Influence of Melatonin and iV-Acetylserotonin on the Cyclic AMP Concentration in the Rat Thyroid Lobes Incubated In Vitro

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Abstract
Effects of melatonin and N-acetylserotonin on the cyclic AMP (cAMP) concentration in the organ-cultured rat thyroid gland were investigated. Exposure of the thyroid explants to melatonin (10-8 M) resulted in a decrease of cAMP levels. Melatonin at higher concentrations (10-7 M and/or 10-6 M) failed to influence the thyroid cAMP level. N-acetylserotonin (10-6 M), like melatonin in the lowest concentration employed, reduced cAMP concentrations in the thyroid explants when compared with controls. Unexpectedly, melatonin (at a concentration of 10-7 M) added to the incubation medium with TSH (60 mU/ml), decreased the cAMP concentration in the thyroid compared with with the group exposed to melatonin (10-7 M) alone.