Goldstein D L, Braun E J
Am J Physiol. 1986 Jan;250(1 Pt 2):R89-95. doi: 10.1152/ajpregu.1986.250.1.R89.
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.
鸟类的输尿管排入下肠道的后部，因此后一个器官有可能对输尿管尿液进行调节。我们利用体内灌注法来测量麻醉的家麻雀（Passer domesticus）下肠道（结肠和粪道）对Na⁺、K⁺和水的转运。Na⁺从所有灌注盐溶液中被重吸收（Vmax约为22 μeq·cm⁻²·h⁻¹，Km约为69 meq/l），K⁺则以可变速率分泌到其中。肠道上皮的渗透通透性在黏膜到浆膜方向为0.39微升·cm⁻²·h⁻¹·mosM⁻¹，在浆膜到黏膜方向为0.43微升·cm⁻²·h⁻¹·mosM⁻¹。在等渗灌注时，与Na⁺相关的水转运速率为1.7微升/μeq Na⁺。在水分充足的家麻雀中，输尿管尿液的成分（渗透压 = 351 mosM，Na⁺ = 86.5 meq/l，K⁺ = 60.5 meq/l）在下肠道转运后有显著改变（排出液体渗透压 = 344 mosM，Na⁺ = 60 meq/l，K⁺ = 90 meq/l）。在组织、器官和整个动物水平上对下肠道吸收表面积和转运参数进行种间比较，未发现与栖息地相关的一致适应模式。
