Sex differences in estrogen receptor binding in the rat hypothalamus: effects of subsaturating pulses of estradiol

Abstract

The effects of subsaturating pulses of estradiol on cell nuclear retention of estrogen receptors in brain regions of male and female rats were determined. In the first experiment, age-matched adrenalectomized/gonadectomized (ADX/GDX) rats were killed 1 h after i.v. injection of a subsaturating dose of free estradiol (1.0 microgram/kg b. wt.) and cell nuclear estrogen receptor binding was measured in microdissected brain areas by an in vitro exchange assay. As we have previously reported with saturating doses of estradiol (3.6-36.0 micrograms/kg b. wt.), a greater concentration of receptors was measured in the ventromedial nucleus (VMN), periventricular preoptic area (PVPOA), and medial preoptic area (mPOA) of the female than in the same regions of the male brain. Binding levels did not differ between the sexes in the bed nucleus of the stria terminalis, arcuate nucleus, or the corticomedial amygdala. In the second experiment, GDX/ADX male and female rats received either a single or double pulse of 0.5 microgram estradiol/kg b. wt. administered 6 h apart. Rats were killed 1 h after the second pulse. In animals treated with a single pulse of estradiol 1 h before sacrifice, higher concentrations of estrogen binding were measured in the female VMN and PVPOA than in the male. Except in the mPOA, the concentration of estrogen receptor binding measured was not different from that measured in animals that had received an additional, earlier pulse of estradiol. In this area, receptor…