Differential regulation of the luteinizing hormone genes in teleosts and tetrapods due to their distinct genomic environments--insights into gonadotropin beta subunit evolution

The pituitary gonadotropins, follicle-stimulating hormone (FSH) and luteinizing hormone (LH), are essential for the control of vertebrate reproduction. Although the molecular structures of these two hormones are well conserved from teleosts to mammals, some studies report differences in their regulatory mechanisms of gene expression between teleosts and tetrapods. In the present study, we examined the molecular evolution of the gonadotropin gene loci in vertebrates and found that there is a syntenic conservation among the teleost fshb and tetrapod fshb and lhb loci. However, the teleost lhb locus has no syntenic homology to either tetrapod lhb or teleost fshb; this fact suggests that an extensive genome-wide rearrangement of the lhb locus, caused by an accelerated genome evolution speed after the third round of genome-wide duplication, occurred in the teleost lineage. We subsequently demonstrated by double labeling in situ hybridization using a teleost medaka that the fshb and lhb genes in teleosts are expressed in completely separate cellular populations in the pituitary, which is different in tetrapods. Furthermore, the expression analysis in ovariectomized and steroid-treated medaka revealed that, under breeding conditions, the expression of the medaka LHβ was down-regulated by ovariectomy and recovered by treatment with gonadal steroids; this result is also completely opposite in mammals, where the steroids have negative-feedback effects on LHβ expression. We suggest that these differences between teleosts and mammals in the cellular expression pattern and dynamic expressional changes of the lhb gene are the result of the drastic changes in the genomic environment of the lhb gene that occurred early in teleost evolution.     

Kisspeptin signaling in the brain: Recent developments and future challenges

Kisspeptins, a family of peptides encoded by the KISS1 gene which binds GPR54 (or KISS1 receptor), have recently emerged as essential neuropeptide regulators of key aspects of reproductive maturation and function, including puberty onset, neuroendocrine control of ovulation and metabolic regulation of fertility. Yet, while the neuroanatomy of kisspeptin system has begun to be deciphered, and the involvement of kisspeptins in the above phenomena has been experimentally documented in recent years, precise information on the signaling events underlying these functions has remained scarce. Similarly, the nature and mechanisms of action of most of the regulatory signals of KISS1 expression in the brain are largely unknown. In this review, we will comprehensively summarize some of the recent developments in these areas of kisspeptin physiology, with the ultimate aim to delineate unresolved questions and future pathways for the progression of this active field of Neuroendocrinology.     

Effects of hormone treatment and age on the stimulation of rat anterior pituitary adenylate cyclase and cyclic adenosine 3',5' monophosphate by hypothalamic extract

Crude ovine hypothalamic extract in vitro significantly stimulated adenylate cyclase activity and LH release by pituitary gland obtained from newborn rats (0.25–0.5 days old) and increased cyclic adenosine 3′,5′-monophosphate (cyclic AMP) in 2-day-old rats. In adult rats, the stimulation of adenylate cyclase activity and cyclic AMP formation, but not LH release, induced by hypothalamic extract was inhibited by adrenalectomy. In vivo administration of pharmacologic doses of 1 mg dexamethasone asd 100 μg thyroxine for 1 day markedly reduced the effect of 0.2 mg/ml but not 1 mg/ml hypothalamic extract on cyclic AMP concentrations. The action of the latter dose of hypothalamic extract on cyclic AMP was inhibited by injection of dexamethasone and thyroxine for 3 days, while the stimulation of LH release was preserved. Such dissociation between activation of the adenylate cyclase-cyclic AMP system and LH release suggests that cyclic AMP formation may not be essential for increased release of LH. Adrenalectomy did not inhibit stimulation of adenylate cyclase activity or cyclic AMP formation caused by prostaglandin E₁ (PGE₁). Hypothalamic extract or PGE₁ added to intact pituitary in vitro increased protein kinase activity and decreased the protein binding of exogenous cyclic AMP, reflecting the increased generation of endogenous cyclic AMP.     

