Mechanism of relaxant response to papaverine on the smooth muscle of non-pregnant rat uterus.

In the present paper, we examined a mechanism of the papaverine-induced relaxation in the smooth muscle of non-pregnant rat uterus. The hyperosmotic 65 mM KCl (H-65K+)-or oxytocin-induced contraction in the uterus was inhibited by an addition of papaverine in a concentration-dependent manner. Papaverine did not increase both cAMP and cGMP contents in the uterus in the presence of H-65K+ or oxytocin. In fura 2 loaded muscles, papaverine did not affect an increase of [Ca2+]i level by high K+ or oxytocin. In permeabilized muscles, papaverine had no effect on the Ca2+-induced contraction. H-65K+ and oxytocin increased the rate of oxygen consumption 1.8 and 1.5 times higher than that in the resting condition, respectively. The increase of oxygen consumption in the H-65K+ or oxytocin was significantly inhibited by papaverine (1-100 μM). These results suggested that papaverine inhibits smooth muscle contraction mainly by inhibition of mitochondrial respiration in rat uterus as well as guinea pig ileum, which shows a highly spontaneous activity and a highly metabolic dependency of a contraction.