MELATONIN CONCENTRATIONS IN SERUM AND TISSUES OF PORCINE GASTROINTESTINAL-TRACT AND THEIR RELATIONSHIP TO THE INTAKE AND PASSAGE OF FOOD

Melatonin concentrations were determined in serum and 10 segments of t he gastrointestinal tract (GIT) of 48 pigs (100 kg weight). The animal s were fasted for 30 hr and then sacrificed 0, 1, 2, 5, 10, and 20 hr after refeeding. Peak amount of gastric digesta (2,428 g) and ileum di gesta (850 g) were observed 1 hr and 5 hr, after refeeding, respective ly. Conversely, colon content reached a minimal weight (726 g) at 2 hr after refeeding. Serum levels of melatonin increased from 3.4 pg/ml t o 15.5 pg/ml (peak 5 hr after refeeding). Melatonin levels in GIT tiss ues before refeeding varied from 23.8 pg/g (stomach-fundus) to 62.1 pg /g (rectum). Increasingly higher levels of melatonin were detected in the distal segments of the GIT. Higher melatonin levels after refeedin g were observed in most GIT tissues except the rectum. In most tissues , peak melatonin values were detected 5 hr after refeeding. A signific ant change in weight of digesta across time (P<0.05) was detected in t he stomach, ileum, and cecum. Similar changes in melatonin levels acro ss time were found in most tissues except the esophagus, stomach (card ia and pylorus), and rectum. Adjacent GIT tissues exhibited similar (P <0.05) melatonin levels. The GIT melatonin levels correlated best with the variation of digesta weight in the ileum. In addition, the increa se of serum melatonin levels correlated best with the increase of GIT melatonin levels in the distal part of the GIT. Our results suggest th at melatonin produced in the ileum, cecum, and colon may contribute si gnificantly to the short-term increase of serum melatonin levels obser ved after refeeding.