Prolactin (PRL), Follicle-Stimulating Hormone, and Luteinizing Hormone Are Regulators of Testicular PRL Receptors in Golden Hamsters* (original) (raw)
Related papers
Hormonal regulation of testicular prolactin receptors and testosterone synthesis in golden hamsters
Biology of Reproduction, 1990
A study was conducted with hypophysectomized hamsters to determine effects of administration of prolactin (PRL), luteinizing hormone (LH), and follicle-stimulating hormone (FSH)-alone or in combination-on testicular PRL receptors and in vitro testosterone production. Hormonal injections commenced the second day after hypophysectomy, and hamsters were killed on Day 5, approximately 13 h after the last hormonal injection. PRL receptor numbers were reduced by hypophysectomy, and PRL administration alone lessened the extent of this decrease. By themselves, neither LH nor FSH affected PIlL receptors, but a combination of PIlL + FSH + LII produced the greatest effect on these receptors. Receptor affinity was only modestly affected by any treatments. In vitro testosterone synthesis was measured after addition of 0, 2, 10, and 50 mIU of human chorionic gonadotropin (hCG) to incubations of testicular tissue. Neither PRL nor FSH by themselves in vivo affected basal or hCG-stimulated testosterone production. However, PIlL + FSH increased (p < 0.05) the magnitude of the in vitro testosterone response to hCG, as well as the sensitivity of that response (slope of the dose-response curve). LII alone increased both basal and trophic effect of LH and FSH. The data also indicate that PRL by itself is incapable of supporting steroidogenesis in the absence of either LII or FSH.
Journal of Pineal Research, 1984
The combination of pituitary grafts and daily injections of gonadotrophin-releasing hormone (GnRH) completely prevents gonadal atrophy in blind (BL) and melatonin (Mel)-treated male hamsters. In order to avoid potential problems associated with the use of pituitary grafts and further define the interactions between prolactin (PRL) and GnRH in preventing reproductive regression, we injected various doses of each hormone either alone or in combination into BL or Mel-treated male hamsters. In another experiment, BL hamsters received either weekly beeswax implants of estradiol benzoate (EB) (1 mg) alone or EB implants in combination with daily injections of GnRH (2 micrograms). In each experiment the hamsters were BL and/or treated with hormones for 10 wk. Either GnRH (8 micrograms) or PRL (5 micrograms) per d partially prevented gonadal atrophy in BL hamsters. However, increasing doses of GnRH plus PRL were more effective than either hormone alone in preventing gonadal atrophy. The combined effect of these hormones was greater than the algebraic sum of their individual effects. Injections of either GnRH or PRL alone resulted in a significant maintenance of gonadal and accessory organ size in Mel-treated animals. The combination of GnRH and PRL resulted in virtually complete maintenance of testicular weight while the accessory sex organs remained atrophic. The combined effect of these hormones was equivalent to the algebraic sum of their individual effects. The treatment of BL animals with EB implants with or without GnRH did not prevent reproductive regression in spite of elevated serum PRL levels. In conclusion, the effects of GnRH and PRL were synergistic in BL hamsters and additive in Mel-treated animals. The data suggest that there is a differential responsiveness of BL v. Mel-treated hamsters to the individual as well as the combined actions of GnRH and PRL.
Prolactin Release in Golden Hamsters: Photoperiod and Gonadal Influences1
Biology of Reproduction, 1981
Serum prolactin (PRL) in male golden hamsters was determined under a variety of experimental conditions. The pattern of daily PRL release appears to be only slightly altered by mild stress, and serum PRL levels are unaltered by castration. Exposure to short photoperiod induces a marked decline in serum PRL titers. Serum PRL levels remain depressed for 19-21 weeks of short-day treatment and then increase spontaneously. The spontaneous elevation of PRL titer appears to be relatively independent of testicular influence since it occurs at the same time in intact and castrated males, as well as in castrated males bearing testosterone implants. Spontaneous PRL release in intact males bearing testosterone implants was delayed 2 weeks. Changes in serum PRL concentrations may have a role in mediating the inhibition of testis function which occurs during exposure to short photoperiod.
Prolactin Release in Golden Hamsters: Photoperiod and Gonadal Influences
Biology of Reproduction, 1981
Serum prolactin (PRL) in male golden hamsters was determined under a variety of experimental conditions. The pattern of daily PRL release appears to be only slightly altered by mild stress, and serum PRL levels are unaltered by castration. Exposure to short photoperiod induces a marked decline in serum PRL titers. Serum PRL levels remain depressed for 19-21 weeks of short-day treatment and then increase spontaneously. The spontaneous elevation of PRL titer appears to be relatively independent of testicular influence since it occurs at the same time in intact and castrated males, as well as in castrated males bearing testosterone implants. Spontaneous PRL release in intact males bearing testosterone implants was delayed 2 weeks. Changes in serum PRL concentrations may have a role in mediating the inhibition of testis function which occurs during exposure to short photoperiod.
