The subcutaneous (s.c.) administration of isoprenaline to rats produced a dose-dependent increase in water drinking which was effectively antagonized by propranolol. This dipsogenic response was significantly inhibited after the intraperitoneal (i.p.) administration of imipramine (15 mg/kg/day), together with either of the following calcium entry blockers, for four days: diltiazem (15 mg/kg/day), verapamil (10 mg/kg/day), nifedipine (10 mg/kg/day) or nicardipine (15 mg/kg/day). Simultaneous injection of the inhibitor of the synthesis of serotonin, p-chlorophenylalanine (200 mg/kg/day, i.p.), did not affect this attenuation of the isoprenaline-induced response. Similarly, the selective 5-HT2receptor agonist, 1-(2,5-dimethoxy-4-methylphenyl)-2-aminopropane (DOM) or the 5-HT2receptor antagonist, ketanserin, had no significant effect on the attenuation of isoprenaline-induced drinking behaviour. The inhibition of isoprenaline-induced drinking, was, however, effectively attenuated after treatment of the animals with 6-hydroxydopamine (2.5 μg) or clonidine (30 μg), injected intracerebroventricularly (i.c.v.). These results indicate that the calcium entry blockers accelerate the desensitization of central β-adrenoceptors possibly by an action on central adrenoceptors of the rat. © 1991.
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