Effects of chronic smoking on testosterone metabolism in dogs.

The effects of long-term cigarette smoking on androgen hydroxylases and peripheral hormones were studied in male beagles. In the testis, chronic smoking of high nicotine/tar cigarettes was associated with decreased activity of the 7 alpha-hydroxylase active on testosterone (68% of control, P less than 0.05). Testicular 6 beta and 16 alpha-hydroxylases were not altered. The hepatic androgen 6 beta-hydroxylase activity in control animals was approximately 6 times the testis levels and was stimulated markedly by smoking. This increase ranged from 221% in the low nicotine/tar group (P less than 0.02) to 304% in the high nicotine/tar group (P less than 0.006). Serum testosterone levels were reduced to 54% of control (P less than 0.02) and prostate size to 44% (P less than 0.001) of control with heavy smoking. Serum LH levels were elevated with smoking. These results suggest that chronic cigarette smoking increased hepatic metabolism of testosterone. In addition, serum testosterone levels and prostate size decreased and LH levels increased. Whether the hepatic and the endocrine effects are causally related cannot be determined from this preliminary study.