Influence of acetaldehyde on the vasopressor effect of serotonin in pithed rats

In pithed rats, the intravenous (i.v.) administration of serotonin (3, 10, 30, 100, 300 and 1000 micrograms/kg) produced a dose-dependent increase in blood pressure. The pressor response to serotonin was reduced by acute acetaldehyde administration in a dose of 30 mg/kg i.v. and by 5-HT2 antagonist ketanserin (0.03 mg/kg i.v.). However, the lowest doses of acetaldehyde (10 and 20 mg/kg) were ineffective. In in vitro studies we also demonstrated that acetaldehyde (0.43 mM/l) and ketanserin (0.1 microM/l) inhibited the serotonin-induced vasoconstriction of isolated rat tail artery. In both experimental models the combination of acetaldehyde with ketanserin decreased the action of serotonin to the same extent as did ketanserin alone. In pithed rats pretreated with a high dose of ketanserin (3 mg/kg i.v.) serotonin produced hypotension by stimulation of 5-HT1 receptors. This effect was not enhanced by acetaldehyde (30 mg/kg) injection. Our data suggested that the action of acetaldehyde on the effects of serotonin in pithed rats was non-specific and independent of its interaction with serotonergic 5-HT1 and 5-HT2 receptors in blood vessels.