The influence of drugs on the kinin-forming system in relation to pregnancy and parturition in the rat.

The duration of normal gestation and parturition in the rat can be changed by treatment with drugs which alter the equilibrium of the kallikrein-kinin system. The kallikrein inhibitor, aprotinin, when given from Days 19-22 of pregnancy prolongs gestation. Treatment with aprotinin from Days 20-22 of pregnancy prolongs the parturient process, as does a single dose given on the morning of Day 22. Kallikrein, when administered from Days 19-22 of pregnancy, results in a prolongation of gestation and abolishes the pre-parturient behaviour ('labour'). Parturition is prolonged and many fetuses are stillborn. Soya bean trypsin inhibitor when given from Days 19-22 of pregnancy delays and prolongs parturition; maternal haemorrhage occurs during birth and many fetuses are born dead or are abandoned at birth. It is suggested that the kallikrein-kinin system plays a functional role in the normal process of parturition in the rat.