Effect of opioid agonists selective for three subclasses of opioid receptors and one sigma receptor agonist on dopamine stimulated adenylate cyclase in rat caudate nucleus.

The adenylate cyclase in rat caudate nucleus homogenate could be stimulated by dopamine and less potently by the dopamine D1 receptor specific agonist SKF38393. Agonists selective for mu[D-Ala2, MePhe4Gly(ol)5]enkephalin (DAGO) and delta opioid receptors [D-Pen2, D-Pen5]enkephalin (dPen-dPen), inhibited the dopamine but not the dopamine D1 stimulated adenylate cyclase. The kappa opioid agonist, U69593, had no effect, probably due to low kappa receptor contents in rat caudate nucleus. 10(-4) M of the sigma receptor specific agonist, 1,3-di-o-tolylguanidine (DTG), potentiated the dopamine as well as the dopamine D1 stimulated adenylate cyclase while lower concentrations of DTG had no effect.