No description available.

The purpose of this investigation was first, to make a histological and cytological study of the testis of male frogs, Rana pipiens, and to determine if there were tissue or cellular changes as well as physiological effects caused by fish pituitary-extract injections. Second, to determine if injections of fish pituitary extract into immature female white mice caused histological changes in the ovaries and uteri.

The effect of forced molt on pituitary function and other endocrine parameters was investigated in three year old hens subjected to a dietary forced molting procedure. In addition to molting, fasting caused cessation of egg production, body and organ weight loss, alterations in hormone secretion and morphological changes in some endocrine glands. Body and ovary weights decreased but returned to normal with ad libitum feeding. Pituitary, thyroid and adrenal weights were not affected but serum hormone levels measured by RIA revealed a decrease in LH, FSH and PRL and increases in TSH, T₃ and GH all of which returned to higher levels with ad libitum feeding. Serum P₄ levels remained low (and egg-laying stopped) until ad libitum feeding was resumed and then increased and egg-laying returned to a typically productive level. Serum ACTH and T₄ increased with fasting and remained elevated. Gonadotrophs and corticotrophs increased in numbers with fasting and/or food restriction but thyrotrophs, somatotrophs and lactotrophs decreased. Correlations between cell populations and serum hormone levels was quite common. Colloid-filled follicles resembling a hypertrophic thyroid gland occurred throughout the pituitary pars distalis. Granules appear to be discharged into the follicular lumen through exocytotic pores in the apical plasmalemma of follicular cells. Lactotrophs, corticotrophs and somatotrophs are commonly arranged in follicles or clusters. PRL-containing granules are in the center of some follicles and are concentrated near pituitary cysts. Pituitary cysts, lined with ciliated epithelium and sparse mucous cells, are more prevalent in fasted hens and decline with the resumption of feeding. Reduced lactotroph populations and presumptively degenerated lactotrophs in cyst lumens are correlated with reduced serum PRL levels. Necrotic cells occurred in the pituitary parenchyma of fasted birds but dilated RER in the thyrotrophs of fasted hens indicate enhanced activity of these cells. Ultrastructural evidence presented here indicates that pituitary secretion by lactotrophs occurs both intraluminally and perivascularly.

Bibliography: leaves 129-158. / xvii, 159, [11] leaves, [24] leaves of plates : ill. (some col.) ; 35 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / The major estrogen inducible protein in zebra fish liver has been purified to homogeneity by FPLC using anion exchange chromatography (Mono-Q Pharmacia) with purification being monitored by SDS-PAGE electrophoresis. / Thesis (Ph.D.)--University of Adelaide, Dept. of Obstetrics and Gynaecology, 1995?

Graduation date: 1992

Urinary steroids have been studied during early and late pregnancy in domestic horses or sporadic samples at various stages of pregnancy in wild equidae. In our studies, urinary estrone sulfate (E1S) and pregnanediol glucuronide (PdG) were monitored throughout pregnancy in six pony mares by enzyme immunoassay (EIA). Both hormones were corrected by creatinine (Cr) index to compensate for the variation in specific gravity. The mean concentration for ElS, (μg/mg Cr), was .38 ± .03 at d 0, decreased to .17 ± .04 at d 1, and maintained at less than .5 μg/mg Cr until d 30. Although, there was an apparent increase to .80 ± .34 at d 34 (NS, P = .122), the first significant increase was .69 ± .15 at d 46 (P = .0275). Mean concentrations remained relatively stable at this approximate level until d 60. This level was followed by a sustained significant increase observed from d 60 onwards. Mean concentrations of El S increased to 1.11 ± .25, 2.01 ± .45, and 5.48 ± 1.47 at d 64, d 76, and d 86, respectively. Levels of EIS further increased reaching a peak of 143.3 ± 9.51 at d 142 (P = .0006), with maximum for individual mares ranging from d 114 to 170, and also ranging from 115.4 to 286.1 pg/mg. In all cases, maximum concentrations were followed by a gradual decline toward parturition with a more rapid decrease 1 to 3 days before parturition. The first significant decrease following the maximum concentration was 91.40 ± 13.11 (P = .0024) at d 184. Estrone sulfate was 12.1 ± 3.8 one day prepartum and decreased to .4 ± .1 and .1 ± .01 at d 1 and 4 postpartum, respectively. The mean concentrations of PdG (ng/mg Cr) increased from 147 ± 4.3 at d 0 to 50.87 ± .17 (NS, P> .05), 36.8 ± 8.1 (P = .016), and 27.6 ± 7.3 (P = .049) at d 6, 8 and 10, respectively. This increase was followed by a decline and generally the levels fluctuated ranging from 20 to 30 ng/mg Cr until d 80. At d 86, the PdG levels increased to 54.7 ± 11.7 (P = .033). This was followed by a further increase to 141.8 ± 21.4 (P = .0139, compared to d 93) at d 135, then continued to increase to 213.0 ± 25.2 at d 198, and remained at this approximate level until d 303. During the last month of gestation, the mean concentrations of PdG increased from 171.8 ± 9.8 at d 29 prepartum to reach a peak of 388.4 ± 108.6 at d 7 prepartum. Maximum concentrations were followed by a slight decrease to 354.5 ± 84.0 at d 1 prepartum and then decreased to 150.6 ± 23.4 and 39.6 ± 9.3 ng/mg Cr at d 1 and 4 postpartum. In comparing the two hormones, E1S remained baseline followed by a slight increase at d 35, whereas PdG was relatively stable until both hormones increased after d 70 of gestation. This might be related to secretion of both hormones by the fetus and their rapid metabolism by placenta. Estrone sulfate reached a peak at approximately d 142 followed by a decline toward parturition while PdG showed a rapid increase from d 70 to 150, followed by a slow sustained increase to d 300 then increased dramatically again before parturition, while El S continued to decline. The profile of these urinary hormones throughout pregnancy appeared to parallel previously published concentrations in blood. Since the patterns of urinary EIS and PdG are different, their sites and mechanism of metabolism are likely different. The results indicate that the presence of the feto-placental unit is important for the secretion of both estrogens and progestins throughout pregnancy and thus could be utilized as a reliable method for pregnancy determination after three months of pregnancy. / Graduation date: 1993

