Abstract
Rat pineal organs of spayed rats took up and retained estradiol in vitro up to 32-fold the concentration present in the incubation media. This phenomenon was maximum at 37°C and after 2-h incubations. Most (86–91%) of [ 3H] radioactivity recovered from the incubated pineals was identified as estradiol by thin-layer chromatography. Treatment with dextran-coated charcoal of nuclei-free pineal homogenates incubated with [ 3H] estradiol of different SA uncovered a high affinity, low capacity binding of estradiol to cytosol components. Uptake of estradiol by the nuclear fraction also proceeded in a saturable fashion. Similar findings were made in uterine homogenates of spayed rats. Estradiol uptake by the pineal organ and the uterus of cycling rats varied as a function of the stage of the estrous cycle, maxima being observed in diestrus and minima in proestrus. The administration of a priming dose of estradiol benzoate to spayed rats caused high affinity binding components of the pineal cytosol to increase by about 150%. Nuclear binding of estradiol was also increased by the estradiol priming dose. Pineal denervation, i.e., by superior cervical ganglionectomy, caused pineal estradiol uptake to decrease significantly by about 20%. These data suggest that the early steps of estradiol action on the pineal organ may resemble those of the uterus.
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