The mechanism of contraction of rat aorta to various agonists.

To elucidate the mechanism of contraction of the smooth muscle of the rat's aorta, its response to norepinephrine (NE), 5-hydroxytrypatamine (5-HT) and potassium chloride (KCI) was determined before and after pretreatment with reserpine and beta-diethylamionethyl 2-2-diphenylpropyl acetate (SKF 525-A). Unlike the rabbit's aorta, contraction of the rat's aorta induced by NE was inhibited by SKF 525-A. After the induction of maximal contraction, SKF 525-A induced a graded rapid relaxation after KCl, less so after 5-HT, and least after NE. Pretreatment with reserpine failed to induce supersensitivity to NE. After incubation in a Ca++-free or Na+ and Ca++-free Krebs solution, the rat's aorta failed to contract even on the addition of Ca++ or NE.