Circannual variation and genetic regulation of hepatic testosterone hydroxylase activities in inbred strains of mice.

Hydroxylation of testosterone by hepatic microsomes at positions 6 alpha, 6 beta, 7 alpha, 15 alpha, and 16 alpha has been studied in C57BL/6J, 129/J, and A/J mice. Differences in hydroxylase activities between the C57BL/6J and A/J strains and between the C57BL/6J and 129/J strains were investigated using standard genetic breeding protocols. In the C57BL/6J X A/J line, 6 alpha- and 7 alpha-hydroxylase activity appeared to be under polygenic control in both sexes, as did 15 alpha-hydroxylase activity in females. The lack of 16 alpha-hydroxylase activity observed in 129/J females behaved as a recessive, autosomal, single locus, sex-limited trait. In several instances, the level of hydroxylase activity at one position appeared to be affected by the level of hydroxylase activity at a second position; however, no clear-cut pattern was discerned. Over a period of a year, a remarkable cycle in total hydroxylase activity for all mice was observed; the average activity was greatest in December and least in April.