Atrial natriuretic peptide (ANP) of atrial myocyte origin, has been shown to play a role in the diuresis, natriuresis, and antagonism of angiotensin and vasopressin. However, it is now apparent that in addition to the production of the peptide in the heart and in its role in fluid and electrolyte homeostasis, it is also produced in the central nervous system participating in the regulation of pituitary hormone secretion. Administration of ANP through both central and peripheral routes has been shown to inhibit secretion of luteinizing hormone (LH) in the gonadectomized rat model. A better understanding of the modulatory role of ANP on LH secretion and its possible mechanisms will add to our knowledge of the effects of neuropeptides on reproductive function. Brain natriuretic peptide (BNP) is a bioactive peptide of 26 amino acid residues recently identified in porcine brain. The peptide exerts potent diuretic-natriuretic and vasorelaxant effects, in a manner similar to that of ANP. BNP has a remarkable high sequence homology to ANP, especially in the 17 amino acid ring formed by an intramolecular disulfide linkage which is required for biological activity. The presence of BNP with ANP in the mammalian brain and remarkable resemblance in their molecular structures and physiological functions implies that BNP may also exert an inhibitory effect on LH secretion like ANP. This research focused on the effects of centrally administered ANP and BNP on pulsatile LH secretion and their possible mechanisms of action in ovariectomized rats. After third ventricle infusion of ANP or BNP, inhibition of mean plasma LH level, LH pulse amplitude and pulse frequency was observed. In searching for the possible mechanisms of inhibitory effect of ANP or BNP on pulsatile LH secretion, the effect of inhibiting the endogenous opiate system with naloxone on the action of centrally administered ANP or BNP was tested. Application of naloxone reversed the inhibitory effect of ANP and BNP on mean plasma LH level and LH pulse amplitude, but in terms of pulse frequency, naloxone treatment failed to reverse the inhibitory effect of ANP or BNP. In separate experiments, pretreatment with pimozide, a dopaminergic receptor blocker, prevented the inhibitory action of ANP and BNP on LH secretion. After infusion of ANP or BNP, there were no significant decrease in mean plasma LH level, pulse amplitude and pulse frequency in the pimozide-pretreated rats. In summary, the present study shows that both ANP and BNP inhibit pulsatile LH secretion, suggesting that the inhibitory effects on LH secretion once thought to be mediated by ANP alone may be regulated through a dual mechanism involving both ANP and BNP. Furthermore, the inhibitory mechanisms may involve the interactions of ANP and BNP with central opiate system and dopaminergic system on LH secretion. / Medicine, Faculty of / Obstetrics and Gynaecology, Department of / Graduate

Four experiments were conducted to investigate the effect of naloxone, an opioid receptor antagonist, on pituitary LH secretion in Holstein cows during two periods after parturition and two phases of the estrous cycle. In experiment 1, 24 cows (12 primiparous; 12 multiparous) received either saline (n = 12) or 1 mg/kg naloxone (n = 12) i. v. at 14 1 days postpartum. Blood samples were collected at 15-minute intervals for 2 hours before and 2.5 hours after naloxone or saline. Serum LH concentrations increased (P < .05) in response to naloxone injection in both primi- and multiparous cows. Saline injection did not affect LH concentrations. In experiment 2, 27 cows (13 primiparous; 14 multiparous) received either saline (n=14) or 1 mg/kg naloxone (n=13) i. v. at 28 ± 1 days postpartum. Blood samples were collected as in the previous experiment. Naloxone did not affect serum LH concentrations in either primi- or multi-parous cows at 28 days postpartum. In experiment 3, estrous cycles were synchronized via prostaglandin administration (25 mg) in 22 cows (10 primiparous; 12 multiparous). Cows received either saline (n=11) or 1 mg/kg naloxone (n=11) Lv. during the luteal phase of the estrous cycle. Blood samples were collected as in the previous experiments. Luteinizing hormone concentrations were not affected by naloxone in either primi- or multi-parous cows during the luteal phase of the estrous cycle. In experiment 4, the same cows used in experiment 3 received a second dose of prostaglandin (25 mg). Thirty-six hours later, during the follicular phase of the estrous cycle, the cows received either saline (n =9) or 1 mg/kg naloxone (n = 11) i. v. Naloxone increased (P < .05) serum LH concentrations in both primi- and multi-parous cows in the follicular phase. These results suggest that LH release in the early postpartum dairy cow is regulated, at least in part, by endogenous opioid pep tides , and the ability of naloxone to affect LH secretion may change as days postpartum increases, perhaps due to changes in degree of inhibition by endogenous opioid peptides, and (or) changes in serum progesterone concentration due to onset of ovarian activity during postpartum period. It appears that the modulation of LH secretion may be mediated via opioids during the follicular phase of the estrous cycle. However, an opioid-mediated mechanism for modulation of LH secretion was absent or overridden by progesterone feedback during the luteal phase of the estrous cycle. / Master of Science

No description available.

