The effects of intravenous glucose and fructose on insulin levels in sheep

Background - A high fructose diet is known to cause insulin resistance in a wide range of mammals. An acute oral loading of fructose has no effect on the insulin level of normal or diabetic animals. No studies have investigated the effects of intravenous fructose loading in sheep, a species which generally derives all blood glucose from gluconeogenesis. Objective - To compare the effects of a bolus loading of intravenous fructose and glucose on blood glucose and insulin levels in sheep. Design - Ten crossbred wethers were fed lucerne chaff ad libitum. They were given either 0.24 g/kg of glucose or fructose intravenously in a single bolus dose. Plasma glucose, fructose and insulin were measured in serial blood samples for the following six hours. Outcomes - As expected glucose infusion resulted in a substantial rise in blood glucose and a modest increase in insulin level. The fructose infusion led to very a modest rise in blood fructose and large increase in plasma insulin level with a resultant fall in blood glucose level. Conclusion - Sheep respond differently to other mammals to fructose loading. Intravenous fructose stimulates insulin release in sheep. This response is different to most other mammals which show insulin refractoriness to fructose loading.