Reproductive senescence in females is a natural part of the aging process. However, the process by which it occurs, and the relative role of each level of the hypothalamic-pituitary-gonadal axis, remains largely unknown. The neural circuitry regulating the hypothalamic axis, including glutamate acting through N-Methyl-D-Aspartate receptors (NMDARs) on GnRH neurons, appears to be key to this process. The NMDAR is tetrameric and composed of an obligatory NR1 subunit together with NR2 subunits. The subunit composition determines the channel kinetics of the receptor and changes through the life span. This dissertation examines the physiological role of the NR2b subunit on LH pulsatile release and LH surge, both important for reproductive function. The expression of NR2b subunits in the anteroventral periventricular (AVPV) nucleus of the hypothalamus was also examined in aging rats. Experiment 1 showed that the NR2b-antagonist, ifenprodil, enhanced pulsatile LH release in estradioltreated females (both age groups). Experiment 2 showed that the LH surge in middle-aged animals was slightly accelerated and that results were dependent upon prior reproductive status of the animals. In Experiment 3, examination of the NR2b-immunoreactive cell population in young, middle-aged, and aged ovariectomized females given vehicle, estradiol, or estradiol with progesterone showed an age-associated decline in NR2b density. However, the immunofluorescent fraction volume of NR1 colocalized with NR2b increased with aging, and that of immunofluorescent fraction volume of NR2b increased with estradiol treatment. This is indicative of the amount of protein expressed in the AVPV. In total, NR2b cell density in the AVPV declines with age, but the amount of NR2b expressed in NR1-positive cells increases, suggesting a larger population of NR2b containing channels. This may translate to age-associated inhibition of GnRH/LH activity, which is relieved with blockade of NR2bcontaining NMDARs. Thus, this dissertation describes a novel way to examine the mechanism by which age-associated changes to neuromodulators of the HPG axis may affect the onset of reproductive senescence. / text

D. Tech. Biomedical Sciences. / Discusses despite significant advances in andrological techniques, the execution of semen analysis is currently not performed in a sequential manner. As such, it is important that reproductive biology laboratories establish an optimal diagnostic scheme that will assist reproductive health workers to direct patients to a specific therapeutic intervention and procedure.

Please read the abstract in the section 00front of this document / Dissertation (MSc (Agric))--University of Pretoria, 2007. / Animal and Wildlife Sciences / unrestricted

[Truncated abstract] The activity of the reproductive endocrine axis is the result of interactions among many organs and tissues, particularly the hypothalamus, pituitary gland and gonad. However, it depends on more than the communication between anatomical structures because it is also affected by genotype, internal factors (e.g., metabolic inputs) and external factors (e.g., photoperiod, socio-sexual cues, stress, nutrition). This multifactorial complexity makes it difficult to use animal experimentation to investigate the pathways and mechanisms involved. Therefore, in this study, I have turned to mathematical modelling. The general hypothesis was that, by modelling the hormonal feedback loop that links the hypothalamus, pituitary gland and gonad, I would be able to discover the critical control points in this homeostatic system. This would allow me to inform and direct research into the processes that control reproduction, including inputs from environmental factors. My studies began with the development of a model of the negative feedback loop through which testosterone controls the secretion of pulses of gonadotrophin-releasing hormone (GnRH) by the hypothalamus. The model incorporated two critical factors: testosterone concentration and a time delay in the inhibition of the activity of the GnRH 'pulse generator' by testosterone. The general assumptions were: i) there are two positive feedforward processes (GnRH pulses stimulate LH pulses, and, in turn, LH pulses stimulate testosterone secretion); ii) testosterone exerts negative feedback that reduces the frequency of GnRH pulses. The model incorporated a group of equations that represent the GnRH pulse generator, through which the inhibitory effect of testosterone acted to reduce GnRH pulse frequency. Simulations were run with various values for the time delay in feedback and, as model development progressed, the simulations were extended to include combinations of time delays and levels of sensitivity of the GnRH pulse generator to inhibition by testosterone. The output of the simulations showed clearly that a time delay in negative feedback, as well as the concentration of testosterone, can greatly affect the frequency of GnRH pulses and the shape of the GnRH secretory profile. Importantly, the effect of the time delay depends on the sensitivity of the pulse generator to testosterone. In addition, the simulations suggested two additional components that might be involved in the control of the GnRH pulse generator: i) a delay in the rate of adaptation to a change in steroid feedback; and ii) a minimum pulse interval (maximum frequency). These studies iii therefore suggest that the regulation of the activity of the GnRH pulse generator, and thus the frequency and profile of GnRH and LH pulses, requires interactions among these four components. These interactions should be tested in animal experimentation. In the next stage, I extended the model so I could test whether the feedback delay might involve the process of aromatization in which testosterone is converted to oestradiol at brain level. ... This information can be used to direct future experimental studies that will help us to understand the factors that underlie the dynamic behaviour of the hypothalamic and pituitary systems that control reproduction.