Clearance of renin in unanesthetized rats: effects of chronic lead exposure

These experiments studied the influence of chronic lead exposure on the steady-state clearance of exogenous homologous renin in unanesthetized, unrestrained rats. Relative to time controls (TC), rats chronically exposed to 500 ppm lead in drinking water had significantly elevated basal plasma renin concentrations (PRC) (Pb = 12.0 +/- 1.6 ng/ml/hr, TC = 7.6 +/- 0.8). During the infusion of homologous renin sufficient to increase plasma renin approximately 10-fold, the clearance of renin was not different between the two groups (after 60-min infusion, Pb = 16.1 +/- 1.8 ml/kg/min, TC = 15.9 +/- 1.5). Rats exposed to 1000 ppm lead did not have higher PRCs than time controls (Pb = 10.9 +/- 2.2 TC = 9.2 +/- 1.8). The clearances of renin in these two groups were also not significantly different (Pb = 15.3 +/- 2.8 TC = 18.3 +/- 2.5). Renal renin concentrations were significantly elevated in the 500 ppm rats (Pb = 1426 +/- 110 micrograms/kidney, TC = 1065 +/- 118) consistent with an increased basal renin secretion, but were not elevated in the 1000-ppm rats. There were no significant differences in the clearances of sulfobromophthalein (BSP) between any of the groups. The renin infusion significantly reduced BSP clearance, but did not so equally in all groups. It is concluded that in unanesthetized, unrestrained rats the clearance of renin is not altered by chronic lead exposure of either 500 or 1000 ppm and that increased secretion of renin accounts for the elevated basal PRC observed in rats exposed to the lower dose of lead.