Selective reduction by serotonergic agents of hypertonic saline consumption in rats: evidence for possible 5-HT1C receptor mediation.

Previously, it has been shown that, in small doses, putative 5-HT1A receptor agonists selectively increase ingestion of hypertonic saline without affecting either water or isotonic saline intake. Evidence was obtained in the present series of experiments for selective reduction in hypertonic saline following the administration of a variety of serotonergic directly- and indirectly-acting agonists. Water, isotonic saline (0.9%), or hypertonic saline (1.8%) were made available to separate groups of water-deprived rats. The results indicated some selectivity with the 5-HT-uptake inhibitor and releaser d-fenfluramine and the 5-HT uptake inhibitor fluoxetine, and with the 5-HT agonists mCPP [1-3-chlorophenyl)piperazine] and MK 212 [6-chloro-2-(1-piperazinyl)pyrazine]. In each case, hypertonic intake was significantly suppressed. Distinct from these compounds were TFMPP [1-(3-(trifluoromethyl)phenyl)piperazine], RU 24969 [5-methoxy-3-(1,2,3,6-tetrahydropyridinyl)1H-indole], and quipazine. This second group either reduced fluid intake indiscriminately or reduced water and isotonic saline drinking. Selective reduction in the intake of hypertonic saline did not occur. Finally, peripheral-administration of 5-HT or the 5-HT1B agonist CGS 12066B [7-trifluoromethyl-4(4-methyl-1-piperazinyl-pyrolo) (1,2-a) 1:2 maleate], had no significant effect on fluid intake in any fluid condition. The results are discussed in terms of a possible serotonergic mechanism which may underlie inhibition of hypertonic salt drinking, and which involves mediation through a subtype of the 5-HT1 receptor.