Presence and steroidogenetic activity of β-endorphin in the ovary of the lizard, Podarcis s. sicula raf

Abstract

In mammals, proopiomelanocortin (POMC)-related peptides are involved in reproductive processes at both the hypothalamo-pituitary and ovarian levels. Through immunocytochemical and physiological in vitro studies, evidence for a diffuse POMC-related opioid system in the lizard Podarcis s. sicula is provided. In the lizard ovary, β-endorphin (β-EP)-like immunoreactive cells were observed within the granulosa layer; the immunoresponse showed seasonal variation, being most pronounced in the winter ovary. HPLC followed by immunoassay showed that acetyl β-EP is the main form of POMC-related peptide in both pituitary and ovary. In vitro studies showed that picomolar amounts of β-EP stimulate follicular estrogen production during both the reproductive and winter phases; induction was found to be higher in the reproductive phase. The data reported here provide evidence for the physiological role played by β-EP in the reproductive function of Podarcis s. sicula via induction of ovarian production of estradiol-17β, which is the main factor responsible for the vitellogenic process.