Zonal differentiation in the rat adrenal cortex

The factors that establish and maintain adrenocortical zonation are poorly understood. The capsular adrenal gland of the rat has been shown to develop into a functionally zoned tissue in autotransplanted glands in vivo. To examine this in vitro, capsular gland preparations (largely glomerulosa (zg) with some fasciculata (zf) were cultured in vitro in Eagles MEM (3.6mM K+) for 14 days. Zonal differentiation was determined by immunocytochemical localisation of inner zone antigen (IZA, zf/reticularis specific) and Pref-1 (zg specific). In the absence of further additions these preparations invariably maintained a good zonal arrangement of zg and zf over the whole period, though without significant cellular proliferation. Neither the daily addition of the stimulants, maximally 8.3mM potassium, 1nM ACTH, or 100nM angiotensin II (AII), or the AII type 1 receptor antagonist losartan (10microM) had any significant effect on the glands intrinsic capacity to maintain zonation in vitro. Aldosterone output declined rapidly under control conditions (3.6mM K+), but was stimulated by AII, or high K+ reaching a maximum after 7 days, and thereafter declined. However at higher K+ conditions (5.6mM) aldosterone was not supported by angiotensin II. Corticosterone secretion increased autonomously after 2 days in 3.6mM K+ then declined. At higher K+ conditions corticosterone rapidly declined. The factors studied had no effect on the inherent property of the adrenal gland to express the zg or zf phenotype. However the functional steroidogenic capacity of the adrenocortical cells was affected in a highly specific and complex manner by the added stimulants.