Prejunctional adrenoceptor activity of N-0437: a relatively selective DA2 dopamine receptor agonist

Prejunctional adrenoceptor activity of N-0437, 2[N-n-propyl-N-2-(thienylethyl-amino)-5-hydroxytetralin], was investigated by means of the cat nictitating membrane (CNM) preparation. Intra-arterial (i.a.) administration of N-0437 produced a dose-related inhibition (ED50 = 14 micrograms) of the CNM contractions elicited by electrical stimulation of pre- and postganglionic sympathetic nerves of the superior cervical ganglion. Pretreatment with domperidone i.a., a relatively selective DA2 receptor antagonist, markedly attenuated the CNM response to racemic N-0437 (ED50 = 6.7 x 10(2) micrograms). However, pretreatment with rauwolscine i.a., a relatively selective alpha 2-receptor antagonist, did not alter the CNM responses to racemic N-0437. Evaluation of the (R)-(+) and (S)-(-) enantiomers showed that only the (S)-(-) enantiomer was active in suppressing the contractions in the CNM preparation. These results demonstrate that N-0437 is a potent agonist for prejunctional DA2 dopamine receptors on peripheral sympathetic nerves in the CNM and that these peripheral DA2 receptors appear to be enantioselective.