DIFFERENCE IN THE ENDOTHELIUM-MEDIATED EFFECTS OF A23187 ON THORACIC AORTA BETWEEN NEONATAL AND ADULT GUINEA-PIGS

Developmental changes in the functional properties of thoracic aorta w ere examined in neonatal and adult guinea-pigs. Norepinephrine-induced contractions of the neonatal aortic rings were markedly enhanced by r emoval of the endothelium, whereas those of the adult rings were only slightly enhanced. Carbachol induced endothelium-dependent relaxation to a similar extent in both neonatal and adult aortic rings precontrac ted with 30 mu M norepinephrine. A23187 induced endothelium-dependent relaxation in the adult aortic rings precontracted with 30 mu M norepi nephrine, whereas it failed to induce the relaxation in the neonatal a ortic ring. Sodium nitropurusside induced endothelium-independent rela xation to a similar extent in both neonatal and adult aortic rings pre contracted with 30 mu M norepinephrine. The endothelium-dependent rela xation induced by carbachol and by A23187 were inhibited either by N-G -nitro-L-arginine or by methylene blue, but not by indomethacin, indic ating that both the relaxations were mediated by nitric oxide, but not by prostacyclin. These results suggest that, although the neonatal en dothelium of the guinea-pig aorta is capable of releasing nitric oxide , the mechanisms underlying the synthesis and/or release of nitric oxi de may be different between the neonatal and adult endothelium.