Uptake and incorporation of myo-inositol by bovine preimplantation embryos from two-cell to early blastocyst stages.

The uptake of myo-inositol and its incorporation into the phosphoinositides and inositol phosphates of the phosphatidylinositol (PtdIns) signal transduction system by in vivo preimplantation cattle embryos was investigated using [(3)H] myo-inositol. Uptake of inositol was examined in two-cell and four-cell embryos (day 2 after insemination), morulae (day 6) and early blastocysts (day 7). Uptake in all stages examined was largely sodium-dependent indicating the presence of a sodium-dependent inositol transporter. Uptake of inositol did not vary significantly from two-cell to early blastocyst stages when expressed either on a per embryo or a per microg of protein basis. Incorporation of inositol into the three phosphoinositides, PtdIns, PtdInsP, and PtdInsP(2), was detectable at all stages examined. In contrast, incorporation of inositol into inositol phosphates was not detected until blastocyst formation at day 7. The second messenger, Ins(1,4,5)P(3), was first detected in day 7 blastocysts.