Blunted prolactin response to exogenous luteinizing hormone releasing hormone in superovulated women

Abstract

To investigate the prolactin (PRL) response to luteinizing hormone releasing hormone (LHRH) in superovulated cycles, eight normally ovulating women were studied in two cycles, i.e. a spontaneous (control) and a cycle treated with 'pure' follicle stimulating hormone (FSH) (225 IU/day). LHRH was given to the women i.v. (a single injection of 100 micrograms) in the late follicular phase of both cycles. The oestradiol levels (mean +/- SEM) at the time of the LHRH challenge were 635 +/- 31 and 1707 +/- 225 pmol/l respectively (P less than 0.001). The size of the leading follicle was similar in both cycles. Basal PRL levels (mean +/- SEM) on the day of the LHRH experiment were significantly higher in the FSH (250 +/- 31 microIU/ml) than in the spontaneous cycles (133 +/- 15 microIU/ml. P less than 0.05). In the latter cycles, LHRH induced a significant increase in serum PRL and LH levels, while the FSH cycles, the prolactin (PRL) response to LHRH was blunted and LH response markedly attenuated. We conclude that superovulation induction stimulates basal but suppresses LHRH-induced PRL release. It is suggested that basal PRL secretion is LHRH-independent and the suppressing effect is mediated via previously described paracrine interactions between the gonadotrophs and lactotrophs and/or through ovarian inhibitory substances.