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.