Conversion of progesterone-1,2-3-H to 5beta-pregnane-3,20-dione by brain tissue

The presence of a 5beta-reductase acting to convert progesterone to 5beta-pregnane-3,20-dione is described in the soluble 105,000 x g fraction of a preparation of dog cerebral cortex. The function of this enzymatic activity is obscure but may be important in regulation of sensorium. 5beta-pregnane compounds are potent depressors of the central nervous system.