Gene expression of gonadotropin-releasing hormone in early pregnant rat and steroid hormone exposed mouse uteri

Effect of chronic administration of a gonadotropin-releasing agonist on luteal function and pregnancy rates in dairy cattle

Increased embryonic losses may be associated with inadequate progesterone (P4) concentrations in high-producing lactating dairy cattle. The objectives of the present studies were to determine if chronic administration of a gonadotropin-releasing hormone (GnRH) agonist, Deslorelin, would increase circulating P4 concentrations and subsequently increase pregnancy rates in dairy cattle. Administration of Deslorelin for 12 days increased (p < .05) luteal volume and circulating P4 concentrations in primiparous lactating dairy cows, but increased only luteal volumes in multiparous cows. Treatment with Deslorelin increased Day 45 pregnancy rates in cows as compared to untreated controls. Chronic treatment with Deslorelin in dairy cattle; (a) increased luteal volume of the primary CL, (b) induced accessory CL, (c) increased circulating P4 concentration in primiparous cows only, (d) did not lengthen the estrous cycle upon removal of treatment, and (e) increased pregnancy rates. Although luteal volume was increased in multiparous cows and circulating P4 concentrations were not with Deslorelin treatment, there was an apparent effect on pregnancy rates. This hormonal strategy may represent a suitable model to address local effects of P4 and GnRH/luteinizing hormone on uterine environment and subsequent embryonic survival.

GnRH agonist (buserelin)-induced in vitro apoptosis in bovine endometrium

Singh, R., Pretheeban, T. and Rajamahendran, R. 2011. GnRH agonist (buserelin)-induced in vitro apoptosis in bovine endometrium. Can. J. Anim. Sci. 91: 265–273. Apoptosis is a vital physiological process. The local modulatory role of the GnRH, GnRH-R system in uterine physiology is not clear. We investigated GnRH agonist (buserelin)-induced apoptosis in bovine endometrium. Reproductive tracts were collected from a local abattoir. The endometrial explants were sliced into smaller pieces, cultured for 20 h and then treated (6 h) with buserelin (0, 200, 500, 1000 ng mL−1), the GnRH antagonist-antide (500 ng mL−1) and antide+buserelin (500+200 ng mL−1), and stored at −80°C for RNA extraction. Two micrograms of total RNA was subjected to reverse transcription-polymerase chain reaction using gene-specific primers. Subsequently, endometrial epithelial cells were isolated from the follicular and luteal phase uteri, cultured for 48 h, characterized and treated with buserelin (200 ng mL−1), antide (500 ng mL−1), and antide+buserelin (500+200 ng mL−1) for 6 h. The cells were stained with acridine orange-ethidium bromide and visualized and counted under a fluorescent microscope. Buserelin up-regulated BAX (200 ng mL−1) and CASPASE3 mRNA (200 and 500 ng mL−1) and induced apoptosis (200 ng mL−1) at the cellular level in the follicular phase endometrium. GnRH appears to regulate uterine homeostasis in bovine endometrium at the transcriptional and cellular levels.

Is the metalloendopeptidase EC 3.4.24.15 (EP24.15), the enzyme that cleaves luteinizing hormone-releasing hormone (LHRH), an activating enzyme?

LHRH (GNRH) was first isolated in the mammalian hypothalamus and shown to be the primary regulator of the reproductive neuroendocrine axis comprising of the hypothalamus, pituitary and gonads. LHRH acts centrally through its initiation of pituitary gonadotrophin release. Since its discovery, this form of LHRH (LHRH-I) has been shown to be one of over 20 structural variants with a variety of roles in both the brain and peripheral tissues. LHRH-I is processed by a zinc metalloendopeptidase EC 3.4.24.15 (EP24.15) that cleaves the hormone at the fifth and sixth bond of the decapeptide (Tyr5-Gly6) to form LHRH-(1–5). We have previously reported that the auto-regulation of LHRH-I (GNRH1) gene expression and secretion can also be mediated by itself and its processed peptide, LHRH-(1–5), centrally and in peripheral tissues. In this review, we present the evidence that EP24.15 is the main enzyme of LHRH metabolism. Following this, we look at the metabolism of other neuropeptides where an active peptide fragments is formed during degradation and use this as a platform to postulate that EP24.15 may also produce an active peptide fragment in the process of breaking down LHRH. We close this review by the role EP24.15 may have in regulation of the complex LHRH system.

