ROLE OF PHOSPHOLIPASE-C AND PHOSPHOLIPASE A(2) IN THE NITRIC OXIDE-INDEPENDENT VASODILATOR EFFECT OF BRADYKININ IN THE RAT PERFUSED HEART

The cytochrome P450-dependent component of the coronary vasodilator ac tion of bradykinin which requires activation of K+ channels was examin ed in terms of the contribution of phospholipases in the rat Langendor ff heart preparation. This component was isolated by inhibition of nit ric oxide synthase with nitroarginine and cyclooxygenase with indometh acin, neither of which affects the coronary vasodilator action of brad ykinin. However, nitroarginine elevated coronary perfusion pressure fr om approximately 40 to 130 mm Hg. The phospholipase C inhibitor, U7312 2 {1-(6-((17 0)-trien-17-yl)amino)hexyl)-1H-pyrrole-2,5-dione}, reduce d coronary vasodilator responses to bradykinin by greater than 80%. U7 3122 also diminished the coronary vasodilator action of cromakalim whi ch activates ATP-sensitive K+ channels. The maleimide moiety of U73122 that has the capacity to affect K+ channels inhibited cromakalim-indu ced coronary vasodilation, but did not affect that to bradykinin. Inhi bition of diacylglycerol lipase with RHC 80267 {1,6-bis-(cyclohexyloxi minocarbonylamino)-hexane} was without an overall effect on coronary v asodilator responses to bradykinin. The cytosolic phospholipase A(2) i nhibitor, AACOCF(3) {arachidonyl trifluoromethyl ketone}, decreased re sponses to bradykinin by up to 90%, whereas inhibitors of the secretor y form of phospholipase A(2), oleyloxyethyl phosphorylcholine and ONO- RS-082 {2-(p-amylcinnamoy)amino-4-chlorobenzoic acid} were less effect ive than either AACOCF(3) or U73122. The phospholipase inhibitors demo nstrated selectivity as they did not affect the coronary vasodilator r esponses to nitroprusside. We obtained additional evidence for the ant iphospholipase activity of the inhibitors by demonstrating their capac ity to suppress bradykinin-stimulated increases in the release of pros tacyclin, measured as 6-keto prostaglandin F-1 alpha. The phospholipas e inhibitors did not affect cyclooxygenase activity as the ability of arachidonic acid to stimulate prostaglandin formation was unimpaired. These results indicate that the coronary vasodilator action of bradyki nin is linked to the activities of both phospholipase C and A(2).