The two objectives for this thesis were to 1) validate a bovine luteinizing hormone (LH) ELISA for use in the laboratory and 2) validate interstitial glucose sensors designed for humans for use in lactating dairy cattle. The first experiment required validation of a bovine LH ELISA in order to measure the circulating concentration of LH in the blood of cows in altered thermal and/or metabolic states. Assays from two separate companies were tested. Half of one plate was run at a time resulting in a total of 6 separate analyses (3 plates total). Despite early, promising results, neither LH ELISA could be successfully validated. For many analyses, the standard curves did not even meet the minimal criteria to allow calculation of a formula for determining the concentrations of the unknowns. In analyses where the standard curves were acceptable, the coefficients of variation (CV%) for the unknowns were unacceptable. The second experiment attempted to validate the use of commercially available human interstitial glucose sensors (FreeStyle Libre and Dexcom G6) in lactating dairy cows. Blood glucose concentrations correlated well with sensors secured behind the cow's ear for both FreeStyle Libre (r=0.82) and Dexcom (r=0.88). Unfortunately, however, the absolute relative error's highest value was 47% for the FreeStyle Libre ear. In summary, neither the LH ELISAs nor the interstitial glucose sensors could be validated. / Master of Science / Two separate studies were performed with the purpose of one, measuring a hormone significant to reproduction, Luteinizing Hormone (LH), and two, measuring glucose in interstitial fluid in lactating cows. The first experiment required the use of a commercially available ELISA test to measure LH concentrations. While using radioimmunoassay (RIA) is the preferred method for measuring LH in dairy cattle, an ELISA is an alternative method that is generally more accessible. There was also little published research available illustrating the accuracy of the LH ELISAs. Therefore, we attempted to validate the assays for bovine samples. Despite several attempts, the LH ELISA was unsuccessfully validated. The second study attempted to validate commercially available continuous interstitial glucose sensors designed for humans for use with lactating Holstein cows. Validation of interstitial sensors for use in dairy cattle would decrease the amount of stress and handling when measuring circulating glucose for research, clinical diagnostics and application in industry. While early data suggested that sensors behind a cow's ear may work, further analysis illustrated the sensors were not accurate enough when used on cows. In conclusion, the lab was unsuccessful in proving that continuous interstitial glucose monitors and LH ELISAs could be utilized in the lab.

