Renin response to hemorrhage in conscious rats: effect of acute reductions in hematocrit.

This study examined the effect of prior exchange transfusion and acute reduction in hematocrit on the subsequent plasma renin concentration (PRC) response to 15 ml/kg hemorrhage in conscious cannulated rats. Long-Evans rats (400-500 g) were assigned to one of eight groups (6-8 rats/group). Rats were exchanged transfused (5 ml total) with whole blood, red blood cells and saline, plasma, or isotonic saline, with the two latter groups showing a decrease in hematocrit of 10-20%. Thirty minutes after exchange transfusion, rats were either subjected to a 0- (control) or 15-ml/kg hemorrhage. Control rats showed no change in mean arterial pressure or PRC regardless of exchange transfusion. The rats exchange transfused with saline had a significant decrease in arterial pH and a more profound hypotension after hemorrhage. PRC ranged from 7 +/- 1 to 11 +/- 1 ng.ml-1.h-1 after exchange transfusion. Subsequent hemorrhage resulted in an increase in PRC that was significantly greater in the saline-transfused group (45 +/- 16 ng.ml-1.h-1) 10 min after hemorrhage. We conclude that exchange transfusion with saline leads to an augmented renin response to hemorrhage in part due to a decrease in arterial pH and more severe hypotension.