Graduation date: 1992

In vivo experiments were conducted to determine if elevated plasma glucocorticoid concentrations would suppress intrafollicular prostaglandin F2$ alpha$ (PGF2$ alpha$) synthesis and, thereby, inhibit ovulation in the pig. Following ACTH administration, PGF2$ alpha$ concentrations in FF tended to be lower than in controls. Injections of betamethasone partially suppressed the preovulatory rise of PGF2$ alpha$ in FF at 40h, although the effect was less marked than that produced by indomethacin. While no ovulations occurred in the indomethacin-treated group at any time, betamethasone resulted in a lower number of ovulated follicles at 44h than in the control animals. Progesterone concentrations were unaffected by the treatments. / In vitro studies were conducted with a spontaneously established cell line developed through continuous culturing of primary granulosa cells collected from prepuberal gilts six hours after they had received PMSG. Characterization of these cells revealed that aromatase and steroidogenesis were functional but gonadotropin receptors were not present. When extracellular PGF2$ alpha$ levels were measured, dexamethasone was able to significantly suppress PGF$ sb{2 alpha}$ concentrations, but not as effectively as with indomethacin. (Abstract shortened by UMI.)

It is widely accepted that prostaglandins (PGs), produced via the cyclooxygenase pathway from arachidonic acid, are essential to the ovulatory process in the pig. In support of this, ovulation is preceded by an increase in follicular fluid (FF) PG concentration, indomethacin (INDO) suppresses both the PG increase and ovulation, and ovulation can be restored by administration of exogenous PGs (Downey and Ainsworth, 1980; Prostaglandins 19: 17-22). Recent studies in the rat have shown that ovulation is also preceded by a rise in ovarian concentrations of 15-hydroxyeicosatetraenoic acid (15-HETE), a product of the lipoxygenase pathway (Tanaka et al., 1989; Endocrinology 15: 1373-1377) and inhibition of this pathway suppresses ovulation (Reich et al., 1983; Prostaglandins 26: 1011-1020). Furthermore, INDO, a cyclooxygenase inhibitor, inhibits 15-lipoxygenase as well as PG synthesis (Tanaka et al., 1989 Endocrinology 15: 1373-1377). The PMSG/hCG prepuberal gilt model was used to investigate the involvement of 15-HETE in the procine ovulatory process, and the effect of INDO on the 15-lipoxygenase pathway. Follicular fluid concentrations of 15-HETE were elevated 40 h post hCG (p $<$ 0.01). The effects of INDO and nordihydroguaiaretic acid (NDGA), an inhibitor of lipoxygenase activity, on ovulation rate, FF 15-HETE and FF PGF$ rm sb{2a}$ were investigated by intraovarian administration of INDO or NDGA. INDO inhibited ovulation rate (p $<$ 0.01) and PGF$ rm sb{2a}$ (p $<$ 0.01) as well as 15-HETE (p $<$ 0.01). NDGA also suppressed ovulation rate (p $<$ 0.01) but did not inhibit 15-HETE or PGF$ rm sb{2a}$ production. In in vitro experiments, 15-HETE production by both granulosa cell (GC) and theca interna cell (TIC) cultures 40 h post hCG was greater (p $<$ 0.01) than at 0 h post hCG. INDO inhibited 15-HETE production in 40 h post hCG TIC cultures (p $<$ 0.01) but not GC cultures, while NDGA inhibited 15-HETE production by both cell types (p $<$ 0.01). These results sugges

Five experiments were undertaken to identify metabolites and hormones that could mediate the effect of dietary energy status on reproduction, particularly pulsatile secretion of luteinizing hormone (LH) postpartum dairy cows. / In the first two experiments, the concentration of progesterone (P4) in tailhead adipose tissue and plasma in 12 cows at different stages of pregnancy and lactation was determined as was P4 produced in vitro by explants of tailhead adipose tissue. Concentration of P4 in adipose tissue was correlated with that of plasma P4 near estrus and during the luteal phase of the estrous cycle, and P4 was released in vitro by fat mobilization. / In the third and fourth experiments, blood was collected continuously for 16 h from four ovariectomized cows offered maintenance or restricted energy diets after priming with P4 or estradiol (E2) using a crossover experimental design. The results indicated that P4 released during body fat mobilization is minor and is not related to LH secretion. Dietary energy restriction influenced plasma LH concentration and pulse amplitude but the effect was modulated by P4 and E2 priming. Dietary energy restriction decreased glucose concentration but did not influence plasma non-esterified fatty acids (NEFA), cortisol, P4 and insulin levels. Cortisol was negatively related to LH pulse frequency. Glucose and insulin were positively and negatively correlated with LH pulse amplitude, respectively. Cortisol, NEFA and glucose jointly had a negative correlation with LH concentration. / In the fifth experiment, blood samples were collected daily for 60 d and every 10 min for 8 h on 18, 36 and 54 d postpartum from 24 cows (12 ovariectomized) fed low (1.4 Mcal/kg DM) (L) or high (1.7 Mcal/kg DM) (H) energy in a 2 x 2 factorial treatment design. LH pulse frequency was reduced at 18 d postpartum in ovariectomized cows, but not in intact cows, fed L. First postpartum ovulation occurred later in intact cows fed L compared to those fed H. Energy balance and plasma glucose concentration were lower, but plasma NEFA, $ beta$-hydroxybutyrate (BHB) and E2 concentrations higher, in cows fed L compared to those fed H. E2 concentration in intact cows fed L was elevated for a prolonged period prior to first ovulation. Diet had no influence on plasma P4 and insulin concentrations. Plasma E2 and BHB concentrations were positively correlated with LH pulse frequency in intact cows across diets and ovariectomized cows fed L, respectively. NEFA were negatively correlated with LH pulse amplitude in ovariectomized cows fed L. Glucose, NEFA and P4 were negatively, but BHB, E2 and insulin positively correlated, individually or in association, with LH concentration. / Overall, the results suggest that the effect of dietary energy status on LH patterns and timing of onset of postpartum ovulation is modulated by priming with or presence of ovarian steroids. The relationships of metabolites and hormones with LH patterns appear to change with dietary energy level, ovarian status and mutual associations among the metabolites and hormones. These parameters, especially glucose and BHB, may be potential mediators of the effect of dietary energy status on LH patterns. (Abstract shortened by UMI.)