Exogenous PGF_2α, (see Appendix I for definitions of abbreviations) is luteolytic in midluteal (1.e., d 9 of a 17 d estrous cycle) sheep. However, the pharmacokinetic responses to PGF_2α-induced luteolysis are not known. This study (Exp. 1 and 2) was conducted to determine several pharmacokinetic responses to two dosing regimens of Lutalyse® (PGF_2α). Experiment 1 was a 2 x 2 factorial design, with Lutalyse and H/Ox as main effects. Lutalyse (15 mg) was injected i.m., and blood samples were collected, relative to the time of injection, from the vena cava at points cranial and caudal to the uteroovarian vein. Progesterone and PGF_2α, were measured in blood plasma. The PGF_2α concentrations were greater in H/Ox and sham H/Ox ewes treated-with Lutalyse® than in control ewes. Peak concentrations of PGF_2α were greatest in sham H/Ox Lutalyse-treated ewes, indicating that the uterus and(or) ovaries secrete PGF_2α, in response to exogenous PGF_2α. In Lutalyse-treated ewes, progesterone concentrations decreased by 50% within 8 h after treatment. The design of Exp. 2 was also a 2 x 2 factorial, with Lutalyse (2 x 5mg at 3 h intervals) and H/Ox as main effects. Prostaglandin F_2α and PGFM were measured in blood plasma collected, relative to the time of injections, from the vena cava at points cranial and caudal to the uteroovarian vein. The PGF_2α concentrations were greater in sham H/Ox ewes treated-with Lutalyse than in control ewes. Peak concentrations of PGF_2α were greater in sham H/Ox than in ewes in all other treatment groups, indicating again that the uterus and(or) ovaries secrete PGF_2α in response to exogenous PGF_2α In general, PGFM concentrations increased in a pattern similar to that of PGF_2α after Lutalyse injection; although there was a short delay of approximately 2 min. Caudal vena caval PGF, concentrations in H/Ox Lutalyse-treated ewes were greater than that after saline injection, which indicates that metabolism may depend on the presence or absence of the uterus and(or) ovaries. In Exp. 1, caudal PGF, concentrations were greater in H/Ox ewes injected with 15 mg of Lutalyse than in ewes in all other treatments . However, in response to 5 mg Lutalyse, caudal PGF_2α concentrations were greater in sham H/Ox ewes than in all other treatment groups. This indicates that the larger dose in H/Ox ewes supersedes the capacity of the lung and kidney to dispose of PGF_2α, and PGF_2α is more tightly regulated in intact ewes. The lungs and kidney are capable of metabolizing the smaller dose of Lutalyse but not the resulting PGF_2α production in intact ewes. A short validation experiment was conducted to determine the effects of sampling location on progesterone, PGF_2α and PGFM concentrations. Sampling location did not affect the mean concentration of progesterone or PGFM. However, location affected the mean PGF_2α concentration. The concentration of PGF_2α, was greater (P < .05) in saphenous vein and caudal vena caval blood plasma than in jugular plasma. In summary, the uterus and(or) ovaries produce and regulate PGF_2α concentration in response to Lutalyse. It is speculated that a threshold PGF_2α concentration or duration of the PGF_2α peak concentration exists because these PGF_2α, responses differed in intact Lutalyse-treated and saline-treated ewes in both experiments. The mean cranial PGF_2α concentration, peak concentration, duration of the peak, increase in PGF_2α and AUC were greater in response to 15 mg of Lutalyse, although the two smaller doses have been shown to be more efficacious in inducing luteolysis. The second dose of PGF_2α may act by mimicking pulses of PGF_2α and initiate the luteolytic cascade two times. / Master of Science

