The effect of MAO-A inhibition and cold-immobilization stress on N- acetylserotonin and melatonin in SHR and WKY rats

Abstract

Selective monoamine oxidase (MAO) A inhibitors and cold-immobilization stress (which increases the production of the endogenous MAO-A inhibitor, tribulin) stimulate rat pineal melatonin biosynthesis in Sprague-Dawley and Fisher 344N rats. Considering the hyperactive sympathetic response of the hypertensive rats, it was interesting to compare the effect of clorgyline and cold-immobilization stress on pineal melatonin and related indoles levels in SHR and WKY rats (HPLC-fluorimetric method). Clorgyline (0.5 mg/kg and 1.5 mg/kg, sc) induced a higher elevation of pineal melatonin and N- acetylserotonin (NAS) in SHR than in WKY rats. Cold immobilization stress resulted in lower serotonin, and higher NAS levels in SHR than in WKY rats with similar elevations in melatonin levels. Our results suggest increased serotonin conversion into NAS and decreased NAS conversion into melatonin with decreased production of tribulin in SHR in comparison with WKY rats.