Metabolism of biogenic amines in the common leopard frog, Rana pipiens
Clay, George A.
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Serotonin (5-hydroxytryptamine), one of the biologically active amines, has been found in rather large quantities in the dorsal skin of Rana pipiens. Quantitative determination of the endogenous levels of the amine in the whole dorsal skin homogenate extracts were made on a Farrand spectroflourometer, and ranges of 120-200 micrograms per gram of fresh tissue were established. Comparison of whole skin homogenates and homogenates of just the dorsal cutaneous ridges, or dermal plicae, indicated that the amine is localized in these ridges. Acid treatment of the denser more fibrous portions of the homogenate prior to extraction more then noublcc the yields of serotonin. This result showed that the amine is found primarily in the deeper portions of the skin, very likely in the poison glands which are concentrated in the dermal plicae. Skin homogenates were also studied to determine if serotonin is actually synthesized in the skin. A precursor of the amine, 5-hydroxytryptophan, decarboxylates in tne presence of 5-hydroxytryrtophan decarooxylase to produce the amine. 5-hydroxytryrtophan was incubated with the homogenate, under nitrogen, for two hours to determine enzymic activity. Under the conditions of the experiment, no enzymic activity could be shown, indicating that serotonin is not produced in the skin of the frog in detectable amounts. The fact that serotonin levels are so high, and the lack of enzymic activity indicates that once synthesized serotonin is stored in an inactive form or is synthesized elsewhere and transnorted to the skin.
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