MELATONIN DEACETYLASE ACTIVITY IN THE PINEAL-GLAND AND BRAIN OF THE LIZARDS ANOLIS-CAROLINENSIS AND SCELOPORUS-JARROVI

Melatonin modulates a variety of rhythmic processes in vertebrates, an d is synthesized in both the retina and pineal gland. We have shown pr eviously that retinal melatonin is deacetylated generating 5-methoxytr yptamine, which is then deaminated by monoamine oxidase, producing 5-m ethoxyindoleacetic acid and 5-methoxytryptophol. This process occurs w ithin the eyes of a variety of vertebrates including the iguanid lizar d Anolis carolinensis. To determine whether melatonin deacetylase acti vity also occurs in the pineal organ or in other parts of the lizard b rain, pineals and brains of Anolis carolinensis and Sceloporus jarrovi were cultured in the presence of [H-3-methoxy]-melatonin. High-perfor mance liquid chromatography of the resulting culture media and tissues revealed the generation of radiolabeled 5-methoxytryptamine and 5-met hoxyindoleacetic acid. These two methoxyindoles were the only radiolab eled metabolites detectable, and together accounted for all melatonin lost. Both the loss of melatonin and the production of melatonin metab olites were inhibited by inclusion of 100 mu M eserine, an inhibitor o f the melatonin deacetylase. Pargyline, a monoamine oxidase inhibitor, reduced the production of 5-methoxyindoleacetic acid and increased th e production of 5-methoxytryptamine relative to control incubations. S imilar effects of eserine and pargyline were seen in eyecup, brain and pineal gland, but the specific activity of melatonin deacetylation in cultured pineal glands was much greater than in either brains or eyec ups. These results indicate that pineal glands of both Anolis caroline nsis and Sceloporus jarrovi can rapidly catabolize melatonin by a mech anism very similar to that in the eye, that the melatonin deacetylatio n pathway exists elsewhere in the iguanid brain, and also extend our p revious observations of ocular melatonin deacetylation to an additiona l species.