Abstract

Pentobarbital-anesthetized dogs were bled to, and maintained at, a fixed hypotensive level of 45 mm Hg for a two-hour period. Controlled hypotension was achieved by means of an arterial stabilization reservoir. The relative effect of the renal presser and sympathetic nervous system on vascular capacity during hypotension was determined by comparisons of bleeding volumes between nephrectomized and sham-operated dogs with and without spinal anesthesia. Sham-operated dogs without spinal anesthesia did not bleed more than their nephrectomized counterparts within the first 2 minutes, but lost significantly more blood within 10 minutes. Thirty minutes after the onset of hypotension the blood loss of sham-operated animals was 45.3 ml/kg, whereas that of nephrectomized animals was 34.9 ml/kg. Spinal anesthesia induced prior to hypotension reduced the blood loss of both shamoperated and nephrectomized dogs throughout the hypotensive period and reduced the blood loss attributable to vasoactive substances of renal origin. Thirty minutes after the onset of hypotension the blood loss of sham-operated animals was 23.8 ml/kg and that of nephrectomized dogs was 19.9 ml/kg. It is concluded that the potential of the renal pressor system to reduce vascular capacity during hypotension is approximately 60% of that of the sympathetic nervous system and that release of pressor substances from the kidney may be partially under neurogenic control.