Progesterone 5α-reductase in mouse brain

We have examined the distribution of progesterone 5α-reductase activity in minces of discrete brain areas from two strains of adult ovariectomized mice known to be differentially responsive to the behavioral effects of exogenously administered 5α-pregnane-3,20-dione (5α-DHP). Minces of freshly dissected midbrain tegmentum (TEG), hypothalamus-preoptic area (HPOA), hippocampus (HIP), and parietal cortex (CTX) were incubated with [4-¹⁴C]progesterone in a Krebs-Henseleit bicarbonate buffer solution containing 10 mM glucose for 2 h at 37°C. The [¹⁴C]5α-DHP produced was identified by comparison with known standards in paper and thin-layer chromatography systems, derivative formation, and recrystallization to a constant ¹⁴C/³H ratio. We found a 6-fold difference in the extent to which various brain areas formed 5α-DHP. The amount of conversion was similar for both strains of mice. When expressed as picomoles of 5α-DHP formed per 2 h per 20 mg of tissue, the following order of activity was observed: TEG > HPOA > HIP > CTX.