Relation Between Prolactin and Gonadotrophin Secretion in Post-Partum Lactating Rats

Abstract

In post-partum lactating rats, sucking by the young was associated with high prolactin release and maintenance of lactation but severe inhibition of LH and FSH release and suspension of oestrous cycles. Shortly after the pups were removed on day 22 post partum LH and FSH release returned to normal and oestrous cycles resumed. Twice-daily injections of ergocornine methanesulphonate (ERG) into mothers beginning at 5 or 7 days post partum, resulted in sustained inhibition of prolactin release and diminished mild secretion. By frequent exchange of pups between control and ERG-treated mothers, it was possible to maintain vigorous sucking and almost normal pup growth despite low serum prolactin levels and diminished lactation. In these rats, serum levels of LH remained low during 11 or more days of treatment with ERG, but serum FSH was consistently higher than in untreated control mothers. After 11 or more days of ERG treatment, most rats showed a return to normal LH and FSH release and resumption of oestrous cycles. These results suggest (a) that the sucking stimulus rather than high prolactin levels in the circulation is mainly responsible for inhibition of LH and FSH release during the first 11 days post partum, (b) that the sucking stimulus acts to increase prolactin and inhibit LH release by separate hypothalamic mechanisms, and (c) that administration of ERG results in diminished prolactin release and lactation, and in increased release of FSH and subsequently of LH with earlier resumption of oestrous cycles.

Effect of naloxone on plasma concentrations of prolactin and LH in lactating sows

“…Hyperprolactinaemia has been described as able to affect LH secretion in the rat (Lu et ., 1976), man (Roland, Lequin, Schellerens & de Jong, 1975) and sheep (Kann, Martinet & Schirar, 1977), and so one possible hypothesis to explain the inverse relationship occurring between LH and prolactin during lactation is that suckling stimulates the secretion of prolactin which in turn suppresses LH secretion. However, the present results seem to indicate that both high prolactin and low LH concentrations are the results of the same factor, acting through an opioid-mediated mechanism.…”

Variations in Serum Gonadotropin and Prolactin Levels during Consecutive Reproductive States in Mongolian Gerbils (Meriones unguiculatus)

“…This may be explained by the fact that the suckling stimulus suppresses gonadotropin secretion during the first half of lactation [12,33] and inhibin may play a primary role in the suppression of FSH secretion, whereas ovarian steroids have been shown to play a primary role in the suppression of LH secretion during the second half of lactation [33]. Similar to the levels reported in rats [8], PRL levels in Mongolian gerbils during early lactation were high and subsequently decreased.…”

Prolactin Causes the Dissociation of Prolactin from Plasma Membrane Receptor in Lactating Mouse Mammary Cell: Action of High Prolactin Concentration.

“…The level of Bmax of the mammary cell reaches a maximum during mid-lactation [11] and at this stage, correlates positively with the lactational performance of the lactating mouse [23]. In lactating rats at mid-lactation, serum PRL increases to levels of 380-505 ng/ml from those of 26-35 ng/ml during the 1 h-nursing period [24]. Recently, it was demonstrated that PRL receptor in the rabbit mammary gland is phosphorylated very rapidly in response to PRL [12].…”

“…One hundred µg of CB-154, suspended in 0.2 ml of 0.9% saline, was administered ip 7 h prior to the assay in order to reduce the level of circulating PRL [24]. Mice were administered CB-154 (closed) or 0.9% saline (open).…”