INHIBITORY EFFECT OF ENALAPRIL ON THE CONSTRICTION OF THE DUCTUS-ARTERIOSUS IN NEWBORN RATS

Caesarean newborn rats were given subcutaneously enalapril maleate (EM ), an angiotensin-converting enzyme inhibitor, (1) immediately or (2) 180 min after delivery. The ductus arteriosus (DA) in these newborn pu ps was calibrated 30, 60 and 90 min after the EM-treatment. The result s were as follows : (1) DA calibers of the pups given 10 or 50 mg/kg E M just at caesarean delivery remained significantly larger than those of the controls thereafter until 90 min. (2) The DA was completely clo sed 180 min after caesarean delivery. However, with 50 mg/kg EM given at this time, the DA was temporarily re-opened and then constricted. I t is concluded that, in newborn rats, EM has the direct inhibitory act ion on the constriction of the DA, and that it also has the re-opening action on the once-constricted DA.