GAS-CHROMATOGRAPHIC MASS FRAGMENTOGRAPHIC QUANTITATION OF 3-ALPHA-HYDROXY-5-ALPHA-PREGNAN-20-ONE (ALLOPREGNANOLONE) AND ITS PRECURSORS IN BLOOD AND BRAIN OF ADRENALECTOMIZED AND CASTRATED RATS

Coupling high performance liquid chromatography with gas chromatograph y-mass fragmentography has made it possible to simultaneously measure subpicomolar concentrations of allopregnanolone and its precursors, pr egnenolone, progesterone and 5 alpha-dihydroprogesterone (5 alpha-DHP) in various brain areas, Allopregnanolone was measured in the brain of adrenalectomized/castrated (ADX/CX) rats in nanomolar concentrations long after peripheral sources of allopregnanolone were removed, A part ial decrease (approximately 30%) in the content of allopregnanolone wa s found in the brains of ADX/CX rats compared to sham-operated rats, M oreover, the content of allopregnanolone in brains of sham-operated as well as ADX/CX rats was nonuniformly distributed (olfactory bulb > st riatum > cortex > hippocampus) and was one to two orders of magnitude higher than in plasma or liver, Infusion of pregnenolone sulfate in AD X/CX rats elicited a fourfold increase in alpha-DHP and progesterone c ontent and a seven- to eightfold increase in the content of allopregna nolone in brain but not in liver or plasma, Furthermore, the content o f allopregnanolone in brain increased to the same extent in both sham- operated and ADX/CX rats following pregnenolone sulfate infusion, The 5 alpha-reductase inhibitor, (17 beta)17[[bis(1-methylethyl)amino]carb onyl] androstane-3,5-diene-3-carboxylic acid (SKF 105111), reduced the brain content of allopregnanolone and blocked the increased formation of allopregnanolone in brain following pregnenolone sulfate infusion, The results clearly demonstrate that the synthesis of allopregnanolon e from 5 alpha-DHP and progesterone occurs in the brain and that a sig nificant amount of allopregnanolone is synthesized locally in brain fr om its precursors, These experiments suggest that the brain, like adre nals and gonads, is a steroidogenic organ which produces allopregnanol one as one of its own most important physiologically relevant steroids .