RESUMO
Experimental studies on pinealectomized animals and in vitro studies using pancreatic tissue, have indicated that the pineal gland has a suppressive effect on the pancreatic B cells which secrete insulin. In this study, melatonin, was injected into rabbits and a statistically significant decrease in glucose tolerance was noted. The effect of melatonin in influencing the circadian rhythm of blood glucose was also studied in rabbits. Results showed that melatonin influences the circadian rhythm leading to a shift in the occurrence of minimum levels from 16.00 hr to 04.00 hr (next day) during fasting and from 16.00 hr to 20.00 hr during feeding. Also melatonin treatment lead to a statistically significant rise in blood glucose levels. It is probable that melatonin administration reduces glucose tolerance and influences the blood glucose circadian rhythm mainly through its effects on insulin release by pancreatic B cells.