Ko Nga Ling. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2002. / Includes bibliographical references (leaves 98-131). / Abstracts in English and Chinese. / Abstract (in English) --- p.ii / Abstract (in Chinese) --- p.v / Acknowledgements --- p.vii / Table of Contents --- p.ix / List of Figures --- p.xiv / List of Tables --- p.xvii / Symbols and Abbreviations --- p.xviii / Scientific Names --- p.xxi / Chapter Chapter 1 --- General Introduction / Chapter 1.1 --- Gonadotropins --- p.1 / Chapter 1.1.1 --- Structure --- p.1 / Chapter 1.1.2 --- Function --- p.3 / Chapter 1.1.3 --- Regulation --- p.5 / Chapter 1.1.3.1 --- Hypothalamic regulators (GnRH) --- p.5 / Chapter 1.1.3.2 --- Endocrine regulators from gonads (steroids) --- p.7 / Chapter 1.1.3.3 --- Paracrine regulators (activin) --- p.9 / Chapter 1.1.4 --- Promoter analysis --- p.9 / Chapter 1.2 --- Activin Family of Growth Factors --- p.12 / Chapter 1.2.1 --- Activin --- p.12 / Chapter 1.2.1.1 --- Structure --- p.12 / Chapter 1.2.1.2 --- Function --- p.13 / Chapter 1.2.1.3 --- Signaling --- p.15 / Chapter 1.2.2 --- Follistatin --- p.16 / Chapter 1.2.2.1 --- Structure --- p.16 / Chapter 1.2.2.2 --- Function --- p.17 / Chapter 1.3 --- Objectives --- p.18 / Chapter Chapter 2 --- Establishment and Characterization of Stable LβT2 Cell Lines Containing and Expressing SEAP Driven by the Goldfish FSHβ Promoter / Chapter 2.1 --- Introduction --- p.29 / Chapter 2.2 --- Materials and Methods --- p.31 / Chapter 2.2.1 --- Construction of expression plasmid --- p.31 / Chapter 2.2.2 --- Cell culture --- p.32 / Chapter 2.2.3 --- Cotransfection of LβT2 cells --- p.32 / Chapter 2.2.4 --- G418 selection of transfected LpT2 cells --- p.33 / Chapter 2.2.5 --- SEAP reporter gene assay --- p.33 / Chapter 2.2.6 --- Cloning of pSEAP/gfFSHβ promoter and pBK- CMV-transfected LβT2 cells by limited dilution --- p.34 / Chapter 2.2.7 --- Extraction of genomic DNA --- p.34 / Chapter 2.2.8 --- Isolation of total RNA --- p.35 / Chapter 2.2.9 --- Reverse transcription-polymerase chain reaction (RT-PCR) --- p.35 / Chapter 2.3 --- Results --- p.36 / Chapter 2.3.1 --- Optimization of G418 concentration for selection --- p.36 / Chapter 2.3.2 --- Expression of SEAP reporter gene by pSEAP/gfFSHβ promoter and pBK-CMV-transfected LβT2 cells --- p.37 / Chapter 2.3.3 --- Establishment of LβT2 cell lines that contain a functional gfFSHp promoter --- p.37 / Chapter 2.3.4 --- Characterization of LβT2#23 that contains a functional gfFSHβ promoter --- p.38 / Chapter 2.4 --- Discussion --- p.39 / Chapter Chapter 3 --- Hormonal Regulation of Goldfish Follicle-Stimulating Hormone β (FSHβ) Promoter Activity in LpT2#23 Cells / Chapter 3.1 --- Introduction --- p.52 / Chapter 3.2 --- Materials and Methods --- p.54 / Chapter 3.2.1 --- Cell culture --- p.55 / Chapter 3.2.2 --- Drug treatment --- p.56 / Chapter 3.2.3 --- SEAP reporter gene assay --- p.56 / Chapter 3.2.4 --- Isolation of total RNA --- p.57 / Chapter 3.2.5 --- Reverse transcription-polymerase chain reaction (RT-PCR) --- p.57 / Chapter 3.2.6 --- Data analysis --- p.58 / Chapter 3.3 --- Results --- p.59 / Chapter 3.3.1 --- Effects of goldfish activin on FSHβ promoter --- p.59 / Chapter 3.3.2 --- Blockade of activin effects by follistatin --- p.59 / Chapter 3.3.3 --- Effects of different hormones and steroids on FSHβ promoter --- p.60 / Chapter 3.4 --- Discussion --- p.61 / Chapter Chapter 4 --- Promoter Analysis for the Activin Responsive Element (ARE) in the Goldfish Follicle-Stimulating Hormone β (FSHβ) Gene / Chapter 4.1 --- Introduction --- p.71 / Chapter 4.2 --- Materials and Methods --- p.74 / Chapter 4.2.1 --- Generation of SEAP reporter plasmids containing the gfFSHβ promoter of different lengths --- p.74 / Chapter 4.2.2 --- PCR screening and restriction analysis --- p.75 / Chapter 4.2.3 --- Midiprep --- p.76 / Chapter 4.2.4 --- Cell culture --- p.77 / Chapter 4.2.5 --- Transfection of the pSEAP/gfFSHβ promoter constructs into LβT2 cells --- p.77 / Chapter 4.2.6 --- Activin treatment --- p.77 / Chapter 4.2.7 --- SEAP assay --- p.78 / Chapter 4.3 --- Results --- p.78 / Chapter 4.3.1 --- Subcloning of the gfFSHβ promoter of decreasing length into SEAP reporter vector --- p.78 / Chapter 4.3.2 --- Activin stimulation of the pSEAP/gfFSHβ promoter constucts in LβT2 cells --- p.79 / Chapter 4.4 --- Discussion --- p.80 / Chapter Chapter 5 --- General Discussion / Chapter 5.1 --- Overview --- p.92 / Chapter 5.2 --- Contribution of the present research --- p.95 / Chapter 5.2.1 --- Establishment of stable LβT2 cell lines containing and expressing SEAP driven by gfFSHβ promoter --- p.95 / Chapter 5.2.2 --- Hormonal regulation of the gfFSHβ promoterin LβT2#23 cells --- p.95 / Chapter 5.2.3 --- Identification of the activin responsive element (ARE) on the gfFSHβ promoter --- p.96 / Chapter 5.3 --- Future research direction --- p.96 / References --- p.98

No description available.

