Δ4-Hydrogenase in Guinea Pig Adrenal: Evidence of Localization in Zona Reticularis and Age-Related Change*

Publisher Website
Google Scholar
Abstract
The guinea pig adrenal increases in size with age, yet cortisol secretion per gram adrenal declines. It has been suggested that this could be due to catabolism of cortisol by increased adrenal Δ4-hydrogenase. In this paper we show that Δ4-hydrogenase is localized in the zona reticularis and increases coincidently with the large increase in the volume of this zone with age. Glands were microdissected to give inner vs. outer cortices, and the postmitochondrial supernatants of these two portions were assayed for Δ4-hydrogenase activity. The enzyme was found almost solely in preparations from inner cortices, which were predominantly zona reticularis. Cells were isolated from each portion and assayed for Δ4-hydrogenase activity. Again, only those which contained zona reticularis cells, that is, those from the inner cortices, had activity. The activity was shown to be present in both microsomes and cytosol, although the latter was preferentially expressed in a 15,000 × g supernatant. When the metabolites were separated by thin layer chromatography, the products of the microsomal enzyme were 5α-and 5β-dihydrocortisol (1:1) and that of the cytosolic enzyme was 5β-dihydrocortisol, whereas in the 15,000 × g supernatant the 5β-isomer was the predominant product. Its identity as 5β-dihydrocortisol was confirmed by mass spectroscopy. Tetrahydrocortisol comprised a minor portion of the products.