Mechanism of action of luteinizing hormone and follicle-stimulating hormone on the ovary in vitro.

The mechanism of action of luteinizing hormone (LH) and follicle-stimulating hormone (FSH) upon various cell types of the mammalian ovary is reviewed. Emphasis is placed upon in vitro studies using organ and cell culture as well as short-term incubations. FSH and LH actions upon the following ovarian functions are discussed: steroidogenesis and metabolism of the ovary as a whole and of the isolated follicle and its component cell types, the granulosa and thecal cells, as well as folliculogenesis and follicular growth, oocyte maturation, follicular rupture, and corpus luteum maintenance and steroidogenesis. The roles of gonadotropin receptors, AMP, prostaglandins, protein kinase, and protein synthesis in these LH and FSH actions are discussed. Intra-ovarian regulation of LH and FSH action is reviewed, including a discussion of the possible roles of follicular fluid inhibitors upon oocyte maturation and granulosa cell luteinization.     

The ontogeny of hypothalamic pituitary function in the pig. I. Pituitary LH and FSH in the fetus and neonate

Pituitaries were collected from fetal and postnatal pigs from day 55 p.c. until 6 weeks after birth at closely spaced intervals. LH and FSH in individual pituitaries were quantified by both homologous RIA and homologous RRA. No significant difference was found between results obtained by RIA and RRA. Both LH and FSH are first detected by RIA and RRA in the porcine fetal pituitary at 75 days p.c. Thereafter both LH and FSH pituitary content rises until term. LH pituitary concentration in both male and female fetuses and FSH pituitary concentration in males exhibit a peak just before birth. FSH pituitary concentration in females rises until birth and thereafter remains elevated. A statistically significant sex difference was found postnatally with regard to FSH content and concentration but not for LH.     

Hormones in synergy: Regulation of the pituitary gonadotropin genes

The precise interplay of hormonal influences that governs gonadotropin hormone production by the pituitary includes endocrine, paracrine and autocrine actions of hypothalamic gonadotropin-releasing hormone (GnRH), activin and steroids. However, most studies of hormonal regulation of luteinizing hormone (LH) and follicle-stimulating hormone (FSH) in the pituitary gonadotrope have been limited to analyses of the isolated actions of individual hormones. LHβ and FSHβ subunits have distinct patterns of expression during the menstrual/estrous cycle as a result of the integration of activin, GnRH, and steroid hormone action. In this review, we focus on studies that delineate the interplay among these hormones in the regulation of LHβ and FSHβ gene expression in gonadotrope cells and discuss how signaling cross-talk contributes to differential expression. We also discuss how recent technological advances will help identify additional factors involved in the differential hormonal regulation of LH and FSH.     

Calcium-cyclic AMP interactions in prothoracicotropic hormone stimulation of ecdysone synthesis

The calcium-dependence of ecdysone synthesis by the insect prothoracic glands was examined in vitro using glands from day 0 pupae of the tobacco hornworm, Manduca sexta. Stimulation of ecdysone synthesis by the cerebral neuropeptide, prothoracicotropic hormone (PTTH), requires extracellular calcium; peptide-stimulated steroidogenesis is blocked by omission of calcium or by addition of the calcium antagonist lanthanum. By contrast, basal synthesis of ecdysone is not calcium-dependent. A stimulatory, as opposed to simply a permissive, role for calcium is indicated by the ability of the calcium ionophore A23187 to mimic the steroidogenic effects of PTTH. Agents that act by increasing the intracellular levels of cAMP (dibutyryl cAMP, 1-methyl-3-isobutylxanthine, forskolin) enhance ecdysone synthesis equally well in the presence or absence of extracellular calcium, indicating that the site of action of the cation in the steroidogenic pathway occurs prior to that of cAMP. Both PTTH and A23187 enhance the formation of cAMP, as measured by the conversion of [3H]ATP to [3H]cAMP, in a manner absolutely dependent upon the presence of extracellular calcium. The results suggest sequential roles for calcium and cAMP in PTTH-stimulated steroidogenesis by the insect prothoracic glands. A model is presented in which the peptide stimulates cAMP formation in a calcium-dependent manner, with the cyclic nucleotide in turn enhancing ecdysone synthesis.     

