CALF ADRENOCORTICAL FASCICULATA CELLS SECRETE ALDOSTERONE WHEN PLACEDIN PRIMARY CULTURE

Aldosterone production occurs in the outer area of the adrenal cortex, the zona glomerulosa. The glucocorticoids cortisol and corticosterone , depending upon the species, are synthesized in the inner cortex, the zona fasciculata. Calf zona glomerulosa cells rapidly lose the abilit y to synthesize aldosterone when placed in primary culture unless they are incubated in the presence of the antioxidants butylated hydroxyan isol and selenous acid, the radioprotectant DMSO, and the cytochrome P -450 inhibitor metyrapone. In the presence of these additives, calf zo na fasciculata cells in primary culture synthesize aldosterone at rate s which can approach those from cells isolated from the zona glomerulo sa. Calf zona glomerulosa and fasciculata cells both responded well to ACTH and angiotensin II, but the zona fasciculata cells respond very poorly compared to glomerulosa cells to increased potassium in the med ia. Rat zona fasciculata cells in primary culture under similar condit ions did not synthesize aldosterone, suggesting that the regulation of the expression of the enzymes responsible for the biosynthesis of ald osterone in the two species is different. Two distinct cytochrome P450 cDNAs which hydroxylate deoxycorticosterone at the 11beta position ha ve been described in the rat, human and mouse. Both cytochrome P-450 c DNAs have been cloned and expressed in non-steroidogenic cells, but on ly one is expressed in the zona glomerulosa and only this glomerulosal cytochrome P450 can further hydroxylate deoxycorticosterone to genera te aldosterone. Two bovine adrenal cDNAs have been described with 11be ta-hydroxylase activity and their expression products in transiently t ransfected COS cells can convert deoxycorticosterone into aldosterone. Both enzymes are expressed in all zones of the adrenal cortex. Zonal regulation of aldosterone synthesis in the bovine adrenal gland may be due to an 11beta-hydroxylase with aldosterone synthesizing capacity w hich has not yet been isolated. Alternatively, a single enzyme might b e responsible for the several hydroxylations in the pathway between de oxycorticosterone and aldosterone and zonal synthesis might be control led by unknown factors regulating the expression of C-18 hydroxylation . The incubation of zona fasciculata with antioxidants and metyrapone results in atypical expression of this activity by an unclear mechanis m.