Induction of transient hyperprolactinaemia in neonatal rats by direct or maternal treatment with the dopamine receptor blocker, sulpiride.

Prolactin was measured in the plasma of neonatal rats after iv and ip injection of the dopamine receptor blocking drug sulpiride, and after its ip injection to neonatal rats' nursing mothers. The sulpiride dose PRL response relationship in 10-25 day old neonatal rats was similar to that found in lactating rats, with a threshold sensitivity around 29 nmol sulpiride/kg body weight and a maximal response at about 2.9 mumol/kg. Absolute levels of PRL in the neonate (both peak and increment-over-basal) were, however, 90% lower than in adults. Treatment of lactating mothers with a maximally stimulatory dose of sulpiride (2.9 mumol/kg) twice daily for 4 days resulted in small but highly significant increases in neonatal PRL on days 1 and 2 but complete loss of response by day 4. These data demonstrate that there is a close similarity between the responses of maternal and neonatal rats to sulpiride and that transfer of the drug to the neonate via milk can induce neonatal hyperprolactinaemia. The subsequent loss of the neonatal PRL response on chronic exposure to sulpiride may indicate a degree of disturbance of hypothalamic dopaminergic mechanisms. In the clinical situation this would suggest that doses of dopamine receptor-blocking drugs used to enhance maternal milk production should be carefully chosen.