Effects of dopamine and apomorphine on the response of rabbit isolated atria to sympathetic nerve stimulation.

In isolated rabbit atria, dopamine (10(-6) M to 3 X 10(-6) M), in the presence of cocaine and atropine, inhibits the chronotropic responses to electrical stimulation of the sympathetic nerves without influencing the responses to isoprenaline. The inhibitory effect of dopamine is antagonized by cis-flupenthixol in a concentration (2.5 X 10(-6) M) that does not antagonize the inhibitory effect of clonidine. Phentolamine, in a concentration (10(-5) M) that antagonizes clonidine, does not influence the inhibitory effect of dopamine. Apomorphine (10(-6) M) also produces an inhibition of the nerve stimulation-induced chronotropic responses that can be prevented by cis-flupenthixol. These data suggest that prejunctional dopamine receptors are present in rabbit atria.