The separate and combined influences of common carotid occlusion and nonhypotensive hemorrhage on kidney blood flow.

The separate and combined effects of bilateral common carotid occlusion (C.C.O.) and hemorrhage on renal blood flow (R.B.F.) were studied in 11 unanesthetized dogs. C.C.O. increased arterial blood pressure (4.4 kPa; 33 mm Hg) and heart rate (10 beats/min) while R.B.F. remained unchanged. When kidney perfusion pressure was maintained at its resting level during C.C.O. (implanted pneumatic cuff) there was also no change in R.B.F. After cutting the aortic nerves in 2 dogs the increase in blood pressure and heart rate with C.C.O. was greater (10.6 kPa; 80 mm Hg and 72 beats/min); however, there was no change in R.B.F. A blood loss of 16% (13.6 ml/kg) reduced central venous pressure (0.3 kPa; 2 mm Hg), increased heart rate (8-14 beats/min) and decreased arterial mean pressure by a maximum of 0.7 kPa (5 mm Hg) (non-hypotensive hemorrhage, N.H.H.). R.B.F. showed a tendency to rise and 90 min after the onset of bleeding was slightly increased (12% of control). After N.H.H. carotid occlusion had no effect on R.B.F. when kidney perfusion pressure increased; when perfusion pressure was controlled during C.C.O. the maximum observed decrease of R.B.F. was 15 ml/min (5% of control). It is concluded that the control of R.B.F. during the baroreceptor reflex under normovolemia and after a blood loss of 16% in the conscious dog at rest does not involve sympathetic vasoconstrictor effects which result in a significant change in total blood flow.