of the New Zealand Society of Endocrinology

Ovulation rate in mammals is determined by a complex exchange of hormonal signals between the pituitary gland and the ovary and by a localised exchange of hormones within ovarian follicles between the oocyte and its adjacent somatic cells. From examination of inherited patterns of ovulation rate in sheep, several breeds have been identified with point mutations in two growth factor genes and a related receptor (i.e. ALK6 otherwise known as BMPRIB) that are expressed in oocytes. Currently, five different point mutations have been identified in the BMP15 (GDF9B) gene, one in GDF9 gene and one in ALK6. Animals heterozygous for any of the aforementioned mutations, heterozygous for the above GDF9 mutation as well as one of the BMP15 mutations, homozygous for the above ALK6 mutation, heterozygous for the ALK6 as well as heterozygous for one of the BMP15 mutations, have higher ovulation rates (i.e. +0.6-10) than their wild-type contemporaries. In contrast, those homozygous for any of the aforementioned five BMP15 or GDF9 mutations are sterile due to arrested follicular development from the primary (type 2 stage) of growth. The BMP15 and GDF9 mutations are thought to result in reduced levels of mature protein or altered binding to cell-surface receptors. In sheep, GDF9 mRNA is present in germ cells before and after ovarian follicular formation as well as throughout follicular growth. In contrast, BMP15 mRNA is found in oocytes only from the primary stage of growth. Both GDF9 and BMP15 proteins are present in follicular fluid indicating that they are secreted products. In sheep, ALK6 together with related cell-surface receptors such as ALK5 and BMPRII mRNA are present in oocytes at most, if not all, stages of follicular growth. In granulosa cells, BMPRII the type 1 (primordial) stage of ALK6 and ALK5 the type 2 and 4 stages of growth. Imunisation studies with GDF9 or BMP15 peptides show that growth for ovarian follicular development and normal ovulation and/or corpus luteum formation in sheep. In sheep with mutated ALK6, ovarian follicles undergo precocious maturation leading to 3-7 follicles ovulating at smaller follicular diameters without any increase above wild-types in the ovarian secretion of steroids or inhibins. important consequence of the mutated ALK6 a ability of some BMPs to inhibit differentiation of follicular cells. Current findings in sheep that BMP15, GDF9 and ALK6 are targets for new methods of fertility regulation in some During pregnancy, food intake increases resulting in increased deposition of adipose tissue, with a consequent increase in plasma leptin. Pregnant rats become resistant to the satiety action of leptin, allowing food intake and body weight to continue increasing. We hypothesised that the hormones of pregnancy may be inducing leptin resistance in the rat. The aim of this experiment was to examine whether pseudopregnancy, induced by a sterile mating, could adequately mimic the hormonal changes of pregnancy, thereby serving as a model to investigate hormonal regulation of leptin sensitivity. Serial blood samples were taken from pseudopregnant and cycling rats via an indwelling jugular cannula at 1000, 1700, 2200 and 0300 hours. Plasma prolactin and leptin concentrations were measured by radioimmunoassay (RIA). Terminal blood samples were collected from diestrous controls and day 3, 6 and 9 pseudopregnant rats, sera removed and progesterone and estradiol measured by RIA. Leptin was administered via an intracerebroventricular cannula in fasted pseudopregnant and cycling rats and food intake measured over 24 hours. Like pregnancy, pseudopregnancy was characterised by twice-daily prolactin surges. These surges have a luteotrophic role, maintaining pregnancy-like, high progesterone levels during pseudopregnancy. Unlike pregnancy, however, there was no significant increase in plasma leptin levels during pseudopregnancy. Furthermore, pseudopregnant rats respond to exogenous leptin by reducing food intake, suggesting that they do not become leptin resistant. These data suggest pseudopregnancy does not completely model the metabolic conditions of pregnancy, and some other aspect of pregnancy, such as placental hormones, must contribute to induction of central leptin resistance seen in the pregnant rat. REDUCED ACTIVATION Phytoestrogens are plant-derived compounds that are particularly abundant in soy-based foods. Exposure to exogenous oestrogenic chemicals has been implicated in declining male fertility. The aim of this study is to deduce whether adult phytoestrogen exposure affects the reproductive function of male rats, and by what mechanisms phytoestrogens may be acting. Six male rats were transferred from a low soy diet (control) to an experimental high soy diet, while 9 males remained on the control diet. On days 3, 6 and 12 all males were mated and litter sizes recorded. A second group of male rats kept on the same dietary regimen were killed after 3, 6 and 12 days