No description available.

Thesis (Ph.D.) -- University of Adelaide, Dept. of Physiology, 2001. / Includes bibliographical references (leaves 228-257).

Thesis (M.Sc.)--York University, 2006. Graduate Programme in Kinesiology and Health Science. / Typescript. Includes bibliographical references (leaves 66-88). Also available on the Internet. MODE OF ACCESS via web browser by entering the following URL: http://gateway.proquest.com/openurl?url_ver=Z39.88-2004&res_dat=xri:pqdiss&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&rft_dat=xri:pqdiss:MR19754

Thesis (Ph. D.)--University of Missouri-Columbia, 1999. / Typescript. Vita. Includes bibliographical references (leaves 92-101). Also available on the Internet.

Thesis (Ph.D.) -- University of Adelaide, School of Medicine, Discipline of Medicine, 2007. / "April 2007" Bibliography: leaves 165-189. Also available in print form.

Thesis (Ph. D.)--University of Missouri-Columbia, 1999. / Typescript. Vita. Includes bibliographical references (leaves 92-101). Also available on the Internet.

Thesis (Ph.D.) - University of Queensland, 2003. / Includes bibliography.

There has been a global rise in obesity in the last three decades, and at present one in five women are obese at antenatal booking. Maternal obesity is associated with an increased risk of adverse pregnancy outcomes, including increased fetal size and prolonged pregnancy. In the longer-term, offspring of obese are at increased risk of premature death from a cardiovascular event in their adulthood. One mechanism that has been linked to these outcomes is fetal exposure to glucocorticoids in utero. During normal pregnancy, the maternal hypothalamic pituitary adrenal (HPA) axis undergoes major changes, resulting in exponentially increasing levels of the major circulating glucocorticoid cortisol, and other HPA axis hormones, such as corticotrophin releasing hormone (CRH). Cortisol and CRH are vital for normal fetal growth and length of gestation, but in excess they are associated with fetal growth restriction and preterm labour. In non-pregnant obesity, it is thought that the HPA axis is dysregulated, although evidence is inconclusive. Little is known about the effects of maternal obesity in pregnancy on the HPA axis. The work in this Thesis used clinical studies to test the hypothesis that the HPA axis is dysregulated in obese pregnant women with altered release, clearance and placental metabolism of cortisol. Associations with clinical outcomes related to fetal size and length of gestation were also studied. The HPA axis activity during pregnancy was investigated in a prospective case-control study cohort. Fasting serum cortisol levels were measured at 16, 28 and 36 weeks of gestation (obese n=276, lean n=135). In a subset (obese n=20, lean n=20), corticosteroid binding globulin (CBG), CRH, estrogens and progesterone were measured. Salivary cortisol was measured in samples collected at bedtime, waking and 30 minutes after waking at 16 weeks. Urinary glucocorticoid metabolites were measured at 19 weeks and 36 weeks (obese n=6, lean n=5) and non-pregnant (obese n=7, lean n=7) subjects. All circulating hormone levels rose similarly in obese and lean during pregnancy, but were significantly lower in obese women. The diurnal rhythm of cortisol was maintained. Urinary glucocorticoids increased with gestation in lean, but not in obese, indicating a lesser activation of the HPA axis in obese compared with lean pregnancy. These findings associated with increased birthweight and longer gestation in obese pregnancy, suggesting that decreased HPA axis activity may underlie these obese related adverse pregnancy outcomes. Whether or not lower glucocorticoids in obese pregnancies are maintained at delivery was investigated by measuring active glucocorticoids (cortisol and corticosterone) and their inactive versions (cortisone and 11- dehydrocorticosterone, respectively) from matched maternal and cord plasma samples (n=259, BMI 18 – 55 kg/m2). Active glucocorticoids were significantly higher in maternal than cord blood, and inactive versions were significantly higher in cord than maternal blood. Increased maternal BMI associated with lower maternal cortisol, corticosterone and 11-dehydrocorticosterone. Despite significant correlations between maternal and cord blood glucocorticoid levels, increased maternal BMI did not associate with lower cord blood glucocorticoids. This suggests that conditions at delivery may overcome any potential negative effects of low maternal glucocorticoids on the fetus in the short-term. However, it may not preclude the longer-term effects of fetal exposure to lower glucocorticoid levels during obese pregnancy, and offspring follow-up studies are required. Potential mechanisms leading to altered HPA axis activity in obese pregnancy were explored by studying the pulsatile release and placental metabolism of glucocorticoid hormones. Glucocorticoid pulsatility is thought to be important for transcriptional regulation of glucocorticoid responsive genes, and disruptions to pulsatility have been reported in some disease processes. Glucocorticoids were measured in 10-minute serum sampling between 08.00h-11.00h and 16.00h- 19.00h. Peripheral tissue cortisol was measured from 20-minute sampling of interstitial fluid, over 24-hours, at 16-24 weeks and 30-36 weeks (obese n=7, lean n=8), and non-pregnant controls (obese n=4, lean n=3). Total circulating serum cortisol levels were higher in pregnancy than non-pregnancy in lean and obese, and increased significantly with advancing gestation in lean but not in obese. Pulsatility of cortisol was demonstrated in interstitial fluid in both non-pregnancy and pregnancy. In obese pregnancy, interstitial fluid pulse frequency was lower with advancing gestation. This may be a novel mechanism underlying the observed decreased HPA axis activity in obese pregnancy. Placental cortisol metabolism and transport was studied using an ex vivo placental perfusion model, perfused with a deuterium-labelled cortisol tracer combined with computational modeling. The findings challenge the concept that maternal cortisol diffuses freely across the placenta, but confirmed that 11β- HSD2 acts as major ‘barrier’ to cortisol transfer to the fetus, protecting the fetus from the high maternal circulating cortisol levels. In addition we showed preliminary evidence of local cortisol production within the placenta. The model is able to predict maternal-fetal cortisol transfer and can now be used in future experimental design. In conclusion, in obese pregnancy, lower maternal cortisol and urinary clearance suggested reduced HPA axis activity. Altered glucocorticoid pulsatility may underlie this change. Future studies of placental cortisol metabolism in maternal obesity could be conducted using an ex vivo perfusion model. The lower HPA axis activity in obese pregnancy represents a novel pathway underlying increased fetal growth.

