Meeting Abstract
Hummingbirds are one of two flying nectarivores that can uniquely use recently ingested fructose or glucose to power flight. Previous work in our lab suggests that for hummingbirds this could partly be due to muscle physiology having both glucose and fructose transporters, and high hexokinase activity. These may give the hummingbird an ability to metabolize native fructose directly in muscles, unlike other vertebrates. However, the observed hexokinase activity rate is not high enough to support flight direct oxidation in the muscle with fructose. Thus, it is unclear how hummingbirds maintain a high sugar flux, particularly for fructose, while hovering. First, we examined changes in plasma metabolites of fasted birds versus those fed sucrose (glucose and fructose). Our fasted birds showed blood fructose levels of 0.2mM whereas fed birds had around 5mM blood fructose levels. In contrast, blood glucose levels remain similar after one hour of fasting, suggesting fructose levels are much more dynamic than glucose levels in the blood. To explore the differential use of these sugars we examined sugar flux by comparing fed birds given glucose or fructose and fasted birds. Ruby-throated hummingbirds’ metabolites were quantified from birds that were fasted, or fed glucose, or fructose. We used LC-MS based metabolomics to determine the metabolite concentrations in highly metabolic tissues (liver, heart, pectoralis muscle). Specifically, we were interested in central carbon metabolism which helped elucidate which pathways fructose and glucoses are using. In addition, relative amounts of glucose transporters and monocarboxylate transporters at the tissues provide support for metabolite data. We also show that the ruby-throated hummingbird has higher capability to use exogenous fructose via different metabolic pathways in tissues, like muscle, than that of mammals.
