Involvement Of Gonadotropin-releasing Hormone Research Articles

Immunohistochemical evidence for the involvement of gonadotropin releasing hormone in neuroleptic and cataleptic effects of haloperidol in mice

Blockade of dopamine D2 receptor by haloperidol is attributed for neuroleptic and cataleptic effects; and also for the release of gonadotropin releasing hormone (GnRH) from the hypothalamus. GnRH agonist is reported to exhibit similar behavioural effects as that of haloperidol, and pre-treatment with GnRH antagonist is shown to attenuate the effects of haloperidol, suggesting a possibility that GnRH might mediate the effects of haloperidol. To substantiate such possibility, the influence of haloperidol on GnRH immunoreactivity (GnRH-ir) in the brain was studied in vehicle/antide pre-treated mice by peroxidase–antiperoxidase method. Initially, an earlier reported antide–haloperidol interaction in rat was confirmed in mice, wherein haloperidol (250μg/kg, i.p.) exhibited suppression of conditioned avoidance response (CAR) on two-way shuttle box, and induced catalepsy in bar test; and pre-treatment with antide (50μg/kg, s.c., GnRH antagonist) attenuated both effects of haloperidol. Immunohistochemical study was carried out to identify GnRH-ir in the brain, isolated 1h after haloperidol treatment to mice pre-treated with vehicle/antide. The morphometric analysis of microphotographs of brain sections revealed that haloperidol treatment increased integrated density units of GnRH-ir in various regions of the limbic system. Considering basal GnRH-ir in vehicle treated group as 100%, the increase in GnRH-ir after haloperidol treatment was by 100.98% in the medial septum; 54.26% in the bed nucleus of the stria terminalis; 1152.85% in the anteroventral periventricular nucleus; 120.79% in the preoptic area–organum vasculosum of the lamina terminalis and 138.82% in the arcuate nucleus. Antide did not influence basal and haloperidol induced increase in GnRH-ir in any of the regions.As significant increase in GnRH-ir after haloperidol treatment was observed in such regions of the brain which are reported to directly or indirectly communicate with the hippocampus and basal ganglia, the regions respectively responsible for neuroleptic and cataleptic effects; and as GnRH antagonist eliminated the effects of haloperidol without affecting GnRH-ir, it appears that GnRH released by haloperidol mediates its neuroleptic and cataleptic effects.

Regulation of the cell proliferation and migration as extra-pituitary functions of GnRH

GnRH was originally identified as a hypothalamic factor which promotes gonadotropin release from the pituitary and was named gonadotropin-releasing hormone (GnRH). However, broad tissue distributions of GnRH and the GnRH receptor in various extrapituitary tissues and organs have been revealed and it has been suggested that GnRH has extrapituitary effects such as neuromodulation, immunomodulation, and regulation of follicular atresia and ovulation. Although a number of studies have been performed on these effects, little is known about the molecular mechanisms and physiological settings in which GnRH exerts its activities in extrapituitary organs or tissues. Our recent studies had demonstrated that GnRH is able to regulate both cell proliferation and cell migration at much lower concentration than that in the peripheral circulation by using human carcinoma cell lines. Moreover, stimulating activity of GnRH on the developing chick embryonic GnRH neurons was also demonstrated and strongly suggests possible involvement of GnRH in some of extrapituitary functions. This mini-review intends to provide solid evidence of GnRH activity in the regulation of cell proliferation and migration and its physiological relevance in extra-pituitary functions. Recent other research, including that in various invertebrates, provides new insight into the evolutionary scenarios of GnRH signaling systems, and GnRH functions. Both proliferating and migrating activities are important fundamental cellular activities and could provide an important clue into understanding what the driving force behind the evolution of the GnRH signaling system was.

Involvement of GnRH, PACAP and PRP in the Reproduction of Blue Gourami Females (Trichogaster trichopterus)

In vertebrates, gonadotropin-releasing hormone (GnRH) and pituitary adenylate cyclase-activating polypeptide (PACAP) are key hormones regulating growth and reproduction in the brain-pituitary axis. The regulating hormonal interactions are of great interest, therefore, the aim of this study is to provide novel insights into the involvement of brain GnRH and PACAP in oogensis and spermatogenesis in a fish model, the blue gourami (Trichogaster trichopterus). cDNA cloning of two GnRH forms combined with phylogenetic analysis revealed that three paralogous GnRH forms exist in blue gourami and evolve as a result of genome duplication. GnRH1 mRNA levels are related to final oocyte maturation (FOM), and this peptide stimulated β follicle-stimulating hormone (βFSH) and growth hormone (GH) gene expression; GnRH2 stimulated β gonadotropins (GtH) gene expression and GnRH analog combined with PACAP-38 synergistically upregulate GH and βFSH gene expression. The data presented, together with previous studies in our lab, enable suggesting mechanisms explaining the physiological relevance of these peptides in the regulation of gametogenesis and steroidogenesis in blue gourami females. These findings support the biological importance of the GnRH and PACAP hormones family, enabling them to stimulate differential biological functions in the regulation of growth and reproduction.