The objectives were: (1) to determine the pre-ovulatory changes in plasminogen activator (PA) and (PA) inhibitor (PAI) activities in the porcine follicle, and, (2) to determine if changes in the PA/plasmin system associated with ovulation were prostaglandin (PG)-dependent. PA activity (change in absorbance/h/mg wet tissue weight, three gilts per treatment group) was elevated in both granulosa cells (GC) and theca interna cells (TIC) prior to human chorionic gonadotropin (hCG) administration (0.582 $ pm$ 0.171 and 0.718 $ pm$ 0.221, respectively) but returned to basal levels in these two compartments (0.023 $ pm$ 0.013 and 0.052 $ pm$ 0.024, respectively) at 29 h post-hCG. PA activity remained basal thereafter in GC but increased approximately ten-fold in the TIC (0.549 $ pm$ 0.239) at the time of ovulation (three gilts at 41 h and one of three gilts at 38 h). PAI activity did not change in TIC over the pre-ovulatory period but increased in GC as ovulation approached. PAI activity in GC peaked at 38 h (being significantly different (p $<$ 0.05) to all other times except 41 h). Although indomethacin (INDO) effectively inhibited both PG synthesis (1.1 $ pm$ 0.2 vs. 9.2 $ pm$ 0.9 ng/ml in controls) and ovulation (0 vs. 27-61% in controls), elevated PA activity (0.801 and 0.349) was detected in the TIC of two out of nine INDO-treated gilts. Levels were basal (0.074 $ pm$ 0.028) in the other gilts. These inconclusive results are believed to reflect the occurrence of ovulation earlier than predicted, in as many as 40% of control gilts, and the short duration of increased PA activity at this time. In conclusion, elevated PA activity, in GC and TIC prior to ovulation induction, may play a role in follicular development. Elevated TIC PA activity may play an important role in the ovulatory process, but is probably PG-independent.

[Truncated abstract] Reproductive activity is affected by external factors such as photoperiod, social cues, stress and nutrition, all of which can alter the pulsatile activity of the GnRH neurons, which is the major neuroendocrine system used by the brain to control gonadal function. In the male Merino sheep, nutrition is one of the most powerful factors that affect pulsatile LH secretion, used commonly to bioassay GnRH neuronal activity. More accurately, the reproductive system responds to “metabolic status”, rather than “nutrition”, and the three factors that contribute to metabolic status are food intake, the amount of body reserves and the rate of energy expenditure ... In this thesis, I tested the general hypothesis that the metabolic hormones and hypothalamic neuropeptides that are known to control food intake also mediate the effect of metabolic status on the activity of the GnRH neurons ... In conclusion, the results from my experiments provide some insight into the mechanisms by which metabolic status affects reproductive activity in male sheep. Plasma insulin, which changes with alterations in metabolic status, appears to play a critical role in the regulation of GnRH neuronal activity. The level of leptin seems to have a permissive role only in lean animals. Orexins acting via OX2 receptors could be involved in the activation of reproductive function following an acute increase in nutrition. However, the neuropeptidergic systems can not be ruled out because they might be involved in very early steps of responses to nutrition.

M.Sc. (Zoology) / The histomorphology of the ovaries of Cyprinus carpio L., as well as the histomorphological changes that occur in these ovaries during the breeding cycle, were investigated. Concurrently, the blood plasma and ovarian cytosol were analized for the presence of gonadotropin (GtH), FSH, LH, Oestriol, Cortisol and Progesterone, with the aid of Test Kits which are commonly used for determining the levels of these hormones in human blood plasma. C. carpio possesses cystovaria which are continuous with the oviducts which unite before opening to the exterior via a gonopore. The results clearly show that C. carpio has a four season breeding cycle and that egg laying occurs during Spring and Summer. Furthermore morphological changes of the ovary (which occurred during the breeding cycle) as well as the oocyte developmental stages, closely resemble those respectively described for teleosts in general by Kesteven (1960) and Malhotra et al., (1978). The endocrinological tests clearly indicated the presence of GtH, FSH, LH, Oestriol and Cortisol, while all the tests for Progesterone were negative. A comparison between the presence of the abovementioned hormones and the histomorphological development of the ovaries during the breeding cycle indicate that the endocrinological control mechanisms are similar to those which have been described for other teleosts. However, a clear distinction was found between FSH and LH which is a possible indication that C. carpio does not possess a single gonadotropin, but rather that FSH and LH have evolved in this species.

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