Natriorexigenic effect of DAMGO is decreased by blocking AT1 receptors in the central nucleus of the amygdala.

ABSTRACT

µ-Opioid receptor (µ-OR) activation with agonist [D-Ala², N-Me-Phe4, Gly5-ol]-enkephalin (DAMGO) in the central nucleus of the amygdala (CeA) induces sodium (0.3M NaCl) intake in rats. The purpose of this study was to examine the effects of pre-injections of losartan (AT1 angiotensin receptor antagonist) into the CeA on 0.3 M NaCl and water intake induced by DAMGO injected bilaterally in the same area in rats submitted to water deprivation-partial rehydration (WD-PR) and in rats treated with the diuretic furosemide (FURO) combined with a low dose of the angiotensin-converting enzyme inhibitor captopril (CAP) injected subcutaneously (FURO/CAP). Male Sprague-Dawley rats with stainless steel cannulas implanted bilaterally into the CeA were used. In WD-PR rats, bilateral injections of DAMGO (2 nmol in 0.5 µL) into the CeA induced 0.3 M NaCl and water intake, and pre-treatment with losartan (108 nmol in 0.5 µL) injected into the CeA reduced 0.3 M NaCl and water intake induced by DAMGO. In FURO/CAP rats, pre-treatment with losartan (108 nmol in 0.5 µL) injected into the CeA attenuated the increase in 0.3M NaCl and water intake induced by DAMGO (2 nmol in 0.5 µL) injected into the same site. The results suggest that the natriorexigenic effect of DAMGO injected into the CeA is facilitated by endogenous angiotensin II acting on AT1 receptors in the CeA, which drives rats to ingest large amounts of hypertonic NaCl.