Effect of aging on corticosterone secretion in diestrous rats

Abstract

The roles of age and prolactin (PRL) in regulating glucocorticoid secretion in diestrous rats were investigated. Adrenal zona fasciculata-reticularis (ZFR) cells from young, adult, middle (mid)-aged, and old female rats were isolated. Estrous cycle stage was determined by light microscopy after vaginal smears. Blood samples were collected from right jugular vein at 0, 30, 60, and 120 min after challenge with adrenocorticotropin (ACTH). During the diestrous phase, plasma levels of estradiol and progesterone were lower in mid-aged and old rats than in either young or adult rats. Age-dependent increases of the basal levels of plasma PRL and corticosterone were observed. No difference of ACTH-increased plasma concentrations of corticosterone was observed among young, adult, mid-aged, and old rats. Aging increased the basal, ACTH-, PRL-, forskolin (an adenylate cyclase activator)-, and 3-isobutyl-l-methylxanthine (IBMX, a non-selective phosphodiesterase inhibitor)-stimulated release of corticosterone and production of adenosine 3', 5'-cyclic monophosphate (cAMP) in ZFR cells. However, the 8-Br-cAMP (a membrane-permeable cAMP)-stimulated release of corticosterone was not affected by age. Taken together, these data indicated that aging increased corticosterone secretion in female rats during diestrous phase, which is in part due to an increase in cAMP accumulation. In conclusion, aging and PRL play a stimulatory role in the co-regulation of corticosterone secretion.

Physiological Roles of Prolactin in the Adrenocortical Response to Acute Restraint Stress

“…These results also suggest that hypersecretion of CRH probably occurs in hypoprolactinemia rats. Previous studies have shown that PRL could act directly on adrenal gland to drive corticosterone secretion [2,4,6,[7][8][9][10]. In the present study, PRL stimulated the secretion of corticosterone from cultured adrenal cells in synergy with low levels of ACTH in all rat models.…”

“…Several studies in the literature have examined the role of PRL on adrenal gland function as well as its effects on lactation and reproduction [1][2][3][4][5][6]. Although adrenocorticotropic hormone (ACTH) is generally considered to play a major role in the regulation of adrenocortical secretion, previous reports showed that PRL could act directly on adrenal gland to drive corticosterone secretion [2,4,6,[7][8][9][10]. Additionally, PRL receptors (PRL-R) are expressed in the adrenal cortex in several species [1,7,[11][12][13].…”

Impact of Aging on Steroid Hormone Biosynthesis and Secretion

“…Further studies from our own laboratory have shown that these changes in steroid hormone production and secretion are not a function of reduced ACTH receptors, cAMP production, cAMP phosphodiesterase, steroidogenic enzymes or lipoprotein-mediated cholesterol delivery and the major alteration in the respective cell types occurs distal to cAMP generation [297,298,[303][304][305]. In contrast, several reports from one laboratory, however, suggests that the adrenocortical cells isolated from aged female rats in fact possess an enhanced capacity to secrete corticosterone in response to ACTH stimulation than cells from young or adult animals [306][307][308][309][310]. Finally, there is also evidence for age-related impaired aldosterone secretion by the isolated rat adrenal capsules and glomerulosa cells [311,312].…”

“…In contrast, stress-stimulated corticosterone levels declined more rapidly in young than aged rats following the cessation of isolation stress.  Lo et al, [473] demonstrated that plasma corticosterone levels were significantly increased in middle-aged (12-mo) and aged (22-24-mo) as compared to young (3-mo) or young mature (6-mo) rats. However, no age-related differences in ACTH stimulation of plasma corticosterone levels were noted among the four groups.…”

Learning during middle age: A resistance to stress?

“…Aged male rats tend to experience elevated basal levels of glucocorticoids, lower levels of testosterone, as well as disrupted feedback of the hypothalamic-pituitary-adrenal axis [3,5,12,14,19]. By middle age (17 months) female rats also experience increased basal concentrations of corticosterone and a prolonged glucocorticoid response to ACTH [8]. Their estrogen levels begin to decline in middle age, with cessation of the estrous cycle by 12 months [10,18].…”