Abstract
The effect of estradiol on the brain concentration of immunoreactive β-endorphin (β-EP) and C-terminal ACTH (CLIP) was studied in ovariectomized rats. Dopamine, a known inhibitor of pituitary intermediate lobe pro-opiomelanocortin (POMC), was examined as a possible mediator of the estradiol induced changes in brain POMC. Animals were treated for 1 or 3 weeks with either 1) saline; 2) silastic estradiol implants; or 3) estradiol implants plus haloperidol 1 mg/kg/day. After one week of treatment no significant change in hypothalamic β-EP content was noted in any group compared to the control level of 4.13 ± .33 (SEM) pmoles although in the neurointermediate lobe β-EP increased from 566 ± 72 to 942 ± 73 pomles after haloperidol (p < .005). After 3 weeks, however, hypothalamic β-EP decreased from 3.96 ± .28 to 2.74 ± .19 pmoles (p < .005) and C-terminal ACTH decreased from 3.78 ± .33 to 2.82 ± .18 pmoles (p < .02) in the estradiol treated rats. This estradiol induced decrease in the hypothalamic content of β-EP and C-terminal ACTH was not blocked by haloperidol. We conclude that estradiol lowers the hypothalamic content of β-EP and CLIP and that this effect does not appear to be mediated by dopamine.
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