Renal response to dietary protein in the house sparrow Passer domesticus.
Many birds switch seasonally or during ontogeny between diets of varying protein content. In mammals, high-protein diets induce hypertrophy of the kidney in general and of the thick ascending limbs (TAL) in particular, along with increases in glomerular filtration rate (GFR) and urine flow. A hypothesis to explain these phenomena is that the TAL become increasingly sensitive to peptide hormones (glucagon and antidiuretic hormone [ADH]) released in response to protein feeding; the consequent enhancement of ion reabsorption dilutes urine reaching the macula densa, thereby suppressing tubulo-glomerular feedback (TGF) and causing a rise in GFR. Avian kidneys possess most of the elements involved in this mechanism, including loops of Henle with TAL, sensitivity of TAL to ADH (arginine vasotocin [AVT] in birds), and the elements of TGF. We therefore hypothesized that switching from a low-protein to a high-protein diet would induce responses in birds similar to those found in mammals. We tested this hypothesis by feeding house sparrows, Passer domesticus, isocaloric diets containing either 8% or 30% protein. Birds on high-protein food had larger renal medullae, both in mass and in TAL diameter, but no increase in whole-kidney mass. Urine flow was approximately doubled on high-protein food, but there was no change in GFR. We were not able to detect an increased sensitivity of AVT-induced adenylyl cyclase activity in TAL from high-protein animals, and responsiveness to glucagon was higher in TAL from birds eating low-protein food. We are unable to conclude that a suppression of TGF is responsible for the rise in urine flow in birds eating high-protein foods, and the mechanisms behind the medullary hypertrophy and the diuresis remain to be fully explored.
Goldstein
D L
DL
Department of Biological Sciences, Wright State University, Dayton, OH, 45435, USA. david.goldstein@wright.edu
Guntle
L
L
Flaugher
C
C
D000818:Animals; D005576:Colforsin / Q000494:pharmacology; D018753:Diet, Protein-Restricted; D004044:Dietary Proteins; D004231:Diuresis; D005260:Female; D005919:Glomerular Filtration Rate / Q000187:drug effects; D005934:Glucagon / Q000494:pharmacology; D007668:Kidney / Q000033:anatomy & histology / Q000187:drug effects / Q000502:physiology*; D007685:Kidney Tubules, Collecting / Q000187:drug effects / Q000502:physiology; D008138:Loop of Henle / Q000502:physiology; D008297:Male; D009929:Organ Size; D012621:Seasons; D020308:Songbirds / Q000502:physiology*; D014668:Vasotocin / Q000494:pharmacology
D004044:Dietary Proteins; D005576:Colforsin; D005934:Glucagon; D014668:Vasotocin