Altered local regulation of blood flow and shear rate in renal hypertension.

The purpose of this study was to evaluate acute and chronic autoregulation of blood flow in the cremaster muscle of one-kidney, one-clip (1K1C) hypertensive rats and to investigate alterations of shear stress during the development of hypertension. Unilateral renal artery stenosis and contralateral nephrectomy were performed in half of the rats and a sham operation was carried out in the other half. Mean blood pressure was significantly increased at 1 (38%) and 4 (34%) weeks in 1K1C rats v age-matched controls. Heart rate was significantly increased 15% at 1 week in 1K1C rats but returned to the control level at 4 weeks. Cremaster arteriolar dimensions were measured in vivo by intravital microscopy. Resting diameter of the first-order arteriole (1A) in 1K1C rats was decreased by 25% (P < .05) at 1 week and by 16% at 4 weeks (ns). Measured by the dual-slit technique, total blood flow to the cremaster muscle in 1K1C rats was reduced by 58% (P < .05) at 1 week but was not significantly different from control at 4 weeks. Wall shear rate calculated in the 1A of 1K1C rats was not significantly different from control at 1 week but was elevated 70% (P < .05) at 4 weeks. Therefore, autoregulation of blood flow in skeletal muscle is impaired and/or overridden in the acute phase of 1K1C hypertension. Shear rate, however, did not deviate from the control level until later, which might be the result of impaired function of the endothelium in chronic hypertension.