Differential responses to endothelial-dependent relaxation of the thoracic and abdominal aorta from male Sprague-Dawley rats.

Regional heterogeneity exists in reactivity of different vascular beds to vasoactive substances. Experiments were designed to determine if there are differences between thoracic and abdominal aorta response to acetylcholine-induced relaxation. Ten male Sprague-Dawley rats with a weighing between 200g-250g were used. The aorta was isolated and 3mm aortic rings were cut and suspended in organ baths containing physiological salt saline (PSS). Contractile and relaxation responses to noradrenaline (NA) and ACh, in the presence or absence of L-NNA and high K+ concentration were studied. Contractile response to NA was similar along the aorta. At the higher doses, ACh elicited a greater (p < 0.05) relaxation in the abdominal aorta when compared with the thoracic aorta. However, inhibition of eNOS was more effective (p<0.05) in preventing ACh-induced relaxation in the thoracic aorta when compared with the abdominal aorta. Conversely, inhibition of endothelial hyperpolarizing factor (EDHF) by high K+ concentration blocked ACh-induced relaxation to a greater extent in the abdominal aorta (p<0.05) when compared with the thoracic aorta. ACh-induced relaxation differs in the thoracic and abdominal aorta. Differences in the EDHF activity along the aorta underlie the differential response of the thoracic and abdominal aorta to ACh-induced relaxation.