Human chorionic gonadotrophin inhibition of pregnant human myometrial contractility.

OBJECTIVE: To evaluate the effect of human chorionic gonadotrophin (hCG) on pregnant human myometrial contractility in vitro and to determine whether the hCG-elicited effect was oestrogen dependant.
METHODS: Isometric tension recording was performed under physiological conditions in isolated myometrial strips from biopsies obtained at elective caesarean section. The effect of cumulative additions of hCG (0.001, 0.01, 0.1, 1.0 and 10 iu/mL) on myometrial contractility was evaluated. Secondarily, the contractile activity of pregnant myometrium following hCG exposure was investigated in tissue pre-treated with beta-oestradiol.
RESULTS: hCG exerted a statistically significant relaxant effect on pregnant human myometrial tissue. The relaxant effect increased with increasing concentrations of hCG from 8.96% (SEM 2.06) (0.001 iu/mL hCG: P < 0.01 ) to a net cumulative total of 58.50% (SEM 3.74) (10 iu/mL hCG; P < 0.01). The relaxant effect was also time-dependant, increasing in magnitude throughout the duration of experiments. Beta-oestradiol did not significantly affect the response of myometrial tissue to hCG.
CONCLUSIONS: These results clearly demonstrate that hCG exerts a significant concentration-dependant relaxant effect on human myometrial tissue obtained rate in pregnancy. These findings outline an inhibitory physiological role of hCG on human myometrial contractility and raise the possibility of its potential use as a tocolytic.