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Abstract Gonadal steroids are potent modulators of gonadotropin releasing hormone (GnRH) secretion, and androgen binding sites and 5α-reductase activity have been found in the immortalized GnRH secreting cell line GT1-1, suggesting the existence of a direct androgenic control of GnRH dynamics. Two isoforms of the 5α-reductase have been cloned with very different biochemical/functional properties: 5α-reductase type 1 (widely distributed in the body) and 5α-reductase type 2 (confined in androgen target structures). We have analysed whether, in GT1-1, androgen binding sites are linked to ‘classical’ androgen receptor, and which 5α-reductase isoform is active. Reverse transcriptase-polymerase chain reaction analysis showed that the mRNAs coding for androgen receptor and for the two 5α-reductase isoforms are all expressed in GT1-1 cells. However, the 5α-reductase enzymatic reaction showed a peak of activity at a narrow pH around 5.5, the optimum for the 5α-reductase type 2. The affinity for testosterone, of the enzyme present in GT1-1 cells, was very similar to that observed for the recombinant type 2 isozyme expressed in yeasts. The data indicate that GT1-1 cells (i) express a ‘classical’ androgen receptor and (ii) contain the 5α-reductase type 2 isoform, a specific marker of androgen-responsiveness. [ABSTRACT FROM AUTHOR]

Abstract Spinal cord motoneurones express high levels of androgen receptor. However, in responsive tissue, the effects of testosterone is often mediated by the more potent androgenic derivative 5-alpha-dihydrotestosterone (DHT). This compound is formed in androgen target cells by the enzyme 5-alpha-reductase. Two isoforms of the 5-alpha-reductase, with limited degree of homology, have been cloned, type 1 and type 2. The low affinity-constitutive type 1 isoenzyme is widely distributed in the body; the high affinity-androgen regulated 5-alpha-reductase type 2 is confined to androgen-dependent structures and shows a peculiar pH optimum at acidic values. We have previously shown that high levels of 5-alpha-reductase activity are detectable in rat spinal cord. Here, using reverse transcriptase-polymerase chain reaction, we show that both isoforms are expressed in the whole spinal cord of the rat. The enzymatic pH optimum measured in immortalized spinal cord motoneurones (NSC34) is typical of the type 2 isoenzyme. Using in situ hybridization technique, we found that 5-alpha-reductase type 2 is confined to the motoneuronal cells of the anterior horns of the rat spinal cord, the cells that also are known to express high levels of androgen receptor. Because of the close association of androgen receptor and 5-alpha alpha-reductase type 2, motoneuronal cells should be considered as target cells for androgens. [ABSTRACT FROM AUTHOR]