Analysis of oviduct-derived embryonic growth stimulator activity.

A co-culture study was carried out using primary cultures of hamster oviduct tissues to analyze oviduct-derived embryonic growth stimulating factor. In co-cultures of mouse pronuclear embryos and hamster oviduct tissue, the 4-cell rate after 48 hours (53.2%, 109/205) and blastocyst rate after 96 hours (22.4%, 46/205) were significantly higher than those of the standard culture group (4-cell rate, 41.8%, 76/182; blastocyst rate, 4.4%, 8/182), suggesting an embryonic growth stimulating effect of the co-culture. Similar effects were observed in co-cultures of both 2-cell mouse embryos collected 40 or 48 hours after the hCG administration and morulae collected 64 hours after hCG, but no such effect was observed in co-cultures of hamster embryos. When mouse embryos were cultured in a conditioned medium, which was the supernatant of the hamster oviduct tissue culture in Biggers-Whitten-Whittingham's (BWW) solution, no embryonic growth stimulating effect was observed. Further, no stimulating effect was observed in the conditioned medium obtained from 24-hour co-cultures of embryos and oviduct tissue. From these results, we considered the embryonic growth stimulating factor to be labile, with concentration-dependent effects. The absence of a stimulatory effect of co-culturing on the growth of hamster embryos also suggests the presence of species variations in the in vitro arrest of embryogenesis.