Phospholipase C activity in rat kidney. Effect of deoxycholate on phosphatidylinositol turnover.

Rat renal cortical and medullary slices incorporate [14C]arachidonate into phosphatidylcholine, phosphatidylethanolamine, phosphatidylinositol and triacylglycerols. The percent distribution of [14C]arachidonate among the various phospholipids is similar in renal cortex and medulla, although the total amount of radioactively labeled phospholipids is higher in the renal medulla. Subsequent incubation of prelabeled slices in the presence of deoxycholate induces a loss of radioactivity from [14C]phosphatidylinositol, with a concomitant increase in 1,2-[14C]diacylglycerol. Neutral lipids are not affected. The degradation of phosphatidylinositol to [14C]diacylglycerol indicates the presence of phospholipase C activity. Renal medulla seems to be more sensitive to deoxycholate than the renal cortex. Deoxycholate also induces slightly the disappearance of some 14C radioactivity from phosphatidylethanolamine and phosphatidylcholine, which might reflect activation of phospholipase A2. The activity of the phospholipase C could constitute the first step in the sequence of reactions that leads to the release of arachidonic acid.

Effect of omapatrilat on the aging process of the normal rat.

Previous results have shown that inhibition of the renin-angiotensin system (RAS) either with an angiotensin II (Ang II), type 1 receptor blocker (losartan) or with an angiotensin converting enzyme inhibitor (ACEI, enalapril) has a protective effect on cardiovascular, renal, hepatic and cerebral structure and function during aging. The present study has analyzed the effect of chronic administration of a newly developed compound, omapatrilat, on clinical, histological and biochemical changes due to aging. Omapatrilat combines the action of an ACEI and of an inhibitor of a neutral endopeptidase involved in the metabolism of the atrial natriuretic peptide. The final effect is a decrease of a vasoconstrictor and proinflammatory mechanism like the RAS and the potentiation of two vasodilating compounds like bradykinin and the atrial natriuretic peptide. Based on these actions, its protective effect might be greater than formerly used pharmacological agents. Determinations have been performed on young adults (6 months old), adults (12 months old) or senile (18 months old) rats. Omapatrilat (35 mg/kg/day during 6 months and 20 mg/kg/day thereafter) was administered in the drinking water since weaning until sacrifice. Cardiovascular, renal, and cerebral structure as well as cognitive behavior, cardiovascular and renal function has been analyzed. The biochemical analysis has also established whether the beneficial action of Ang II inhibition is related to an increased activity of the nitric oxide synthase as observed in previous studies. Moreover, this study has tried to determine the relationship between the protective effect of these drugs and the levels of antioxidant defenses present in the blood and/or in the tissues. Hence, enzymatic and non-enzymatic antioxidants have been evaluated.

Prostaglandins, antidiuretic hormone and renin angiotensin system.

Current knowledge on prostaglandin biosynthesis is reviewed, centering on how PGs participate in the regulation of vascular tone and the prevention of platelet deposition on endothelial surfaces. Discussion includes review of the vasoactivity of the PG endoperoxides, thromboxane, prostacyclin, and prostaglandin E2; prostaglandin-catabolizing enzymes; polyunsaturated fatty acid precursors; nutritional factors; antidiuretic hormone; and interrelations of PGs with the renin-angiotensin system.

Effect of chronic angiotensin II inhibition on the nitric oxide synthase in the normal rat during aging.

