Abstract

Guanethidine in a restricted concentration range produced a small, slowly developing and sustained contraction in some but not all of the untreated aortic strips to which it was added. In strips contracted with norepinephrine, guanethidine invariably elicited a large, rapidly developing and sustained contraction in the same concentration range. Cocaine did not contract untreated strips. However, in the presence of norepinephrine, cocaine elicited sustained contractions. Guanethidine and cocaine in concentrations which contracted norepinephrine treated strips relaxed aortic strips which were contracted with tyramine. Iproniazid did not inhibit the contractions which cocaine or guanethidine produced in norepinephrine treated strips. Catechol did not inhibit the contractions produced by cocaine in norepinephrine treated strips but apparently interfered with the action of guanethidine. Cocaine, guanethidine and methylphenidate inhibited the capacity of each other to shorten strips exposed to norepinephrine. The catecholamine content of aortic strips was not significantly changed by exposure to norepinephrine. Administration of guanethidine to untreated strips or strips treated with norepinephrine did not significantly alter their catecholamine content. The significance of these findings is discussed.