Abstract:
The mechanisms of zona pellucida (ZP) loss in peri-implantation hamsterembryos in vivo versus in vitroare distinctly different. To investigate if ZP lossin vivo is the result of transient uterine pH changes,the luminal pH of the pregnant uterus was measured during the ZP loss period.Prior to ZP loss, pH was 7.30 0.05 (mean SE; left uterine horn) and 7.35 0.03(right horn). During ZP loss, pH was 7.26 0.07 (left) and 7.35 0.03 (right),and after embryo attachment, 7.25 0.02 (left) and 7.27 0.02 (right). None ofthese values are statistically different. The pseudopregnant uterine pH was7.30 0.04 (left) and 7.31 0.04 (right), not statistically different from eachother or from pregnant uteri. Blastocyst ZP lossin vitro (pH 3.0-8.5) occurred only at pH 3.0.Loss of ZP occurred in uterine flushings from pregnant or pseudopregnanthamsters, evidence that ZP loss is related to uterine factors. Complete ZPloss occurred at pH 6.8, but was incomplete at pH 6.6, 7.0 and 7.2. No ZP lossoccurred in uterine flushings from non-mated females. In summary:(i) a change in uterine pH does not cause ZP lossin vivo in the Syrian hamster;(ii) a pH-sensitive factor in pregnant andpseudopregnant uterine fluid is responsible for ZP loss.