The effect of aprotinin on luteolytic and uterine contractile mechanisms in the pregnant rat at term.

The effect of the kallikrein inhibitor aprotinin on luteal function, uterine activity and parturition was studied in primigravid pregnant rats. Luteal function was monitored by the determination of serum progesterone levels. Aprotinin given daily from Day 19 to Day 22 of gestation had no effect on progesterone concentrations compared to saline-treated controls, but indomethacin delayed the decline in progesterone levels over the same time period. Aprotinin treatment had no effect on fetal and placental weights from Days 19 to 22 of gestation. Aprotinin infusion in Day-22 pregnant rats resulted in a reduction in uterine motility (studied by continuous recording in conscious rats by means of an intrauterine microballoon) in 10/12 rats. Continuous infusion of aprotinin into rats which had been allowed to deliver one young resulted in a significantly prolonged duration of parturition compared to that in saline-infused controls. In one rat the delivery process was completely arrested and recommended only when the infusion was stopped. Aprotonin had no effect on either the spontaneous or oxytocin-induced uterine contractions of the isolated Day-22 pregnant rat uterus. It is concluded that the kallikrein-kinin system in the late pregnant rat does not appear to be involved in the luteolytic process but may play a functional role in the control of uterine and/or cervical function before and during parturition.