Multifunctional angiogenic factors: add GnRH to the list. Focus on “Gonadotropin-releasing hormone-regulated chemokine expression in human placentation”

the historical view that angiogenesis is governed by the action of a few dominant trophic factors, such as VEGF, FGF, and transforming growth factor-β (TGF-β), has steadily eroded over the past two decades to give rise to the vision of a much more dynamic regulation in which angiogenesis is

Involvement of Gonadotropin-Releasing Hormone in Thyroxine Release in Three different forms of Teleost Fish: Barfin Founder, Masu Salmon and Goldfish

Effects of gonadotropin-releasing hormone (GnRH) on thyroxine (T4) release in vivo and in vitro were studied in barfin flounder Verasper moseri, masu salmon Oncorhynchus masou and goldfish Carassius auratus. Seabream GnRH (sbGnRH) at a dose of 200 ng/50 g body weight (BW) significantly increased plasma T4 levels 1 h after the in vivo injection in the barfin flounder, but thereafter the levels normalized. Salmon GnRH (sGnRH) significantly increased plasma T4 levels l h after the injection with a significant return to initial levels in male masu salmon and male goldfish. In contrast, sGnRH and cGnRH-II in barfin flounder, and cGnRH-II in male masu salmon and male goldfish were not effective in stimulating T4 release. To clarify direct involvement of GnRH in T4 release, dissected lower jaw including scattered thyroid follicles was incubated with sbGnRH (1 µg/well) in barfin flounder, and with two doses (0.1 and 1 µg/well) of sGnRH in masu salmon and goldfish in vitro. T4 concentrations of control were stable during 24 h. Incubation of lower jaw with high dose (1 µg/well) of GnRH significantly (P<0.05) increased T4 concentrations of incubation medium at 1 h in all experimental fishes. These results indicate that direct stimulation of T4 secretion by GnRH occurs widely in teleost fish.

GnRH-Bik/Bax/Bak chimeric proteins target and kill adenocarcinoma cells; the general use of pro-apoptotic proteins of the Bcl-2 family as novel killing components of targeting chimeric proteins.

In recent years chimeric proteins carrying bacterial toxins as their killing moiety, have been developed to selectively recognize and kill cell populations expressing speciific receptors. The involvement of Gonadotropin releasing hormone (GnRH) has been demonstrated in several adenocarcinomas and a GnRH-bacterial toxin chimeric protein (GnRH-PE66) was thus developed and found to specifically target and kill adenocarcinoma cells both in vitro and in vivo. Because of the immunogenicity and the non-specific toxicity of the bacterial toxins, we have developed new chimeric proteins, introducing apoptosis inducing proteins of the Bcl-2 family as novel killing components. Sequences encoding the human Bik, Bak or Bax proteins were fused to the GnRH coding sequence at the DNA level and were expressed in E. coli. GnRH-Bik, GnRH-Bak and GnRH-Bax new chimeric proteins efficiently and specifically inhibited the cell growth of adenocarcinoma cell lines and eventually led to cell death. All three Bcl2-proteins-based chimeric proteins seem to induce apoptosis within the target cells, without any additional cell death stimulus. Apoptosis-inducing-proteins of the Bcl-2 family targeted by the GnRH are novel potential therapeutic reagents for adenocarcinoma treatment in humans. This novel approach could be widely applied, using any molecule that binds a specific cell type, fused to an apoptosis-inducing protein.

Adenocarcinoma Cells Are Targeted by the New GnRH-PE66 Chimeric Toxin through Specific Gonadotropin-releasing Hormone Binding Sites

Luteinizing hormone-releasing hormone, also termed gonadotropin-releasing hormone (GnRH), accounts for the hypothalamic-pituitary gonadal control of human reproduction. The involvement of GnRH has been demonstrated in several carcinomas of hormone-responsive tissues. Exploiting this common feature, we constructed a Pseudomonas exotoxin (PE)-based chimeric toxin (GnRH-PE66) aimed at targeting those cancer cells bearing GnRH binding sites. We report here the strong growth inhibition and killing of a surprisingly wide variety of cancers, confined to the adenocarcinoma type. These cancer cells arising from hormone-responsive tissues, as well as non-responsive ones, express specific GnRH binding sites as indicated by the marked killing of ovarian, breast, endometrial, cervical, colon, lung, hepatic, and renal adenocarcinoma. This cytotoxicity is specific as it could be blocked upon addition of excess GnRH. The specificity of GnRH-PE66 chimeric toxin was also confirmed by GnRH binding assays, and its ability to prevent the formation of colon cancer xenografts in nude mice is presented. Although the functional role of specific GnRH binding sites in human carcinomas remains obscure, GnRH-PE66 displays considerable targeting potential and its use as a therapeutic agent for cancer should be considered.

