Pinealectomy reduces melatonin levels in the serum but not in the gastrointestinal tract of rats.

Abstract

Melatonin levels were determined in serum and gastrointestinal tract (GIT) tissues of control (C), sham-pinelaectomized (SPx) and pinealectomized (Px) rats sacrificed in mid scotophase. Serum melatonin concentrations of Px rats exhibited the significantly lowest values (8.6 pg/ml), followed by SPx (20.1 pg/ml) and C (37.5 pg/ml) rats. In C, the ileum (542 pg/ml) and jejunum (531 pg/ml) exhibited the highest average GIT concentrations, followed by the colon (362 pg/ml), stomach (359 pg/ml) and cecum (164 pg/ml). However, only jejunum and ileum samples had significantly higher melatonin levels than cecum samples. There were no major differences between GIT melatonin levels in Px and C rats (range: 169-247 pg/ml). Statistically, pinealectomy did not influence melatonin levels in the GIT of rats. The findings support the hypothesis that melatonin concentrations in the tissues of the GIT are independent of pineal production.