Nongenotropic, sex-nonspecific signaling through the estrogen or androgen receptors: dissociation from transcriptional activity.

The relationship of the classical receptors and their transcriptional activity to nongenotropic effects of steroid hormones is unknown. We demonstrate herein a novel paradigm of sex steroid action on osteoblasts, osteocytes, embryonic fibroblasts, and HeLa cells involving activation of a Src/Shc/ERK signaling pathway and attenuating apoptosis. This action is mediated by the ligand binding domain and eliminated by nuclear targeting of the receptor protein; ERalpha, ERbeta, or AR can transmit it with similar efficiency irrespective of whether the ligand is an estrogen or an androgen. This antiapoptotic action can be dissociated from the transcriptional activity of the receptor with synthetic ligands, providing proof of principle for the development of function-specific-as opposed to tissue-selective-and gender-neutral pharmacotherapeutics.

Messenger ribonucleic acid for gonadotropin-releasing hormone receptor and numbers of gonadotropin-releasing hormone receptors in ovariectomized ewes after hypothalamic-pituitary disconnection and treatment with estradiol.

To study the regulation of ovine GnRH receptors in the absence of GnRH, hypothalamic input was removed by hypothalamic-pituitary disconnection (HPD). Steady-state concentrations of GnRH receptor mRNA and numbers of GnRH receptors were measured after HPD and subsequent treatment with estradiol. Anterior pituitary glands were collected 24 (n = four), 36 (n = two), 48 (n = four), and 72 h (n = four) after HPD. An additional group of ewes received subcutaneous implants of estradiol 24 h after HPD, and pituitary glands were collected 0 (n = four), 12 (n = four), 24 (n = three), and 48 h (n = four) after exposure to estradiol. Pituitary glands were also obtained from four ovariectomized ewes that did not undergo HPD (OVX controls). At 24 h after HPD, mean number of GnRH receptors had decreased (P < .05) by 73%; however, mean concentration of GnRH receptor mRNA was not different from OVX controls. Relative to HPD ewes, treatment with estradiol increased mean concentrations of GnRH receptor mRNA and mean numbers of GnRH receptors (P < .01 and P < .001, respectively). From these data we conclude that 1) acute removal of GnRH decreases the numbers of GnRH receptors but does not affect steady-state concentrations of GnRH receptor mRNA and 2) estradiol increases the numbers of GnRH receptors and steady-state concentrations of GnRH receptor mRNA via direct effects at the level of the pituitary gland.

Cell-specific expression of the mouse gonadotropin-releasing hormone (GnRH) receptor gene is conferred by elements residing within 500 bp of proximal 5' flanking region.

Gonadotropin-releasing hormone (GnRH) is a decapeptide produced by the hypothalamus. Upon binding to specific high-affinity receptors on gonadotrope cells of the anterior pituitary gland, GnRH stimulates the synthesis and secretion of LH. In light of the critical role of GnRH in reproduction much effort has been directed toward understanding the regulation of this hormone and its cognate receptor. The recent availability of genomic clones for the GnRH receptor has facilitated research to address the molecular mechanisms underlying regulation of GnRH receptor gene expression. We have expanded the analysis of the promoter for the mouse GnRH receptor gene and report that in addition to transcriptional start sites located within 100 bp of the translation start codon there is a more distal transcriptional start site approximately 200 bp 5' of the initiation codon. The initiation of transcription from this more distal site was sufficient to confer cell-specific expression on luciferase. Further, transient expression assays of constructs containing progressive 5' deletions in the GnRH receptor gene promoter reveal the presence of one or morecis-acting elements located between -500 and -400 (relative to ATG) necessary for transcriptional activity in the gonadotrope-derived αT3 cell line. Finally, αT3 but not COS-7 cell nuclear extract contained protein(s) that bind to at least two separate motifs contained within the -500 to -400 region. We suggest that activation of GnRH receptor gene expression in the αT3 cell line requires the binding of at least two transcriptional regulatory proteins to basal enhancer elements located within a 100 bp region between -500 to -400 relative to the translation start codon in the mouse GnRH receptor gene.

Roles of melatonin and prolactin in testicular crudescence in mink (Mustela vison).

Peripubertal male mink (Mustela vison) were treated with prolactin, melatonin or antibodies against melatonin to determine the effects of altered circulating concentrations of prolactin and melatonin throughout one season of testicular development. Treatment began on 1 October and continued until 4 March. Administration of 0.5 mg ovine prolactin day-1 by minipump increased the circulating concentration of prolactin for the duration of the study and increased serum concentrations of LH. This treatment had no effect on the testosterone concentration or on testis size. Neither chronic treatment with melatonin throughout the period of crudescence nor passive immunization against melatonin for 79 days affected the circulating concentrations of prolactin, LH, testosterone or testis size. These results show clearly that, unlike in other seasonally breeding species, prolactin does not play a significant role in testis growth in the mink. Administration of melatonin to male mink in October did not affect testis growth, presumably because the melatonin signal that cues photoperiodic events had already been received. Administration of antibodies against melatonin did not affect any of the features measured, suggesting that melatonin may have neural but not peripheral effects. Further support for this view can be found in the absence of an influence of melatonin on testis growth or on the plasma concentration of testosterone.

Interactions between melatonin and prolactin during gestation in mink (Mustela vison).

Immature female mink, 8 weeks of age in July, were treated with implants releasing melatonin. Mating, which induced ovulation, took place during the normal breeding season in the following March. Circulating prolactin and progesterone concentrations did not undergo the expected gestational increases, and no embryos implanted. A similar absence of gestational changes in prolactin and progesterone values ensued in primiparous mink treated with the melatonin implant 2-3 days after the second of 2 matings. Administration of exogenous sheep prolactin (0.5 mg/day) by minipump induced precocious elevation of progesterone concentrations in mated mink. Prolactin administration overcame the effects of melatonin, in that the corpora lutea were activated and embryos implanted, but exogenous prolactin resulted in degeneration of implanted embryos both in the presence and absence of chronic melatonin. The results suggest that melatonin has a single effect in alteration of gestation in mink; i.e. the prevention of prolactin secretion. Hyperprolactinaemia may inhibit embryo development in this species.