Effects of caffeine on the vascular smooth muscles isolated from two-kidney, one-clip renovascular hypertension in rabbits

To examine the intracellular calcium content of the vascular smooth muscle in the chronic phase of renovascular hypertension, the effects of caffeine on isolated aortic, renal and iliac arterial strips were evaluated in two-kidney, one-clip renovascular hypertension in rabbits. 10 weeks after left renal artery constriction in the constricted group, systemic blood pressure (BP) was significantly higher than in the control group, but plasma renin activity was similar to the control value. The amplitude of caffeine-induced contraction of various vascular strips in the constricted group gradually increased and, at 10 weeks, this was higher in the constricted group than in the control group. In the constricted group, sodium loading produced BP elevation and increased the amplitude of caffeine-induced contraction, whereas sodium constriction decreased BP and the amplitude. In the control group, altered sodium intake did not affect BP and the amplitude of caffeine-induced contraction. These results suggest that in the chronic phase of renovascular hypertension, the increased caffeine-sensitive intracellular calcium store on vascular smooth muscle, which is increased by sodium loading and is decreased by sodium restriction, may contribute to the maintenance of hypertension.