DAYTIME AND NIGHTTIME CONTENT OF MONOAMINES AND THEIR METABOLITES IN THE PINEAL-GLAND OF RAT AND HAMSTER

Day- and nighttime content of catecholamines, serotonin and their meta bolites were measured in the pineal gland of Sprague-Dawley rats and D jungarian hamsters. In addition, monoamine turnover rates were determi ned in the hamster pineal gland following administration of alpha-meth yl-p-tyrosine. Animals were decapitated in the middle of the light or dark period, respectively, and pineal tissue was analysed by high perf ormance liquid chromatography with electrochemical detection. Pineals of both species exhibited day/night-differences in serotonin, 5-hydrox yindole-3-acetic acid and dopamine content. The hamster pineal gland f urther showed day/night differences in its content of epinephrine and 3-methoxy-4-hydroxyphenylethyleneglycol. The dopamine turnover rate wa s augmented at night, while norepinephrine turnover was constant. Immu nohistochemical incubations of pineal paraffine sections showed fibers and terminals stained by antisera to tyrosine-hydroxylase (TH) and do pamine-beta-hydroxylase, and a few perikarya-like structures exhibitin g TH immunoreactivity. The results support the view that dopamine, rat her than only functioning as a norepinephrine precursor, is actively i nvolved in the control of melatonin synthesis.