RHYTHMIC CONTRACTIONS OF ISOLATED SMALL ARTERIES FROM RAT - INFLUENCEOF THE ENDOTHELIUM

Small arteries of the mesenteric arcade from Wistar rats display rhyth mic oscillations superimposed on the tonic contractile response when e xposed to submaximal doses of noradrenaline. We have previously shown that mechanical removal of the endothelium abolishes these oscillation s. In the present study different methods to eliminate or modify the i nfluence of the endothelium were used in order to further characterize the mechanisms behind rhythmic contractions in these vessels. Endothe lium was removed either mechanically or chemically by perfusing the ve ssels with 0.3% CHAPS. The absence of functional endothelium enhanced noradrenaline sensitivity and simultaneously abolished oscillations in tension and membrane potential, but did not affect resting membrane p otential. The rhythmic activity was also reduced or abolished by expos ure to haemoglobin, methylene blue, LY83583 or L-NNA. Indomethacin and propranolol were without effect. Sodium nitroprusside or the permeant analogue of cyclic GMP, 8-bromo cyclic GMP, restored rhythmic activit y in precontracted endothelium-denuded vessels. The data suggest that release of nitric oxide from the endothelium, and subsequent generatio n of cyclic GMP in the smooth muscle, activates oscillations in membra ne potential and tension; the oscillator itself appears to be located within the smooth muscle cells.