INSULIN INCREASES CELL NUMBERS AND MORPHOLOGICAL DEVELOPMENT IN MOUSE PREIMPLANTATION EMBRYOS INVITRO

Insulin, alone or in combination with bovine serum albumin (BSA), was investigated for its effects on cell proliferation and on the proportions of mouse pre-implantation embryos reaching compaction and forming blastocysts during culture in a common basal medium in vitro. Insulin promoted cleavage by 16-20% when added to medium for culture of 2-cell embryos to morulae, blastocysts and expanded blastocysts over 24, 48 and 72 h. These effects on cell division were supported by increases of 65-100% and 31-100% in the rates of compaction and blastocyst formation respectively. The results indicate that the receptor responsible for these actions is probably expressed prior to compaction and possibly at the 4-cell stage. Identical responses to 1.7 and 170 nM insulin suggest that the insulin receptor is capable of mediating both of these developmental effects, although similar mediation by an insulin-like growth factor-1 (IGF-1) receptor is not excluded. BSA, normally a component of culture media, promoted cleavage between 24 and 48 h of culture as well as compaction and blastocyst formation at 15 mu-M (1 g L-1), probably through nutritional support. Compaction appeared to be promoted by some non-specific action of BSA. Blastocysts that had developed in the presence of both 170 nM insulin and 15 mu-M BSA contained similar numbers of cells to blastocysts that had developed in vivo.