A comparison of effects measured with isotonic and isometric recording: I. Concentration-effect curves for agonists
作者:R B Barlow、Susan M Bond、Claire Grant、D S McQueen、Zeenat Yaqoob
DOI:10.1038/sj.bjp.0704168
日期:2001.8
Concentration‐effect curves were obtained with carbachol tested on isolated preparations of guinea‐pig ileum taken from adjacent sites in the same animal, one recorded isotonically, the other isometrically: similar experiments were made with histamine as agonist and with carbachol on rat uterus (in oestrus).
The position and steepness of the curves was expressed as the values of [EC50] and the exponent, P: with carbachol or histamine on guinea‐pig ileum the curves were significantly steeper with isotonic recording (P<0.02, sign test) and displaced towards lower concentrations (P<0.005) but there were significant correlations (P<0.05) between values obtained with tissues from the same animal.
The curves for carbachol on the rat uterus were very steep: with isotonic recording the exponent (often eight or more) was consistently higher than with isometric (P<0.001): there was no significant displacement but there was a significant correlation (P<0.05) between values of [EC50] obtained with tissues from the same animal.
Although the results obtained by the two methods are different, they are correlated.
These effects are to be expected because with isotonic recording there can be no change in length until the tension exceeds the load and the tissue bulk sets an upper limit to shortening: the range within which an effect can be measured (the ‘operational window’) is smaller. The observed effects on [EC50] and P have been reproduced with theoretical data.
British Journal of Pharmacology (2001) 133, 1081–1086; doi:10.1038/sj.bjp.0704168
通过在取自同一动物体相近部位的分离制备物——豚鼠回肠上测试卡巴胆碱,可以获得浓度-效应曲线:其中一份制备物以等张记录,另一份以等长记录。类似地,分别以组胺作为激动剂以及在大鼠子宫(发情期)上测试卡巴胆碱也进行了实验。
曲线的位置和陡峭程度分别由[EC50]和指数P的值表示:在豚鼠回肠上使用卡巴胆碱或组胺时,等张记录下的曲线明显更陡峭(P<0.02,符号检验),且向较低浓度方向偏移(P<0.005);然而,同一动物来源的组织间获得的值存在显著相关性(P<0.05)。
卡巴胆碱在大鼠子宫上产生的曲线非常陡峭:等张记录下的指数(通常为8或更高)始终高于等长记录下的指数(P<0.001);虽然没有显著的浓度偏移,但同一动物来源的组织间[EC50]的值存在显著相关性(P<0.05)。
尽管两种方法获得的结果不同,它们之间存在相关性。
这些效应是可以预期的,因为等张记录下,直至张力超过负荷且组织体积限制了缩短的程度之前,长度不会有变化:可以测量效应的范围(“操作窗口”)较小。观察到的[EC50]和P值的变化,已通过理论数据得到再现。
British Journal of Pharmacology (2001) 133, 1081–1086; doi:10.1038/sj.bjp.0704168