REGIONAL DISTRIBUTION OF PROGESTERONE AND 5-ALPHA-PREGNANE-3,20-DIONE IN RAT-BRAIN DURING PROGESTERONE-INDUCED ANESTHESIA

Progesterone and 5α-pregnane-3,20-dione (5α-DHP) concentrations were measured in seven brain areas and in plasma during "anesthesia" induced by progesterone (1-2 mg IV) in female rats. The highest levels of progesterone were detected in the striatum and hypothalamus (23.3±5.27 and 22.7±4.30 μ mg/g ± SEM, respectively); these concentrations were approximately 1000 times higher than those during the post-ovulatory phase. Highest levels of 5α-DHP were detected in the striatum and hippocampus (11.5±1.74 and 10.4±3.15 μg/g ± SEM, respectively). The ratio of 5α-DHP to progesterone was approximately 100 times higher in brain tissue than in plasma. We conclude that a conversion of progesterone to 5α-DHP occurs in the brain during the course of progesterone-induced "anesthesia". This metabolic step may be an important contributory factor to the anesthetic potency of progesterone. © 1990.