OBJECTIVE: To assess the effect on the cardiovascular system, of enalapril (E) or losartan (L) given since weaning during 6 or 18 months to normal rats. METHODS: Animals were divided in three groups: control (C), E-treated and L-treated; treated rats received 10 mg/ kg per day of drug. Systolic blood pressure (SBP), body weight, water and food intake (WI, FI), cardiac, left ventricular and aortic weight as well as the length of the tail were recorded. NADPH-diaphorase activity was determined as a marker of nitric oxide synthase (NOS) activity in aorta, arterioles of small intestine, heart and kidney of normal rats. NOS activity was measured as optical density (OD) in the stained tissue. Nitrate + nitrite urinary excretion was measured in 24 h urine. Only significant differences (P < 0.05) are reported. RESULTS: SBP, absolute cardiac, left ventricular and aortic weight increased with age. Both treatments delayed these increments. At 6 and 18 months, NOS activity was higher in aortic endothelium (Em) of L- and E-treated animals. Losartan treatment during 6 months also increased NOS activity in aortic smooth muscle (SM). Aortic Em NOS activity fell in the 18 months-treated and untreated animals. E increased NOS activity in the SM of intestinal arterioles at 6 months but reduced it at 18 months. CONCLUSIONS: The fact that both E and L delayed cardiac hypertrophy/hyperplasia and aortic growth and raised aortic endothelium NOS activity indicates a protective effect on cardiovascular damage due to aging, exerted through inhibition of angiotensin II.

Estrogens induce lipoxygenase derivative formation in rabbit lens.

The effect of estrogens on arachidonic acid metabolism was studied in lenses from normal and sex hormone-treated female rabbits. Analysis of the metabolites derived from incubation of these lenses with (1-14C) arachidonic acid provides the first evidence that estradiol activates the lipoxygenase pathway, as indicated by 5-S-hydroxy-6,8,11,14-eicosatetraenoic acid--like product formation, an effect that can be prevented by progestin treatment. Prostaglandin synthesis was not demonstrated by the control or estrogen-treated rabbit lenses, suggesting that lipoxygenase is the major arachidonic acid pathway in the lens.

Role of naturally occurring vasoactive principles in hypertension. State of the art.

Hypertension may result from excessive activity of one or more components of the blood pressure-elevating system. These include the adrenergic nervous system, the renin-angiotensin axis, and mineralocorticoids (aldosterone), which potentiate each other, reinforcing their effects on renal hemodynamics and electrolyte transport and thereby affecting extracellular fluid volume, vascular tone, and reactivity. We consider of no less importance in the genesis of hypertension the failure of one or more components of the blood pressure-lowering system: the kallikrein-kinin system, prostaglandin, or one or more lipids associated with the renomedullary interstitial cells. As a corollary of this hypothesis, if one assumes tonic activity of these opposing blood pressure-regulating systems, in the case of a deficiency of the vasodepressor system, hypertension should result. That is, unopposed activity of the pressor system should be sufficient to increase blood pressure without an increase in the "basal level" of its activity. Hypertension, then, may be considered to result from either uncompensated deficiencies or excesses, which may be relative or absolute, of one or more components of the vasodepressor and vasopressor systems.

Pressor effects of indomethacin in two anephric patients with chronic hypotension.

Two anephric patients with chronic hypotension were treated with indomethacin (150 mg/day). Indomethacin increased supine blood pressures from 63 +/- 4/37 +/- 3 mm Hg (mean +/- SD) to 76 +/- 5/48 +/- 6 mm Hg (patient 1) and 93 +/- 6/47 +/- 6 mm Hg to 112 +/- 8/61 +/- 5 mm Hg (patient 2), P less than .01. Similar changes occurred in standing pressures. The increases in pressures were associated with decreases in blood concentrations of prostaglandins 6-keto-F1 alpha, E2, and F2 alpha, measured by radioimmunoassay. These results suggest that indomethacin may raise blood pressure in certain anephric patients by inhibiting synthesis of extra-renal, vasoactive prostaglandins. Indomethacin may be useful in the treatment of chronic hypotension in anephric patients.

History about the discovery of the renin-angiotensin system.

