Uptake and effect of 17β-estradiol on pineal hydroxy-indole-o-methyl transferase (HIOMT) activity

Abstract

In the present work we have studied a) the uptake of estradiol by the pineal gland and b) the effects of exogenous estradiol and norepinephrine on pineal hydroxy-indole-O-methyl transferase (HIOMT) activity. The uptake of estradiol by the pineal gland, the uterus and the cerebral cortex of castrated rats was determined 15–240 min after the intraperitoneal administration of a single dose of [6,7− 3H] 17β-estradiol. The pineal took up and retained significantly more [ 3H] estradiol per mg of tissue than either the uterus or the cerebral cortex (p<0.01). The simultaneous injection of norepinephrine plus labeled estradiol did not modify significantly the estradiol uptake by the pineal gland. Estradiol administration for 3 days decreased pineal HIOMT activity (p<0.01), this effect being reversed by the simultaneous injection of norepinephrine. When norepinephrine was injected alone, no effects on pineal HIOMT were observed. These results suggest the existence of an estradiol receptor system in the rat pineal gland.