The high metabolism of hummingbirds is fueled principally by the sugar found in nectar, but consumed along with the sugar is an excess of water that can amount to several time the bird's own body mass per day. In hummingbirds, the kidney and the gastrointestinal tract mush consequently play coordinated roles in the regulation of water, electrolyte, and energy balance. Beuchat describes a series of experiments, including measurements of GFR and tubular water reabsorption in the kidney, and of water and glucose absorption in the intestine, that will isolate fundamental components of the mechanisms hummingbirds use to regulate energy, water, and electrolyte balance. The project's focus on basic kidney function and on the integration of renal with intestinal function in hummingbirds will provide fundamental information about the physiology of these animals. In a broader perspective, this study will be the first to closely examine the osmoregulatory physiology of a bird or mammal that is a model organism for the study of chronic diuresis. Finally, this study will be first in vivo test of the hypothesis that paracellular fluid flux activated by Na+- coupled glucose transport can play a significant role in nutrient uptake in vertebrates.