The postnatal period is a critical time for development where external influences can help shape the long-term structure and function of the brain. Adverse experiences or stressors during the postnatal period, such as abuse or neglect, can have huge consequences on the long term function, health and susceptibility to disease. One environmental factor, whose importance is becoming increasingly more recognised for normal development, is light. Abnormal light during the first three weeks of life has been shown to have long term effects on the circadian system of rodents. On the other hand, the effects of abnormal light during the postnatal period on the stress system have yet been relatively unexplored. Therefore the aim of this thesis was to assess if altered postnatal light environment, such as that a preterm baby might be exposed to, has any long-term effects on the stress system. Mice were raised under constant light (LL), constant darkness (DD) or a normal 12:12hr light:dark cycle (LD) for the first three weeks of life from postnatal day (P)1 up until P21. From P21, all mice were then housed in LD conditions and the stress system was assessed by looking at several different levels of the HPA axis including neuropeptide expression in the brain, body and adrenal weight, and plasma corticosterone levels under both basal and stressed conditions. Learning and memory, anxiety-like behaviour and circadian output rhythms were also evaluated. Finally, mother-pup behaviour and maternal HPA axis were assessed to see if maternal care was changed by altered postnatal light. Both LL and DD rearing caused changes in the HPA axis of offspring with LL raised mice showing alterations in neuropeptide and glucocorticoid receptor expression in the brain. Postnatal DD resulted in a blunted corticosterone response to a stressor in females but had no effect in males. In terms of behaviour, LL raised mice had increased depressive-like behaviour. In contrast, postnatal light appears to have no effect on learning and memory or anxiety behaviour. When we looked at circadian output rhythms, we found that LL rearing appears to confer resilience to the rhythm disrupting effects of LL later on in life as seen by the maintenance of locomotor activity, body temperature and plasma corticosterone rhythms in LL. Maternal care and maternal stress systems appeared unaltered under the different postnatal light environments suggesting that the changes we see in the offspring are attributed to mechanisms other than alterations in maternal care.

