Peripheral blood flow response to step-wise increase of arterial pressure in conscious rats

In conscious rats, changes in renal or superior mesenteric flow were observed when arterial pressure was elevated by occluding the terminal aorta. Blood flow was measured with an implanted electromagnetic flow probe and terminal aorta occlusion (TAO) was induced with an implanted pneumatic occluder. Arterial pressure was recorded with an indwelling catheter in the common carotid. Each TAO lasted for 20 seconds and flow and pressure at the end of this period were noted as those during TAO. After elimination of the reflexive compensation of arterial pressure by ganglionic blockade, the renal flow increase during TAO was slight but significant (p <0.01), although the relative increase in flow was less than that in pressure. In other words, renal autoregulation, constancy of renal blood flow in the face of arterial pressure change, was imperfect. After further pentobarbital anesthesia, however, renal autoregulation was more complete to such an extent that the renal flow increase was insignificant during TAO. In contrast, the relative increase in superior mesenteric flow during TAO was larger than that in pressure with or without anesthesia.