THE EFFECT OF MAO-A INHIBITION AND COLD-IMMOBILIZATION STRESS ON N-ACETYLSEROTONIN AND MELATONIN IN SHR AND WKY RATS

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