Cortisol, the principal glucocorticoid secreted from the adrenal glands, is essential for life. Healthy cortisol levels are maintained through negative feedback on the central nervous system (CNS) – pituitary stimulatory apparatus which regulates production of adrenocorticotropin (ACTH) and contains a light–entrained intrinsic CNS driven diurnal rhythm. Cortisol participates in a regulatory mechanism where inflammatory cytokines stimulate cortisol release and cortisol in turn suppresses cytokine release. The effects of cortisol in inflammatory states include elevating blood pressure and metabolic regulation. This thesis contains three exploratory studies examining circulating cortisolaemia using the best available methodologies (total and free cortisol and corticosteroid-binding globulin (CBG)) in clinical states characterized by immune activation/ inflammation and altered blood pressure. These clinical states include: (1) septic shock, (2) hypertensive disorders of pregnancy and (3) obesity-induced hypertension. Prior to the studies described here, little was know about cortisolaemia in these common pathological states. Septic shock is a life threatening condition that complicates severe infection and is characterized by systemic inflammation and refractory hypotension. High plasma total cortisol levels and attenuated responses to synthetic ACTH stimulation are associated with increased mortality. The use of corticosteroids in septic shock has been highly controversial for decades, however recent trials have reported haemodynamic and survival benefits associated with the use of physiologic steroid replacement in patients with relative adrenal insufficiency (RAI) – currently defined as a total cortisol increment of 248 nmol/L or less following ACTH (250 μg) stimulation. However, CBG and albumin levels fall by around 50% with an increase in plasma free cortisol in critical illness. Hence, total cortisol may not reflect the biologically active free (unbound) cortisol, suggesting that standard assays for plasma cortisol (which measure total plasma cortisol) underestimate HPA axis activity. In this study, we have showed that plasma free cortisol is a better guide to circulating glucocorticoid activity in systemic infection than total cortisol. We have also validated the use of Coolens’ method in estimating free cortisol in systemic infection, using plasma total cortisol and CBG measurements as plasma free cortisol is not performed in clinical laboratories. Free cortisol measurement allows better categorization of RAI and non-RAI groups with a free cortisol increment of 110 nmol/L as cut-off. Moreover, we have shown that survivors of RAI have normal adrenocortical function on follow-up testing suggesting a lack of functional adrenal reserve rather than adrenal damage during critical illness. Larger randomized controlled trials will be required to redefine RAI using free cortisol measurements and relate that to clinical outcomes and responses to corticosteroid therapy. Nitric oxide (NO) is normally produced in the endothelium by the constitutive form of the NO synthase and this physiologic production is important for blood pressure regulation and blood flow distribution. Studies have shown that an overproduction of NO by the inducible form of NO synthase (iNOS) may contribute to the hypotension, cardiodepression and vascular hyporeactivity in septic shock. Clinical studies of non-selective inhibitors of the L-arginine nitric oxide pathway showed increased mortality from cardiovascular complications. However, glucocorticoids, which improve vasopressor sensitivity, may act by partially suppressing NO synthesis through selective direct inhibition of iNOS, and suppression of inflammatory cytokine synthesis. Hence, plasma nitrate/ nitrite (NOx) levels may provide a titratable end point to individualize glucocorticoid therapy in sepsis. The NOx study in this thesis showed that cortisol (total and free), CBG and NOx correlated to illness severity. Free cortisol, and to a lesser extent total cortisol, but not NOx levels, predicted septic shock. NOx levels were characteristically stable within individuals but inter-individual differences were only partly accounted for by illness severity or renal dysfunction. NOx levels correlated weakly with cortisol, did not