Inactivation of bradykinin in the pulmonary vascular bed of newborn and fetal lambs.

Bradykinin is largely inactivated in one passage through the pulmonary vascular bed of adult animals. We studied pulmonary inactivation of bradykinin in newborn lambs, fetal lambs at term, fetal lambs preterm, and adult ewes by comparing the systemic pressure response to infusions proximal to the pulmonary vascular bed with the response to infusions distal to the pulmonary vascular bed. A high degree of inactivation was confirmed in mature ewes (93 ± 1.2%); newborn lambs showed significantly less pulmonary inactivation (68 ± 5.2%) and fetal lambs at term showed only 46±4.8% inactivation. In the preterm fetuses (gestational age 110-128 days), no inactivation could be demonstrated in the pulmonary vascular bed. The return to base-line diastolic pressure after the infusion was discontinued was much slower in the fetus than it was in the newborn and the adult animal, indicating a prolonged effect of bradykinin. The results suggest that inactivation of bradykinin is a pulmonary function that develops late in fetal life and is still less than adult levels at birth. This Ending could be of particular interest if bradykinin participates in mediating the circulatory changes occurring at birth.