Assay and properties of 18-hydroxylation of endogenous and exogenous corticosterone in rat adrenals. Evidence for heterogeneity of 18-hydroxylase activity

Gerbil adrenal 11 beta- and 19-hydroxylating activities respond similarly to inhibitory or stimulatory agents: two activities of a single enzyme

A high level of steroid 19-hydroxylation is exhibited by adrenal mitochondria of the gerbil, Meriones, unguiculatus, that accounts for the ability of that species to produce nearly equal amounts of corticosterone and 19-hydroxycorticosterone (Proc. Soc. exp. Biol. Med. 165 (1980) 69-74). Inhibitors of steroidogenesis and a polyclonal antibody against bovine cytochrome P-450(11 beta) were used to determine if the agents would effect differential or parallel suppression of 19- vs 11 beta-hydroxylation by gerbil adrenal mitochondria in vitro. The inhibitors (0.1-60 microM) tested (listed in order of decreasing effectiveness) were imazalil, metyrapone, miconazole and 4-hydroxyandrostenedione. With each inhibitor the degree of suppression of 11 beta-hydroxylation was accompanied by a parallel decline in 19-hydroxylation. The addition of the polyclonal antibody preparation also produced equivalent declines in the rates of the two hydroxylation reactions. The addition of ACTH 1 microM to primary cultures of gerbil adrenal cells brought about nearly equal increases in the secretion of 11 beta- and 19-hydroxylated steroids into the culture media. These results support the hypothesis that the 11 beta-hydroxylase of gerbil adrenal mitochondria has the capacity to carry out 11 beta- and 19-hydroxylations with nearly equal facility.

18-Hydroxy-11-deoxycortisol: a new steroid isolated from incubations of the adrenal with 11-deoxycortisol

Cortisol has been shown to be metabolized in the zona glomerulosa of the adrenal gland through the same pathway involving the cytochrome P-450, corticosterone methyl oxidase by which corticosterone is transformed to 18-hydroxycorticosterone and aldosterone. When cortisol is the precursor, 18-hydroxycortisol and 18-oxocortisol are formed. 18-Hydroxycortisol can also be made at a similar rate in the bovine zona fasciculata and reticularis as in the zona glomerulosa. We studied the possibility that the formation of 18-hydroxycortisol in the zona fasciculata and reticularis might be through a different pathway involving initial 18-hydroxylation of 11-deoxycortisol before 11 beta-hydroxylation. Rat adrenal capsules or cores were incubated with 10 micrograms of cortisol or 11-deoxycortisol and the formation of 18-hydroxycortisol was measured by radioimmunoassay. Both capsules and cores transformed 11-deoxycortisol to 18-hydroxycortisol, but cortisol was only transformed in the capsular portion. Sixty-two rat adrenals were incubated with 10 mg of 11-deoxycortisol and the putative steroid, 18-hydroxy-11-deoxycortisol, was purified by TLC and HPLC and subjected to gas chromatography mass spectrometry. The mass spectra indicated that the steroid isolated was indeed 18-hydroxy-11-deoxycortisol. The function of this steroid is still unknown.

Regulation of 18-hydroxycorticosterone formation in bovine adrenocortical mitochondria

The conversion of deoxycorticosterone to 18-hydroxycorticosterone was examined by using sonicated mitochondrial suspension of bovine adrenocortex. The KM's of deoxycorticosterone for the 11 beta- and 18-hydroxylations were in the same range (1 microM), while the turnover number for the 11 beta-hydroxylation (50 nmol/min/nmol cytochrome P-450) was 6 times as great as that for the 18-hydroxylation (7.3). The KM and turnover number for the 18-hydroxylation of corticosterone were 6 microM and 0.4, respectively. Those for the 11 beta-hydroxylation of 18-hydroxy-11-deoxycorticosterone were 120 microM and 5. When products were analysed in the incubation of deoxycorticosterone with the mitochondrial suspension containing a larger amount of cytochrome P-450, the formation of 18-hydroxycorticosterone was observed in addition to the formation of corticosterone and 18-hydroxy-11-deoxycorticosterone. The kinetic interrelation between the two pathways was further examined together with consideration of the cytochrome P-450-linked hydroxylation system. The result suggests that the pathway via 18-hydroxy-11-deoxycorticosterone substantially participates in the formation of 18-hydroxycorticosterone from deoxycorticosterone. The perturbation of this network by an artificial means, such as the addition of Triton X-100, revealed that the detergent (0.02%) facilitated the production of 18-hydroxycorticosterone from deoxycorticosterone, regardless of its inhibitory effect on the production of corticosterone and 18-hydroxy-11-deoxycorticosterone from deoxycorticosterone. These studies provide an important insight into the regulation mechanism of 18-hydroxycorticosterone formation from the precursors on the mitochondrial level.