Gas Chromatographic-Mass Fragmentographic Quantitation of 3a-Hydroxy-k-pregnan-20-one (Allopregnanolone) and Its Precursors in Blood and Brain of Adrenalectomized and Castrated Rats

Coupling high performance liquid chromatography with gas chromatography-mass fragmentography has made it possible to simultaneously measure subpicomolar concentrations of allopregnanolone and its precursors, pregnenolone, progesterone and 5cu-dihydroprogesterone (5~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 partial decrease (approximately 30%) in the content of allopregnanolone was found in the brains of ADWCX rats compared to sham-operated rats. Moreover, the content of allopregnanolone in brains of sham-operated as well as ADWCX rats was nonuniformly distributed (olfactory bulb > striatum > cortex > hippocampus) and was one to two orders of magnitude higher than in plasma or liver. Infusion of pregnenolone sulfate in ADWCX rats elicited a fourfold increase in 5~ DHP and progesterone content and a sevento eightfold increase in the content of allopregnanolone in brain but not in liver or plasma. Furthermore, the content of allopregnanolone in brain increased to the same extent in both sham-operated and ADX/CX rats following pregnenolone sulfate infusion. The 5cY-reductase inhibitor, (17P)17[[bis(lmethylethyl)amino]carbonyl] androstane-3,5-diene-3-carboxylic acid (SKF 10511 l), 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 allopregnanolone from 5~DHP and progesterone occurs in the brain and that a significant amount of allopregnanolone is synthesized locally in brain from its precursors. These experiments suggest that the brain, like adrenals and gonads, is a steroidogenic organ which produces allopregnanolone as one of its own most important physiologically relevant steroids. [