[Evaluation of the dopaminergic neuroendocrine control of prolactin release during labor in humans].

Eight women with normal term pregnancy were i.v. administered 10 mg Metoclopramide (M), dopamine antagonist, before and during labor. Serum prolactin (PRL), TSH, GH and cortisol levels were measured at -30, 0, 30 and 60 minutes after M administration by specific radioimmunoassay. Basal serum PRL levels before labor, 287.5 +/- 28.6 ng/ml (mean +/- S.E.), significantly declined during labor to 237.0 +/- 22.4 and 216.4 +/- 22.9 ng/ml (p less than 0.05 at both) at 0 and 30 minutes before M administration, respectively. The increments in serum PRL at 30 and 60 minutes after M administration during labor (209.5 +/- 33.9 and 120.0 +/- 27.1 ng/ml, respectively) were not significantly different from those before labor (202.1 +/- 48.7 and 89.9 +/- 30.1 ng/ml, respectively), suggesting that the decline in serum PRL levels during labor is not due to the dopaminergic control. Basal serum TSH and GH levels were not significantly changed by labor and M administration either before or during labor. Serum cortisol levels tended to increase during labor, but these changes were not significant. The data suggest that the PRL releases from the pituitary during labor are not controlled by the dopaminergic mechanism.