Thesis (MSc (Biochemistry))--Stellenbosch University, 2008. / Gonadotropin-releasing hormone (GnRH) acting through the cognate GnRH receptor (GnRH-R) plays an important role in the regulation of mammalian reproductive function by regulating the synthesis and release of follicle stimulating hormone (FSH) and luteinizing hormone (LH). The sensitivity of pituitary gonadotropes to GnRH depends on the number of GnRH receptors present on the gonadotrope cell surface. GnRH-R is regulated at a transcriptional, post-transcriptional and post-translational level. Hormones such as GnRH and glucocorticoids (GCs) regulate GnRH-Rs in a time- and dose-dependent manner. Previous studies have shown that the GnRH-R promoter confers glucocorticoid-dependent activation via the activating protein 1 (AP-1) site in the nongonadotrope GGH3 cell line. The mechanism by which GCs regulate the GnRH-R promoter is not precisely known as the literature is contradictory. Therefore this study investigates the mechanism of transcriptional regulation of the mouse GnRH-R promoter in the mouse gonadotrope cell line LβT2, treated with the synthetic GC dexamethasone (dex). Assays used include promoter-reporter studies, Western blotting, endogenous mRNA expression studies, electrophoretic mobility shift assay (EMSA) as well as the in vivo chromatin immunoprecipitation (ChIP) assay. A transfected promoter-reporter plasmid containing 600 bp of the mouse GnRH-R promoter was used to investigate the effect of dex on transcriptional regulation. Previously it was determined in our laboratory that the GnRH-R promoter is activated via an AP-1 binding site in the LβT2 cell line, and is regulated in a time- and dose-dependent manner by dex. In the present study in the LβT2 cell line a small induction was indeed seen upon dex treatment. Cotransfecting a expression vector for rat GR succeeded in inducing a 2 fold positive dex response. Western blot analysis revealed that GR levels remain consistent even after 8 hours dex induction. The effect of dex on the endogenous GnRH-R gene was investigated by means of real-time RT-PCR. Dex did indeed upregulate the gene in a time-dependant manner. Maximal induction (7.4 fold) was obtained after at least 12 hours of dex treatment. Untreated LβT2 nuclear extracts were investigated using EMSA, for protein binding to the mouse GnRH-R promoter AP-1 binding site, and these proteins were identified as c- Fos and GR. This suggests that the GR interacts with the AP-1 transcription factor via a tethering mechanism to mediate the positive dex response. The results of an in vivo ChIP assay were consistent with this hypothesis, showing that the GR interacted with a genomic fragment containingthe AP-1 site, in response to dex. The transactivation of the GnRH-R promoter by means of the GR tethering to AP-1 has not been shown before in the LβT2 cell line.

