Immunoreactive dynorphin is regulated by estrogen in the rat anterior pituitary

M. J. Fullerton, A. I. Smith, J. W. Funder

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The pituitary and hypothalamic content of dynorphin was determined by radioimmunoassay and characterized by high-performance liquid chromatography (HPLC) in adult female Sprague-Dawley rats, intact and ovariectomized with and without estrogen treatment. Animals were given estradiol benzoate, or vehicle (oil) by six daily intramuscular injections. Anterior pituitary content of immunoreactive (ir)-dynorphin in ovariectomized rats was approximately twice that of intact animals, and consisted of a single HPLC peak co-eluting with dynorphin 32. Administration of estradiol benzoate (0.06-6 μg/day) caused a marked decrease of ir-dynorphin in the anterior lobe of castrate female rats, with a half-maximal effect at 0.2 μg/day; levels were restored to those seen in intact animals with 6 μg estradiol benzoate per day, an effect which was not influenced by concomitant administration of progesterone (1 mg/day), or bromocriptine (100 μg/day). In the hypothalamus and neuro-intermediate lobe multiple peaks of immunoreactive dynorphin were seen, coeluting with dynorphin A 1-8, dynorphin A 1-17 and dynorphin 32. Neither castration nor estrogen treatment altered ir-dynorphin content in these tissues. These findings suggest that the ovary exerts a specific modulating influence on AP ir-dynorphin in the rat, and that in addition this inhibition appears to be mediated by ovarian estrogen.

Original languageEnglish
Pages (from-to)1-6
Number of pages6
Issue number1
Publication statusPublished - 1 Jan 1988

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