Progesterone receptors in the cerebral cortex of neonatal female rats

Progestin-binding components were detected in cerebral cortical cytosols from female rats at 7 days of age. These components labeled in vitro with a tritiated synthetic progestin. R5020, sediment in the 7S region in sucrose density gradients containing 10% glycerol. The dissociation constants and the number of binding sites of the components were 3.9 X 10(-10)M and 47.5 fmol/mg cytosol protein, respectively, indicating high affinity and low capacity binding. The 7S-binding components were specific for progestational compounds. Estradiol competed weakly. Incubation with pronase abolished the 7S progestin binding. Heat experiments suggested a thermolabile nature of the components. These results suggest that the cytosols from the cerebral cortex of 7-day-old female rats contain progesterone receptors.