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 were examined in neonatal and adult guinea-pigs. Norepinephrine-induced contractions of the neonatal aortic rings were markedly enhanced by removal 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 precontracted with 30 microM norepinephrine. A23187 induced endothelium-dependent relaxation in the adult aortic rings precontracted with 30 microM norepinephrine, whereas it failed to induce the relaxation in the neonatal aortic ring. Sodium nitropurusside induced endothelium-independent relaxation to a similar extent in both neonatal and adult aortic rings precontracted with 30 microM norepinephrine. The endothelium-dependent relaxation induced by carbachol and by A23187 were inhibited either by NG-nitro-L-arginine or by methylene blue, but not by indomethacin, indicating that both the relaxations were mediated by nitric oxide, but not by prostacyclin. These results suggest that, although the neonatal endothelium of the guinea-pig aorta is capable of releasing nitric oxide, the mechanisms underlying the synthesis and/or release of nitric oxide may be different between the neonatal and adult endothelium.