We have studied cortisol and androstenedione secretion by dispersed cells of the outer zona fasciculata (ZF) plus zona glomerulosa, and the inner zona reticularis (ZR) plus medulla of the guinea-pig adrenal. The ZF and ZR were microdissected apart, the cells dispersed and incubated (200 000 cells/ml) for 90 min in the presence of adrenocorticotrophin (ACTH; 500 ng/l), dibutyryl cyclic AMP (dbcAMP; 1 mmol/l), pregnenolone, 17-hydroxypregnenolone, 17-hydroxyprogesterone, 11-deoxycortisol and 21-deoxycortisol. The steroid concentrations were 5–25 μmol/l. Cortisol secretion was assayed by radioimmunoassay. There was no detectable cortisol secretion ( < 50 nmol/l) from the ZR in the controls (no additive) or after dbcAMP stimulation. Adrenocorticotrophin-stimulated cortisol secretion was also low (range < 50–340 nmol/l). In contrast the ZF secreted 177–379 (control), 828–2052 (dbcAMP) and 2863–9735 (ACTH) nmol cortisol/l. There was no detectable (i.e. < 2 nmol/l) cAMP production by ZR or ZF either basally (no ACTH) or after ACTH stimulation (500 ng/l). Challenge of the ZR cells with each cortisol precursor steroid (5 μmol/l) increased (P < 0·05) cortisol secretion over that seen with the corresponding basal and ACTH-stimulated controls. Thus pregnenolone, 17-hydroxypregnenolone, 17-hydroxyprogesterone, 11-deoxycortisol and 21-deoxycortisol (converted directly to cortisol by 21-hydroxylase) gave rise to (mean ± s.d., n = 4) 406 ± 86, 680 ± 180, 1307 ± 111, 1141 ± 234 and 3160 ± 419 nmol cortisol/l respectively. The corresponding figures for the ZF prepared from the same adrenal cortex were 3919 ± 309, 4122 ± 97, 5766 ± 615, 5035 ± 260 and 6954 ± 755 nmol cortisol/l. With pregnenolone (25 μmol/l), cortisol secretion increased to 7847 ± 1424 (ZR) and 12880 ± 982 nmol/l (ZF), a ZR:ZF ratio of 0·6 compared with 0·1 for pregnenolone at 5 μmol/l. Androstenedione was secreted in the basal state by both ZF and ZR in similar quantities, i.e. 3·7 ± 0·3 and 3·7 ± 0·4 nmol/l (n = 9 and 14 respectively). Both cell types were ACTH sensitive, with androstenedione secretion increasing to 28 ± 4·8 (ZF) and 12·5 ± 0·9 (ZR) nmol/l.
There was a direct correlation (r = 0·924, P < 0·05) between total adrenal weight and body weight, between the percentage ZR in the cortex and adrenal weight (r = 0·96, P < 0·05) and between the percentage ZR and body weight (r = 0·981, P< 0·05). In a mature animal (800–1000 g) the ZR may occupy > 66% of the adrenal cortex. The mean diameters of cells from the ZF and ZR were 21 and 25 μm respectively.
J. Endocr. (1986) 109, 399–404
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