Effect of carotid occulsion on intrarenal haemodynamics

Renal cortical medullary autoregulation was investigated by Sapirstein's 42K and 86Rb isotope fractionation methods under pentobarbital anaesthesia in nondiuretic dogs under normal conditions and during carotid occlusion. Cortical circulation appeared to be autoregulated in both conditions while medullary blood flow showed moderate autoregulation in the control as well as during carotid occlusion. In contrast to expectation, medullary blood flow was not increased by the blood pressure elevation following carotid occlusion but was reduced as a consequence of the simultaneously evoked reflectory vasoconstriction. Carotid occlusion resulted in a more pronounced enhancement of vascular resistance in the medulla than in the cortex. It was concluded that non-uniform intrarenal distribution of the autoregulatory as well as the reflectory vasoconstriction left pressure and filtration rate essentially unchanged in the cortical glomeruli but increased both in the iuxtamedullary ones. Carotid-occlusion diuresis, therefore, cannot be explained by increased medullary blood flow but may be result of augmented flow rate of tubular fluid through the loops of Henle.