Hemorrhage and regional renal blood flow in the conscious dog

The effects of hemorrhage on renal blood flow and the extent to which the responses are modulated by prostaglandins were investigated in 23 conscious, splenectomized dogs. Renal blood flows were measured with radioactive microspheres injected into the left atrium. The renal cortex was divided into four layers for studies of regional flow distribution. Sequential hemorrhage of 10 ml/kg, 20 ml/kg, and 30 ml/kg was performed in six dogs. Total renal blood flow did not change at 10 ml/kg or 20 ml/kg blood loss, but at 30 ml/kg, when mean aortic pressure fell by 41 +/- 9 (SE) mm Hg, there was a reduction in total renal flow from 6.09 +/- 1.04 to 3.00 +/- 0.74 ml/min/gm (P < 0.01). No redistribution in renal cortical blood flow occurred at any level of hemorrhage. Meclofenamate--5.0 mg/kg IV--a prostaglandin synthetase inhibitor, induced vasoconstriction without redistribution of cortical flow. When 10 ml/kg blood loss with subsequent reinfusion was studied before and after meclofenamate in nine normal dogs and two dogs with bilateral adrenalectomy and unilateral renal denervation, neither total nor regional renal flow were altered further. Thus, in conscious dogs, hemorrhage has no effect on total renal blood flow until blood volume is reduced by approximately 3% of body weight and renal cortical blood flow is not redistributed. In addition, an inhibitor of prostaglandin synthetase does not influence the renovascular response to hemorrhagic stress, although it increases renal vascular resistance at rest.