Endocrine Abstracts

It has been noted that there are differences in the hypothalamic-pituitary-adrenal (HPA) axis between the sexes, as well as changes in the axis with age. The differences in the HPA axis between the gender and age groups are thought to be due to differences in the efficiency of glucocorticoid (GC) negative feedback. The pituitary, a principle site of GC negative feedback, is the focus of this investigation. Annexin-1 (ANXA1) is a member of the annexin family of phospholipid- and calcium-binding proteins with a well demonstrated role in early delayed (30 min-3h) inhibitory feedback of glucocorticoids in the pituitary. The relative total content of anterior pituitary ANXA1 of old/young and male/female Long Evans rats were investigated by western blotting. No significant differences were found in the amount of ANXA1 between young males, young females or old females. However, there was a significant (p < 0.003) increase in the amount of ANXA1 detected in the old male compared to the other three groups (170% increase, n=11). Arginine vasopressin (AVP) production has also been shown to change with age (Keck et al 2000, Eur J Neurosci, 12:1487) and AVP is a potent facilitator of CRH action in the pituitary corticotroph. In order to investigate if AVP action is linked to pituitary ANXA1 content, a comparison was made of pituitary ANXA1 content in old and young, male and female Brattleboro rats, which lack AVP. No significant differences in ANXA1 content were measured within Brattleboro groups though there was a trend to increased ANXA1 in the old male Brattleboro rats. This suggests that AVP may not affect the pituitary content of ANXA1. This project has provided novel evidence that there are differences in the total quantities of ANXA1 between the sexes and with age.