The involvement of IGF-I, leptin and some intracellular signalling mechanisms in nutrition-induced changes in rabbit ovarian cell functions

Abstract

The aim of our experiments was to examine the role of IGF-I, leptin (the hormone of adipose tissue), in controlling ovarian function in different species, as well as of some protein kinases in mediating IGF-I and leptin effects. In in-vivo experiments, rabbits were subjected to food restriction (50% of normal intake) and IGF-I (2µg/animal) treatments, whilst plasma leptin and IGF-I levels were measured using RIA/EIA. In in-vitro experiments, rabbit ovarian cells were cultured in the presence of leptin, antiserum against IGF-I, inhibitors of MAP kinase and of CDC2 kinase or their combination. Expression of intracellular peptides associated with proliferation (PCNA), apoptosis (bax),CDC2/p34 kinase, cyclin B, protein kinase A, ERK1, 2 MAP kinase, CREB-1 and IGF-I, as well as the secretion of progesterone (P), estradiol (E), IGF-I, and IGFBP-3 were determined using SDS PAGE-Western blotting, immunocytochemistry, RIA and ELISA. Food restriction in rabbits in the periovulatory period results in a significant reduction in plasma leptin levels, which was associated with a significant decrease in IGF-I plasma concentrations. IGF-I addition signicantly increased plasma leptin levels. In in-vitro experiments there was no accumulation of immunoreactive leptin in culture medium conditioned by rabbit granulosa cells. Both leptin and IGF-I additions altered progesterone, estradiol, IGF-I and IGFBP-3 release by cultured granulosa cells, as well as changing the expression of IGF-I, PCNA, bax, protein kinase A, ERK1, 2 MAP kinase, p34 CDC2 kinase, cyclin B and CREB within these cells. Previous food restriction enhanced the response of ovarian cells to leptin and IGF-I treatment. The present observations suggest