Thesis (MSc)--Stellenbosch University, 2001. / ENGLISH ABSTRACT: The regulation of gonadotropin releasing hormone (GnRH) receptor numbers in the pituitary is a crucial control point in reproduction. Pituitary sensitivity to GnRH can be directly correlated with GnRH receptor levels, which can be regulated at transcriptional and post-transcriptional level. The proximal promoter of the mouse GnRH receptor gene contains two cis elements bearing the consensus sequence for a Steroidogenic Factor-l (SF -1) binding site. The distal site has previously been shown to be involved in basal and tissue-specific transcriptional regulation, whereas the function of the proximal site was not established. SF-I, a member of the nuclear receptor superfamily of transcription factors, is involved in the transcriptional regulation of a large number of genes involved in steroidogenesis and reproduction. The consensus SF-I binding site can serve as a binding site for several members of the nuclear receptor superfamily. The aim of this study was to investigate the binding of SF-I protein from the aT3-1 gonadotrope cell line to the two putative SF-I binding sites in the mouse GnRH receptor promoter in vitro, in order to provide supporting evidence for their functional roles in GnRH receptor gene regulation. It was shown by Western blotting that SF-I and Nur77, another nuclear receptor transcription factor, are both expressed in aT3-1 cells, in a manner that is influenced by cell culture conditions. Gel mobility shift assays using specific antibodies showed that both SF-I and Nur77 protein in aT3-1 nuclear extracts bind to both sites in a mutually exclusive fashion. As shown by competition assays using mutated versions of the two sites, Nur77 protein had different base pair requirements than that of SF-I protein for binding to the sites. Additionally, SF-I mRNA was shown by Northern blotting to be increased in aT3-1 cells in response to stimulation of the Protein Kinase A (PKA) pathway by forskolin. These results highlight unexpected degeneracy in so-called "consensus" nuclear receptor binding sites. Furthermore, since Nur77 protein is involved in the stress response of the hypothalamic-pituitary-adrenal (HPA) axis, the unexpected presence of Nur77 protein in a gonadotrope cell line has potentially important implications for cross-talk between the HPA and hypothalamic-pituitary-gonadal (HPG) axes. / AFRIKAANSE OPSOMMING: Daar bestaan 'n direkte verband tussen pituïtêre sensitiwiteit vir gonadotropien-vrystellingshormoon (GnRH) en GnRH-reseptorvlakke Die regulering van GnRH-reseptorvlakke op transkripsionele en post-transkripsionele vlak in die pituïtêre klier is belangrik by die beheer van voortplantingsfunksies. Die proksimale promotor van die GnRH-reseptorgeen in die muis bevat twee cis elemente met die konsensus volgorde vir 'n Steroidogenic Factor-l (SF-I) bindingsetel. Die distale element is betrokke by basale en weefsel-spesifieke transkripsionele regulering, maar die funksie van die proksimale element is nog nie vasgestel nie. SF-1 is 'n lid van die superfamilie van selkernreseptore en is betrokke by die transkripsionele regulering van gene verantwoordelik vir steroïedogenese en voortplanting. Die konsensus SF-I bindingsvolgorde kan dien as bindingsetel vir verskeie selkernreseptore. Ten einde 'n beter insig ten opsigte van die regulering van die GnRH reseptorgeen te verkry, is ondersoek ingestel na die binding van SF-I-proteïen, afkomstig van die aT3-1 pituïtêre gonadotroopsellyn, aan die twee moontlike SF-l bindingsetels in die GnRH-reseptor promotor, in vitro. Die Western-klad metode het getoon dat beide SF-l en Nur77, 'n ander selkernreseptor-transkripsiefaktor, in die aT3-1 sellyn uitgedruk word. Die uitdrukking is afhanklik van selkultuurtoestande. Elektroforetiese mobiliteitsessais met spesifieke antiliggame het getoon dat SF-l en Nur77 proteïene in aT3-1 selkernproteïenekstraksies eksklusief aan beide bindingsetels bind. Nur77 proteïen benodig ander basispare as SF-l proteïen om aan die bindingsetels te bind. Hierdie resultate dui op onverwagse degenerasie in sogenaamde "konsensus" selkernreseptor-bindingsvolgordes. Die Northern-kladmetode het ook getoon dat SF-l mRNA vlakke in aT3-1 selle styg wanneer die proteïenkinase A (PKA) pad gestimuleer word met forskolin. Aangesien Nur77 proteïen betrokke is by die stres-respons van die hipotalamus-pituïtêre klier-adrenale (HP A) aksis, hou die onverwagse teenwoordigheid van Nur77 proteïen in 'n gonadotroop-sellyn potensieel belangrike inplikasies in vir kommunikasie tussen die HPA-aksis en die hipotalamus-pituïtêre klier-gonadale (HPG) aksis.

