The conversion of testosterone into 5 alpha-dihydrotestosterone (DHT) has been studied in different hypothalamic nuclear areas and in the superficial layers of the cerebral cortex of normal and castrated male rats. The tissue fragments utilized in each incubation have been punched from frozen brain sections utilizing calibrated needles. Castration has been performed 12 (short term) and 180 (long term) days before sacrifice. The nuclear areas studied include: the medial preoptic nucleus (MPN), the lateral preoptic nucleus (LPN), the anterior hypothalamic nucleus (AHN), the lateral hypothalamic nucleus (LHN), the posterior hypothalamic nucleus (PHN), the nucleus ventromedialis (HVM), the arcuate nucleus (AR), the median eminence (ME), the nucleus paraventricularis (HPV), the supraoptic nucleus (SO) and the suprachiasmatic nucleus (SC). The possible effect of castration on the 5 alpha-reductase, were assessed in the MPN,LPN,AHN,LHN,PHN and in the cerebral cortex. The results indicate that, in the male rat: 1) the lateral preoptic(LPN) and the lateral hypothalamic nuclei(LHN) possess a 5 alpha-reductase activity higher than that present in the cerebral cortex and in the other hypothalamic nuclei considered; 2)the suprachiasmatic nucleus (SC) apparently possesses a testosterone metabolizing activity lower than that found in any other nervous structures studied so far; 3) castration does not seem to influence the 5 alpha-reductase activity either in the hypothalamic nuclear structures considered or in the cerebral cortex.

3-Oxo-5-alpha-Steroid 4-Dehydrogenase↗

PubMedDate not supplied

The 5 alpha-reductase activity of the subcortical white matter, the cerebral cortex, and the hypothalamus of the rat and of the mouse: possible sex differences and effect of castration.

Previous studies have shown that the central nervous system is able to convert testosterone into 17-beta-hydroxy-5-alpha-androstan-3-one (DHT), by the action of the enzyme 5-alpha-reductase. The data here presented show that, in the brain of the rat and the mouse of both sexes, the 5-alpha-reductase activity is more concentrated in the subcortical white matter than in the hypothalamus and in the cerebral cortex. The enzymatic activity is apparently higher in the rat than in the mouse brain. The formation of DHT in the subcortical white matter, in the hypothalamus and in the cerebral cortex of both rats and mice does not show any sexual difference. Moreover, in the rat no effect of short- or long-term castration or neonatal castration or testosterone replacement could be observed on the formation of DHT in the three brain structures considered (even in the subcortical white matter, the cerebral tissue more active in converting testosterone into DHT). The present data support the view that the 5-alpha-reductase present in the brain is not under androgenic control.

3-Oxo-5-alpha-Steroid 4-Dehydrogenase↗

PubMedDate not supplied

Effect of aging on opioid and LHRH receptors in the brain, pituitary, and testis of the male rat.

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Aging↗

PubMedDate not supplied

5 alpha-reductase isozymes in the central nervous system.

The enzyme 5 alpha-reductase (5 alpha-R) activates several delta 4-3keto steroids to more potent derivatives which may also acquire new biological actions. Testosterone gives rise to the most potent natural androgen dihydrotestosterone (DHT), and progesterone to dihydroprogesterone (DHP), a precursor of the endogenous anxiolytic/anesthetic steroid tetrahydroprogesterone (THP). Two isoforms of 5 alpha-R, with a limited degree of homology, different biochemical properties and distinct tissue distribution have been cloned: 5 alpha-R type 1 and type 2. In androgen-dependent structures DHT is almost exclusively formed by 5 alpha-R type 2; 5 alpha-R type 1 is widely distributed in the body, with the highest levels in the liver, and may be involved in steroid catabolism. In the brain, the roles of the two isozymes are still largely unknown. This brief review will summarize recent experimental data from our laboratory which try to assign possible functional roles to the process of 5 alpha-reduction, and to the two 5 alpha-R isoforms in the CNS.

Animals↗