Early life environment: does it have implications for predisposition to disease?

Relationship of early childhood illness with adult cortisol in the Barry Caerphilly Growth (BCG) cohort

BACKGROUND

The developmental origins hypothesis suggests that pre- and postnatal exposures may influence vulnerability to later disease. The hypothalamic-pituitary-adrenal (HPA) axis is one pathway by which this may occur. Analyses were conducted in the Barry Caerphilly Growth (BCG) cohort to explore whether the postnatal exposure of childhood infections was related to HPA axis activity in adulthood.

METHODS

Detailed data on type and frequency of illnesses were collected in the first 5 years of life. At the recent follow-up of this cohort (N=566; mean age of participants=25 years) three salivary cortisol samples were taken: two fasting samples in the morning (within 30 min of arrival at the study site and after venesection and cognitive test procedures) and one evening sample (2200 h). These data were transformed to provide AUCi and AUCg (indices reflecting axis reactivity and total hormonal output, respectively).

FINDINGS

Negative associations were evident between number of upper respiratory illnesses and adult cortisol (as captured by the second morning sample, evening sample and AUCg). These relationships remained after controlling for other potential prenatal, postnatal and adult determinants. These associations were not observed for gastrointestinal illnesses suggesting that confounding by socioeconomic factors is unlikely to be the explanation.

CONCLUSIONS

Childhood respiratory illnesses were associated with reduced HPA axis activity in adulthood. Further follow-ups will determine whether this pattern of activity influences vulnerability to diseases associated with HPA regulation.

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.

Stress-related gene expression in brain and adrenal gland of porcine fetuses and neonates

This study was conducted to examine stress-induced effects on gene expression of specific markers for HPA axis and neuronal activity in fetuses and neonatal pigs. Brain, pituitary gland, and adrenal gland were obtained to determine the mRNA levels for corticotropin-releasing hormone (CRH), CRH receptor 1 (CRHR1), pro-opiomelanocortin (POMC), ACTH receptor (MC2R), c-jun and c-fos. The suitability of these molecular markers was determined in neonatal pigs which were maternally deprived for two hours. It was found that maternal deprivation caused significantly higher transcript levels of c-fos and CRH in brain accompanied by a down-regulation of CRHR1 mRNA and an up-regulation of c-jun in the pituitary gland. To determine the effect of elevated maternal cortisol levels on gene expression of these molecular markers in fetuses, pregnant sows were treated with 100 IU ACTH (Synacthen Depot) s.c. every two days between Day 49 and Day 75 of gestation (normal gestation length 114 days). Animals were killed 48 hours after the last ACTH administration and fetuses of each sow were isolated. The ACTH treatment of sows significantly increased mRNA expression of c-fos but not of CRH in the fetal brain, and significantly decreased MC2R mRNA expression in the adrenal gland. However, HPA axis seems not to be fully developed in Day 77-fetuses because fetal pituitary CRHR1 and POMC mRNA expression was low in most of the fetuses. Although the expression of endocrine regulatory factors was partially incomplete in fetuses at the beginning of the third-trimester, ACTH dependent activation of c-fos mRNA in brain indicates a stress-related increase of neuronal activity. Based on these results it is assumed that prenatal stress in pigs may also have effects on the activity of the HPA axis in the offspring.