RENAL EFFECTS OF ALDOSTERONE IN THE SODIUM-BICARBONATE INFUSED RAT

The present study investigated the renal function in male Sprague-Dawley rats receiving continuous NaHCO3 (0.077 M) infusion. The renal effects of aldosterone administration in this preparation were also examined. Continuous NaHCO3 infusion significantly (p < 0.01) depressed plasma aldosterone concentration to 2.36 +/- 1.22 nmol (n = 8) when compared to saline infused rats (4.36 +/- 0.72 nmol, n = 7). The low plasma aldosterone levels in HCO3--infused rats was associated with renal loss of large amounts of K+ and hypokalaemia. Aldosterone administration (42 pmol/min) for 2 h significantly (p < 0.01) reduced the Na+ excretion rate in bicarbonate infused rats from a mean peak of 9.82 +/- 1.16 to 5.16 +/- 1.20-mu-mol/min (n = 8). Aldosterone administration did not alter renal excretion in saline-infused rats. It is concluded that NaHCO3 loading depressed endogenous aldosterone secretion, and that this lowered endogenous plasma aldosterone level allows the mineralocortoid effect of exogenous aldosterone to be observed.