Sustained increases in plasma epinephrine concentration do not modulate renin release

Abstract

We examined the relationship between plasma renin activity (PRA) and renal arterial pressure (RAP) during 1) control conditions, 2) acute, and 3) chronic intravenous epinephrine (EPI) infusion (125 ng.kg-1.min-1). In eight conscious uninephrectomized dogs maintained on a normal sodium intake, the renin stimulus-response curve (RSRC) was determined by a stepwise reduction in RAP with an inflatable occluder around the renal artery controlled by a servo unit. The RSRC could be approximated by two lines intersecting at a threshold pressure (approximately 20 mmHg below control RAP). In the high-pressure range, PRA was relatively insensitive to changes in RAP, whereas, below threshold pressure, changes in RAP had large effects on PRA. During acute EPI infusion there was approximately a 40% increase in heart rate (control = 57 +/- 3 beats/min) and hematocrit (control = 30 +/- 1%) in association with a rise in plasma EPI concentration from 73 +/- 16 to 1,413 +/- 100 pg/ml; mean arterial pressure (MAP) was unchanged (94 +/- 3 mmHg). Moreover, EPI acutely increased basal PRA from 0.3 +/- 0.1 to 0.8 +/- 0.3 ng angiotensin I.ml-1.h-1 and shifted the RSRC to the right (increasing threshold pressure 7 mmHg) without altering the slope of the RSRC curve either above or below threshold pressure. In contrast, although plasma EPI concentration and hematocrit remained elevated during chronic EPI infusion, heart rate and basal PRA returned to preinfusion values. In addition, there were no significant long-term changes in MAP or in any of the parameters of the RSRC.(ABSTRACT TRUNCATED AT 250 WORDS)