EFFECT OF FOLLICULAR CELLS, IGF-I AND TYROSINE KINASE BLOCKERS ON OOCYTE MATURATION

The aim of this study was to test the following hypotheses: (i) that o ocyte maturation is controlled by surrounding follicular cells; (ii) t hat a meiosis-regulating factor of follicular origin is not species-sp ecific; (iii) that one of the follicular regulators of oocyte maturati on is IGF-I; and, (iv) that Cumulus oophorus and tyrosine kinase-depen dent intracellular mechanisms do not mediate IGF-I action on oocytes. It was found that co-culture of cumulus-enclosed bovine oocytes with i solated bovine ovarian follicles or with isolated porcine ovarian foll icles significantly increased the proportion of matured oocytes (at me taphase II of meiosis) after culture. Porcine oocytes without cumulus investments had lower maturation rates than cumulus-enclosed oocytes. Go-culture with isolated porcine ovarian follicles resulted in stimula tion of maturation of both cumulus-free and cumulus-enclosed porcine o ocytes, These observations suggest that follicular cells (whole follic les or Cumulus oophorus) support bovine and porcine oocyte maturation, and that follicular maturation-promoting factor is not species-specif ic. The release of significant amounts of IGF-I by cultured bovine and porcine isolated follicles and granulosa cells was demonstrated. Addi tion of IGF-I to culture medium at 10 or 100 (but not 1000) ng/ml stim ulated meiotic maturation of both cumulus-enclosed acid cumulus-free p orcine oocytes. Neither of the tyrosine kinase blockers, genistein or lavendustin (100 ng/ml medium), changed the stimulating effect of IGF- I on porcine oocytes. The present data suggest that at least one of th e follicular stimulators of oocyte nuclear maturation is IGF-I, and th at its effect is probably not mediated by cumulus investment or by tyr osine kinase-dependent intracellular mechanisms. (C) 1998 Elsevier Sci ence B.V. All rights reserved.