Psychosocial stress affects pineal function in the tree shrew (Tupaia belangeri).

Using a recently developed commercially available radioimmunoassay the concentration of the principal melatonin metabolite 6-sulfatoxymelatonin (aMT6s) in the morning urine of male tree shrews was determined. Chronic social confrontation elicited a drastic increase of aMT6s excretion in subordinate tree shrews, whereas there was a tendency to reduced excretion of the melatonin metabolite in dominant animals. These results substantiate the function of the pineal gland in transforming stimuli from the social environment to endocrine information and, therefore, are indicative for the relevant role the gland may play in the physiological reactions to chronic psychosocial stress.