Adiponectin, the most abundantly synthesized protein in adipose tissue, circulates as multimers of low, medium and high molecular weight in the serum. Recently, studies have demonstrated adiponectin expression in tissues other than adipose, including the placenta. We previously demonstrated that adiponectin, alone and associated with insulin and gonadotropins, induces a gene expression pattern consistent with the changes occurring during the periovulatory remodeling of the ovarian follicle. The purpose of this study was to investigate the pattern of circulating adiponectin and its association with ovarian function, as well as to localize the adiponectin system in the pig ovary. Herein we demonstrated that adiponectin and its receptors R1 and R2 are expressed in the large cells of the corpus luteum and in follicular granulosa and theca cells. Based on pig serum western blotting analysis we could identify two pig populations in which variations in abundance and multimerization of circulating adiponectin isoforms differed in both serum and follicular fluid. The presence of one pattern of these variations was correlated with fewer large follicles and fewer corpora lutea in pig ovaries as well as with an increase of receptor R1 and R2 mRNA expression in corpora lutea and a decrease of R1 mRNA expression in theca cells. Furthermore, analysis of receptor R1 and R2 gene expression performed across a group of 15 Landrace pigs demonstrated that levels of receptor R1 in theca cells were significantly correlated to number of large follicles in the ovary. Taken together, these results indicate that the adiponectin system plays an important role in follicular development and ovulation process and suggests that impaired multimerization of circulating adiponectin isoforms is related to ovarian dysfunction. Supported by a NSERC Strategic Grant to BDM, MFP and VB. DBC is supported by FAPESP. (poster)