Brain Research, 1994
Specific binding of 125I-labeled rat prolactin (~251-rat PRL) to hypothalamic membranes was studied in Sprague-Dawley rats after ovine PRL administration and in relation to rat PRL serum variations induced by ectopic pituitary implants or by drugs which stimulate (domperidone) or inhibit (bromocriptine) PRL release. Repeated treatments with ovine PRL markedly increased specific binding values of 125I-rat PRL to hypothalamic membranes of female rats. Repeated treatments with domperidone also increased specific PRL binding in the hypothalamus. This effect was associated with an increase in PRL serum levels. Similar results were obtained in male rats after renal pituitary implants which resulted in a state of chronic hyperprolactinaemia. In contrast, a subchronic treatment with bromocriptine decreased specific PRL binding in the hypothalamus and concomitantly caused a sharp reduction in PRL serum levels. Scatchard analysis of data obtained from competition curves showed that the variations in the level of PRL binding to hypothalamic membranes were related to the number of PRL binding sites but not to the dissociation constant (Ka), which was unaffected by different treatments or by pituitary implantation. These results demonstrate a correlation between circulating concentrations of PRL and number of its receptors in the rat hypothalamus and give further support to the hypothesis that these binding sites may have a specific functional role in regulating the homeostasis of pituitary PRL secretion.
Reproduction, 1983
Adult male golden hamsters were given ectopic pituitary transplants at the time of transfer from a long (stimulatory) photoperiod (14 h L:10 h D) to a short photoperiod (5L:19D) or at various intervals thereafter. Grafts given at the time of transfer to 5L:19D failed to maintain plasma FSH levels significantly above those observed in sham-operated controls or to prevent regression of the testes. Grafts given after 4 weeks in 5L :19D increased plasma FSH levels and significantly diminished the decrease in testicular volume. Grafts given 14 weeks after transfer to 5L :19D caused a modest increase in plasma FSH levels and did not significantly alter the time course of testicular redevelopment. Similarly, grafts given 18 weeks after transfer to 5L :19D had no effect on testicular weight measured 2\m=.\5weeks later. These results indicate that the ability of prolactin (secreted by the grafted pituitary) to increase testicular size and the responsiveness of the hypothalamic\p=n-\pituitarysystem to prolactin gradually increase during short photoperiod-induced testicular regression, are maximal when the testes are fully regressed and decrease again during spontaneous redevelopment of the testes. We suggest that the effects of prolactin on the testes in golden hamsters are partly mediated by prolactin-induced stimulation of FSH release from the in-situ pituitary.
Common and specific effects of the two major forms of prolactin in the rat testis
AJP: Endocrinology and Metabolism, 2007
Prolactin (PRL) has both stimulatory and inhibitory effects on testicular function, a finding we hypothesized may be related in some part to the form of the hormone present or administered. In the analysis of the pituitary secretion profiles of early pubescent vs. mature male rats, we found PRL released from early pubescent pituitaries had about twice the degree of phosphorylation. Treatment of mature males with either unmodified PRL (U-PRL) or phosphorylated PRL (via the molecular mimic S179D PRL) for a period of 4 wk (circulating level of ∼50 ng/ml) showed serum testosterone decreased by ∼35% only by treatment with the phospho-mimic S179D PRL. Given the specificity of this effect, it was initially surprising that both forms of PRL decreased testicular expression of 3β-hydroxysteroid dehydrogenase and steroidogenic acute regulatory protein. Both forms also increased expression of the luteinizing hormone receptor, but only S179D PRL increased the ratio of short to long PRL receptors...
Regulatory Peptides, 1986
We have examined the effects of a single subcutaneous reJection of an LHRH agomst, D-Trp-6-LHRH, m blodegradable mlcrocapsules of poly(DL-lactlde-co-glycohde) on plasma gonadotropm and prolactm (PRL) levels m castrated and m castrated-hypophysectomlzed-pltmtary grafted (CAST-APX-GRAFT) male rats The results were compared to the effects of dally mjecUons of the same LHRH agomst &ssolved m sahne In castrated rats, there were no slgmficant alterations m plasma LH or PRL levels durmg the 10 days following the reJection of LHRH agonlst mlcrocapsules, whde FSH levels were generally reduced In castrated males given dally injections of 6 #g of LHRH agomst m sahne, plasma LH levels were slgmficantly reduced whde plasma PRL levels were not changed In CAST-APX-GRAFT rats, both o-Trp-6-LHRH mlcrocapsules and dally LHRH agomst reJections appeared to increase plasma PRL levels The pattern of changes m PRL release m both groups was slmdar, with levels on day 6 bemg significantly higher than those measured on days 1, 3 and 10 after onset of treatment As expected, LH and FSH levels m these animals were extremely low Immunoreactwe D-Trp-6-LHRH was consistently detectable in the plasma of CAST-APX-GRAFT animals after mlcrocapsule administration, whereas mammals gwen dally reJections of thts agomst m sahne, its plasma * Present address and reprmt requests Department of Physiology, Southern Ilhnols Umverslty, School of Me&tree, Carbondale, IL 62901, U S A 0167-0115/86/$03 50