The history of the discovery of the renin-angiotensin system began in 1898 with the studies made by Tigerstedt and Bergman, who reported the pressor effect of renal extracts; they named the renal substance renin based on its origin. In 1934, Harry Goldblatt induced experimental hypertension in dogs by clamping a renal artery. About 1936, simultaneously in the Medical School of the University of Buenos Aires, Argentina, and in the Eli-Lilly Laboratories in Indianapolis, 2 independent groups of researchers, using the Goldblatt technique to produce experimental hypertension, demonstrated renal secretion of a pressor agent similar to renin. In the following years, both teams described the presence of a new compound in the renal vein blood of ischemic kidneys. This agent was extracted from blood with 70% acetone and had a short pressor effect. The final conclusion was that renin acted enzymatically on a plasma protein to produce the new substance. In Buenos Aires, it was called hypertensin; in the United States, angiotonin. In 1958, Eduardo Braun Menéndez from Argentina and Irving H. Page from the United States agreed to name it angiotensin.

Prostaglandin metabolism in the fetal and maternal vasculature.

The capacity of fetal and maternal blood vessels to synthesize the antithrombotic vasodilator agent prostacyclin (PGI2) suggests that this substance participates in the circulatory adjustments to pregnancy. We studied the capacity of fetal and maternal blood vessels to metabolize [1(-14)C]arachidonic acid; thin-layer chromatography was used to separate PGE2, PGF2alpha, and 6-keto-PGF1alpha (the stable hydrolysis product of PGI2), and these were then quantitated by scintillation counting. Fetal vascular tissues (aorta, ductus arteriosus, and pulmonary arteries) generated tenfold more PGI2 than PGE2. Prostacyclin accounted for more than 50% of the prostaglandins synthesized by fetal blood vessel measured by recovery of its hydrolysis product, 6-keto-PGF1alpha. In contrast, in the mature animals, the aorta and pulmonary artery generated less PGI2 than did fetal tissue, whereas the mesenteric arteries exhibited high biosynthetic capacity comparable to that of the fetal vasculature. Release of prostaglandins by the umbilical blood vessels and ductus arteriosus was also measured by mass fragmentography. The identity of 6-keto-PGF1alpha was confirmed by mass spectroscopy. The high and almost identical capacity of all fetal blood vessels, except the umbilical arteries and veins, to synthesize PIG2 could reflect an important role for this prostaglandin in the regulation of the fetal circulation.

The actions of bradykinin and eledoisin in the canine isolated kidney: relationships to prostaglandins.

1. The effects of two vasodilator polypeptides, bradykinin and eledoisin, were studied in isolated blood-perfused canine kidneys before and after administration of indomethacin, an inhibitor of prostaglandin synthesis, Bradykinin, but not eledoisin, releases renal prostaglandins. 2. Before administration of indomethacin, bradykinin decreased urinary osmolality and increased free qater clearance, whereas eledoisin did not affect the excretion of solute-free water. After administration of indomethacin, the renal vasodilator action of bradykinin was reduced but the vasodilator action of eledoisin was unaffected. 3. Fractional excretion of sodium was not affected by bradykinin before but was increased after administration of indomethacin. Reduction in glomerular filtration rate contributed to changes in sodium excretion produced by bradykinin and eledoisin. 4. The release of prostaglandins from the kidney by bradykinin amplifies the renal vasodilator action of the kinin and possibly mediates its effect on excretion of solute-free water.

Prostaglandins as determinants of vascular reactivity.

Prostaglandins are primarily local or tissue hormones that have their effects at, or near to, the site of synthesis. Some blood vessels synthesize prostaglandins intramurally, where their local release influences vascular tone and reactivity. Endogenous prostaglandins (primarily prostaglandin E2 (PGE2) participate in the regulation of vascular reactivity by opposing the vasoconstrictor and antinatriuretic actions of circulating pressor hormones; and by braking the release of norepinephrine from vasoconstrictor nerves. The proposal that one or more prostaglandins affect vascular reactivity is supported by the following observations: enhanced vascular reactivity to pressor stimuli occurs in organs with low basal rates of prostaglandin synthesis and after inhibition of prostaglandin synthetase in organs with high biosynthetic capacity; and exogenous PGE2 reversibly inhibits the vasoconstrictor activity of pressor stimuli.

