PROPRANOLOL INHIBITS THE SPONTANEOUS CLOSURE OF THE DUCTUS-ARTERIOSUSIN NEWBORN RATS

Newborn rats delivered by cesarean section were given subcutaneously p ropranolol (PRO), a beta-adrenergic blocker, (1) immediately or (2) 18 0 min after delivery. The diameter of the ductus arteriosus (DA) of th e newborn pups was calibrated at 30, 60 and 90 min after the PRO-admin istration. The results were as follows : (1) The DA calibers of the pu ps given 0.2, 1.0, 5.0 mg/kg PRO immediately after cesarean delivery r emained significantly larger than those of controls in a dose-dependen t manner for 30 min after treatment. In the 5 mg/kg group, the enlarge ment of the DA was prolonged for 90 min after treatment. (2) In untrea ted pups, the DA completely closed by 180 min after cesarean delivery. The DA was not affected by the administration of 5 mg/kg PRO at 3 hr after delivery. It was concluded that, PRO inhibits the spontaneous co nstriction of the DA, suggesting an important role of beta-adrenergic stimulation on the spontaneous closure of the DA in newborn rats.