AJP - Regulatory, Integrative and Comparative Physiology, Vol 250, Issue 1 89-R95, Copyright © 1986 by American Physiological Society
Lower intestinal modification of ureteral urine in hydrated house sparrows
D. L. Goldstein and E. J. Braun
The ureters of birds empty into the posterior portion of the lower
intestine, thereby providing the possibility for modification of ureteral
urine by this latter organ. We have used in vivo perfusion to measure the
transport of Na+, K+, and water across the lower intestine (colon and
coprodaeum) of anesthetized house sparrows (Passer domesticus). Na+ was
reabsorbed from (Vmax = approximately 22 mu eq . cm-2 . h-1, Km =
approximately 69 meq/l) and K+ was secreted (at variable rates) into all
saline perfusion fluids. The osmotic permeability of the intestinal
epithelium was 0.39 microliter . cm-2 . h-1 . mosM-1 in the
mucosal-to-serosal direction and 0.43 microliter . cm-2 . h-1 . mosM-1 in
the serosal-to-mucosal direction. At isosmotic perfusion, Na+-linked water
transport occurred at a rate of 1.7 microliter/mu eq Na+. In hydrated house
sparrows the composition of ureteral urine (osmolarity = 351 mosM, Na+ =
86.5 meq/l, K+ = 60.5 meq/l) was significantly modified by transport in the
lower intestine (voided fluid osmolarity = 344 mosM, Na+ = 60 meq/l, K+ =
90 meq/l). Interspecific comparisons of lower intestinal resorptive surface
area and transport parameters at the level of the tissue, organ, and whole
animal reveal no consistent pattern of adaptation related to habitat.
