Intactness of zona pellucida does not affect the secretion of a trypsin-like protease from mouse blastocyst

Assisted hatching (AH), which is known to improve the hatching potential of mammalian embryos, has been used to increase the pregnancy rate in in vitr o fertilization cycles. However, the effect of AH on a trypsin-like proteas e, which is known to be associated with the hatching process, has not been studied. In this study, we evaluate whether the intactness of zona pellucid a affects the secretion of a trypsin-like protease from mouse blastocyst. F our- to 8-cell stage mouse embryos were collected at 66- to 68 hr after hCG injection and divided into 3 groups according to the manipulation of zona pellucida, The groups are no treatment (control), drilling of zona pellucid a (ZD) and thinning of zona pellucida (ZT). The activity of a trypsin-like protease, blastocyst development and hatching rate were compared among the three groups at 110 and 135 hr after hCG injection, respectively. The prote ase activity and blastocyst development were not significantly different am ong control, ZD and ZT groups at 110 and 135 hr after hCG injection, respec tively. However, the hatching rate of ZD and ZT groups was significantly hi gher than that of control group at each time, respectively (p<0.001). Even in the zona pellucida removed embryos, the protease activity did not differ from the control group. In conclusion, the secretion of a trypsin-like pro tease from mouse blastocyst does not seem to be affected by the intactness of zona pellucida.