressure increase may be due to circulating Vp. We now report that blockade of CNS Vp receptors in rats, via a fourth ventricle infusion of a Vp receptor antagonist, attenuated greater than 70% of the pressor response to lateral ventricle infusion of HS, ANG II, or hypertonic glucose (HG). Intravenous administration of the Vp antagonist could block only 40% of the HS response. When lateral ventricle infusion of HS was performed in rats with a hereditary lack of Vp (diabetes insipidic rats) no pressor response was obtained. Because centrally administered Vp has autonomic nervous system effects that are similar to those induced by HS or ANG II, our results suggest that CNS Vp may provide a link between forebrain acting pressor agents and autonomic nervous system regulation. Finally, HG produced a pressor effect that had an equivalent peak response to HS. However, unlike the HS response, the pressor effect to HG returned to base line within approximately 5 min during a 10-min infusion. Thus there appears to be a quantitative difference in the pressor responses produced by activation of sodium vs. osmoreceptors.

Novel peptides in the lung.

Peptides found in the normal lung are described, and present theories as to their functions are presented.

[Some properties of a vasopressor substance generated in human plasma by incubation and its clinical significance in pregnancy-induced hypertension].

A study to measure the pressor substance, called active pressor principle (APP), which is generated in incubated human plasma was performed using anesthetized and ganglion blocked rats. It was found that APP has properties characteristic of protein. APP was not extractable with mixtures of chloroform: methanol. APP was present at 50 to 70% saturation with ammonium sulfate. By treating the plasma with Pronase, the pressor activity of the plasma was almost completely abolished. The molecular weight of APP as determined by gel filtration was about 68,000. By adding diisopropyl fluorophosphate before incubation of the plasma, the generation of vasopressor substance was prevented. Treatment of the rat with captopril was ineffective in inhibiting the pressor effect of incubated plasma. It was found that the plasma of normal pregnant women generated significantly higher amounts of APP than the plasma of nonpregnant women. The plasma obtained from patients with pregnancy-induced hypertension generated significantly lower amounts of APP than the plasma of normal pregnant women. These findings suggest that a vasoactive protein (APP) is generated during simple incubation of plasma, and a serine protease is involved in the formation of this substance. Concerning the relevance of these results to blood pressure regulation in pregnancy-induced hypertension, probably APP is involved in blood pressure regulation via a compensatory mechanism.

[A critical review of hypothetical causes of EPH-gestosis]. / Kritische Ubersicht über die Theorien der EPH-Gestose

The essential EPH-gestosis seems to have multiple aetiological factors and the disease develops already a long time before the appearance of the classical symptoms. The disturbed renal function is the main point among secondary pathological effects as the damaged placenta, the disseminated coagulation, the glomerular endotheliosis, the increased retention of water and sodium with increased arterial responsiveness. It may be that this reduced reversible renal function is of extra-renal origin. As predisposing factors were discussed the reduced uteroplacental circulation with the release of still unknown pressor substances or decreased inactivation of pressor amines, the uterorenal reflex mechanism, the disturbed homeostasis of the body fluids and the vegetativ-hypothalamic crisis etc. But other factors may also be participate on this disease as immunological and hormonal aspects, especially the renin-angiotensin-aldosteron-system and prostaglandins. To find out the aetiological factors we should examine the disease at the beginning in comparison with normal pregnancy. These factors must explain why the true EPH-gestosis appears mainly during the first pregnancy and frequently in twins and so on.