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Post-coital unilateral ovariectomy and ipsilateral survival of the conceptus.

Post-coital unilateral ovariectomy in rabbits (Little, Haynes & Lamming, 1970), rats (Lamming & Little, 1968) and mice (Bruce, Renwick & Finn, 1968) impairs embryonic survival in the ipsilateral uterine horn. These findings suggest that each ovary controls conceptus survival in its adjacent uterine horn. The existence of such a mechanism has been disputed in the rat (Wu & Dickmann, 1971) and mouse (McLaren, 1970), and conflicts with the premises involved in induction of bilateral blastocyst implantation after ovariectomy using exogenous hormones. McLaren (1970) worked with the Q strain, and Bruce et al. (1968) demonstrated a variation of the local effect between the P and TO strains. Our aim was to uncover any local effect in a fourth strain of mice. Swiss Webster albino mice were maintained and anaesthetized as described previously (Holmes & Dickson, 1971). Bilaterally ovariectomized, sham bilaterally ovariectomized, left unilaterally ovariectomized and right unilaterally ovariectomized groups were studied. The experimental groups were considered separately to investigate any non-symmetrical distribution of implantations between left and right uterine horns as suggested by McLaren (1963). All surgery was done between 09.00 and 12.00 h on day 3, and evidence of successful implantation was sought at autopsy on the morning of day 14. Student's i-test was applied when valid. Table 1 shows the total number of implantation sites observed at autopsy in the four groups of mice, dividing them into morphologically normal and resorbing sites. No significant difference (P > 0-1) was evident between the number of sites in the left and right uterine horns in either the left or right unilaterally ovariectomized groups or between the numbers of implantation sites in the left and right horns of the sham ovariectomized mice. Furthermore, the percentage of résorptions in the uni¬ laterally ovariectomized groups was not significantly different (P > 0-1) from those in the intact, sham-operated group. The lack of significant correlation between unilateral ovariectomy and ipsilateral embryonic loss is inconsistent with the observations of Bruce et al. (1968) but confirms the work of McLaren (1970) and Wu & Dickmann (1971). An insignificant difference in percentage of résorptions between the unilaterally ovariectomized mice and the sham-operated controls indicates that, if reduced hormone levels are created by unilateral ovariectomy, as suggested by Chatterjee & Harper (1970) and Chatterjee & Greenwald (1971) in rats, they are not the prime cause of the résorptions. Division of Morphological Science, Faculty of Medicine, The University of Calgary, Calgary 44, Alberta, Canada