Endothelial modulation of resting and stimulated vascular tone in the pig capsular testicular artery.
We have investigated the wall tension characteristics and the role of endothelium on vascular tone, at rest and under K+ depolarization, in isolated rings from the pig capsular testicular artery. The active tension reached a maximum that was significantly lower in vessels without endothelium, whereas the passive tension and the Ca2+-dependent myogenic tone were not significantly affected by endothelium removal. Both NG-nitro-l-arginine (L-NOARG, 10(-4) M) and methylene blue (10(-5) M), increased the basal resting tension (BRT) in vessels with endothelium, while indomethacin (10(-6) M) decreased BRT in vessels both with and without endothelium. Either removal of endothelium or treatment with indomethacin (10(-6) M), quinacrine (10(-5) M) or ibuprofen (10(-5) M), significantly depressed the K+ concentration response curve, while dazoxiben (10(-5) M) and SQ 30,741 (10(-5) M) had no effect. L-NOARG (10(-6) M) potentiated the contractile response to K+ in vessels with endothelium, whereas L-NOARG (10(-4) M) was ineffective in vessels devoid of endothelium. These results suggest that a predominating NO release from endothelium, together with a cyclooxygenase-derived vasoconstrictor, modulate vascular tone at rest. In contrast, predominant endothelial release of a cyclooxygenase-derived contractile factor, but different from TXA2, PGH2 or superoxide anions, is induced by K+ depolarization and leads to vasoconstriction.