Plasma renin activity during pentobarbital anesthesia and graded hemorrhage in dogs

Six dogs were implanted with chronic arterial and venous catheters and were trained to lie quietly on a padded table. The effect of pentobarbital anesthesia and of graded hemorrhage on plasma renin activity (PRA) was then examined in the absence of surgical stress. Pentobarbital anesthesia resulted in a fivefold increase in PRA within 15 min, followed by a slow decline to a level 3 times control at 1.5 h. Mean arterial pressure (MAP) fell transiently but returned to control values. In the unanesthetized dog, graded hemorrhage to 12 ml/kg resulted in a twofold increase in PRA with no change in MAP or heart rate. The same hemorrhage in pentobarbital-anesthetized dogs resulted in a similar increase in PRA, accompanied by a substantial increase in heart rate. It is concluded that 1) pentobarbital anesthesia in the dog results in a rapid and sustained increase in PRA, and 2) in the conscious dog, increased PRA in response to graded hemorrage appears to be independent of an arterial baroreceptor mechanism and of generalized increased sympathetic nervous system activity.