Effect of dopamine on length of gestation and on the release of fetal oxytocin in rats.

Oxytocin (OT) release from the maternal posterior pituitary gland has been implicated in the process of spontaneous labor. The possibility that OT release from a fetal source may also be involved in this process was investigated. Administration of dopamine (DA), 150 mg/kg/ui hr, or L-dopa, 200 mg/kg/12 hr, plus carbidopa, 20 mg/kg/12 hr, to pregnant rats beginning on day 16 of gestation delayed the mean delivery time by 10 to 18 hr. These drug treatments also inhibited the release of OT from fetal pituitary glands which normally occurred during parturition. Release of OT from maternal pituitary glands was not affected and no alterations in the duration or outcome of labor were noted. Administration of [3H]DA to pregnant rats resulted in higher amounts of labeled DA in fetal brain tissues than in maternal brain. These studies suggest that fetal OT is involved in the timing of parturition in the rat and that DA may prolong gestation by affecting fetal OT.