Possible involvement of atrial natriuretic factor in the antihypertensive action of a high-calcium diet in spontaneously hypertensive and Wistar-Kyoto rats

Abstract

The present study was designed to determine the possible involvement of atrial natriuretic factor (ANF) in the hypotensive action of a high-calcium diet. The effects of increased dietary calcium (2.9% calcium, HCa) on blood pressure, urinary sodium excretion, and ANF were examined in 30 spontaneously hypertensive rats (SHR) and 30 Wistar-Kyoto rats (WKY). Control groups of 30 SHR and 30 WKY were fed normal calcium lab chow (0.4% calcium, NCa). The HCa diet reduced blood pressure and serum phosphorus concentration and increased urinary excretion of sodium and calcium in SHR and WKY. The HCa diet also caused a sustained increase in plasma ANF concentration and, finally, a decrease in atrial ANF concentration in both groups. A significant inverse correlation was observed between ANF concentrations in plasma and atria of the four experimental groups. Plasma ANF concentration was positively correlated with daily calcium consumption, and blood pressure was inversely correlated with daily calcium consumption in HCa- and NCa-SHR groups and in HCa- and NCa-WKY groups, respectively. Furthermore, a significant inverse correlation between blood pressure and plasma ANF concentration was observed in SHR groups and in WKY groups, respectively. The observed sustained increment in endogenous plasma ANF concentration, which is probably caused by increased secretion from the atrium, may contribute, in part, to the blood-pressure-lowering effects of the HCa diet.