Effect of nickel on uterine contraction and ultrastructure in the rat.

The in vitro effects of nickel chloride (NiCl2) on uterine contractile activity and ultrastructure were studied in uterine strips isolated from 20-day-pregnant Wistar rats. Ni2+ had a dual action on uterine spontaneous contractions. In low concentrations (10(-7) M to 10(-5) M), NiCl2 increased basal tone significantly but had no effect on the amplitude or frequency of development of isometric force. High concentrations of NiCl2 (10(-4) M to 10(-3) M inhibited spontaneous contractile activity and decreased basal tone, which was antagonized by elevation of the extracellular concentration of Ca2+. Electron microscopic localization of Ni by the dimethyl glyoxime cytochemical technique showed that, after incubation of uterine strips in a physiologic medium that contained 10(-6) M NiCl2, electron-dense Ni-dimethyl glyoxime particles could be observed in the cytoplasm and in the mitochondria of uterine smooth muscle cells. Exposition of Ni caused mitochondrial structural damage and accumulation of glycogen. The experimental results indicate that, because of its oxytocic action, the increase in the serum level of Ni in the advanced stage of human labor (Rubányi and associates, 1982) may support separation of the placenta and/or may contribute to the prevention of atonic bleeding in the postpartum period.