von Engelhardt W, Dycker Ch, Lechner-Doll M
Department of Physiology, School of Veterinary Medicine, Bischofsholer Damm 15/102, 30173 Hannover, Germany.
J Comp Physiol B. 2007 Aug;177(6):631-40. doi: 10.1007/s00360-007-0161-8. Epub 2007 Apr 12.
In camelids the ventral parts of compartments 1 and 2 (C1/C2) and the total surface of compartment 3 of the forestomach are lined with tubular glands, whereas in ruminants the surface of the forestomach is composed entirely of stratified, squamous epithelium. Thus, differences in absorption rates between these foregut fermenters can be expected. In five camels C1/C2 was temporarily isolated, washed and filled with buffer solutions. Absorption of short-chain fatty acids (SCFA) and net absorption of sodium and water were estimated relative to Cr-ethylenediaminetetraacetic acid as a fluid marker. SCFA were extensively absorbed in the forestomach; clearance rates of SCFA with different chain lengths were equal. After lowering the pH of solutions SCFA absorption rates increased, but much less than the increase of the non-ionized fraction. Absorption of propionate was lower when acetate had been added. Findings suggest that most of the SCFA in camels are transported in the ionized form, most likely via an anion exchange mechanism. Net water absorption is closely related to net sodium absorption. Apparently water absorption results from an iso-osmotic process. Differences between absorption mechanisms of SCFA from the forestomach of camelids and ruminants are discussed.
在骆驼科动物中，前胃的第1和第2隔室（C1/C2）的腹侧部分以及第3隔室的整个表面都衬有管状腺，而在反刍动物中，前胃的表面完全由复层鳞状上皮组成。因此，可以预期这些前肠发酵动物之间的吸收速率会有所不同。在5头骆驼中，C1/C2被暂时分离、冲洗并充满缓冲溶液。相对于作为流体标记物的铬-乙二胺四乙酸，估计了短链脂肪酸（SCFA）的吸收以及钠和水的净吸收。SCFA在前胃中被大量吸收；不同链长的SCFA清除率相等。降低溶液的pH值后，SCFA吸收速率增加，但远低于非离子化部分的增加。添加乙酸盐后，丙酸盐的吸收降低。研究结果表明，骆驼体内的大多数SCFA以离子形式运输，最有可能通过阴离子交换机制。净水吸收与净钠吸收密切相关。显然，水吸收是一个等渗过程。讨论了骆驼科动物和反刍动物前胃中SCFA吸收机制的差异。
