Abstract
Naturally ovulated eggs from mature rats were inseminated with spermatozoa recovered from the cauda epididymidis of mature males in modified Krebs-Ringer bicarbonate solution. High proportions (77-100%) of eggs were penetrated with no statistical difference among different sperm concentrations (0.05-1.0 × 106 spermatozoa/ml) and 25-61% of penetrated eggs showed polyspermy. When penetrated eggs were transferred into modified rat 1-cell embryo culture medium (mR1ECM) 10 h after insemination, 58% of them developed to the blastocyst stage 130 h after insemination. These results indicate that rat eggs collected from naturally ovulated females can be penetrated in vitro by epididymal spermatozoa and the eggs penetrated in vitro can develop to the blastocyst stage in a chemically defined medium.
