Expression of the gene for the receptor of gonadotropin-releasing hormone in the rat mammary gland

Molecular cloning, immunological characterization, and expression analysis of gonadotropin-releasing hormone (GnRH) in the brain of the Chinese alligator during different stages of reproductive cycle

The neurohormone gonadotropin-releasing hormone (GnRH) plays an essential role in the control of reproductive functions in vertebrates. However, the full-length complementary DNA (cDNA) encoding the GnRHs precursor and it role in the reproductive cycles regulating has not been illustrated in crocodilian species. In the present study, full-length cDNAs encoding GnRH1 forms, its predominant localization within brain and peripheral tissues, and GnRH1 peptide concentrations in the hypothalamus and pituitary in relation to seasonal gonadal development of Chinese alligator were investigated. The cDNA of GnRH1 is consisted of 282 bp open reading frame encoding 93 amino acids. The deduced amino acid sequence of alligator GnRH1 contains several conserved regions and shows a closer genetic relationship to the avian species than to other reptile species. The GnRH1 immunopositive cells were not only detected widely in cerebrum, diencephalon, medulla oblongata but also observed in peripheral tissues, these widespread distribution characteristics indicated that GnRH1 possibly possess the multi-functionality in Chinese Alligator. GnRH1 peptide concentration within hypothalamus were observed be the highest in RP group (P < 0.05), in association with an peak value in GSI and emerging of late vitellogenic follicles in the ovary. Taken together, our results suggested that GnRH1 was predominantly involved in the vitellogenesis process of seasonal gonadal development of Chinese Alligator.

The effect of GnRH on in vitro bovine myometrial activity

The aim of this study was to evaluate, in vitro, the effects of increasing concentrations of GnRH on spontaneous mechanical activity patterns of uterine smooth muscle preparations of cows during the follicular and the luteal phases of the oestrus cycle. Uterine smooth muscle strips from 14 cows in follicular and 9 in luteal phase were collected immediately after slaughter and processed within 60 min from collection. Two strips of the same uterus were mounted in an isolated organ bath with two chambers to evaluate the role of decapeptide GnRH on spontaneous myometrial contractility. After equilibration period at 20 mN resting tension, the mechanical activity of the uterus was recorded for 10 min and the mean contractile force (MCF) was calculated. Then GnRH antagonist (antide) was added to one chamber at fixed concentration (10(-4)mol) and allowed to diffuse in solution and make contact with the strips. Subsequently, GnRH was added to the two baths at the same time at increasing concentration and MCF was recorded for 10 min. The effect of GnRH on spontaneous myometrial activity was evident only in the strips from subjects in follicular phase. Our results are suggestive of the presence of GnRH receptors in bovine myometrial tissue. The involvement of GnRH on uterine contractions at mating can be postulated.

Regulation of expression of mammalian gonadotrophin-releasing hormone receptor genes

Gonadotrophin-releasing hormone (GnRH), acting via its cognate GnRH receptor (GnRHR), is the primary regulator of mammalian reproductive function, and hence GnRH analogues are extensively used in the treatment of hormone-dependent diseases, as well as for assisted reproductive techniques. In addition to its established endocrine role in gonadotrophin regulation in the pituitary, evidence is rapidly accumulating to support the expression and functional roles for two forms of GnRHR (GnRHR I and GnRHR II) in multiple and diverse extra-pituitary mammalian tissues and cells. These findings, together with findings indicating that mutations of the GnRHR are linked to the disease hypogonadotrophic hypogonadism and that GnRHRs play a direct role in neuronal migration and reproductive cancers, have presented new therapeutic targets and intensified research into the structure, function and mechanisms of regulation of expression of GnRHR genes. The present review focuses on the current knowledge on tissue-specific and hormonal regulation of transcription of mammalian GnRH receptor genes. Emerging insights, such as the discovery of diverse regulatory mechanisms in pituitary and extra-pituitary cell types, nonclassical mechanisms of steroid regulation, the use of composite elements for cell-specific expression, the increasing profile of hormones involved in regulation, the complexity of kinase pathways that target the GnRHR I gene, as well as species-differences, are highlighted. Although further research is necessary to understand the mechanisms of regulation of expression of GnRHR I and GnRHR II genes, the GnRHR is emerging as a potential target gene for facilitating cross-talk between neuroendocrine, immune and stress-response systems in multiple tissues via autocrine, paracrine and endocrine signalling.

