[Effects of PGF2 alpha prostaglandins on milk ejection in the ewe. Consequences of ovariectomy with or without...

The intrajugular administration of 200 micrograms of Dinolytic (tromethamine salt of PGF2 alpha) to lactating ewes caused an intramammary pressure (IMP) increase only during the luteal phase of the sexual cycle (group A). The increase in progesteronemia, induced by three daily injections of 2.5 micrograms of LH-RH, did not modify response amplitude (group B). On the other hand, bilateral ovariectomy (groupe C) led to the suppression of those responses, but supplementary oestroprogestative (table 1) did not re-establish them. It is probable that the milk ejection caused by PGF2 alpha resulted from a release of oxytocin by the corpus luteum. The ineffectiveness of the exogenous and endogenous reinforcement of progesterone therefore suggests that this hormone plays no part in the putative control of hypothalamic receptivity to prostaglandins.