Basal steroid production by the zona reticularis of the guinea-pig adrenal cortex

The zonae glomerulosa and fasciculata (ZG/ZF) have been separated by microdissection from the zona reticularis (ZR) of the guinea-pig adrenal cortex. Using non-proliferative organ culture and specific radioimmunoassay the basal secretion of 12 steroids from each zone have been studied. The ZG/ZF secreted 9 times more cortisol (in pmol/mg dry weight 5 h culture) than the ZR. In contrast the androgens (androstenedione, 5-androstenediol, dehydroepiandrosterone, dehydroepiandrosterone-sulphate and testosterone) were preferentially produced (by a factor of 3) by the ZR which also secreted more of all the other steroids studied, with the exception of progesterone and 17-hydroxyprogesterone. The mean molar ratios of total androgen output to cortisol secretion were 1:1.7 and 1:45 for the ZR and ZF respectively. Using computerised image analysis the relative volumes of the ZG/ZF and ZR in the cortex were calculated to be 65 and 35% respectively. The medulla occupies 4.6% of the total gland. From the zonal composition of the cortex, the relationship between wet and dry weight for each zone and the basal secretion rate of each steroid/mg dry weight/5 h culture, we calculated that the ZR could be responsible for 7 and 66% of the cortisol and total androgen secretion respectively from the guinea-pig adrenal gland. It is concluded that the ZF and ZR are functionally as well as morphologically distinct.