The evaluation of melatonin as a possible anti-stress hormone

Abstract

Various stressful stimuli alter pineal melatonin production. It has recently been shown that melatonin counteracts the effects of acute stress on thymus weight via an opiatergic mechanism. A preliminary study done in our laboratory indicated that melatonin inhibited the effects of stress on the incidence of gastric ulceration. At the doses used in this preliminary study, the inhibitory effect of melatonin was not dose-dependent. This study was undertaken to evaluate a role for melatonin as a possible anti-stress hormone, and to examine if melatonin’s inhibitory action on gastric stress ulceration is exerted via an opiatergic mechanism. We have found that at night, when the endogenous level of melatonin is high in rats, exposure to stressful stimuli results in a lower incidence of gastric ulceration than during the day. We have also found that small doses of melatonin inhibited gastric stress ulceration in a dose dependent manner. Administration of opiates, opiate antagonists and melatonin prior to the induction of stress yielded the following results: naloxone exacerbated stress lesion production in a dose dependent manner, and this effect was not antagonized by melatonin. Morphine also showed a dose dependent inhibition of lesion production. At the doses used in this study, melatonin does not appear to be acting via an opiatergic mechanism. The results of these studies suggest a role for melatonin in stress.