Cyclic nucleotide phosphodiesterase in developing rat testis. Identification of somatic and germ-cell forms

Several forms of phosphodiesterase are present in the male gonad, and their relative concentrations vary during testicular development. On the basis of kinetic analysis and chromatography on DEAE cellulose, 3 forms were separated: (a) a high-affinity cGMP phosphodiesterase, regulated by Ca2+ and calmodulin, similar to a form described in different tissues (peak I); (b) a high-affinity cAMP form insensitive to Ca2+, which cannot be readily compared with forms described elsewhere (peak II); and (c) a high-affinity cAMP phosphodiesterase, Ca2+- and calmodulin-insensitive, corresponding to the "hormone-regulated" form described in several systems (peak III). The elution pattern of peak I and calmodulin stimulation were dependent on free calcium concentration during cytosol preparation and chromatography. This datum and rechromatography in the presence or absence of excess calmodulin suggested that the enzyme complexes calmodulin in a Ca2+-dependent manner and is therefore activated. Moreover, whereas peak I was observed in all cell compartments of the testis, peak II was present in germ cells and peak III was found mainly in somatic cells. During development of the testis, a relevant enhancement in the ratio between cAMP and cGMP hydrolytic activity was observed together with an overall increase of phosphodiesterase activity, thus suggesting that the previously described increase in cAMP phosphodiesterase activity during testis maturation should be ascribed to forms present in both germ cells and somatic cells.     

The role of endocannabinoids in gonadal function and fertility along the evolutionary axis

Endocannabinoids are natural lipids able to bind to cannabinoid and vanilloid receptors. Their biological actions at the central and peripheral level are under the tight control of the proteins responsible for their synthesis, transport and degradation. In the last few years, several reports have pointed out these lipid mediators as critical signals, together with sex hormones and cytokines, in various aspects of animal and human reproduction. The identification of anandamide (AEA) and 2-arachidonoylglycerol (2-AG) in reproductive cells and tissues of invertebrates, vertebrates and mammals highlights the key role played by these endogenous compounds along the evolutionary axis. Here, we review the main actions of endocannabinoids on female and male reproductive events, and discuss the interplay between them, steroid hormones and cytokines in regulating fertility. In addition, we discuss the involvement of endocannabinoid signalling in ensuring a correct chromatin remodeling, and hence a good DNA quality, in sperm cells.     

Effect of a gonadotrophin-releasing hormone analogue on lung function in lymphangioleiomyomatosis

BACKGROUND: Lymphangioleiomyomatosis (LAM), a multisystem disease occurring primarily in women, is characterized by cystic lung destruction, and kidney and lymphatic tumors, caused by the proliferation of abnormal-appearing cells (ie, LAM cells) with a smooth muscle cell phenotype that express melanoma antigens and are capable of metastasizing. Estrogen receptors are present in LAM cells, and this finding, along with reports of disease progression during pregnancy or following exogenous estrogen administration, suggest the involvement of estrogens in the pathogenesis of LAM. Consequently, antiestrogen therapies have been employed in treatment. The goal of this prospective study was to evaluate the efficacy of triptorelin, a gonadotrophin-releasing hormone analogue, in 11 premenopausal women with LAM. METHODS: Patients were evaluated at baseline and every 3 to 6 months thereafter, for a total of 36 months. Hormonal assays, pulmonary function tests, 6-min walk tests, high-resolution CT scans of the chest, and bone mineral density studies were performed. RESULTS: Gonadal suppression was achieved in all patients. Overall, a significant decline in lung function was observed; two patients underwent lung transplantation 1 year after study enrollment, and another patient was lost to follow-up. Treatment with triptorelin was associated with a decline in bone mineral density. CONCLUSIONS: Triptorelin appears not to prevent a decline in lung function in patients with LAM. Its use, however, may be associated with the loss of bone mineral density.