Interactions between angiotensin II and delta opioid receptor subtype agonists upon water intake in rats

Delta opioid receptor agonists, like those of mu and kappa receptors, stimulate water intake. To assess the relative contributions of delta1 and delta2 receptors in the modulation of water intake stimulated by Angiotensin II (AII), the present study examined the respective actions of [D-Pen2, D-Pen5]-enkephalin (DPDPE: 5-20 ug, i.c.v.) and [D-Ala2, Glu4]-Deltorphin (Delt II: 5-20 ug, i.c.v.) upon water intake per se, and upon AII (0.02-20 ng, i.c.v.)-induced hyperdipsia in rats. Both DPDPE and Delt II dose-dependently stimulated spontaneous water intake. An ineffective (5 ug) dose of DPDPE differentially altered water intake when paired with AII, significantly increasing intake at the 0.02 ng dose, not changing intake at the 0.2 ng dose and significantly decreasing intake at the 2 ng dose. In contrast, pairing ineffective doses of Delt II (5 ug) and AII (0.2 ng) significantly increased water intake that persisted when either the Delt II dose (1 ug) or the AII dose (0.02 ng) was lowered. However, neither delta1 nor delta2 opioid agonists significantly altered the ED50 for AII-induced drinking. Thus, delta2 opioid agonism appeared more consistent and reliable than delta1 opioid agonism in stimulating water intake when paired with AII, and these data indicate interactions between delta1 and delta2 agonists and AII in mediating water intake.