EFFECT OF IGF-I ON PIG OOCYTE MATURATION, FERTILIZATION, AND EARLY EMBRYONIC-DEVELOPMENT IN-VITRO, AND ON GRANULOSA AND CUMULUS CELL BIOSYNTHETIC ACTIVITY

Porcine granulosa cells have been shown previously to both secrete and respond to insulin-like growth factor-I (IGF-I), suggesting an autocr ine function of this peptide in the follicle. The present work was und ertaken to determine possible effects of IGF-I on in vitro maturation, in vitro fertilization, and early embryonic development in culture. G ranulosa and cumulus cell proliferation and differentiation based on H -3-thymidine uptake and progesterone production, respectively, were al so assessed. The results showed that the cleavage rate of oocytes was markedly stimulated in a dose-dependent manner by the addition of IGF- I to the oocyte maturation medium (P < 0.05). Embryo development beyon d the 8-cell stage was improved by IGF-I, reaching a maximum of 22% at 200 ng/ml IGF-I. Treatment with IGF-I after fertilization increased t he percentage of total oocyte cleavage (P < 0.05) to approximately 52% , 43%, and 57% at, respectively, 25, 50, and 100 ng/ml IGF-I. H-3-thym idine incorporation by granulosa cells was significantly increased in cultures treated with FSH (3-fold) or IGF-I (6-fold) compared to the c ontrol. For the cumulus cells, FSH caused a similar increase (3-fold) in H-3-thymidine incorporation while IGF-I stimulated a 15-fold increa se. Progesterone production by the granulosa cells was increased to th e same extent by treatment with FSH or IGF-I (4.7 and 5.1-fold, respec tively). However, for the cumulus cells, while FSH caused a marked 16- fold increase in progesterone production, IGF-I caused only a marginal increase of 2.5-fold. These results indicate a beneficial effect of I GF-I on in vitro porcine oocyte maturation and pre-implantation embryo development, suggesting a physiological role for IGF-I in vivo. The i n vivo effect of IGF-I may be indirect via autocrine stimulation of cu mulus and/or granulosa cells resulting in enhanced oocyte maturation a nd fertilization. (C) 1994 Wiley-Liss, Inc.