Effect of age and diet on glucose tolerance in Sprague-Dawley rats

Male Sprague-Dawley rats ages 12 and 27 mo were used to evaluate intravenous glucose tolerance. Rats were fed ad libitum a purified diet containing either 33% sucrose and 33% starch or 66% starch, 17.5% casein and 7% fat (g/100 g) for 4 mo. Each animal was fitted with a cannula in the left carotid artery while anesthetized with methoxyflurane and was allowed to recover without food for 10-12 h. A resting blood sample was withdrawn, and then each rat received 1 mL of 50% glucose in saline per kilogram body weight throughout the carotid cannula. The cannula was washed with the rat's blood to remove any excess glucose, and blood samples were taken at 5, 10, 15, 30, 45 and 60 min after infusion. The 12-mo-old rats in both the high sucrose and sucrose-free diet groups had significantly greater resting plasma glucose and insulin concentrations than did their 27-mo-old counterparts. Diet had no effect on resting glucose or insulin levels. Neither age nor diet had a significant effect on plasma glucose or insulin concentrations following the glucose infusion. These data suggest that the pancreatic response to a glucose load is not altered by age or high sucrose diets.