The effects of exogenous melatonin upon the gut of larval Xenopus laevis.

Abstract 1. 1. Xenopus laevis embryos were reared in melatonin solutions of 2 μg/ml and 20 μg/ml for periods of 2 hr and 20 hr during stage 48, and between stages 38–48. All larvae were observed for their behavior and some were sectioned for microscopic observation. The enzymes 5-hydroxytryptophan decarboxylase (5-HTPD), monoamine oxidase (MAO) and hydroxyindole- O -methyltransferase (HIOMT) were assayed in whole embryo, brain, eyes and gut. 2. 2. Defecation and gulping occurred in all but control and 2 hr exposed larvae and larvae showing these responses were found to have empty intestines when examined in section under the microscope. 3. 3. Only MAO changed in activity and only in the gut and whole embryo of larvae exposed from stage 38–48. In these larvae the MAO was elevated and dose related.