Effects of 2% sodium chloride imbibition on various opiate related hyperphagic conditions.

Dynorphin is one of the most potent appetite stimulants among the endogenous opioids. In this study, we describe the anorexic effects of 5 days of forced 2% NaCl drinking in rats, a regimen which depletes vasopressin as well as dynorphin in the neurohypophysis. Feeding induced by direct activation of kappa-opioid receptors with ketocyclazocine was unaffected by the NaCl regimen. However, 2% NaCl imbibition reduced 2-deoxy-D-glucose (2-DG) induced feeding by 65% and spontaneous nocturnal feeding by 38%. Feeding subsequent to 24 hour food deprivation was not decreased. Naloxone-resistant hyperphagia induced by insulin and spontaneous daytime feeding were also not reduced. The combination of naloxone (3.0 mg/kg) and the NaCl regimen produced an additional 50% reduction in 2-DG induced feeding and an extra 40% decrease in nocturnal feeding. Naloxone, given with 2% NaCl to food deprived animals, retained its appetite suppressing activity, indicating that the NaCl regimen did not deplete the endogenous opioid which mediates food deprivation hyperphagia. These results demonstrate that 2% NaCl imbibition suppresses certain opioid mediated hyperphagias. However, the failure of 2% NaCl to affect all of the naloxone-sensitive types of feeding and the independence of naloxone-sensitive and NaCl-sensitive components suggests that NaCl drinking does not deplete dynorphin in the brain areas which mediate opiate-sensitive hyperphagias.