The effects of hCG and growth factors on in vitro nuclear maturation of dog oocytes obtained during anoestrus

Abstract

The effects of human chorionic gonadotrophin (hCG) and a combination of growth factors on the developmental competence of canine oocytes during in vitro maturation was examined. Oocytes recovered from domestic dog ovaries at routine ovariectomy were cultured in a basic tissue culture medium with 0.3% BSA, 7 μg mL–1 progesterone and antibiotics. After the appropriate culture periods (up to 96 h), they were fixed and labelled by double-antibody immunofluorescence for tubulin and with propidium iodide for chromatin. Human chorionic gonadotrophin increased the proportion of oocytes resuming meiosis and reduced the degeneration rate. Supplementing with hCG in declining concentrations was of no superior benefit but the presence of a combination of growth factors (growth hormone, insulin-like growth factor-1, transforming growth factor-α and fibroblast growth factor) improved both the resumption of meiosis and the degeneration rate. No particular synergisms between pairs of growth factors could be demonstrated. Human chorionic gonadotrophin and growth factors together gave poorer results, implying that hCG inhibited the beneficial effects of the growth factors. A growth factor combination is the present most successful treatment, with 49% of total oocytes (inclusive of degenerated) recovered from anoestrous bitches at MI or MII by 96 h of culture. This is the highest result so far demonstrated for cultured dog oocytes.