Developmental dynamics of endothelial and neurogenic control of canine thoracic aorta.

The purpose of the study was to confront the range of endothelial relaxation and neurogenic contraction of the thoracic aorta in fetuses (1 week before birth), puppies (1, 2, 4 and 6 weeks old), and in adult dogs. Isometric tension of aortic rings was monitored in organ bath. Acetylcholine-induced dose-dependent relaxation of aortic rings precontracted by phenylephrine was pronounced already in fetuses and puppies and significantly larger than in adults. Indomethacin, a cyclooxygenase inhibitor, did not affect the magnitude of aortic relaxation to acetylcholine. Transmural nerve stimulation induced but very slight contractions of the thoracic aorta in fetuses, while in puppies the extent of contractions was increasing with increasing age, reaching its maximum in adults. Contractile responses of aortic rings induced by KCl were fully detectable in fetuses and puppies and increased with increasing age of the animals. Thus in ontogenesis, the extent of endothelium-dependent relaxation and neurogenic contraction of the thoracic aorta displayed an opposite trend. The acetylcholine-induced relaxation was fully operative already in fetuses and puppies and its extent was declining toward adulthood, whereas the neurogenic contraction was hardly detectable in fetuses, increasing in puppies, and showed the highest values in adults.