Structural changes in rat colon under obesity conditions and its correction by morning and evening injection of melatonin

Abstract

The effect of morning and evening administrations of melatonin on structural and functional changes in the large intestine of rats with obesity under conditions of the spring-autumn photoperiod (12L:12D) was studied in this work. The obesity was caused with a high-calorie diet for 6 weeks. After that, the morning or evening melatonin administrations were given to normal and obese animals at a dose of 30 mg/kg for 7 weeks. After 13 weeks, two specimens of the colon 1 cm each were taken at a distance of 3 cm from the anus; fixed in 10% formalin and in Carnua solution; paraffin sections of the large intestine were made; stained them with hematoxylin-eosin, alcian blue-carmine, or toluidine blue. Microscopic and morphometric analysis of these sections was performed. It has been shown, that obesity cause hyperactivation of the colonic mucosa, reduction of colonocytes, hypertrophy of goblet cells and overaccumulation of granules in mast cells. Morning administration of melatonin to obese animals normalizes the colonic mucosa, decreases the reduction of colonocytes, but causes the hypotrophy of goblet cells. Evening administration of melatonin significantly decreases the reduction of colonocytes, but does not eliminate other changes caused by obesity. The administration of melatonin (both morning and evening) to animals without obesity causes an activation of the mucosa, hypertrophy of goblet cells, reduction of colonocytes, and does not change the state of mast cells. Consequently, it cannot make a clear conclusion about the possibility of correction of all structural-functional changes in the large intestine during obesity by melatonin. Although, the morning administration of melatonin had some normalizing effects on the colon and it was more effective than evening administration.