Suppression of drinking by naloxone in the rat: a further characterization.

The effects of naloxone, an opiate antagonist, were examined on drinking induced by various dipsogenic stimuli. In rats deprived of water for 24 h, naloxone (0.1-10 mg/kg) produced a dose-related suppression of drinking immediately following water presentation but did not alter the latency to begin drinking. Naloxone also produced a dose-related suppression of water consumption induced by isoproterenol and angiotensin II, agents simulating conditions of extracellular dehydration. Naltrexone, a congener of naloxone, was more potent than naloxone in reducing isoproterenol-induced water intake. Schedule-induced polydipsia, which occurs in the absence of body fluid deficits, was not altered by either naloxone or naltrexone at doses attenuating drinking induced by the other methods. These data suggest that the suppressant effects of naloxone on water consumption are not a manifestation of an increased latency to drink or an impairment in the motor components of drinking activity. Furthermore, narcotic antagonists appear to attenuate regulatory, but not adjunctive drinking.