EFFECT OF INTRACEREBROVENTRICULARLY INJECTED CHOLINE ON PLASMA ACTH AND BETA-ENDORPHIN LEVELS IN CONSCIOUS RATS

In the present study, we examined the effect of intracerebroventricula rly injected choline on plasma ACTH (adrenocorticotrophin) and beta-en dorphin levels in conscious rats. The intracerebroventricularly inject ion of choline (50-150 mu g) elevated plasma ACTH levels in a dose-dep endent manner. Plasma beta-endorphin levels were also significantly in creased. Pretreatment of rats with mecamylamine (50 mu g; intracerebro ventricularly), the nicotinic receptor antagonist, completely inhibite d the ACTH and beta-endorphin response to choline (150 mu g; intracere broventricularly). An antagonist of the muscarinic receptor, atropine (10 mu g; intracerebroventricularly), failed to alter these effects. P retreatment of rats with hemicholinium-3 (20 mu g; intracerebroventric ularly), a drug which inhibits the uptake of choline into cholinergic neurons, abolished the choline-induced increases in both plasma ACTH a nd beta-endorphin levels. These results indicate that choline can incr ease plasma concentrations of ACTH and beta-endorphin through the acti vation of central nicotinic acetylcholine receptors.