Effect of two types of stress (heat shock/high temperature and malnutrition/serum deprivation) on porcine ovarian cell functions and their response to hormones

The aim of the present study was to understand the interrelationships between stress, hormones and basic ovarian functions in the ovary. For this purpose, we compared the expression of markers of proliferation (PCNA, cyclin B1), of apoptosis (Bax, caspase-3) and secretory activity (release of progesterone, P-4, and insulin-like growth factor, IGF-I) in whole ovarian follicles and granulosa cells cultured in conditions of normal temperature (37.5 degrees C) and feeding (with serum), high temperature (41.5 degrees C, with serum) and malnutrition (37.5 degrees C, without serum), with and without hormones [IGF-I, leptin and follicle-stimulating hormone (FSH)]. The expression of proliferation and apoptosis markers was evaluated by SDS PAGE-western blotting whereas radioimmunoassay (RIA) measured the release of hormones. High temperature dramatically induced a reduction in both proliferation and apoptosis markers in both ovarian follicles and granulosa cells and induced a significant increase in P-4 and IGF-I release by ovarian granulosa cells but not in P-4 secretion by ovarian follicles. Serum deprivation increased accumulation of cyclin B1 but not other markers of proliferation (PCNA) and apoptosis (Bax, caspase-3) or P-4 release in ovarian follicles. On the contrary, it inhibited the expression of apoptotic marker (Bax), release of both P-4 and IGF-I but it did not affect proliferation marker (PCNA) in granulosa cells. Adding IGF-I, leptin and FSH affected proliferation, apoptosis and secretory activity of ovarian cell functions but also prevented an inhibitory effect of high temperature on the expression of Bax and PCNA and an inhibitory action of serum deprivation on PCNA in ovarian follicles. Furthermore, treatment with these hormones prevented an inhibitory action of thermal stress on Bax, PCNA, P-4 and IGF-I in ovarian granulosa cells. The present observations (1) confirm the involvement of hormones (IGF-I, leptin and FSH) in the control of proliferation, apoptosis and secretory activity of ovarian cells, (2) demonstrate for the first time that heat stress/increased temperature can induce a reduction in ovarian cell proliferation and apoptosis and an oversecretion of ovarian hormones, (3) show that malnutrition/serum deprivation can reduce both apoptosis and secretory activity of ovarian cells, (4) demonstrate the differences in the response of granulosa and other ovarian follicular cells to stresses, and (5) are the first demonstration that hormones (IGF-I, leptin and FSH) could be used for preventing the effect of stresses on ovarian cell functions.