INHIBITORY EFFECT OF PROSTAGLANDIN F2α ON OXYTOCIN RELEASE AND ON MILK EJECTION IN LACTATING RATS

Abstract

SUMMARY: The effect of prostaglandin F_2α (PGF_2α) on milk ejection and on oxytocin release during suckling for one or two periods of 30 min was studied in lactating rats. Doses of PGF_2α (20 or 40 μg) were injected i.p. 15 min before the suckling period. Control rats were injected with physiological saline. An inhibition of milk ejection proportional to the dose of drug administered was obtained. A normal milk ejection response was induced with a small dose of oxytocin injected immediately before nursing to mothers treated with PGF_2α, indicating that the blocking effect was not due to a lack of mammary gland response. Two groups of mothers were injected with 40 μg PGF_2α 2 and 4 h respectively before suckling. In both groups milk ejection was partially but significantly inhibited. In rats pre-treated with sodium pentobarbitone (3·5 mg/100 g body wt) to prevent the release of oxytocin induced by suckling, PGF_2α (10 or 20 μg) did not modify the inhibition of milk ejection indicating that PGF_2α does not have milk-ejecting activity. The administration of oxytocin to anaesthetized rats, immediately before a second suckling period, induced a normal milk-ejection response while in the rats treated with PGF_2α, oxytocin was less effective. The results indicate that PGF_2α inhibited milk ejection by a central block on oxytocin release and that the lipid is not able to mimic peripherally the milk-ejecting activity of oxytocin.