Age-related differences in corticosterone secretion in female rats

The effects of age on steroidogenesis in rat zona fasciculata-reticularis ( ZFR) cells were studied. Young, adult, and middle-aged rats were ovariectom ized (Ovx) and received replacement therapy with oil or estradiol benzoate ([EB] 25 mu g/mL/kg). Rat ZFR cells were incubated with corticotropin (ACTH ), prolactin (PRL), or forskolin at 37 degrees C for 1 hour. The effects of age on the activity of steroidogenic enzymes of ZFR cells were measured by the amount of intermediate steroidal products separated by thin-layer chro matography. Plasma revels were higher for PRL (54% to 254%) and corticoster one (179% to 257%) in middle-aged versus young rats. In oil-treated Ovx rat s, basal and ACTH-stimulated corticosterone release by ZFR cells were also greater in middle-aged compared with young rats. Replacement with EB in Ovx rats increased the ACTH-stimulated release of corticosterone, Administrati on of ovine PRL in vitro resulted in a dose-dependent increase of corticost erone production. In oil-treated middle-aged rats, ovine PRL-stimulated cor ticosterone release was higher than in young rats. Forskolin-induced produc tion of cyclic adenosine 3',5'-monophosphate (cAMP) was greater in middle-a ged versus young rats and correlated with the increase of corticosterone pr oduction. The activity of steroidogenic enzymes in rat ZFR cells was unchan ged by age. These results suggest that the age-related increase of corticos terone production in female rats is associated with the stimulatory effect of PRL on ZFR cells and is due in part to an increase of cAMP generation. C opyright (C) 1999 by W.B. Saunders Company.