on the diets. Real-time PCR was performed to measure mRNA quantities of oxytocin (OT), oxytocin receptor (OTR), oestrogen receptors α (ER α ) and (cid:533) (ER (cid:533) ), and the androgen receptor (AR). The average litter size following 3 days on the high soy diet was significantly lower than that for rats maintained on the control diet. Litter sizes returned to control levels by day 12. Following 3 days on the high soy diet, ER α and AR mRNA levels increased in the initial segment of the epididymis, while ER α , AR and OTR decreased in the cauda. Short-term exposure to high phytoestrogen levels transiently reduces male fertility, and may involve disruption of hormone receptor expression. The mechanisms by which such disruptions alter fertility are being investigated. The changes in OTR, ER α and AR mRNA levels indicate differential gene regulation between distinct regions of the epididymis. During late pregnancy, the activity of TIDA neurons (which suppress prolactin secretion) is reduced, resulting in a state of hyperprolactinemia. The reduction in TIDA activity may be mediated by the changes in levels of estrogen and progesterone at this time. The aim of this study was to determine whether ovarian steroid receptors are expressed in TIDA neurons, and whether levels of expression change during late pregnancy and lactation. We perfused animals for brain collection on the morning of diestrus, day 12, 19 and 21 of pregnancy and on day 5 of lactation. Brains were sectioned at 40μm and serial sections containing the arcuate nucleus were stained via dual label peroxidase immunohistochemistry for coexpression of either estrogen receptors (ER α ) or progesterone receptors and tyrosine hydroxylase (a marker for TIDA neurons). Both estrogen and progesterone receptors were expressed in TIDA neurons at all times. There was a significant increase in estrogen receptor coexpression during all stages of pregnancy compared to diestrus and lactating animals (mean increase 27%, p<0.05). In contrast, progesterone receptor coexpression was similar across diestrus and pregnancy, however a significant decrease was observed in lactating compared to diestrus (25.9% decrease) animals. Results show that estrogen receptors are increased within TIDA neurons during pregnancy, and thus could mediate direct actions of circulating estrogen at this time. The decrease in progesterone receptor expression observed between pregnancy and lactation is in accordance with prior work. Progesterone receptor expression would be expected to wane during lactation, a time when circulating estrogen levels are low, as its expression is dependent on circulating estrogen levels. The main fish androgen, 11-ketotestosterone (11KT), has been found to play an influential role in the metamorphosis of female anguillid eels. Adult metamorphosis prepares anguillids for a long-distance marine spawning migration. Changes in oocyte, heart, gut, liver and eye size are all observed before the freshwater eels migrate. Previous studies have implicated 11-KT in controlling these metamorphic changes. In this study, hypophysectomy has been used to answer whether or not the action of 11KT is direct. Nine animals were hypophysectomized and 17 sham-operated. Steroid-treated animals received pellets containing 5mg 11KT per kg body weight, while control animals received placebo pellets. The trial lasted 3 weeks. Hepatosomatic (HeI), gut (GU) and heart (HsI) indices and change in eye index (EI) were calculated at the end of the trial. Plasma 11KT levels in the animals confirmed that the 11KT pellets were effective. 11KT treatment induced significant (p<0.01) increases in HeI, HsI and change in EI, while significantly (p<0.001) decreasing GI. Hypophysectomy, however, did not have a significant effect (p>0.05) on any of the indices. The analysis of changes in gut epithelial cell heights and relative oocyte sizes is ongoing. The preliminary results from this study indicate that the effects of 11KT treatment are direct and not the result of 11KT triggering the increase or decrease of a pituitary factor. This study confirms that hypophysectomy is not required to study the effects of 11KT in female anguillid eels. To develop reproductive control technologies for wild stoat ( Mustela erminea ) populations there is a requirement for year-round breeding in captive animals. This study tested the hypothesis that a long-day photoperiod applied to stoats during winter months would stimulate reproduction in these animals. Adult stoats (12 males and 12 females) were captured from the wild during summer and autumn. From 14 May half of the animals were subjected to artificial lighting, which reached 16 h d -1 on 30 June and continued at this daily duration until November. Controls experienced natural changes in daylight. Faecal samples were collected for hormone analysis. Vaginal cytology and physical changes associated with oestrus were monitored in females and scrotal size was monitored in males. treated and contr