Extracellular calcium dependence of contraction and endothelium-dependent relaxation varies along the length of the aorta and its branches.

Dependence of contraction and endothelium-dependent relaxation of segments of the rabbit aorta and the celiac, superior mesenteric and renal arteries on the presence of calcium in the physiological salt solution in which they were bathed have been studied in vitro. Arteries were tested before and 60 min after removal of Ca++ from the bath solution. Norepinephrine-induced contraction and acetylcholine and A23187-induced relaxation were calcium-dependent in the thoracic and upper abdominal aorta. Contractions were resistant to the effect of calcium removal in segments from the aorta below the origin of the renal artery and from the renal artery itself. The aorta between the superior mesenteric and the renal arteries was intermediate in its dependence. Relaxation of the aorta caudal to the origin of the celiac artery and the renal artery was also resistant. The insertion of an intact everted vessel into an artery whose intima had been inactivated by rubbing restored partially the relaxation to acetylcholine and A23187 in the presence of normal calcium. Vessels that did not relax to acetylcholine after Ca++ exclusion from the bathing solution relaxed when the renal artery was the donor. Donor arteries whose relaxation was sensitive to Ca++ removal did not increase the relaxation response of the renal artery after calcium removal. Diltiazem and D600 reduced the relaxation responses of acetylcholine in the thoracic aorta and enhanced those in the renal artery. It is concluded that there is a transition in the extracellular Ca++ dependence of contraction and endothelium-derived relaxation along the length of the abdominal aorta. Changes in the dependence of contraction occurred more gradually than relaxation.(ABSTRACT TRUNCATED AT 250 WORDS)