Effects of pentazocine and other opioids on the potassium-evoked release of [3H]noradrenaline from guinea pig cortical slices.

Noradrenaline release and its modulation via presynaptic opioid receptors were examined in guinea pig cortical slices. Slices preloaded with [3H]noradrenaline were superfused in the presence of desipramine (1 microM) and were stimulated by 16 mM K+. 1-Pentazocine inhibited the K+-evoked release of [3H]noradrenaline in a dose-dependent manner (3 x 10(-7)-10(-5) M), while d-pentazocine did not inhibit. This inhibitory effect of 1-pentazocine was antagonized by Mr 2266 (10(-6) M) but not by naloxone (10(-6) M). Among other opioids, dynorphin A-(1-13) and ethylketocyclazocine (kappa agonists) decreased the K+-evoked release of [3H]noradrenaline. Tyr-D-Ala-Gly-NMe-Phe-Gly-ol (DAGO, mu agonist) also inhibited [3H]noradrenaline release but was less potent than the kappa agonists. [D-Pen2,D-Pen5]enkephalin (DPDPE, delta agonist) and phencyclidine (sigma agonist) had no effects on the stimulated release of [3H]noradrenaline. Thus, it was shown that kappa receptors are the major subtype of opioid receptor involved in modulation of noradrenaline release in guinea pig cortex, and that 1-pentazocine inhibits the K+-evoked release of noradrenaline through activation of these receptors.