The effect of cold immobilisation stress on brain MAO-A inhibitory activity and pineal N-acetylserotonin and melatonin in spontaneously hypertensive and normotensive rats

The possible role of endogenous monoamine oxidase (MAO) inhibitory activity (tribulin) in the regulation of pineal levels of N-acetylserotonin and melatonin was investigated in normotensive (WKY) and in spontaneously hypertensive (SHR) rats, with and without 2 h of cold-immobilisation stress (CIS). The MAO-B inhibitory activity was similar in all groups. The basal level of the MAO-A inhibitory activity was significantly higher in SHR than WKY rats. CIS increased the MAO-A inhibitory activity and serotonin in WKY but not SHR rats. The initial content of N-acetylserotonin, melatonin, and serotonin did not differ in the two groups, and there were no differences in stress-induced melatonin augmentation. However, after the stress was induced, the level of N-acetylserotonin was higher in SHR rats. Endogenous MAO-A inhibitory activity may have a role in stress induced production of N-acetylserotonin and meiatonin in normotensive rats, but not in hypertensive animals.