Project Summary/Abstract The proposed studies will clarify the mechanisms by which glucose metabolism is dysregulated following consumption of a diet high in fat and fructose (HFHF; i.e. “Western diet”). Studies will be carried out in normal and diet-induced glucose intolerant dogs. The canine model is unique in that it allows infusion into the hepatic portal vein (e.g., insulin, glucagon, glucose, amino acids, etc.), as happens with feeding, something that is not possible in the human or rodent. In the transition from feeding to fasting the liver switches from glucose production to uptake (HGP→HGU), a process critical to the maintenance of normal glucose tolerance. Hepatic glucose metabolism is regulated by three principal signals: insulin, glucose, and neural input (portal glucose signal [PGS]). The latter occurs when the glucose concentration in the hepatic portal vein is greater than in arterial blood, as occurs when glucose is absorbed from the gut. Consuming a HFHF diet severely impairs HGU. Although this is due, in part, to liver insulin resistance, we recently found that hepatic glucose resistance plays an even greater role. In this proposal we: 1) explore the impact of the route of insulin delivery on the compromised liver. Patients with diabetes are normally treated with subcutaneous insulin injection, which results in a very different distribution in the body (enriching the liver with insulin) than when insulin is secreted by the pancreas. We will determine the metabolic consequences of peripheral insulin delivery on liver glucose metabolism in the HFHF dog. This will shed light on the need for ways to insulinize the liver preferentially. 2) We will determine how the signals that regulate mealtime HGU interact with each other in HFHF fed animals and the relative importance of the loss of insulin action and the loss of the PGS in the regulation of HGU. 3) Like with the PGS, there are sensors in the hepatoportal region that detect when protein (amino acids) has been consumed. The body responds to amino acids and glucose by producing insulin and glucagon, hormones that regulate the liver's response to nutrients. While the HFHF diet causes severe hepatic glucose dysfunction, less is known about how it affects the liver's handling of amino acids and protein metabolism. Likewise, the interaction between liver glucose and protein metabolism in the HFHF fed liver will be examined. 4) Glucagon has a complex role in metabolism. It counters the hypoglycemic effects of insulin (its levels increase as glucose levels fall). On the other hand, glucagon also increases when protein is consumed. While this might be expected to negatively impact the glucose lowering effects of insulin, recent evidence suggests that high levels of glucagon might somehow work together with insulin to clear ingested amino acids from the blood and to reduce glucose levels. We will determine if this is the case under more physiological circumstances. We believe that the know...