Melatonin concentrations in the gastrointestinal tissues of bovine fetuses

Day-time tissue levels of melatonin were determined in the rumen, reticulum , omasum, abomasum, jejunum, ileum and colon of cow fetuses of both sexes. The total body length of the fetuses was 14 to 53 cm which corresponds to t he first half of pregnancy; the approximate gestation age was 85-150 days. The data were divided into five equal groups according to fetal length. Ave rage total melatonin concentrations (34.0 to 49.8 pg/g) did not differ grea tly between the developmental stages but nevertheless a positive correlatio n (r(s) = 0.35 P < 0.001) was established between melatonin levels and feta l length. Significantly higher concentrations of melatonin (P < 0.001) were found in the male Off. Finally, colon tissues exhibited higher concentrati ons of melatonin than any other GIT segment. As the average day-time values in fetal GIT (30.2 pg/g) were substantially lower than GIT levels found in adult cows (50-270 pg/g), it could be hypothesized that melatonin levels i n the fetal GIT are derived from the maternal circulation. However, higher melatonin levels in older fetuses, the detection of higher levels in males and substantially higher levels of melatonin in the fetal GIT as compared t o blood levels in adult cows, may indicate either an independent fetal prod uction of GIT melatonin or the capacity of fetal GIT to concentrate melaton in derived from the maternal circulation. In view of these discrepancies it can be only concluded that the origin of melatonin in the bovine fetal GIT is at present unknown. The significantly higher concentration of melatonin found in the colon(P<0.05) may be related to the presence of meconium dete cted in most fetuses in that GIT segment. This finding may indicate that me latonin has a physiological function in the fetal digestive system.