Effects of a Kappa receptor agonist, ethylketocyclazocine, on water consumption in water-deprived and nondeprived rats in diurnal and nocturnal tests

Abstract

In 24 hr water-deprived male hooded rats, ethylketocyclazocine (EKC), 0.1–3.0 mg/kg, dose-dependently suppressed water intake. Within the first 30 min access to water, drinking was virtually abolished by 1.0 and 3.0 mg/kg EKC. Significant reductions in the level of water intake were found after 0.1 mg/kg EKC. After 2 hr access to water, the suppressant effect was attenuated indicating some recovery. The antidipsogenic action of EKC in water-deprived rats was comparable in its effect for both daytime and noctural testing. Circadian variation may not be an important modulator of the antidipsogegic action. Naloxone, an opiate receptor antagonist, when administered in a dose of 0.3 mg/kg also significantly reduced drinking in deprived animals. EKC (0.3 mg/kg) and naloxone (0.3 mg/kg) when administered together displayed mutual antagonism. Drinking was at control levels. In nondeprived male rats, EKC exerted some dipsogenic action, most noticeably during diurnal testing. Within 30 min access to water, 0.1 mg/kg EKC significantly elevated the level of water intake. This effect did not occur during nocturnal testing, when the only immediate effect of EKC was a suppression of drinking at 1.0 and 3.0 mg/kg dose levels. After 2 hr access to water, there was a significant peak effect to enhance drinking at the 0.3 mg/kg dose level during the daytime. Effects of EKC during the night were less pronounced. The dipsogenic action of EKC (0.3 and 1.0 mg/kg) in satiated animals during the day was abolished by naloxone and Mr-2266BS, also an opiate receptor antagonist. The results indicate that the effects of EKC on drinking are profoundly affected by the deprivation status of the animal. Further, the phase of the circadian cycle may be an important modulator of the expression of the dipsogenic action of EKC in nondeprived rats.