The effects of dietary nitrate on plasma glucose and insulin sensitivity in sheep.

Nitrate (NO ) is an effective non-protein nitrogen source for gut microbes and reduces enteric methane (CH ) production in ruminants. Nitrate is reduced to ammonia by rumen bacteria with nitrite (NO ) produced as an intermediate. The absorption of NO can cause methaemoglobinaemia in ruminants. Metabolism of NO and NO in blood and animal tissues forms nitric oxide (NO) which has profound physiological effects in ruminants and has been shown to increase glucose uptake and insulin secretion in rodents and humans. We hypothesized that absorption of small quantities of NO resulting from a low-risk dose of dietary NO will increase insulin sensitivity (S ) and glucose uptake in sheep. We evaluated the effect of feeding sheep with a diet supplemented with 18 g NO /kg DM or urea (Ur) isonitrogenously to NO , on insulin and glucose dynamics. A glucose tolerance test using an intravenous bolus of 1 ml/kg LW of 24% (w/v) glucose was conducted in twenty sheep, with 10 sheep receiving 1.8% supplementary NO and 10 receiving supplementary urea isonitrogenously to NO . The MINMOD model used plasma glucose and insulin concentrations to estimate basal plasma insulin (I ) and basal glucose concentration (G ), insulin sensitivity (S ), glucose effectiveness (S ), acute insulin response (AIRg) and disposition index (DI). Nitrate supplementation had no effect on I (p > .05). The decrease in blood glucose occurred at the same rate in both dietary treatments (S ; p = .60), and there was no effect of NO on either G , S , AIRg or DI. This experiment found that the insulin dynamics assessed using the MINMOD model were not affected by NO administered to fasted sheep at a low dose of 1.8% NO in the diet.