Influence of Ramadan-type fasting on enzymes of carbohydrate metabolism and brush border membrane in small intestine and liver of rat used as a model

During Ramadan, Muslims the world over abstain from food and water from dawn to sunset for a month. We hypothesised that this unique model of prolonged intermittent fasting would result in specific intestinal and liver metabolic adaptations and hence alter metabolic activities. The effect of Ramadan-type fasting was studied on enzymes of carbohydrate metabolism and the brush border membrane of intestine and liver from rat used as a model. Rats were fasted (12 h) and then refed (12 h) daily for 30d, as practised by Muslims during Ramadan. Ramadan-type fasting caused a significant decline in serum glucose, cholesterol and lactate dehydrogenase activity, whereas inorganic phosphate increased but blood urea N was not changed. Fasting resulted in increased activities of intestinal lactate (+34 %), isocitrate (+63 %), succinate (+83 %) and malate (+ 106 %) dehydrogenases, fructose 1,6-bisphosphatase (+ 17 %) and glucose-6-phosphatase (+ 22 %). Liver lactate dehydrogenase, malate dehydrogenase, glucose-6-phosphatase and fructose 1,6-bisphosphatase activities were also enhanced. However, the activities of glucose-6-phosphate dehydrogenase and malic enzyme fell significantly in the intestine but increased in liver. Although the activities of alkaline phosphatase, gamma-glutamyl transpeptidase and sucrase decreased in mucosal homogenates and brush border membrane, those of liver alkaline phosphatase, gamma-glutamyl transpeptidase and leucine aminopeptidase significantly increased. These changes were due to a respective decrease and increase of the maximal velocities of the enzyme reactions. Ramadan-type fasting caused similar effects whether the rats fasted with a daytime or night-time feeding schedule. The present results show a tremendous adaptation capacity of both liver and intestinal metabolic activities with Ramadan-type fasting in rats used as a model for Ramadan fasting in people.