Testosterone 5 alpha-reductase in spinal cord of Xenopus laevis.

Testosterone 5 alpha-reductase, the enzyme that converts testosterone to 5 alpha-dihydrotestosterone, is present in the spinal cord of Xenopus laevis. In adult males the enzymatic activity is optimal at pH 7.4 and 27 degrees C; the apparent Km is 2.0 x 10(-5) M and the Vmax is 10.0 pmol/mg protein/h. Enzymatic activity was assayed in segments of the spinal cord in each of four groups: control untreated males, females, castrated males, and sexually active clasping males. Striking differences in both the amount of dihydrotestosterone produced with time and in the pattern of its distribution were seen in spinal cords of clasping males compared with those of the other groups. The differences are greatest in the basal medulla and rostral segments of the spinal cord. Neurons in these segments innervate the muscles primarily involved in clasping.