Central opioid receptor subtype mediation of isoproterenol-induced drinking in rats

Opioid receptor subtype antagonists differentially alter different types of water intake such that mu2 receptors modulate deprivation-induced water intake, kappa receptors modulate hypertonic saline-induced water intake, and mu2, delta1 and kappa receptors modulate water intake following Angiotensin II (ANG II). Water intake stimulated by peripheral administration of the beta-adrenergic agonist, isoproterenol is attenuated by naloxone and is thought to be mediated by release of renin and production of ANG II. The present study examined whether systemic and i.c.v. administration of general opioid antagonists and central administration of specific opioid receptor subtype antagonists would selectively alter water intake following isoproterenol in rats. Both systemic (1 mg/kg s.c.) and central (1-20 micrograms) naltrexone reduced water intake induced by isoproterenol (25 micrograms/kg s.c.) over a 2-h period. The mu receptor antagonist, beta-funaltrexamine (B-FNA: 1-20 micrograms), but not the mu1 antagonist, naloxonazine (50 micrograms), dose-dependently reduced isoproterenol drinking. Both the kappa antagonist, nor-binaltorphamine (Nor-BNI, 5-20 micrograms) and the delta1 antagonist, [D-Ala2, Leu5, Cys6]-enkephalin (DALCE, 1-40 micrograms) also dose-dependently reduced isoproterenol drinking. These data implicate mu2, kappa and delta1 sites in the opioid modulation of isoproterenol drinking.