Differential gonadotropin-releasing hormone (GnRH) and GnRH receptor messenger ribonucleic acid expression patterns in different tissues of the female rat across the estrous cycle

GnRH, the main regulator of reproduction, is produced in a variety of tissues outside of the hypothalamus, its main site of synthesis and release. We aimed to determine whether GnRH produced in the female rat pituitary and ovaries is involved in the processes leading to ovulation. We studied the expression patterns of GnRH and GnRH receptor (GnRH-R) in the same animals throughout the estrous cycle using real-time PCR. Hypothalamic levels of GnRH mRNA were highest at 1700 h on proestrus, preceding the preovulatory LH surge. No significant changes in the level of hypothalamic GnRH-R mRNA were detected, although fluctuations during the day of proestrus are evident. High pituitary GnRH mRNA was detected during the day of estrus, in the morning of diestrus 1, and at noon on proestrus. Pituitary GnRH-R displayed a similar pattern of expression, except on estrus, when its mRNA levels declined. Ovarian GnRH mRNA levels increased in the morning of diestrus 1 and early afternoon of proestrus. Here, too, GnRH-R displayed a somewhat similar pattern of expression to that of its ligand. To the best of our knowledge, this is the first demonstration of a GnRH expression pattern in the pituitary and ovary of any species. The different timings of the GnRH peaks in the three tissues imply differential tissue-specific regulation. We believe that the GnRH produced in the anterior pituitary and ovary could play a physiological role in the preparation of these organs for the midcycle gonadotropin surge and ovulation, respectively, possibly via local GnRH-gonadotropin axes.

Molecular cloning and characterization of a gonadotropin-releasing hormone receptor in the guinea pig, Cavia porcellus

Guinea pig gonadotropin-releasing hormone (gpGnRH) is predicted to have a unique structure among all known forms of GnRH molecule [Endocrinology 138 (1997) 4123] and it is of great interest to determine whether the unique structure of gpGnRH is manifested in the characteristics of the guinea pig GnRH receptor. In the present study, we isolated a full-length cDNA for a GnRH receptor from the pituitary gland of the guinea pig. The putative guinea pig GnRH receptor protein has an amino acid identity of 79-87% with mammalian type I GnRH receptors. The amino acid residues which have been demonstrated to be important for ligand binding and signal transduction were conserved in the guinea pig GnRH receptor. However, there are several specific amino acid substitutions among mammalian type I GnRH receptors. Moreover, though the guinea pig has generally been classified as a rodent, the putative GnRH receptor protein did not have some rodent-specific characteristics. Total IP assays demonstrated that the cloned guinea pig GnRH receptor is a functional GnRH receptor and that it shows different preference of ligand sensitivities from the rat GnRH receptor.

The genes for gonadotropin-releasing hormone and its receptor are expressed in human breast with fibrocystic disease and cancer

While gonadotropin-releasing hormone (GnRH) or GnRH receptor (GnRHR) have been reported to exist in tissues other than brain and pituitary, there is no report concerning co-expression of GnRH and GnRHR in human breast tissues. To address this question, we have examined whether mRNA for GnRH as well as GnRHR was present in different human breast samples, by employing the reverse transcription-polymerase chain reaction (RT-PCR) protocol followed by Southern blotting of the PCR products. Coexpression of GnRH and GnRHR genes was further confirmed by dot blot hybridization using appropriate [32P]-labeled probes. We thus tested fibrocystic breast (4 cases), invasive ductal carcinomas (6 cases) and 1 adjacent non-neoplastic tissue. GnRHR and GnRH mRNAs were found in all actin-positive samples including malignant as well as nonmalignant tissues. Quantitative determinations of mRNA did not reveal significant differences between malignant and non-malignant breast samples for either GnRH or GnRHR gene expression. Our data show that neither gene was overexpressed in the breast cancer samples compared with normal breast tissue. Since GnRH agonists inhibit breast epithelial cell growth, the presence of GnRHR mRNA suggests that GnRH may specifically affect breast cell growth. Our data thus raise the possibility of an autocrine/paracrine role for GnRH in human mammary gland.