PST2238: a new antihypertensive compound that antagonizes the long-term pressor effect of ouabain.

The inhibition of the long-term pressor effect of ouabain may be useful for the therapy of essential hypertension. Here, for the first time, a selective inhibitor of the ouabain pressor effect is described. In vitro, 17beta-(3-furyl)-5beta-androstane-3beta, 14beta, 17alpha-triol (PST 2238) displaced ouabain from its binding sites on purified sodium, potassium ATPase enzyme (Na-K ATPase) (IC50 1.7 x 10(-6) M) without interacting with other receptors involved in blood pressure regulation or hormonal control. In cultured renal cells, incubation with ouabain (10(-10) to 10(-8) M) for 5 days stimulated the Na-K pump at Vmax, whereas PST 2238 showed the same effect at micromolar concentration. The ouabain-dependent increase in the Na-K pump rate was abolished by PST 2238 at concentrations from 10(-14) to 10(-9) M. In rats made hypertensive by chronic infusion of 50 microg/kg/day of ouabain, PST 2238 given p.o at very low doses (0.1-1 microg/kg/day for 4 weeks) abolished the increase in blood pressure and renal Na-K ATPase activity caused by ouabain. PST 2238 did not affect either blood pressure or renal Na-K ATPase activity in normotensive rats. In conclusion, PST 2238 is a very potent compound that normalizes both blood pressure and alterations in the Na-K pump caused by ouabain. Thus it represents the prototype of a new class of antihypertensive drugs that could be effective in forms of hypertension sustained by the concomitant increase of endogenous ouabain levels and alterations in the Na-K pump.

Relations between hypertension and glomerulosclerosis in first-generation hybrid rats of the Milan strains.

In the Milan hypertensive rats (MHS) glomerulosclerosis is less evident than in the normotensive strain (MNS). To clarify whether this pattern is due to a 'protective effect' of increased afferent arteriolar tone or to a different mechanism, we studied 12 first-generation hybrids (F1), 4 parental MHS and 4 parental MNS rats. Four-micrometer sections were stained with hematoxylin, Mallory's trichrome stain and periodic acid-Schiff reaction. The blood pressure of the F1 rats was only slightly higher than that of the MNS so that very probably renal vascular resistances were similar. The F1 rats had low proteinuria (23.3 +/- 2.7 mg/24 h) like the MHS (25.3 +/- 4.8), and few damaged glomeruli per section (18.5 +/- 1.2), again like the MHS (18.7 +/- 1.1). MNS had higher proteinuria (363.8 +/- 111.6; p less than 0.01 vs. MHS and F1) with a greater number of damaged glomeruli (51.4 +/- 4.5; p less than 0.01 vs. MHS and F1). The difference in afferent arteriolar resistance is not implicated in glomerulosclerosis.

Role of enhanced glomerular synthesis of thromboxane A2 in progressive kidney disease.

Normotensive rats of the Milan strain (MNS) spontaneously develop focal glomerulosclerosis. In order to explore the contribution of glomerular thromboxane (TX) A2 synthesis to the development of the disease, we have characterized the time course of renal functional and biochemical changes, and their modification by long-term treatment with a TX-synthase inhibitor. Oral administration (150 mg.kg-1 from 1 to 14 months of age) of FCE 22178 suppressed enhanced glomerular TXB2 production at all experimental times (mean inhibition 80%) and proteinuria (varying between 27.1 and 73.0%) while preserving renal blood flow and glomerular filtration rate. These effects of TX-synthase inhibition were seen in the absence of any statistically significant changes in systemic blood pressure. Moreover, FCE 22178 had no antihypertensive effects in hypertensive rats of the Milan strain (MHS) nor in spontaneously hypertensive rats (SHR). Treatment also prevented the age-related hypoalbuminemia and hyperlipidemia observed in control MNS and significantly (P less than 0.01) reduced glomerular histologic damage, as demonstrated by light microscopy studies and measurement of sclerotic area. We conclude that: 1) MNS rats provide an animal model of long-lasting proteinuria characterized by an age-related increase in glomerular TXB2 production paralleled by progressive loss of renal structural integrity and function and by a secondary dyslipidemia; 2) pharmacological inhibition of glomerular TX-synthase attenuates the structural as well as the functional expression of kidney disease, without a primary effect on systemic blood pressure. These data are suggestive of an important modulating role of TXA2 in the progression of MNS renal disease.

Decreased level of calpain inhibitor activity in kidney from Milan hypertensive rats.

