Different interaction of bepridil and diltiazem with BAY K 8644 in the abolition of autoregulation of renal blood flow.

The effect of bepridil and diltiazem on autoregulation of renal blood flow was examined in connection with interaction of BAY K 8644 in perfused kidney of anesthetized dogs. When the perfusion pressure was changed stepwise over the range between 60 and 200 mm Hg, renal blood flow remained nearly constant between 100 and 200 mm Hg. Intra-arterial infusion of diltiazem (50 microgram/min) or bepridil (1 mg/min) increased renal blood flow at perfusion pressure above 100 mm Hg and completely inhibited renal autoregulation. Simultaneous infusion of 5 microgram/min of BAY K 8644 with diltiazem antagonized both the increase of renal blood flow and the impairment of autoregulation, whereas simultaneous infusion of BAY K 8644 (5 micrograms/min) could not block the impairment of renal autoregulation induced by bepridil. These results show that the inhibitory effect of bepridil on autoregulation of renal blood flow is due to some mechanism other than Ca channel blocking action in renal vasculature.