Tsubaki H, Komai T
J Pharmacobiodyn. 1986 Sep;9(9):747-54. doi: 10.1248/bpb1978.9.747.
The intestinal absorption of tetramethylammonium (TMA) and its derivatives from rat jejunum has been investigated with an in situ loop method and an in vitro everted sac method. At a low concentration, TMA was absorbed rapidly from the in situ intestinal lumen without being metabolized in the tissue and the rate of absorption was dependent upon the concentration used. The profile of TMA absorption included two processes, i.e. saturable and non-saturable. The absorption of TMA was inhibited competitively by analogs that have a N-trimethyl group in their structure. Among them, choline showed the strongest inhibition to TMA absorption. The inhibitory potency of these analogs was related to their chemical structure. Although TMA was not transported into the intracellular fluid of the everted intestine against a concentration gradient, the tissue accumulation of TMA was inhibited by 2,4-dinitrophenol (2,4-DNP), a metabolic inhibitor, and was highly dependent upon the incubation temperature. These findings demonstrate that TMA is absorbed through the rat small intestine by a carrier mediated transport system. An apparent Kt of 0.73 mM and a maximum V of 11.5 nmol/g tissue wet wt/min were determined by an in situ loop method. It was also suggested that the endogenous quaternary ammonium compound, choline, might be absorbed by the same carrier system.
采用原位肠袢法和体外外翻肠囊法研究了大鼠空肠对四甲基铵（TMA）及其衍生物的肠道吸收。在低浓度下，TMA可从原位肠腔快速吸收，且在组织中不发生代谢，吸收速率取决于所用浓度。TMA的吸收过程包括两个阶段，即可饱和阶段和不饱和阶段。TMA的吸收受到其结构中含有N-三甲基基团的类似物的竞争性抑制。其中，胆碱对TMA吸收的抑制作用最强。这些类似物的抑制效力与其化学结构有关。虽然TMA不能逆浓度梯度转运到外翻肠的细胞内液中，但代谢抑制剂2,4-二硝基苯酚（2,4-DNP）可抑制TMA在组织中的蓄积，且TMA的蓄积高度依赖于孵育温度。这些发现表明，TMA通过载体介导的转运系统被大鼠小肠吸收。通过原位肠袢法测定的表观转运常数Kt为0.73 mM，最大转运速率V为11.5 nmol/g组织湿重/分钟。研究还表明，内源性季铵化合物胆碱可能通过相同的载体系统被吸收。
