L-cysteine and sodium hydrosulphide inhibit spontaneous contractility in isolated pregnant rat uterine strips in vitro

The control of myometrial contractility during pregnancy and parturition is not fully understood. Gas signalling molecules, such as nitric oxide and carbon monoxide, have been shown to relax the myometrium and may be involved in the control of contractility. Hydrogen sulphide has recently been shown to be produced endogenously in animal and human tissue and to have a signalling function. The aim of the study was to investigate the effect of L-cysteine and sodium hydrosulphide, potential hydrogen sulphide donors, on pregnant rat uterine contractility in vitro. Strips of pregnant rat uterus (n=22) were set up in a standard organ bath system. Following equilibration and recording of spontaneous contractility, the tissue was exposed to 45 mM potassium chloride followed by 1 nM oxytocin. Dose ranges of 10(-8) - 10(-3) M of L-cysteine (n=8) or sodium hydrosulphide (n=8) were subsequently applied to the tissue. In a third series of experiments (n=6) the effect of doses of 10(-9), 10(-6) and 10(-3) M of L-cysteine, D-cysteine, L-serine, DL-methionine and DL-homocysteine on myometrial contractility were compared. Contractions were integrated over 10 min. periods and the values were compared by one-way analysis of variance. L-Cysteine and sodium hydrosulphide produced significant dose-dependent decreases in uterine spontaneous contractility. Of the amino acids tested, only L-cysteine produced a significant reduction in spontaneous contractility at a dose of 10(-3) M. This study has demonstrated novel tocolytic actions of L-cysteine and sodium hydrosulphide. however further work is required to determine their mechanisms of action.