Naloxone reduces fluid intake in rats with open gastric fistulas.

Water-deprived rats, fixed with chronically indwelling gastric fistulas, drank with the fistulas open (sham drinking) for 20 min. The subjects were given three doses of naloxone (0.0, 1.0, and 10 mg/kg, SC) 15 min before the opportunity to sham drink. The mean water intakes on days of 0.0, 1.0 and 10 mg/kg of naloxone were 43.3, 36.3 and 23.1 g, respectively. Naloxone clearly reduced fluid intake in rats engaged in sham drinking. This finding, that naloxone reduces fluid intake when post-ingestional absorption is prevented, lends support to the idea that naloxone modified central neural regulatory processes. The results of these experiments do not support the hypothesis that the endorphins are involved exclusively with drive-reduction.