Perturbations of the hypothalamic-pituitary-adrenal axis and the metabolic syndrome in ageing

Individual differences in glucose homeostasis: do our early life interactions with bacteria matter?

Exposure to endotoxin during the neonatal period in the rat has been shown to alter the development of the hypothalamic-pituitary-adrenal axis, inducing hyper-responsivity and increased glucocorticoid production in later-life. Glucocorticoids are known to have major metabolic effects, therefore, early life endotoxin exposure may have potentially serious consequences for metabolic homeostasis in the exposed animal. The aims of this study were therefore to assess the effect of neonatal bacterial endotoxin exposure on subsequent glucose homeostasis, insulin action and corticosterone production from puberty through to senescence. Male Fischer-344 rat pups were treated with bacterial endotoxin (0.05 mg/kg Salmonella enteritidis i.p.) or vehicle (sterile pyrogen free saline) on days 3 and 5 postnatally. Insulin and glucose levels were assessed before and during and intraperitoneal glucose tolerance test (IPGTT) together with body mass on postnatal days 40, 80, and 400. In addition, circulating levels of corticosterone were measured at 0, 30, and 90 min following a 30-min restraint challenge at these ages. Neonatal endotoxin challenge did not alter fasting plasma glucose or insulin, but impaired glucose tolerance at puberty (p<.05), improved glucose tolerance in adulthood (p<.05) and had no effect at senescence. During the IPGTT insulin was reduced at all ages (p<.05) following neonatal endotoxin challenge, but insulin sensitivity was unaltered, except for an increase in adulthood (p<.05), which is consistent with the observed improvement in glucose tolerance at this age. Neonatal endotoxin challenge reduced body mass during puberty and senescence (p<.05) but did not alter basal or stressed plasma corticosterone levels at any of the three developmental time points examined. These findings suggest that variations in an individual's early life bacterial environment may contribute to differences in glucose homeostasis, insulin action and disease susceptibility later in life.

Hormone receptors and proliferation in breast carcinomas of equivalent histologic grades in pre- and postmenopausal women

Breast cancers in younger, premenopausal women are more likely to exhibit an adverse prognostic profile (including negative steroid hormone receptors and a high rate of cellular proliferation) and poor outcome than breast cancers in postmenopausal women. It has been hypothesized that this adverse prognostic profile is a result of the higher histologic grade of breast cancers in pre- compared with post-menopausal women. To assess the association of expression of steroid hormone receptors and indicators of proliferation while controlling for histologic grade, we identified 100 infiltrating ductal carcinomas from premenopausal women 45 years of age or younger and 100 from postmenopausal women 65 years of age or older. The carcinomas were selected so that the histologic grades (low versus high) were distributed equally between the 2 groups. Estrogen receptors (ER), progesterone receptors (PR), p27(Kip1) and Ki-67 (to measure rate of proliferation) were assessed by immunohistochemistry and compared between groups. Clinical information and survival data were also analyzed. ER content was lower and proliferation was higher in carcinomas in premenopausal women (p = 0.048 and p = 0.005, respectively). By univariate analysis, p27(Kip1) and PR were not different between the groups; however, in multivariate analysis, p27(Kip1) was higher in postmenopausal women, but only in a subgroup with highly proliferative carcinomas. Overall survival was similar in the pre- and postmenopausal women. Furthermore, low p27(Kip1) and African-American ethnicity predicted a poorer overall survival in the premenopausal, but not in the postmenopausal, women in our study. After controlling for histologic grade, a lower expression of ER and a higher proliferative index were detected in breast carcinomas in premenopausal women. Therefore, some prognostic indicators, such as ER and proliferative rate, may be more closely associated with menopausal status than histologic grade. Our data also suggest that some prognostic factors are not equally effective as predictors of survival in pre- and postmenopausal women.

Visceral obesity and the role of the somatotropic axis in the development of metabolic complications

It is well recognized that aberrant fat localization such as visceral obesity rather than total body fat mass is a major risk factor for cardiovascular disease and type 2 diabetes mellitus. During recent decades, several studies have described a range of metabolic disturbances associated with abdominal obesity, including glucose intolerance, hyperinsulinaemia, insulin resistance, hypertension and dyslipoproteinaemia, now widely known as the metabolic syndrome. Several abnormalities in the hypothalamic-pituitary axis have been described associated with visceral obesity, suggesting a central neuroendocrine dysregulation including increased cortisol concentration and impaired gonadotropin and growth hormone (GH) secretion. Some steps in the chain of events in this theory still remain unclear, however, although these findings have introduced new therapeutic possibilities. These include therapy with sex steroids in both viscerally obese men and women, and several attempts to use GH to treat the endocrine abnormalities present in visceral obesity. The results of these studies are promising, but the therapies are still not recommended for general use.

Activation of the hypothalamic-pituitary-adrenal axis in obesity: cause or consequence?

Cortisol secretion rate is increased in obesity, but plasma cortisol levels are not consistently elevated. This suggests that the principal abnormality in obesity may relate to enhanced peripheral metabolism. Recent studies have identified enhanced inactivation of cortisol by 5alpha-reductase, and impaired regeneration of cortisol in the liver by 11beta-hydroxysteroid dehydrogenase type 1 (11beta-HSD1), as possible mediators of this increased cortisol clearance rate in obesity. Most intriguingly, the changes in 11beta-HSD1 are tissue-specific, and generation of cortisol from inactive cortisone appears to be increased in adipose tissue in obesity. Selective inhibition of 11beta-HSD1 provides a novel therapeutic target for lowering intra-adipose cortisol concentrations and effect, without inducing other adverse effects of cortisol deficiency.