OPIOIDERGIC MANIPULATIONS AFFECT INTAKE OF 3-PERCENT NACL IN SODIUM-DEFICIENT RATS

On six weekly occasions, a 3% NaCl solution was presented along with w ater to rats for 2 h 1 day after being treated with furosemide, a diur etic/natriuretic drug that causes a strong hunger for 3% NaCl. On some of the days, the sodium-hungry rats were injected with morphine in do ses ranging from 0.3 to 10.0 mg/kg. Morphine produced biphasic effects on intake of 3% NaCl, with doses of 0.3-3.0 mg/kg increasing intakes dose dependently and 10.0 mg/kg decreasing intakes. The 3.0-mg/kg dose nearly doubled rats' mean intake of 3% NaCl. In contrast, naltrexone, an opioid receptor antagonist, reduced intake of 3% NaCl about 25-40% across doses ranging from 0.1 to 10.0 mg/kg. At some doses of morphin e and naltrexone, NaCl ingestion was affected without significant infl uence of water intake. Therefore, it can be inferred that endogenous o pioidergic systems participate in the control of NaCl drinking by sodi um-deficient rats. The range of demonstrations of opioid involvement i n the control of ingestion can now be extended to the hunger for hyper tonic NaCl induced by sodium depletion.