Journal of Clinical Endocrinology & Metabolism, Vol 69, 1221-1224, Copyright © 1989 by Endocrine Society

ARTICLES

Cotinine and nicotine inhibit human fetal adrenal 11 beta-hydroxylase

RL Barbieri, AJ Friedman and R Osathanondh
Department of Obstetrics, Gynecology, and Reproductive Biology, Brigham and Women's Hospital, Boston, Massachusetts.

The effects of nicotine and cotinine on fetal adrenal 11 beta- and 21- hydroxylase were examined using enzymatic and spectral techniques. The addition of nicotine or cotinine to preparations of adrenal mitochondria yielded a type II cytochrome P-450 binding spectrum. The apparent spectral dissociation constants (Ks) for nicotine and cotinine binding to mitochondrial cytochrome P-450 were 20 and 19 microM, respectively. The addition of nicotine to preparations of adrenal microsomes yielded a type II cytochrome P-450 binding spectrum, with an apparent Ks of 70 microM. Adrenal mitochondrial 11 beta-hydroxylase was assayed by measuring the conversion of deoxycorticosterone to corticosterone. Nicotine and cotinine competitively inhibited 11 beta- hydroxylase, with apparent Michaelis-Menten inhibition constants (Ki) of 9.9 and 9.0 microM, respectively. Nicotine competitively inhibited microsomal 21-hydroxylase, with an apparent Ki of 110 microM. Cotinine, in concentrations as high as 1 mM, did not inhibit 21-hydroxylase. These results suggest that nicotine and cotinine inhibit 11 beta- hydroxylase by binding to the heme iron of the cytochrome P-450 component of this enzyme system. Inhibition of 11 beta-hydroxylase could contribute to the altered pattern of steroidogenesis observed in smokers.

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