953-37 Nitric Oxide is a Potent Arterial Duct Dilator in Neonatal Lambs

Abstract

Neonates with duct dependent pulmonary circulations require patency of the arterial duct (AD) to maintain the underdeveloped circulation before palliative or reparative surgery. Nitric oxide (NO) has been used in both animals and patients to relax the pulmonary vasculature and hence reduce pulmonary artery pressure and increase pulmonary blood flow. However AD response to NO is unknown. To determine the responses of the AD to NO, we used the NO donor SIN-l, in vitro on freshly removed ADs and aortas from newborn lambs (aged 1–5 days, n = 7). Vessels were cut into rings and mounted on tension gauges in 3°C organ baths containing Krebs-Henseleit. After equilibration with 1 gm of tension, the rings were tested for smooth muscle responses to oxygen (O 2 ), prostaglandin E 2 (PGE 2 ), potassium (K + ) and SIN-l. O 2 constricted the AD rings at tensions over 89 mmHg. PGE2 had no effect in concentrations ranging from 10 -8 –10 -5 . K + constricted the aortic rings in concentrations ranging from 10–70 mmol/l. SIN-l relaxed the K + preconstricted aortic rings in concentrations ranging from 10 -7 –10 -4 K + constricted the ADs in a similar concentration range to that of aortic rings. PGE 2 had no effect on the post term AD in concentrations ranging from 10 -8 –10 -5 . With preconstriction using 40 mmol/l of K + , the AD relaxed in response to SIN-l in concentrations ranging from 10 -7 –10 -4 in equal proportion to aortic rings from the same animals under identical conditions (p > 0.05). 1) Nitric oxide is a potent dilatorof the arterial duct in a similar fashion to its effects on other vasculature and may have a role in the management of neonates with duct dependent circulations. 2) Previous exposure of the AD to oxygen abolishes the relaxation response to PGE 2 .