Problem: To determine whether Synthetic Serum Substitute (SSS), which contains human globulins in addition to Human Serum Albumin (HSA), is superior to HSA alone as a protein supplement for embryo culture.
Method: Development of mouse zygotes to eight-cell/compacting morulae and to hatching/hatched blastocysts was assessed in Human Tubal Fluid (HTF) medium containing either SSS of HSA.
Results: Although there was no difference in the overall blastocyst rate at 120 h in HTF+SSS versus HTF+HSA, significantly more embryos at 54 h were at the eight-cell/compacting morula stage in HTF+SSS. At 120 h, there were more hatching/hatched blastocysts in HTF+SSS, and hatching correlated with SSS concentration. Addition of isolated globulins to HSA significantly stimulated the number of hatching/hatched blastocysts. Hatching could be "rescued" by transfer of embryos grown in HTF+HSA to globulin-containing media and prevented by removal of globulins as late as the compacted morula stage (54 h).
Conclusions: SSS is superior to HSA alone for embryo culture. The stimulatory effects on mitosis and hatching may be mediated directly by globulins or by other components in the globulin-enriched fraction.