Temporal pattern of secretion of renin in the hemorrhaged dog

The rate of renin secretion (product of renal plasma flow and the arteriovenous difference for plasma renin concentration) was measured by continuous collection of 2-min samples of arterial and left renal venous blood with continuous electromagnetic monitoring of left renal blood flow in 5 anesthetized male mongrel dogs. Measurements were made for 1 h before and at least 53 min after withdrawal of 16 ml blood/kg BW in 2 min. During the 1-h control period, there were no significant changes in measured variables. The hemorrhage was followed by a sustained reduction in average mean arterial blood pressure to 78.5 +/- 2.24% (SD) of average control values and by a sustained reduction in average renal blood flow to 87.3 +/- 4.47% (SD) of average control values. An increase in rate of secretion of renin began during the hemorrhage in every animal. The increase was transient, reaching a peak at 3-5 min and a nadir at 5-11 min after initiation of hemorrhage. At the peak, the mean value was 1996.9 +/- 977.6% (SE) of mean control, and at the nadir, it was 87.6 +/- 44.7% (SE) of mean control. After the initial treatment increase there was a gradual irregular mean increase in the rate of renin secretion. These data demonstrate that the immediate changes in rate of renin secretion in response to a brief hemorrhage sufficient to cause sustained hypotension are biphasic. This characteristic must be taken into account in modeling regulation of renin secretion and in planning experiments.