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The effect of postnatal age on norepinephrine-induced alpha 2-adrenoreceptor-mediated release of endothelium-derived relaxing factor in porcine intramuscular pulmonary arteries was studied. Rings of pulmonary artery from fetal, newborn, 3-d-, 10-d-, 9-wk-, and 15-wk-old pigs with and without endothelium were suspended for isometric force measurement in Krebs-Ringer bicarbonate solution (37 degrees C, 95% O2-5% CO2). In 15- and 10-wk-old pigs, norepinephrine increased tone in arteries with and without endothelium but produced relaxations at high concentrations only in arteries with endothelium. These relaxations were not inhibited by the alpha 1-antagonist prazosin but were completely abolished by the alpha 2-antagonist yohimbine and the inhibitor of nitric oxide release N-omega-nitro-L-arginine methyl ester. This confirms that the norepinephrine-induced relaxations were due to alpha 2-mediated release of endothelium-derived relaxing factor. Arteries from only 50% of the 10-d-old animals showed endothelium-dependent relaxations, and at 3 d of age and younger no relaxations were seen. In animals less than 10 d old, only some of the vessels contracted to norepinephrine and the contractile response was diminished compared with 15-wk-old animals, whereas the response to prostaglandin F2 alpha and histamine was similar in the neonatal group (newborn, 3 d old, and 10 d old). This group showed a dose-dependent relaxation to nitric oxide, with 10-d-old animals more sensitive to nitric oxide than newborn animals.(ABSTRACT TRUNCATED AT 250 WORDS)

Postnatal Adrenoreceptor Maturation in Porcine Intrapulmonary Arteries