The effects of estradiol and mestranol on alpha-adrenoceptors in select regions of the rat brain

The role of estrogens in modulating the concentration of CNS alpha-adrenoceptors has not been elucidated nor has it been determined how different estrogenic compounds affect these receptors. In this study brain alpha-1 and alpha-2-adrenoceptor binding was measured in female rats treated with estradiol and/or the synthetic estrogen mestranol. Rats treated biweekly for 12 weeks with mestranol (50 μg/100 g b.wt.) had a significant reduction in the apparent number of alpha-2-adrenoceptors in the frontal cortex and nucleus tractus solitarius (NTS), while apparent numbers of both alpha-1 and alpha-2-adrenoceptors were depressed in the locus coeruleus. Estradiol treatment (50 μg/100 g b.wt.) caused a significant elevation in apparent alpha-1-adrenoceptor numbers in the NTS relative to control. Alpha-adrenoceptor numbers in the rostral and caudal hypothalamus were not affected by either steroid treatment. These results suggest that regulation of apparent numbers of alpha-1 and alpha-2-adrenoceptors in the CNS depends on the type of estrogen used for treatment.