Gonadotropin releasing hormone receptor gene and protein expression and immunohistochemical localization in bovine uterus and oviducts

Recently GnRH, GnRH-R systems has been demonstrated in various extrahypothalamic and extrapituitary reproductive tissues in different mammalian species, where GnRH acts in an autocrine and or paracrine manner and modulates different biological processes. GnRH-R mRNA has also been demonstrated in bovine ovaries (follicle and corpus luteum) and normal and carcinogenic human endometrium/endometrial cells. This is the first study elucidating presence of GnRH-R mRNA and GnRH-R protein in bovine uterus and oviducts in follicular and luteal phases of the estrous cycle and further localizing the receptors to endometrial and oviductal epithelial cells. To our knowledge this is the first report demonstrating GnRH-R mRNA and protein in mammalian oviducts. We used gene-specific primers and monoclonal GnRH-R antibody to test GnRH-R mRNA and GnRH-R protein through RT-PCR and immunobloting. Immunohistochemistry was employed to localize these receptors to endometrial and oviductal epithelial cells. GnRH-R mRNA and receptor protein were expressed at expected molecular weights of 920bp and 60kD, respectively. Densitometry analysis revealed that expression levels for GnRH-R protein in uterus and oviducts were similar to bovine pituitary. The presence of GnRH receptors in bovine uterus and oviducts is intriguing and it would be imperative to examine the functional role of this system in the regulation of reproductive processes.

Luteinizing Hormone-Releasing Hormone I (LHRH-I) and Its Metabolite in Peripheral Tissues

Luteinizing hormone-releasing hormone (LHRH) was first isolated in the mammalian hypothalamus and shown to be the primary regulator of the reproductive system through its initiation of pituitary gonadotropin release. Since its discovery, this form of LHRH (LHRH-I) has been shown to be one of many structural variants with a variety of roles in both the brain and peripheral tissues. Enormous interest has been focused on LHRH-I and LHRH-II and their cognate receptors as targets for designing therapies to treat cancers of the reproductive system. LHRH-I is processed by a zinc metalloendopeptidase EC 3.4.24.15 (EP24.15) that cleaves the hormone at the fifth and sixth bond of the decapeptide (Tyr5-Gly6) to form LHRH-( 1 – 5 ). We have previously reported that the autoregulation of LHRH gene expression can also be mediated by its processed peptide, LHRH-( 1 – 5 ). Furthermore, LHRH-( 1 – 5 ) has also been shown to be involved in cell proliferation. This review will focus on the possible roles of LHRH and its processed peptide, LHRH-( 1 – 5 ), in non-hypothalamic tissues.

Action of chicken II GnRH on the human placenta

The stability, receptor binding, bioactivity, and production of chicken II GnRH and its analogs in the human placenta were studied. Both chicken II and mammalian GnRH are rapidly degraded by placental enzymes, yet the chicken II isoform is six times more stable. Analogs of chicken II GnRH were synthesized, and their stability in the presence of placental enzymes was tested. The D-Arg(6)-chicken II GnRH-aza-Gly(10)-NH(2) analog was found to be resistant to enzymatic degradation. The placental receptor binding activity of the chicken II GnRH analogs and chicken II GnRH was compared with that of mammalian GnRH and its analogs. Because D-Arg(6)-chicken II GnRH-aza-Gly(10)-NH(2) had the highest affinity for the placental receptor and was stable in placental extracts, the bioactivity of this analog on the regulation of placental human CG (hCG) release was compared with that for mammalian and chicken II GnRH using a human term placental explant culture system. This chicken II GnRH analog effected a stimulation of hCG at the lowest concentration studied (250 nM). With extended exposure and/or higher concentrations of this chicken II GnRH analog, the release of hCG from human placental explants was inhibited. Using a placental explant perifusion system and a highly specific RIA for chicken II GnRH, the pulsatile release of chicken II GnRH from the early human placenta was demonstrated. These studies are the first to demonstrate bioactivity of a second form of GnRH in a human tissue and to identify the pulsatile release of chicken II GnRH from a human tissue. These data led us to propose that chicken II GnRH and its synthetic analogs may be potent ligands for hormone regulation during pregnancy.

Gene expression of gonadotropin-releasing hormone, but not its receptor, in human endometrium and decidua

Gonadotropin-releasing hormone (GnRH) has been reported to exist in extrahypothalamic tissues such as the placenta, gonads and mammary glands. While we have reported the presence of GnRH-mRNA in the rodent uterus, there have been no reports concerning gene expression of GnRH and its receptor (GnRH-R) in human endometrial tissue. In order to investigate the role of GnRH as a local regulator in the human endometrium, we examined the gene for GnRH and GnRH-R in non-pregnant endometrium and decidua of early pregnancy. Using reverse transcriptase-polymerase chain reaction (RT-PCR) and Southern blot analysis we found GnRH-mRNA but not GnRH-R-mRNA transcripts in the human endometrium and decidua at 7-9 weeks gestation. This is the first report that suggests GnRH gene expression in the human endometrium/decidua.