Lithium does not synergize the peripheral action of cholinomimetics as seen in the central nervous system

Lithium is known to synergize the action of cholinomimetics in the CNS such that pilocarpine induces seizures in low concentration (1/13th of per se d ose) in rats. The present study was undertaken to see if lithium priming al so enhances the peripheral effects of acetylcholine and pilocarpine i,e. ch ange in blood pressure in rats and contractions of the isolated guinea pig ileum. In anaesthetized rats the blood pressure was recorded from cannulate d carotid artery connected through the pressure transducer to Coulbourn pol ygraph, The blood pressure response of pilocarpine was not different either in magnitude or in duration when administered 1,2 and 4 h after lithium ch loride (3meq/kg) pretreatment as compared to the control, Similarly acetylc holine effect remained unchanged after lithium chloride priming, In the iso lated guinea pig ileum experiments, ileum was incubated for 1 h in differen t concentrations of lithium chloride and effect on acetylcholine induced co ntractions were observed. Lithium in concentration of 2.8 x 10(-3)M had no effect on acetylcholine induced contractions while incubation with higher c oncentrations of 1.4 x 10(-2) M and 2.8 X 10(-2) M significant inhibition o f acetylcholine contractions were observed. At this concentration, histamin e induced contractions were also inhibited. The results indicate that lithi um does not synergize the action of cholinomimetics in the periphery as tha t seen in the CNS,The inhibition of acetylcholine and histamine induced con tractions in guinea pig ileum at high concentration of lithium seems to be non-specific effect. (C) 2001 Elsevier Science Inc. All rights reserved.