Nucleus-associated steroid 5α-reductase activity and androgen responsiveness. a study in various organs and brain regions of rats

Abstract

1. 1. Purified nuclei were prepared from various organs and brain regions of rats. The preparations were assayed for 5α-reductase activity, and checked for purity by measurement of RNA-DNA ratios. Although prostatic nuclei showed the highest 5α-reductase activity, the other nuclear fractions were also able to reduce testosterone into its active metabolite: 17β-hydroxy-5α-androstan-3-one. In all tissues, however, the nucleus-associated 5α-reductase activity was inversely related to the purity of the nuclear fractions. 2. 2. Prostate, kidney, submaxillary gland, lung and midbrain were completely fractionated. Total 5α-reductase activity varied as follows: lung > prostate > kidney > submaxillary gland > midbrain. The particulate fractions were the major sites of 5α-reductase activity in all tissues except for the submaxillary gland. The nuclear fraction reached 19% of the total 5α-reductase activity in the kidney and 25% in the prostate. 3. 3. The low apparent K m of the 5α-reductase for testosterone reported in prostatic nuclei was also found in lung nuclei (1.56 μM) and kidney nuclei (0.96 μM). 4. 4. It is concluded that the androgen responsiveness of a particular tissue cannot be accounted for by any of the parameters of 5α-reductase activity studied: the occurrence of an enzyme with particularly high affinity for testosterone, the total cellular activity, or the absolute or relative amount of this activity associated with purified nuclei.