Adrenomedullin in the rat ovary: Its production, interaction with endothelin 1, and actions on progesterone secretion during gestation

Abstract

Adrenomedullin (ADM), a novel vasorelaxant peptide, was found in human/rat ovaries and uteri. Plasma ADM level increases in pregnant women and pregnant rats. Our previous study in Sprague-Dawley rats showed that large antral follicles (diameter above 900 lm) and newly formed corpus luteum (CL) expressed higher levels of Adm and one of its receptor activity-modifying protein (Ramp2) than small antral follicles (diameter of 200-400 lm). EDN is luteolytic and is known to inhibit progesterone production. The aims of this study was to study the interaction of ADM and endothelin 1 (EDN1) in follicles and newly formed CL and the action of ADM on progesterone production in CL during pregnancy. Adult Sprague-Dawley rats were induced to ovulate by administration of eCG followed by hCG injection. Isolated large follicles were incubated with ADM/EDN1 for 6 h; newly formed corpora lutea were also incubated with ADM/EDN1 for 6 h with/without hCG. For the effects of EDN1, the gene expression of Adm and its receptor components in the large antral follicles and CL were measured by real-time RT-PCR. For the effects of ADM, the gene expression of Edn1 and endothelin receptor B (Ednrb) was measured. The effects of the ADM and CGRP receptor antagonists (hADM22-25 and hCGRP8-37) were also tested. CL were isolated from early (7-day), mid (12-day), and late (17-day) pregnant rats and were incubated for 6 h with ADM with or without an ADM or a receptor antagonist. Progesterone secretion from CL was measured by Enzyme Immunoassay. EDN1 was found to reduce the gene expression of Adm and Ramp1 in large antral follicles after 6 h incubation with ADM. ADM treatment upregulated Edn1 expression levels in large antral follicles. EDN1 also reduced the gene expression of Adm in the CL with/without hCG. ADM treatment increased Edn1 expression. In the presence of hCG, ADM treatment increased both Edn1 and also Ednrb expression. ADM suppressed progesterone production from the CL in early and late pregnancy while enhancing progesterone production in mid-pregnancy, which correlated well with the greater progesterone production at mid-pregnancy. The effects of ADM on Edn1 gene expression and progesterone production were blocked by the CGRP receptor antagonist. One of the roles of ADM in CL during pregnancy might be the regulation of progesterone production and this may be achieved via the interaction with END1. Acknowledgement: This work was substantially supported by a grant from the Research Grants Council of the Hong Kong Special Administrative Region, China (HKU7736/07M).