Maternal prolactin secretion during labor. The role of dopamine

To investigate the role of dopamine on the mechanisms of maternal prolactin secretion during labor and in the first six hours following delivery.

The study included 30 pregnant women with normal pregnancies, who were meeting the same criteria. They were divided into three subgroups of 10 patients each and they delivered healthy newborns. Group A was the control group. Metoclopramide 10 mg/h intravenously was given in Group B, while bromocryptine 5 mg per os was given in Group C. Maternal blood samples were obtained every hour during labor and in the six hours postpartum. Prolactin values were determined by using a radioimmunoassay method.

Metoclopramide infusion caused an initial significant (p<0.01) rise in PRL level in Group B. Prolactin levels showed the same multiphasic pattern during labor and first h postpartum in both Groups A and B. PRL levels decreased until 1-2 h antepartum, then increased for about 3 h and they finally decreased, starting at 2 h postpartum and reaching values lower than the basic at 6 h postpartum. However, absolute PRL values were higher in Group B (where metoclopramide was given) than in Group A, in every time point. Bromocryptine (Group C) markedly lowered PRL levels, but PRL fluctuation still followed the same trends as in the other two groups.

The different PRL values between the three groups show that maternal PRL is still under dopaminergic influence during labor. However, the fact that PRL levels exhibit the same multiphasic pattern, suggests that there are factors other than dopamine, which strongly influence this pattern.