Negative energy balance in dairy cows is associated with specific changes in IGF-binding protein expression in the oviduct.

Negative energy balance (NEB) during early lactation in dairy cows leads to an altered metabolic state that has major effects on the production of IGF family members. Low IGF-I concentrations are associated with poor fertility and therefore we aimed to determine whether NEB exerts a direct effect on IGF expression in the postpartum oviduct. Multiparous Holstein cows were allocated to two treatments (each n=6) designed using differential feeding and milking regimes to produce either mild NEB (MNEB) or severe NEB (SNEB). Animals were slaughtered in week 2 of lactation when divergent metabolic profiles were evident. Oviducts were collected for RNA analysis by real-time RT-PCR and in situ hybridisation. Quantitative measures in oviduct gene expression were obtained for all members of the IGF family (IGF-I/II, IGF-binding proteins (IGFBP) 1-6 and receptors for IGF types 1 and 2), insulin A/B, GH, glucocorticoid and oestrogen alpha/beta. Expression of IGFBP-2 and IGFBP-6 (both of which have a high affinity for IGF-II) was decreased in SNEB relative to MNEB (P<0.05). No other gene was altered by NEB, but IGF-II, IGFBP-3, IGFBP-5 and IGFBP-6 all showed differential expression in different regions of the oviduct. These results indicate that, in addition to low circulating IGF-I after calving, NEB may also influence IGF availability in the oviduct indirectly through changes in specific IGFBP expression. It is possible that the predicted increased signalling by IGF-II may perturb embryo development, contributing to the high rates of embryonic mortality in dairy cows.

Immunohistochemical localization of active caspase-3 in the mouse ovary: growth and atresia of small follicles.

Caspase-3 belongs to a family of highly conserved cysteine proteases that mediate the course of apoptotic cell suicide. It is recognized that ovarian follicular atresia is associated with apoptosis, a process that has been characterized mainly in larger antral follicles. The aims of this study were to investigate the expression of caspase-3 in the mouse ovary, and determine whether active caspase-3 is present within smaller follicles, which may constitute the resting pool. The inactive enzyme was expressed as a 32 kDa band on a western blot of tissue extracts, whereas the active form was localized immunohistochemically. Bromodeoxyuridine (BrdU) was administered to mice (n = 7) during a 12 h period and subsequently localized to identify potentially quiescent follicles. Measurements of BrdU-positive cells in the mouse ovary were extrapolated with data obtained by morphometric analyses of small follicles using the nucleator technique. BrdU was incorporated into the granulosa cells of follicles regardless of size and the number of cells they contained, but was absent in a large proportion (89%) of small, single layered follicles. Active caspase-3 was localized to both the oocyte and granulosa cells of follicles that were considered to be undergoing atresia, but was not localized to the granulosa cells of any small, single layered follicles. The results of this study indicate that, in small follicles, granulosa cell proliferation occurs independently of the size of follicles and the number of constituent cells, and that follicles of this type may be inherently less susceptible to the normal physiological factors that induce atresia.