The effects of the opiate antagonist, naloxone, alone and in combination with morphine, were examined on drinking induced by water deprivation in homo- and heterozygous Brattleboro rats manifesting an inherited diabetes insipidus. Both naloxone and a structurally-related congener, naltrexone (0.01-10 mg/kg), attenuated water consumption in adose-related fashion of 1 hr water-deprived homozygotes, which exhibit a complete absence of vasopressin. Drinking was also reduced by the two drugs in 24 hr water-deprived heterozygotes, which have detectable levels of vasopressin. Morphine pretreatment enhanced the antidipsogenic effects of naloxone in a dose- and time-dependent manner. The administration of 10 mg/kg of morphine 3 hr before testing, which itself did not affect drinking, maximally potentiated the suppressant effects of naloxone on drinking in homozygotes. This potentiating effect of morphine persisted for at least 48 hr. These results indicate that vasopressin is not essential for the antidipsogenic effects of the narcotic antagonists. The polydipsic Brattleboro rat may provide a convenient animal model for studies of the effects of opiate agonists and antagonists on drinking behavior.
Bibliographical noteFunding Information:
In light of these many characteristics, one objective of this investigation was to evaluate the effects of naloxone and 1This investigation was supported in part by USPHS grants 5T01 GM00179, DA00541 and by Research Scientist Development Award KO2 DA00008 to S. G. H. 2Present address: The University of Chicago, Department of Pharmacological and Physiological Sciences, 947 East 58th Street, Chicago, IL 60637. 3To whom reprint requests should be addressed.
- Brattleboro rat
- Diabetes insipidus
- Water deprivation
- Water intake