relate to the need for vasopressors and were not suppressed by hydrocortisone treatment. Thus, NOx is not a suitable target for glucocorticoid therapy in septic shock. Pregnancy is the only sustained physiologic state of hypercortisolism in humans. A large body of data suggests that excessive foetal and prenatal glucocorticoid exposure leads to reduced birth weight and adverse health in offspring such as elevated blood pressure and insulin resistance. Pre-eclampsia and gamete donor pregnancies are associated with immune activation, elevated inflammatory cytokines as well as elevated blood pressure. Prior to the study described in this thesis however, there was no prospective data on maternal cortisolaemia in these complicated pregnancies. My study has demonstrated for the first time that there was a substantial fall in plasma CBG levels in the last few weeks of gestation with a corresponding rise in free cortisol in normal pregnancy, a finding obscured for methodological reasons in past studies. This free cortisol elevation in late pregnancy may facilitate organ maturation in the foetus and perhaps prepare the mother for the metabolic demands of labour. In pre-eclampsia and gestational hypertension, plasma CBG, total and free cortisol levels were lower in late third trimester; and in IUGR, plasma CBG levels were suppressed from 28 weeks gestation until delivery but with no significant difference in plasma total and free cortisol. Women with assisted reproduction using donor gametes/ embryos had significantly lower plasma CBG, total and free cortisol levels even in those with normal pregnancy outcomes. Low CBG may be due to reduced synthesis or enhanced inflammation-driven degradation. Low maternal cortisol may be due to a lack of placental corticotropin-releasing hormone, or reduced maternal ACTH, driving cortisol production. This unanticipated maternal hypocortisolism in complicated pregnancies may trigger precocious activation of the foetal HPA axis and could have implications for postnatal and adult health. Speculatively, since excess prenatal GCs increase HPA axis activity, we proposed that maternal hypocortisolism may predispose to the hypocortisolaemic state characterized by fatigue, pain and stress sensitivity, in offspring. The third state of immune/ inflammatory activation associated with blood pressure dysregulation studied in this thesis is obesity. The epidemiologic relationship between obesity and hypertension is widely recognised. Central obesity in particular has been associated with exaggerated HPA responses to stimuli. Studies of severe dieting and starvation resulted in hypercortisolism and a significant decrease in CBG. The HPA axis and the renin-angiotensin-aldosterone system (RAAS) have been implicated in the pathophysiology of obesity-induced hypertension. However, there is little data on the effect of moderate weight loss (30% caloric restriction) on adrenocortical function, and the relation of adrenal hormones to altered blood pressure with weight loss. In this study, measures of HPA axis and RAAS and blood pressure monitoring were performed in twenty-five obese subjects before and after a 12-week diet program (6000kJ/day). Short-term, moderate weight loss (mean 8.5 kg) was associated with a small reduction in blood pressure (mean arterial pressure 6 mmHg) and significantly reduced levels of aldosterone and renin but not cortisol levels. These findings suggest that aldosterone may have an important role in the blood pressure reduction with weight loss via a renin mediated mechanism, perhaps involving renal sympathetic tone. In contrast to severe caloric restriction, HPA axis activation does not occur with moderate weight loss. This suggests a threshold effect of weight loss on the HPA axis where greater caloric restriction is required for HPA stimulation, or a counterbalancing of central and direct adrenal effects on HPA axis function. Overall, these three exploratory studies have provided novel data on HPA axis function in systemic infection, pregnancy and in diet-induced weight loss. Each study offers a basis for further studies of HPA axis function in these disorders. / http://proxy.library.adelaide.edu.au/login?url= http://library.adelaide.edu.au/cgi-bin/Pwebrecon.cgi?BBID=1289330 / Thesis(Ph.D.)-- School of Medicine, 2007.