Thesis (MSc)--Stellenbosch University, 2001. / ENGLISH ABSTRACT: The GnRH receptor is a G-protein-coupled receptor in pituitary gonadotrope cells. Binding of its ligand, GnRH, results in synthesis and release of gonadotropin hormones luteinizing hormone (LH) and follicle stimulating hormone (FSH). Steroidogenic factor 1 (SF-1), a transcription factor, binds to specific sites in the promoter region of gonadotropin genes, and thus regulates transcription of these genes. The promoter region of the GnRHreceptor gene contains two SF-1-like binding sites, one at -14 to -8 (site 1) and another at -247 to -239 (site 2), relative to the methionine start codon. The role played by these two SF-1-like sites in basal transcription of the mouse GnRH receptor (mGnRH-R) gene in a pituitary precursor gonadotrope cell line, aT3 cells, was the first area of investigation during this study. Luciferase reporter constructs containing 580 bp of mGnRH-R gene promoter were prepared, where SF-1-like sites were either wildtype or mutated. Four such constructs were made, i.e. wildtype (LG), site 1 mutant (LGM1), site 2 mutant (LGM2) and mutated site 1 plus site 2 (LGM1/2). These constructs were transfected into aT3 cells to determine the effect of mutations of sites 1 and/or 2 on the basal expression of the mGnRH-R gene. Mutation of either site 1 or site 2 had no effect on basal expression of the mGnRH-R gene. It was found that only upon simultaneous mutation of both sites 1 and 2, a 50% reduction in basal transcription took place. The implications of this is that SF-1 protein seems to only require one intact DNA-binding site, to mediate basal transcription of the mGnRH-R gene, suggesting that these two sites lie in close proximity during basal transcription. The effect of the protein kinase A (PKA) pathway on the endogenous mGnRH-R gene was also investigated by incubating non- , transfected aT3 cells with the PKA activators, forskolin and 8-Br-cAMP. Similar incubations were also performed on the wild type and mutated site 1 constructs transfected into pituitary gonadotrope aT3 cells. It was found that forskolin and 8-Br-cAMP were able to increase endogenous mGnRH-R mRNA levels in a concentration-dependent fashion, showing that endogenous GnRH receptor gene expression is stimulated via a protein kinase A pathway. Similar results were obtained with the wildtype promoter construct, showing that the protein kinase A pathway stimulates transcription of the promoter. This effect was only seen with wild type and not with the mutated site 1. These results are consistent with a role for a SF-1-like transcription factor in mediating the protein kinase A effect via binding to the site 1 at position -14 in the GnRH receptor gene. A separate investigation was performed to determine whether 25-hydroxycholesterol (25-0HC) is a ligand for SF-1, by incubating aT3 cells transfected with the various constructs with 25-0HC. Results show a dose-dependant response, with an increase in gene expression at 1 μM and a decrease at higher concentrations, for both mutant and wild type constructs. This suggests that, if SF-1 is indeed the protein binding to sites 1 and 2, then 25-0HC is not a ligand for SF-1 protein in aT3 cells and that the effect of 25-0HC on the mGnRH-R gene is not mediated via site 1. The results indicate that these decreases of expression at the higher concentrations may be due to cytotoxic effects. Towards the end of the study the laboratory obtained a luminoskan instrument with automatic dispensing features. Optimisation studies on the luciferase and β-Gal assays were performed on the luminoskan in a bid to decrease experimental error. It was found that automation of these assays resulted in a decrease in experimental error, showing that future researchers could benefit substantially from these optimisation studies. / AFRIKAANSE OPSOMMING: Die GnRH reseptor is 'n G proteïen-gekoppelde