AHEART August 46/2

Sakai, Hiroshi, Fumitaka Ikomi, and Toshio Ohhashi. Effects of endothelin on spontaneous contractions in lymph vessels. Am. J. Physiol. 277 (Heart Circ. Physiol. 46): H459–H466, 1999.—A mode of action of endothelin (ET) on spontaneous contractions was investigated in ring preparations of isolated bovine mesenteric lymphatics. ET-1 at concentrations between 10210 and 1029 M caused a dose-dependent increase in the frequency of spontaneous contractions. The specific ETA-receptor antagonist BQ-123 (5 3 1027 M) caused a significant inhibition of the ET-1-induced positive chronotropic effect in the ring preparations with and without the endothelium. Mechanical denudation of the lymphatic endothelial cells produced a significant potentiation of the ETinduced positive chronotropic effect. BQ-3020 (1028–1027 M), a selective ETB-receptor agonist, induced dose dependently negative chronotropic and inotropic effects on the spontaneous contractions in the ring preparations with intact endothelium. Mechanical removal of the endothelium caused a significant reduction of the BQ-3020-induced negative chronotropic and inotropic effects. The ET-1-induced positive chronotropic effect was potentiated by pretreatment with Nv-nitro-Larginine methyl ester (L-NAME) (1025 M) but unaffected by aspirin (1025 M). Additional treatment with L-arginine (1024 M) completely reversed the L-NAME-mediated potentiation of the ET-induced chronotropic effect. These results suggest that stimulation of ETA receptors on the lymphatic smooth muscles causes a positive chronotropic effect on the spontaneous contractions, and stimulation of ETB receptors on the lymphatic endothelial cells induces a release of nitric oxide, which results in the chronotropic and inotropic effects on spontaneous contractions in isolated bovine mesenteric lymphatics.