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THE FATE OF SHORT-TAILED WEASEL, MUSTELA ERMINEA, BLASTOCYSTS FOLLOWING OVARIECTOMY DURING DIAPAUSE

Summary.: Blastocysts were obtained from intact or ovariectomized weasels, Mustela erminea, during embryonic diapause. Examination of thirty-five normal blastocysts revealed neither mitotic figures nor other evidence of trophoblast or embryonal knot development beyond the blastocyst stage during diapause. Uncleaved ova were found with normal blastocysts in three intact females, but no evidence of embryonic mortality during diapause was observed.

In spayed females, approximately 60% of the blastocysts recovered 1 to 3 weeks after ovariectomy showed evidence of deterioration, whereas all blastocysts recovered 3 to 9 weeks after ovariectomy were fragmented. Following ovariectomy, however, substantial proliferation of cells occurred in both embryonal knot and trophoblast tissues, cell numbers increasing by as much as five- to seven-fold as compared with normal blastocysts in diapause. These observations suggest that ovariectomy during the delay interval stimulated mitotic activity in the blastocyst, but, in the absence of ovarian support, the uterine environment was incompatible with continued embryonic differentiation and subsequent nidation.