Experiments were designed to determine the dopaminergic and
alpha adrenergic receptors involvement of cis (CS-263) and trans (CS-265) isomers of nonhydroxylated N-propyl
octahydrobenzo[f]quinoline. Both compounds caused competitive blockade of presynaptic alpha-2
adrenoceptors of guinea-pig ileum and rat vas deferens. Postsynaptic alpha-1
adrenoceptors of rabbit aorta was inhibited. In the guinea-pig ileum, these compounds were found to be as active as
yohimbine. In the rabbit aorta, they were weaker antagonists of
phenylephrine than
prazosin. CS-compounds reversed
epinephrine-induced pressor responses and inhibited reflex hypertensive responses to stimulation of the central stump of sciatic nerve in anesthetized cats. Only
CS-265 inhibited reflex
tachycardia of sciatic nerve stimulation. In isolated cat right atria,
CS-265 inhibited stimulation-induced tachycardic response through stimulation of presynaptic
dopamine receptors in contrast to
CS-263 that produced potentiation of stimulation-induced
tachycardia. The results suggest that
CS-265 is an unusual compound having
dopamine receptor stimulating activity and alpha
adrenoceptor blocking properties. These divergent properties provide direct evidence that presynaptic alpha-2
adrenoceptors and
dopamine-receptors are different entities on the sympathetic nerve terminal.