Adiponectin and resistin: potential metabolic signals affecting hypothalamo-pituitary gonadal axis in females and males of different species

Adipokines, including adiponectin and resistin, are cytokines produced mainly by the adipose tissue. They play a significant role in metabolic functions that regulate the insulin sensitivity and inflammation. Alterations in adiponectin and resistin plasma levels, or their expression in metabolic and gonadal tissues, are observed in some metabolic pathologies, such as obesity. Several studies have shown that these two hormones and the receptors for adiponectin, AdipoR1 and AdipoR2 are present in various reproductive tissues in both sexes of different species. Thus, these adipokines could be metabolic signals that partially explain infertility related to obesity, such as polycystic ovary syndrome (PCOS). Species and gender differences in plasma levels, tissue or cell distribution and hormonal regulation have been reported for resistin and adiponectin. Furthermore, until now, it has been unclear whether adiponectin and resistin act directly or indirectly on the hypothalamo-pituitary-gonadal axis. The objective of this review was to summarise the latest findings and particularly the species and gender differences of adiponectin and resistin on female and male reproduction known to date, based on the hypothalamo-pituitary-gonadal axis.