Activation of Salmon Gonadotropin-Releasing Hormone Synthesis by 17α-Methyltestosterone Administration in Yearling Masu Salmon, Oncorhynchus masou

Juvenile salmonid pituitary gonadotropin (GTH) contents are elevated after steroid hormone treatment, but the involvement of gonadotropin-releasing hormone (GnRH) is unclear. Activation of salmon GnRH (sGnRH) synthesis by 17α-methyltestosterone (MT) administration has been examined in the brain of yearling masu salmon (future precocious males and immature females) using an in situ hybridization technique combined with radioimmunoassay. Oral MT application markedly increased pituitary GTH IIβ, but not GTII Iβ, contents in both sexes. In future precocious males, MT treatment increased the number of cells expressing sGnRH mRNA in the preoptic area about threefold, whereas there were no significant differences in the olfactory bulbs and the ventral telencephalon. No significant changes were observed in cell sizes nor the numbers of silver grain per 100 μm 2 cell in any of the brain regions. Thus, in future precocious males, preoptic sGnRH neurons may be activated by sex steroids. In contrast, no significant changes were observed in sGnRH mRNA levels of immature females after MT treatment. These differences in responses to sex steroids of sGnRH cells in the preoptic area between future precocious males and immature females suggest that MT has indirect actions via sGnRH and/or direct actions on the pituitary in the former, and that MT acts directly on the pituitary in the latter.

Effects of gonadotropin-releasing hormone agonist on steroidogenesis in the rat ovary.

To assess the regulatory roles of gonadotropin-releasing hormone (GnRH) in ovarian function, the kinetics of the ovarian GnRH receptor and the effects of the GnRH superagonist buserelin on steroidogenesis in ovarian cell culture were examined. Scatchard analysis of buserelin-binding to crude ovarian cell membrane revealed a specific high-affinity GnRH receptor. Buserelin together with follicle-stimulating hormone stimulated estradiol (E2) production in immature follicles in hypophysectomized and DES-treated rats. On the other hand, applied to developing follicles of rats treated with pregnant-mare-serum gonadotropin buserelin suppressed E2 production to terminate follicle maturation and simultaneously stimulated progesterone (P4) production to induce luteinization. With ovarian cells luteinized by human chorionic gonadotropin in vitro, buserelin suppressed production of both P4 and E2, leading to luteolysis. Buserelin affected steroid production by modulating activities of key enzymes in steroid synthesis. These findings indicate that buserelin action depended on the gonadotropin priming of ovarian cells, and suggest the possible involvement of GnRH in the regulation of steroidogenesis throughout the ovulatory cycle.

Effects of active immunization against gonadotropin releasing hormone on gonadotropin secretion after ovariectomy and testosterone propionate administration to mares.

Five lighthorse mares were actively immunized against gonadotropin releasing hormone (GnRH) conjugated to bovine serum albumin (BSA) to study the involvement of GnRH in luteinizing hormone (LH) and follicle stimulating hormone (FSH) secretion following ovariectomy (OVX) and after administration of testosterone propionate (TP). Five mares immunized against BSA served as controls. Immunizations were started on November 1, and OVX was performed in June (d 1). All mares were treated with TP from d 50 to 59 after OVX. On the day of OVX, concentrations of LH were lower (P less than .05) in GnRH-immunized mares than in BSA-immunized mares and were generally nondetectable; FSH concentrations were reduced (P less than .05) by 50% in GnRH-immunized mares relative to BSA-immunized mares. In contrast to BSA-immunized mares, plasma concentrations of LH or FSH did not increase after OVX in GnRH-immunized mares. The LH response to GnRH analog (less than .1% cross-reactive with GnRH antibodies) on d 50 was reduced (P less than .05) by 97% in GnRH-immunized mares relative to BSA-immunized mares, whereas the FSH response was similar for both groups. Treatment with TP for 10 d reduced (P less than .01) the LH response and increased (P less than .01) the FSH response to GnRH analog in BSA-immunized mares, but it had no effect (P greater than .1) on the response of either gonadotropin in GnRH-immunized mares.(ABSTRACT TRUNCATED AT 250 WORDS)