Effect of Maturation on Endothelium-Dependent Relaxation in Pulmonary Arteries of the Newborn Rabbit

Seo, Bong Hee; Lee, So Hyun; Park, Kook In; Park, Moon Sung; Lee, Chul; Han, Dong Gwan

Abstract

PURPOSE: This study was done to determine whether maturatin alters endothelium- dependent responses in pulmonary arteries.
METHODS
Vascular rings of pulmonary arteries, with and without endothelium, taken from rabbits of 3 and 30 days of age were suspended in organ chambers filled with Krebs-Henseleit solution, bubbled with 95% O2-5% CO2 and maintained at 37degrees C. Immediately after mounting, the rings were stretched progressively until a maximal response to KCl was achieved. The rings were incubated with indomethacin and allowed to equilibrate before contraction and relaxation study.
RESULTS
When the endothelium was intact in arterial rings from 3-day-old rabbits, acetylcholine (ACH) (10-6 M) relaxed preconstricted rings with histamine (5x10-6 M) (98.1 4.7% relaxation, mean SD). In rings without endothelium, KCl (10-2 to 9x10-2 M) and histamine (5x10-8 to 10-5 M) caused concentration-dependent contractions. When normalized to maximal contractions achieved to each agonist, the concentration-effect curves to KCl and histamine in rings without endothelium were similar to both ages. Rings with endothelium showed a progressive shift to the right of the concentration- effect curve to histamine. Relaxation to sodium nitroprusside were unaffected by age. In preconstricted ring, ACH (10-8 to 5x10-6 M) caused relaxations in rings with endothelium which were greater at 30-day compared to 3-day-old rabbits.
CONCLUSION
These study demonstrates that endothelium-dependent relaxation increase with age, possibly due to changes in the release and/or effect of endothelium-derived relaxing factor (EDRF or nitric oxide) from pulmonary arteries during the neonatal period.