Endocrine Abstracts

Uterine involution is a critical component of postpartum reproduction, which involves endometrial tissue repair, myometrial contraction and bacterial clearance. The uterus synthesises insulin-like growth factors (IGF-I and –II), IGF-I receptor (IGF-1R), and IGF binding proteins (IGFBPs -1 to -6) that regulate IGF bioavailability. This study used tissue from 12 multiparous Holstein-Friesian cows at day 14 postpartum to investigate expression of the uterine IGF system during involution. Sections of caruncular and inter-caruncular tissue from the previously gravid and non-gravid uterine horns were studied using in situ hybridisation with bovine specific S³⁵-labelled oligonucleotide probes. Quantification was by optical density measurements in different tissue regions using image analysis and data were analysed by Linear Mixed Model analysis. The strongest expression of IGF-II mRNA was in the endometrial stroma (ES). IGF-1R mRNA was present in myometrium (MYO), ES and caruncular stroma (CS). IGFBP-1 mRNA was undetectable. The strongest expression of IGFBP-2 and IGFBP-6 mRNA was in the sub-epithelial stroma (SES) underlying the luminal epithelium (LE) whereas IGFBP-3 mRNA expression was confined to LE. IGFBP-4 mRNA expression was similar between SES, ES and CS, with lower concentrations in MYO. In contrast, expression of IGFBP-5 mRNA was strongest in MYO. In relation to horn, expression of IGF-II and IGFBP-3 mRNA was highest in the previously gravid horn (P≤0.001), whereas expression of IGF-1R, IGFBP-4, -5 and -6 was lower in the gravid horn, although not in all tissue regions (P≤0.01). In conclusion, IGFs have many known actions on metabolic activity, immune function and tissue proliferation. Differential expression of the uterine IGF system between horns and tissue types during involution suggests that modulating local IGF bioavailability may alter the rate of postpartum uterine recovery. As dairy cows are normally inseminated again within 2–3 months after calving, this may in turn influence their subsequent fertility.