Effects of lead on the secretion and disappearance of renin in rabbits

The disappearance rate of renin from plasma was evaluated in both acutely and chronically lead-exposed rabbits. In addition, the effects of lead (Pb) on in vitro renin secretion were determined with rabbit renal cortical slices. Rabbits acutely exposed to Pb (0.3 to 2.0 mg/kg, iv) demonstrated no increase in plasma renin activity (PRA), but a markedly prolonged disappearance of renin following nephrectomy. Together, these observations suggest that renin secretion must have been inhibited; consistent with this hypothesis was the finding that rabbit renal cortical slices exposed to Pb (10(-5) or 10(-6) M) in vitro secreted significantly less renin than did controls. Thus, the effects of large acute doses of Pb in the rabbit are simultaneous inhibition of both renin secretion and clearance. Chronically Pb-exposed rabbits (500 or 1000 ppm in drinking water) had renin half-lives that were not different from controls (6 to 8 min). PRA was also not significantly different in the three groups. Renal slices from both groups of Pb-exposed rabbits secreted significantly more renin in vitro compared to controls, despite the fact that renal renin concentrations were similar in the three groups. However, the responsiveness to a beta adrenergic stimulus was significantly lower in the slices from rabbits treated with 1000 ppm Pb. Taken together these data suggest that PRA in the chronically Pb-exposed rabbit reflects a tendency for increased basal renin secretion, but a counteracting suppression of renin release secondary to adrenergically mediated stimuli; thus, PRA might be reduced, unchanged, or elevated depending upon experimental conditions. Clearance of renin does not seem to be altered in the chronically Pb-exposed rabbit.