Contribution of prostaglandins to the renal circulation in conscious, anesthetized, and laparotomized dogs.

The effects of an inhibitor of prostaglandin (PG) synthetase, indomethacin, were studied on renal blood flow (RBF) and mean aortic blood pressure (MABP) and related to changes in concentrations of PGs in renal venous blood under widely different experimental conditions. Although levels of PGE-like material ("PGE") in renal venous blood of the chloralose-anesthetized-laparotomized dog were 8-fold greater than in conscious dogs, viz., 0.39 vs. 0.05 ng/ml of blood, respectively, RBF and MABP were similar for each group. Indomethacin in doses as high as 10 mg/kg, iv, affected neither RBF, MABP, nor PG levels either in the conscious dog or in the anesthetized dog. However, in the anesthetized-laparotomized dog, smaller doses of indomethacin (2 mg/kg, iv) decreased RBF by more than 40% and increased MABP by 15%. This was associated with a decline in concentration of renal venous PGs to those levels observed in conscious dogs. The principal renal PG varied according to the experimental conditions. The venous levels of "PGF" were greater than "PGE" in conscious dogs, whereas in acutely stressed dogs the renal venous concentrations of "PGE" were more than 2-fold those of "PGF". Plasma renin activity was highly correlated with "PGE" levels in renal venous blood, but not with "PGF" levels. Thus, in the acutely stressed dog, the renal circulation is supported by a major PG component, withdrawal of which results in a decline in RBF. In contrast, in the conscious dog at rest, renal PGs do not appear to contribute significantly to RBF. The significance of the small basal release of PGs into the renal venous effluent of the conscious dog, which is not affected by indomethacin, remains to be determined.

High performance liquid chromatography and UV detection for the separation and quantitation of prostaglandins.

A fast and reliable method for the separation and quantitation of arachidonic acid metabolites PGF1 alpha, PGF2 alpha, PGD2, PGE1, PGE2, PGB2, PGA2, 6-keto PGE1, 6-keto PGF1 alpha, TxB2 and 15-keto PGE2 by high-performance liquid chromatography has been developed. Utilizing a single reverse-phase column and a UV spectrophotometer, sensitivity as little as 30 nanograms of each of these prostaglandins can be separated and subsequently detected. Although this study was performed using standards, it is highly promising for future application to biological fluids.

Ventilation-induced release of prostaglandinlike material from fetal lungs.

Effects of indomethacin upon ventilation-induced pulmonary vasodilation of fetal goats suggest prostaglandins may be important in perinatal transition of the pulmonary circulation. To further test this hypothesis, left pulmonary arterial and pulmonary venous samples were taken before and after ventilation from anesthetized exteriorized fetal (near-term) goats and sheep utilizing, in different animals, either constant or variable left pulmonary blood flow. Characterization and quantification of prostaglandinlike compounds were accomplished utilizing extraction of acidic lipids, thin-layer chromatography, and tissue cascade bracket bioassay. The primary vascular prostaglandinlike material in both fetal and neonatal animals was PGI2-like (PGI). On passage through the fetal lung, concentrations of prostaglandin I- and E-like compounds decreased considerably. After ventilation and ligation of the umbilical cord, concentrations of both PGE2-like (PGE) and PGI in inferior vena caval blood fell, and there was net production of PGI by the newly ventilated lung. Production of PGI2 by newly ventilated lung could provide an important vasodilator influence that would establish and maintain the low pulmonary vascular resistance that is necessary for successful adaptation to extrauterine life.

Prostaglandins and renal function.

Prostaglandins modulate the effects of vasoactive hormones by attenuating the renal actions of the renin-angiotensin system and contributing to and, perhaps, mediating some of those of the kallikrein-kinin system. A prostaglandin mechanism participates in the regulation of renin and erythropoietin release. When renal function is compromised, the circulation to the kidney is sustained by a major prostaglandin component withdrawal of which results in significant hemodynamic effects, particularly reduction of blood flow to the inner cortex and medulla.