Influence of pinealectomy and pineal stalk deflection on circadian gastrointestinal tract melatonin rhythms in zebra finches (Taeniopygia guttata)

The authors examined levels of melatonin in the plasma and various tissues in intact, pinealectomized, and pineal stalk-deflected zebra finches kept u nder 12:12 LD to determine if the melatonin found in the gastrointestinal t ract is secreted in a circadian manner. In intact and pineal stalk-deflecte d birds, there is a clear day-night rhythm in melatonin content of the plas ma, pineal gland, eyes, proventriculus, crop, duodenum,jejunum/ileum, colon , heart, and liver. In contrast, pinealectomy abolished the day-night rhyth m. These results indicate that most of the melatonin present in the gastroi ntestinal tract of zebra finches is of pineal origin. However, some melaton in remained. This suggests that this melatonin may be locally synthesized a nd has paracrine and/or autocrine functions. Nonetheless, the results do no t lend support to the contention that this putative melatonin secretion by the gastrointestinal tract is circadian.