Rat kidney contains two different calpain isozymes distinguishable on the basis of their Ca2+ requirement and of their activation mechanisms. The two calpain isozymes are present in comparable amounts in kidney of normotensive and hypertensive rats of the Milan strain. Conversely, the level of the natural inhibitor of calpain is significantly decreased in kidney of hypertensive rats as compared to control normotensive rats. This deficiency is more pronounced in the cortical region than in other kidney fractions. These results taken together with previous observations indicating the existence of an identical defect in red cells from the same hypertensive rat strain, (Pontremoli, S., Melloni, E., Salamino, F., Sparatore, B., Viotti, P., Michetti, M., Duzzi, L., and Bianchi, G. (1986) Biochem. Biophys. Res. Commun. 138, 1370-1375) emphasize the possible role of an unbalanced intracellular proteolytic system in the development of genetically determined hypertension.

Cardiac and renal hyperplasia in newborn genetically hypertensive rats.

Newborn spontaneously hypertensive rats (SHR), compared with Wistar-Kyoto (WKY) controls, usually show cardiac and renal hyperplasia. To determine whether these anomalies are common to genetically hypertensive rats, we examined newborn rats from models of essential hypertension (Kyoto, Montreal, Dunedin and Lyon strains of hypertensive rats), renal hypertension (Milan strain of hypertensive rats) and experimental hypertension [deoxycorticosterone acetate (DOCA)-salt hypertensive Wistar rats]. The hearts, kidneys and livers of these newborns were collected on site at various centres and sent to Montreal for protein and DNA determinations. The results showed that protein and DNA, corrected for body weight in models of essential hypertension, were increased in the heart and kidney, and normal or decreased in the liver at birth. This pattern differed in offspring of the Milan strain (renal hypertension) and of DOCA-salt hypertensive animals (experimental hypertension). Since cardiac and renal hyperplasia associated with the hypertensive trait in four different genetic models of spontaneous hypertension was distinct from that observed in renal and experimental hypertension, it is conceivable that a specific cardiovascular growth pattern is a reflection not of a simple linkage or consequence, but of a causal association with spontaneous hypertension.

Decreased level of calpain inhibitor activity in red blood cells from Milan hypertensive rats.

In mature red cells of rats from Milan Normal (MNS) and Hypertensive Strains (MHS), the soluble Ca2+-dependent neutral proteinase (calpain) is present in similar amounts as the form requiring 0.1-0.2 mM Ca2+ for maximum catalytic activity. The amount of the endogenous calpain inhibitor, however, differs greatly in the red cells of the two strains. In red cells from hypertensive rats the activity of the inhibitor is 10 times less with a ratio of inhibitor to calpain activity (unit/unit) of 0.2; compared to red cells from normal rats, in which this ratio is approximately 2. This is the first demonstration of the existence, in a mammalian cell, of such a low ratio of calpain to inhibitor and implies the occurrence of a potentially "unregulated" intracellular soluble proteinase. This abnormal condition may be responsible for some of the structural and metabolic changes reported in rats of the genetically determined MHS strain.

Changes in renin, water balance, and sodium balance during development of high blood pressure in genetically hypertensive rats.

In genetically hypertensive rats of the Milan hypertensive strain (MHS) and normotensive rats (NR) developed from the same Wistar stock colony, blood pressure (BP), plasma renin activity (PRA), sodium balance, and water balance were measured from the time of weaning to the seventh week postweaning in three separate but essentially identical experiments. In a fourth experiment, total and extracellular water, total sodium, and exchangeable sodium were measured in MHS and NR at 24 and 130 days of age. Although the time course of changes varied slightly between experiments, BP of both NR and MHS rose until the second and third weeks postweaning, at which time BP in MHS was 40 to 50 mm Hg higher than in NR. PRA in MHS was one-half that of NR at weaning. Increasing BP was accompanied by falling PRA in both, and PRA was not significantly different when stable, adult blood pressure was reached. Urinary volume in MHS was 50% to 100% greater (P less than 0.001) than in NR at weaning and for a few days after. Sodium was retained to a greater extent by MHS during the period when the blood pressure difference develops, from weaning to the fourth week postweaning. This sodium retention (MHS = 97.0 plus or minus 10.3, NR = 65.2 plus or minus 6.8 SE mu-Eq Na retained/g body weight gain; P less than 0.005) is the result of significantly lower urinary excretion of dietary sodium by MHS. A causative role for the kidney is suggested in the established of high blood pressure in MHS.