reseptor in pituitêre gonadotroopselle. Binding van die ligand, GnRH, lei tot die sintese en vrystelling van die gonadotropien hormone, luteïniserende hormoon (LH) en follikel stimulerende hormoon (FSH). Steroidogeniese faktor-t (SF-1) is 'n transkripsie faktor wat aan spesifieke areas in die promotergebied van die gonadotropien hormone bind, en dus transkripsie van hierdie gene reguleer. Die promotergebied van die GnRH reseptor geen bevat twee SF-1 bindings areas, een by -14 to -8 (area 1) asook by -247 to -239 (area 2), relatief to die metionien beginkodon. Die rol wat hierdie twee SF-1 areas speel in basale transkripsie van die muis GnRH reseptor (mGnRH-R) geen in 'n pituïtêre voorloper gonadotroop sellyn, aT3 selle, was die eerste gebied van ondersoek gedurende hierdie studie. Plasmiede bestaande uit die 580 basispaar mGnRH-R promoter verbind aan 'n lusiferase geen is vervaardig, waar SF-1-soortige areas enersyds onveranderd gelaat is, of gemuteer is. Vier sulke plasmiede is vervaardig, nl. onveranderd (LG), area 1 mutant (LGM1), area 2 mutant (LGM2) en gemuteerde area 1 plus area 2 (LGM1/2). Hierdie plasmiede is gebruik om aT3 selle te transfekteer om die effek van mutasies van areas 1 en/of 2 op die basale ekspressie van die mGnRH-R geen te ondersoek. Daar is gevind dat mutasies van areas 1 of 2 geen effek op basale ekspressie op die bogenoemde geen gehad het nie. Slegs tydens gelyktydige mutasie van areas 1 en 2 het 'n 50% vermindering in basale transkripsie plaasgevind. Die implikasies hiervan is dat die SF-1 proteïen blykbaar slegs een volledige DNA-bindingsarea benodig om basale transkripsie van die mGnRH-R geen te reguleer. Dit wil dus voorkom of hierdie twee areas baie na aan mekaar geposisioneer is tydens basale transkripsie. Die effek van die proteïen kinase A (PKA) roete op die natuurlike mGnRH-R geen is ook ondersoek tydens inkubasie van nie-getransfekteerde aT3 selle met die PKA akiveerders, forskolin en 8-Br-cAMP. Soortgelyke inkubasie is ook gedoen op die onveranderde en gemuteerde area 1 plasmiede wat in aT3 selle getransfekteer is. Daar is gevind dat forskolin en 8-Br-cAMP daarin geslaag het om die natuurlike mGnRH-R geen mRNA vlakke op 'n konsentrasie-afhanklike wyse te vermeerder. Hierdie resultaat dui daarop aan dat die natuurlike mGnRH-R geen se ekspressie gestimuleer kan word via 'n proteïen kinase A roete. Soortgelyke resultate is verkry met die onveranderde promoter plasmied en dit wys ook daarop dat proteïen kinase A transkripsie deur die promoter kan stimuleer. Hierdie effek was slegs aanwesig met die onveranderde en nie met die gemuteerde area 1 plasmied nie. Die resultate stem ooreen met 'n rol vir SF-1 transkripsie faktor in die regulering van proteren kinase A effek deur middel van binding aan die area 1 by posisie -14 in die GnRH-R geen. 'n Afsonderlike ondersoek is gedoen om vas te stel of 25-hidroksiecholesterol (25-0HC) 'n ligand vir SF-1 is deur getransfekteerde aT3 selle met 25-0HC te inkubeer. Resultate toon 'n dosis-afhanklike respons met 'n verhoging in geen ekspressie by 1 μM en 'n verlaging met hoër konsentrasies vir beide onveranderde en gemuteerde plasmiede. Dit impliseer dat, indien SF-1 wel die faktor is wat aan areas 1 en 2 bind, 25-0HC nie die ligand vir SF-1 proteren in aT3 selle is nie en dat die effek van 25-0HC op die mGnRH-R geen nie gereguleer word via area 1 nie. Die verlaging in ekspressie gevind by die hoër konsentrasies is dalk die gevolg van sitotoksiese effekte. Teen die einde van die studie het die laboratorium luminoskan toerusting met outomatiese pipettering verkry. Optimiseringstudies van die lusifirase en β-Galtoetse is met die luminoskan gedoen in 'n poging om eksperimentele foute te minimaliseer. Daar is gevind dat outomatisering van hierdie toetse wel gelei het tot 'n verlaging in eksperimentele foute. Toekomstige navorsers kan dus grootliks voordeel trek uit hierdie optimiseringstudies.