Effect of ovariectomy and estrogen replacement on hypothalamic, pituitary and peripheral blood β-endorphin levels in the rat

Abstract This study was initiated to detect possible changes in β-endorphin (β-EP) levels of the hypothalamus, anterior pituitary gland, and peripheral blood of rats after ovariectomy and estrogen administration. Attempts were also made to determine the correlation between peripheral and central levels of β-EP. Twenty-six Sprague-Dawley rats were decapitated. Nine had intact ovaries (Gr. INT), and 17 were ovariectomized 3 weeks before they were killed. Nine of the ovariectomized rats received estradiol benzoate (EB) (Gr. EB) and the other 8 received peanut oil (Gr. OVX) prior to the decapitation. A β-EP radioimmunoassay was used to analyze homogenates of the hypothalamus and anterior pituitary, and peripheral blood. In the hypothalamus, β-EP levels were significantly lower in Gr. INT and Gr. EB than in Gr. OVX. In the pituitary gland and peripheral blood, β-EP levels were significantly higher in Gr. INT than in Gr. OVX. Pituitary β-EP levels did not vary between Gr. OVX and Gr. EB, although β-EP levels in peripheral blood were significantly higher in Gr. EB than in Gr. OVX. No significant correlations were noted in β-EP levels between the hypothalamus, pituitary gland, and peripheral blood in either Gr. INT, Gr. OVX, or Gr. EB. It appears that EB exerts different effects on β-EP levels in the hypothalamus, anterior pituitary gland, and peripheral blood, and that β-EP levels in these regions may be independent of one another.