RESPONSES OF THE POSTTERM ARTERIAL DUCT TO OXYGEN, PROSTAGLANDIN E(2), AND THE NITRIC-OXIDE DONOR, 3-MORPHOLINOSYDNONIMINE, IN LAMBS AND THEIR CLINICAL IMPLICATIONS

Background-Nitric oxide is a potent dilator of the pulmonary vasculatu re. There have been no previous reports on the action of nitric oxide on the arterial duct. Objectives-To determine the responses of isolate d post-term arterial duct rings from lambs to oxygen, prostaglandin E( 2) (PGE(2)) and the nitric oxide donor, 3-morpholinosyndonimine (SIN-1 ). Setting-Experimental laboratory. Subjects-Six neonatal lambs. Metho ds-Lambs aged 1-5 days were killed and the arterial duct and aorta exc ised and cut into rings. These were mounted on tension gauges in organ baths containing Krebs-Henseleit solution. Rings were exposed to incr easing concentrations of oxygen, PGE, and after preconstriction with p otassium (40 mmol/1) to SIN-1. Tension and relaxation responses were r ecorded. Results-Increased oxygen tension resulted in increased tensio n in the ductal rings above 88.9 mm Hg as previously described. No res ponse to PGE(2) occurred before or after ductal rings were exposed to oxygen. SIN-1 caused relaxation of smooth muscle in the arterial duct to a similar degree as that in the aortic rings. Conclusions-As previo usly shown, oxygen is a potent constrictor of the arterial duct. The p ost-term arterial duct does not relax in response to PGE, possibly as a result of inactivation by oxygen of the special sensitivity of the d uct to PGE(2). SIN-1 is a potent smooth muscle relaxing agent in the t erm arterial duct and may have a role in the initial management of neo nates with duct dependent pulmonary circulation.