Effects of Age and Adrenocorticotropin on Microsomal Enzymes in Guinea Pig Adrenal Inner and Outer Cortices*

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Abstract
Guinea pig adrenals possess a distinctive zona reticularis which increases in volume as the animal matures, coming to occupy over 50% of the gland in mature 800-g animals. The adrenocortical cells of this zone possess abundant smoothsurfaced endoplasmic reticulum. In this paper we demonstrate that microsomes obtained from guinea pig inner cortices of both young and mature animals, consisting predominantly of zona reticularis tissue, possess higher activities of 21-hydroxylase, an enzyme that hydroxylates steroids, and ethylmorphine demethylase, a drug-metabolizyng enzyme, as well as higher contents of cytochromes b5 and P450, than microsomes derived from outer cortices, which contain predominantly zona fasciculatatissue. In addition, we show that while the inner cortex contains 90% of the total adrenal activity for ethylmorphine demethylase, ACTH suppresses this activity by 55% and decreases activity in the outer cortex to negligible levels. ACTH does not affect 21-hydroxylase activity or cytochrome b5 or P450 content in either cortical region. These observations suggest that differential regulation of microsomal functions for steroid hydroxylation and drug metabolism occurs largely in the zona reticularis. Furthermore, they suggest that other activities for xenobiotic metabolism, previously reported as a property of whole guinea pig adrenals, may reside in the inner cortex and be unique functions of the abundant smooth endoplasmic reticulum of the zona reticularis cells.