Decreased hypothalamic epinephrine concentration by quipazine and other serotonin agonists in rats

Abstract

Epinephrine concentrations in rat hypothalamus were decreased after the injection of quipazine, a direct-acting serotonin (5-HT) agonist. The decrease was statistically significant and dosedependent from 0.1 to 10mg/kg, s.c., was apparent within 1hr, and persisted for 8 hr but not 24 hr. There was no decrease in epinephrine concentrations in rat medulla oblongata, a region containing epinephrine cell bodies. Epinephrine concentrations in rat hypothalamus were also decreased by 1-( m-trifluoromethylphenyl)-piperazine (TFMPP) and by 8-hydroxy-2-(di- n-propylamino)-tetralin (8-OH-DPAT), other direct-acting 5-HT agonists, and by d-fenfluramine, a 5-HT-releasing drug. The decrease evoked by quipazine was prevented by pretreatment with metergoline, ketanserin or LY53857 (6-methyl-1-[methylethyl]-ergoline-8-carboxylic acid 2-hydroxy-1-methyl-propyl ester), centrally acting 5-HT antagonists. The lowering of rat hypothalamic epinephrine concentrations by 8-OH-DPAT was prevented by pretreatment with pindolol, a centrally acting 5-HT 1A receptor antagonist. These data suggest that serotonergic drugs affect epinephrine concentrations in rat hypothalamus.