Downes H, Wayson K A, Edney S M, Gerber N
Arch Int Pharmacodyn Ther. 1975 Nov;218(1):66-76.
Pentobarbial, thiopental and the convulsant 5-ethyl-5-(2-cyclohexylideneëthyl) barbituric acid (CHEB) were tested for contractor effect on the isolated lung of the fullfrog at pH 7.0 (7% CO2 and 20 mM HCO3-) and pH 8.4 (0.3% CO2 and 20mM HCO3-). CHEB was a potent contractor, thiopental a feeble contractor, and pentobarbital lacked contractor effect. The contractor potencies of both CHEB and thiopental were greater at the more acid pH. The potencies of formally charged agonists such as acetylcholine and K+ were not altered by the pH differences employed in these experiments. The pKa of CHEB was found to be 8.18 at 15 degrees C and 8.03 at 27 degrees C. Calculation of concentration-effect relationships of ionized and nonionized CHEB showed that only the nonionized CHEB was responsible for the contractor effect.
在pH 7.0（7%二氧化碳和20 mM碳酸氢根）以及pH 8.4（0.3%二氧化碳和20 mM碳酸氢根）条件下，对戊巴比妥、硫喷妥钠以及惊厥剂5-乙基-5-(2-环己叉乙基)巴比妥酸（CHEB）在完整青蛙离体肺上的收缩效应进行了测试。CHEB是一种强效收缩剂，硫喷妥钠是一种弱效收缩剂，而戊巴比妥没有收缩效应。在酸性更强的pH条件下，CHEB和硫喷妥钠的收缩效力都更强。在这些实验所采用的pH差异下，诸如乙酰胆碱和钾离子等带正电荷激动剂的效力并未改变。发现CHEB在15℃时的pKa为8.18，在27℃时为8.03。对离子化和非离子化CHEB的浓度-效应关系进行计算表明，只有非离子化的CHEB产生收缩效应。
