INHIBITORY ACTIONS OF VARIOUS VASORELAXANTS ON THE MYOGENIC CONTRACTION INDUCED BY QUICK STRETCH STUDIED IN CANINE CEREBRAL-ARTERY

Quick stretch at a rate of 10 cm/s with the amount of 30% of the initi al muscle length (= 100%) produced a myogenic contraction in canine ce rebral artery. The inhibitory actions of various vasorelaxants on the stretch-induced contraction were investigated. Ca2+ channel blockers ( nicardipine, D-cis-diltiazem) inhibited the stretch-induced contractio n by 50-60% at the concentrations which abolished high KCl-induced con traction. Inhibitions of the stretch-induced contraction by nitro-comp ounds (nitroglycerin, sodium nitroprusside) were about 50%. In contras t, inhibitions by the compounds which activate ATP-sensitive K+ channe ls (cromakalim, nicorandil, pinacidil) of the myogenic contraction in response to quick stretch were only 20%. Papaverine totally abolished the stretch-induced contraction. It is likely that all the vasorelaxan t compounds tested in the present study except papaverine are benefici al in the sense that they do not suppress the intrinsic myogenic contr action, which may be related to the autoregulation of local blood flow . (C) 1998 Elsevier Science B.V. All rights reserved.