Coexpression of adrenomedullin and its receptors in the reproductive system of the rat: effects on steroid secretion in rat ovary

Abstract

Objective: The expression of adrenomedullin (ADM) in the reproductive system of the female rat and its effect on the secretion of estradiol and progesterone was studied. Materials and Methods: In adult Sprague-Dawley rats gene expression of ADM and its receptor components in the ovarian follicles oviduct were analyzed by real-time PCR (qPCR). Ovarian follicles and corpora lutea isolated from stimulated immature rats were cultured to study the effects ADM on in vitro basal FSH-stimulated estradiol secretion or eCG stimulated progesterone secretion. Results: Ovarian ADM and Adm mRNA levels were decreased at estrus whereas oviductal Adm mRNA levels were low at proestrus. Both tissues were shown to coexpress mRNAs encoding the calcitonin receptor-like receptor and receptor activity-modifying protein 1 (Ramp1) Ramp2 and Ramp3. Gel filtration chromatography of ovarian extracts showed two peaks with the predominant one eluting at the position of authentic rat ADM(1-50) at estrus and at the position of ADM precursor at diestrus. Positive ADM immunostaining was localized in the granulosa and theca cells of the follicle and corpora lutea of the ovary. ADM inhibited FSH-induced estradiol secretion in 2-day-old follicles and also suppressed eCG-stimulated progesterone release in the corpora lutea was abolished by calcitonin gene-related peptide (8-37) and ADM (22-52) respectively. Conclusion: The presence of ADM and the gene expression of ADM and its receptor components in the female reproductive system suggest a paracine effect of ADM on ovarian steroidogenesis.