PROPERTIES OF RAT ADRENAL ZONA RETICULARIS CELLS: PREPARATION BY GRAVITATIONAL SEDIMENTATION

Abstract

An enriched fraction of zona reticularis cells was obtained by unit gravity sedimentation of decapsulated adrenal glands from female rats. From light microscopic and ultrastructural studies of the whole gland and the isolated cell fractions, the zona reticularis cells of the adrenal gland can be classified mainly on the bases of size, position and mitochondrial morphology. This cell population consists of two types of cell, the 'true' zona reticularis cells (Type I, modal diameter 9 μm), which usually constitute 90% of the isolated reticularis fraction and 80% of the intact reticularis tissue, and cells (Type II, modal diameter 13 μm) with fasciculata-like properties (rich in lipid and spherical mitochondria with vesicular cristae). Staining of the cell preparation for 3β-hydroxysteroid dehydrogenase activity also demonstrates the existence of two types of cell in the zona reticularis. The zona reticularis cell fraction, like the zona fasciculata cell fraction, was capable of producing the subsequent steroids from radioactive pregnenolone: corticosterone, deoxycorticosterone, 18-hydroxydeoxycorticosterone, 11-dehydrocorticosterone, progesterone and androstenedione. However, the pattern of steroid production differed markedly between the zona reticularis and zona fasciculata cells, particularly with respect to the production of deoxycorticosterone and corticosterone (and its correlated steroids, 11-dehydrocorticosterone and 18-hydroxydeoxycorticosterone). When R (the ratio of deoxycorticosterone: corticosterone plus 11-dehydrocorticosterone) for the purest preparation of reticularis cells was compared with R for the corresponding preparation of fasciculata cells, the normalized ratio was found to be 6·4, 16·4 and 20·1 in three experiments. The pattern of production of androstenedione per cell was similar in the reticularis and fasciculata cell fractions. The exact mechanism for the altered pattern of steroid metabolism remains to be elucidated. However, these results establish that the corticosteroids produced by the cells of the zona reticularis may be quantitatively, if not qualitatively, different from those produced by the zona fasciculata cells.