HYPERGLYCEMIA IN HUMMINGBIRDS AND ITS CONSEQUENCES FOR HEMOGLOBIN GLYCATION

We measured levels of glucose and glycated hemoglobin in the blood of three of the world's smallest nectarivorous birds, the Anna's (Calypte anna), Costa's (Calypte costae), and ruby-throated hummingbirds (Arch ilochus colubris). Plasma glucose levels of hummingbirds that were fas ted overnight (17 mM) were higher than those in any mammal and are amo ng the highest ever measured in a fasting vertebrate. Glucose levels i n hummingbirds just after feeding were extreme, rising as high as 42 m M. The surprisingly high blood glucose concentrations in hummingbirds were accompanied by glycated hemoglobin levels that are the highest ev er measured in birds but are lower than those of non-diabetic humans. How hummingbirds tolerate blood glucose levels that cause serious neur ological and microvascular pathologies in diabetic humans and animals remains unknown. (C) 1998 Elsevier Science Inc. All rights reserved.