Age-related changes in the morphology and function of the zona glomerulosa of the rat adrenal cortex

The age-related changes in the morphology and function of rat adrenal zona glomerulosa (ZG) were investigated by coupled stereological and radioimmunological techniques. For this purpose 4-, 8-, 16- and 24-month-old rats were studied. Aging caused a notable lowering in the plasma aldosterone concentration and a marked decrease in both basal and ACTH- or angiotensin II (ANG-II)-stimulated secretion of collagenase-dispersed ZG cells. Plasma renin activity (PRA) underwent an age-dependent decrease, while the plasma level of ACTH displayed a significant rise. ZG and its parenchymal cells did not evidence any age-related morphologically demonstrable alteration in their growth, nor ZG cells showed any marked ultrastructural change, with the exception of a severe lipid-droplet repletion. This last finding is in keeping with the aging-induced decrease in the secretory activity of ZG cells, inasmuch as lipid droplets are the intra-cellular stores of cholesterol esters, the obligate precursors of steroid hormones in rat adrenals. ACTH and ANG-II are well known to be involved in the maintenance of the growth of rat ZG; thus, the combined impairment of ANG-II production (as evidenced by PRA lowering) and increase in ACTH secretion may maintain unchanged ZG growth during aging.     

Effects of galanin on the secretion and proliferative activity of the immature and regenerating adrenal glands of rats

The effects of galanin and the galanin-receptor antagonist (galanin-A) [D-Thr(6),D-Trp(8,9),15-ol]-galanin(1-15) on the immature and regenerating rat adrenal glands have been investigated in vivo. Adult female rats with adrenal regeneration and their offpring (20-day-old) were given three subcutaneous injections (28, 16, and 4 h before being killed) of 2 nmol/100 g galanin and/or galanin-A, and 0.1 mg/100 g vincristin 3 h before being killed. Plasma corticosterone concentration was measured by radioimmunoassay, and the mitotic index ( per thousand of metaphase-arrested cells) was evaluated. In immature rats, galanin increased plasma corticosterone concentration, without affecting mitotic index; the secretagogue effect was reversed by galanin-A, which alone was ineffective. In rats with regenerating adrenal, galanin-A increased both blood level of corticosterone and mitotic index; galanin was ineffective, but blocked the effects of galanin-A. These findings allowed us to draw the following conclusions: 1) galanin exerts a moderate glucocorticoid secretagogue action on immature rat adrenals, but endogenous galanin does not play a major physiological role in the functional control of the gland; and 2) endogenous galanin exerts a maximal tonic inhibitory control on both glucocorticoid secretion and proliferative activity of regenerating rat adrenals, whose physiological relevance remains to be investigated.     

Cytochemical and functional evaluation of ACTH responsive isolated rat adrenocortical cells. The maintenance of sex differences

The critical evaluation of isolation methods for obtaining the adrenocortical cell suspension due to trypsin or collagenase digestion was done. Some collagenase advantages were indicated by morphological observations on the staining smears as well as by ACTH stimulation test. The cytochemical reactions for enzyme activities had the limited applications for those purposes. It also appeared that commonly applied dye exclusion tests were inadequate for characterization of cell suspension. The possible role of the adrenocortical cell debris in the basal corticosterone production was pointed out. The maintenance of the sex dimorphism and the functional differences in the adrenocortical cells isolated from male and female rats have been observed.     

Sex differences in adrenocortical structure and function

Summary Adrenal glands of adult female rats are heavier than the glands of corresponding male rats. Postpubertal orchiectomy increases the adrenal weight, an effect restored by testosterone replacement. Under the same conditions ovariectomy of 8 weeks duration does not change the adrenal weight while estradiol replacement enhances the relative adrenal weight.Karyometric studies have shown that nuclei in the female zona fasciculata cells are larger (app. 18%) than those of the male. Similar but only slight differences (2%) were observed in the zona reticularis. Orchiectomy results in enlargement of cell nuclei within all zones of the adrenal cortex; testosterone replacement has the opposite effect. Ovariectomy of 8 weeks duration slightly enhances the volume of nuclei of the zona glomerulosa cells, has no effect on the nuclei of the zona fasciculata and reduces the volume of nuclei in the zona reticularis. Estradiol replacement reduces the volume of nuclei of the zona glomerulosa cells but increases nuclear volume in the zona fasciculata and in the zona reticularis.Thus testosterone has an inhibitory effect on the adrenal cortex of the rat while the physiologic effect of estradiol on the morphology of this gland, particularly on the zona fasciculata cells is rather dubious.The author wishes to thank Mrs. B. Westerska and Miss K. Siejak for excellent technical assistance.This research was supported in part by a grant from the Zoological Committee, 2nd Department, Polish Academy of Sciences.This paper is dedicated to the memory of late Kazimierz Mietkiewski, M.D., Ph.D. whose encouragements and suggestions were most stimulating for my work.     

Evidence that prolonged alpha-MSH infusion enhances the steroidogenic capacity of rat adrenal zona glomerulosa in vivo

Prolonged infusion with 120 micrograms/kg/day alpha-MSH significantly increased basal plasma level of aldosterone in the rat, as well as raised the acute aldosterone response to a bolus administration of a high dose of ACTH or angiotensin II. These findings suggest that chronic alpha-MSH treatment stimulates the steroidogenic capacity of rat zona glomerulosa.     

Evidence suggesting that ghrelin O-acyl transferase inhibitor acts at the hypothalamus to inhibit hypothalamo-pituitary-adrenocortical axis function in the rat

Production of n-octanoyl-modified ghrelin (GHREL), an active form of the peptide requires prohormone processing protease and GHREL O-acyltransferase (GOAT), as well as n-octanoic acid. Recently a selective GOAT antagonist (GO-CoA-Tat) was invented and this tool was used to study the possible role of endogenous GHREL in regulating HPA axis function in the rat. Administration of GOAT inhibitor (GOATi) resulted in a notable decrease in plasma ACTH, aldosterone and corticosterone concentrations at min 60 of experiment. Octanoic acid (OA) administration had no effect on levels of studied hormones. Plasma levels of unacylated and acylated GHREL remained unchanged for 60min after either GOATi or OA administration. Under experimental conditions applied, no significant changes were observed in the levels of GOAT mRNA in hypothalamus, pituitary, adrenal and stomach fundus. After GOATi injection hypothalamic CRH mRNA levels were elevated at 30 min and pituitary POMC mRNA levels at 60 min. Both GOATi and OA lowered basal, but not K(+)-stimulated CRH release by hypothalamic explants and had no effect on basal or CRH-stimulated ACTH release by pituitary slices. Neither GOATi nor OA affected corticosterone secretion by freshly isolated or cultured rat adrenocortical cells. Thus, results of our study suggest that in the rat endogenous GHREL exerts tonic stimulating effect on hypothalamic CRH release. This effect could be demonstrated by administering rats with selected inhibitor of ghrelin O-acyltransferase, the enzyme responsible for GHREL acylation, a process which is absolutely required for both GHSR-1a binding and its central endocrine activities.