Abstract
1 Plasma kininogen concentration of the female rat did not change during the oestrous cycle but increased two-fold during gestation. Plasma kininogen did not change during parturition, rose in the first puerperal day and then rapidly declined to non-pregnant levels. 2 Free kinin levels in the blood of non-pregnant female rats were low and inconstant. Free kinin was undetectable in the blood of pregnant rats, but was found in four out of ten parturient rats. 3 After administration of the kininase inhibitor dimercaprol (30 mg/kg i.p.), free kinin was present in the blood of six parturient rats. Dimercaprol caused appearance of free kinin in the blood of only one out of six non-pregnant rats. 4 It appears that the plasma kinin system is activated to a small degree during parturition.