Microvascular alterations in the one-kidney, one-clip renal hypertensive rat

The microcirculation was studied in one-kidney, one-clip renal hypertensive rats ( 1KG ) and uninephrectomized controls at 4-6 and 8-10 wk postoperation. Under chloralose-urethan anesthesia the gracilis muscle was transilluminated in situ with a light pipe. Measurements of arteriolar and capillary density and arteriolar diameter were made in three consecutive states: innervated, denervated, and vasodilated with nitroprusside. Arteriolar wall-to-lumen ratio was measured after vasodilation. At 4-6 wk vasoconstriction was significantly greater in 1KG and vasodilated arteriolar diameter was significantly smaller, partially because of an elevated wall-to-lumen ratio. Capillary density in 1KG was reduced in the innervated and denervated states compared with controls. At 8-10 wk in the 1KG , arteriolar vasoconstriction was no longer significantly elevated. However, the vasodilated arteriolar diameter was smaller, wall-to-lumen ratio had increased further, and rarefaction of arterioles and capillaries was present. Thus, with time, structural mechanisms for increasing vascular resistance were seen to displace the active mechanism of vasoconstriction.