Canine Adrenal Zonation; The presence of CYP17 and CYP11B in the adrenal cortex of normal adrenals and adrenal tumors

Abstract

The adrenal gland consists of two functionally distinct structures; the outer cortex and inner medulla. In the adrenal cortex, three zones can be distinguished: the zona glomerulosa (zG), zona fasciculata (zF) and zona reticularis (zR), producing mainly mineralocorticoids, glucocorticoids and androgens, respectively. To achieve this functional zonation, zone-specific enzymes are necessary to determine the end product of adrenal steroidogenesis. In humans, Cytochrome P450c17 (CYP17) is present in the zF, making the end-product of glucocorticoid synthesis cortisol and not corticosterone as in rodents, which lack CYP17. Humans and rodents alike have two isoforms of 11β-hydroxylase cytochrome P450 (CYP11B); CYP11B1 and CYP11B2, which are responsible for the last steps of cortisol (or corticosterone) and aldosterone synthesis, respectively. Whether dogs have two isoforms of the CYP11B enzyme as well or only one isoform, as in cattle, pigs, sheep and bullfrogs, is unknown. The goal of this study was to determine the distribution of CYP17 and CYP11B in the normal adrenal cortex and in that of adrenal tumors, and to determine whether dogs have one or two isoforms of the CYP11B enzyme. Techniques used to achieve these results were immunohistochemistry (IHC), Western Blot and Southern Blot. IHC with an anti-CYP17 antibody stained positive in the zF and zR in all normal adrenals, similar to CYP17 distribution in humans. Anti-CYP17 staining in adrenal tumors was very variable. Western Blot confirmed our antibody’s reactivity against CYP17. IHC and Western Blot with an anti-CYP11B antibody produced no specific results. Southern Blot for the determination of the number of CYP11B genes was thus far unsuccessful, which therefore requires further investigation.