Pentazocine-induced catecholamine efflux from the dog perfused adrenals

This study has been undertaken to determine whether pentazocine induces catecholamine efflux from the adrenal medulla as a mechanism for its sympathomimetic effect. Dog isolated adrenals were perfused retrogradely with modified Locke's solution. The efflux of catecholamines from dog perfused adrenals was increased from the resting output of 0.18 +/- 0.04 micrograms min-1 (mean +/- s.e.), to 0.47 +/- 0.13 micrograms min-1 by the administration of pentazocine (50 microM). The pentazocine-induced catecholamine efflux was dose-dependent in the 50-400 microM dose range. This effect of pentazocine was not inhibited by either a combination of atropine and (+)-tubocurarine, or verapamil, in contrast to acetylcholine-induced catecholamine release. There was no significant difference in potency among stereoisomers, i.e. (+)-, (-)- and (+/-)-pentazocine, in inducing catecholamine efflux. Naloxone did not influence the effects of either (+)- or (-)-pentazocine. The interaction of pentazocine with acetylcholine-induced catecholamine release was also examined. Both (+)- and (-)-pentazocine inhibited acetylcholine-induced catecholamine release dose-dependently, and these inhibitory effects were not reversed by naloxone. Acetylcholine-induced catecholamine release was accompanied by increased dopamine-beta-hydroxylase release, whereas pentazocine-induced catecholamine efflux was not. These results suggest that pentazocine directly acts on the adrenal medulla to induce catecholamine efflux via a non-exocytotic mechanism, and that opioid receptors do not play a role in this action.