Effects of hyperprolactinaemia and testosterone on the release of LH-releasing hormone and the gonadotrophins in intact and castrated rats

Abstract

We have investigated the effect of hyperprolactinaemia on the secretion of LH-releasing hormone (LHRH), LH and FSH in male rats of the PVG strain which were left intact, castrated or castrated and then implanted with either a 10 or 30 mm silicone elastomer capsule containing testosterone (T10 and T30 respectively). Hyperprolactinaemia was produced by pituitary grafts under the kidney capsule. Pituitary stalk blood, for LHRH estimation, and peripheral blood, for LH, FSH and prolactin, were collected under alphaxalone anaesthesia. Pituitary stalk blood was collected during three consecutive periods of 30 min each before, during and after the application of an electrical stimulus to the median eminence (ME). Hyperprolactinaemia significantly reduced the plasma concentrations of FSH in intact rats and the post-castration increase in the plasma concentrations of both LH and FSH. Neither hyperprolactinaemia nor castration had any significant effect on the spontaneous output of LHRH, but castration alone or castration plus implantation of a T30 capsule did significantly reduce the increment in LHRH output produced by ME stimulation, an effect not seen in rats bearing pituitary grafts. The T30, but not the T10 capsules suppressed the post-castration increase in the gonadotrophins, and the inhibitory effect of testosterone was not significantly affected by hyperprolactinaemia. An incidental but important finding was that the presence of pituitary grafts under the kidney capsule reduced the anaesthetic dose of alphaxalone by 63%.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of Tumor-Induced Hyperprolactinemia on LH Secretion following Stimulation of the Medial Preoptic Area, Pituitary Responsiveness and the Estrogen-Induced LH Surge

“…ECS of the ventral DBB-MPOA produced an LH response similar to that reported by other workers [14,22,44], ECS [14] and electrical stimulation [6] of the MPOA have been shown to increase LHRH release into hypophyseal portal blood. The re sponse in OVX + Ei-treated rats was somewhat greater and more prolonged than that in OVX rats, a finding which cor roborates data presented by Arendash and Gallo [3].…”

“…We then studied the ability of the LHRH neurons to re lease their neuropeptide by measuring LH secretion following electrochemical stimulation (ECS) of the diagonal band of Broca-medial preoptic area (DBB-MPOA). Disparate results Received: July 13, 1990 Accepted after revision: January 14, 1991 have been reported upon electrical stimulation of the arcuate/ median eminence region of HP male rats [6,41]. We assessed the effect of HP on pituitary responsiveness, including the abil ity to exhibit self-priming, by challenging the in situ pituitary with two injections of LHRH.…”

Suppression of Pulsatile LH Secretion, Pituitary GnRH Receptor Content and Pituitary Responsiveness to GnRH by Hyperprolactinemia in the Male Rat

“…Studies in which GnRH concentrations were deter mined in hyperprolactinemic rats have reported either no effect or a decrease in GnRH concentrations in response to hyperprolactinemia [7,29,42,51], The inability of some in vestigators to demonstrate an inhibition of GnRH release into the pituitary portal plexus in hyperprolactinemic male rats [7,51] may be due to the different methods used to in duce hyperprolactinemia and the levels of prolactin achieved. A deficit in GnRH secretion in hyperprolactine mic rats could be the result of the secretion within the hypo thalamus of a substance that presynaptically inhibits the re lease of GnRH.…”

In vivo Release of Dopamine, Luteinizing Hormone-Releasing Hormone and Thyrotropin-Releasing Hormone in Male Rats Bearing a Prolactin-Secreting Tumor

“…Indeed, in the pre sent study levels of LH and FSH were found to be lower in rats bearing the prolactin-secreting tumor than in the con trol rats. It is possible that prolactin alters LH secretion by affecting hypothalamic LHRH secretion, and one hypothe sis is that tuberoinfundibular dopaminergic neurons ter minating in the lateral aspects of the median eminence function as inhibitory neuromodulators of LHRH release [26], Induction of hyperprolactinemia with pituitary tran splants, however, did not result in decreased concentration of LHRH in hypophysial stalk plasma [4], When much hig her levels of prolactin are attained by a prolactin-and ACTH-secreting tumor (7315a), then reduced LHRFI secre tion in hypophysial portal blood was observed [33], However, the effect of the 7315a tumor on the release of LHRH requires the presence of the adrenal glands, since it was not observed in adrenalectomized rats [33]. The present findings show that also in rats bearing a prolactin-secreting tumor (7315b) the in vivo LHRH release was lower than in control rats, although the rats had been adrenalectomized from the time of tumor inoculation.…”