Brain Metabolism on Steroid Hormones

By the clinical studies on steroid hormones in endogenous mental diseases so far carried out, we have found that it is the steroids belonging to 17-KS rather than 17-OHCS which are associated with the mental excitation. In view of this, we attempted a study about the brain metabolism on testosterone which is an important precursor of 17-KS with a strong biological activity. The materials used were the brain of Donryu rats and human beings. Each of these brain tissues was homogenized in ten-fold volumes of 1/15M phosphate buffer solution. Then, taking 2ml of the brain phosphate buffer homogenate or 2ml each of 1/15M phosphate buffer suspension of the supernatant containing nuclear, mitochondrial or microsomal fraction, prepared from 1g rat brain, the incubation was conducted in the air at 37℃ for 60 minutes after adding 0.1μc [4C(14)] testosterone, 0.2 mg cold testosterone, 0.5 mg each of NAD and NADP as cofactor, and 10 mg nicotinamide. Then, metabolites were extracted, applied on the florisil column, and 2% methanol-chloroform fraction was collected and dried. For the control groups the brain tissues inactivated by heating were employed. Each of the specimens thus obtained was applied on the Silicagel-G thin layer chromatography (TLC), and metabolites were isolated and identified by the 2% NGS gas chromatography. After the TLC-autoradiography the portions that coincided with the radioactive spots was taken and each of these chromatograms was applied to the liquid scintillation counter and the percentage of the conversion of metabolites was calculated from respective radioactivity. 1) Both from the rat brain and the human brain on the TLC (chloroform-acetone-methanol, 90:7:3, developed for 15 cm) there are seen four principal spots, and designating these spots as I, II, III and IV starting from the original point of application, the spot II is testosterone, proving that 90-95% or more of testosterone added has not been metabolized. 2) The spots I and III are minor metabolites, of which I is the substance like ll-OH-Etio-cholanolone. and III is an unknown substance. The conversion rate of each is only about 0.2%, proving to be of no significant value. 3) The spot IV is a major metabolite, and on the further TLC (chloroform-acetone, 85:15, developed for 55 cm) it separated itself into two spots, each of which has been identified to be Δ(4)-androstene-3, 17-dione and dihydrotestosterone. The conversion rate of the two together is 2.46% with the rat brain and 2.29±0.73% with the human brain in average, and without addition of co factors it is decreased to 1.80% and O.5% respectively. 4) The activity of the enzymes responsible for the major metabolite formation, namely, 17β-hydroxysteroid dehydrogenase and 5α-reductase, is detectable in every fraction of the rat brain, but it is highest in the telencephalon mitochondrial and fairly high in the supernatant fraction, and the conversion rate from testosterone is about 0.5% in each case. After all, since the brain is not a metabolic organ nor a target organ, the metabolism of testosterone is extremely low, nonetheless, looking it from the aspect of its potency, we cannot rule out its significance. A further problem which we have to solve will be the role played by the hormones responsible for mental excitation, by investigating the correlation of the brain site to the metabolism of steroids including testosterone.