Guinea pig tracheal strips maintain stable electrical field stimulated contractions for up to 15 hours¹ allowing multiple bronchodilators to be profiled within one tissue. Slow onset compounds, however, can take several hours to equilibrate making it difficult to construct sequential dose response curves within the viable life of the preparation. We have adapted the method of Shepherd et al so that, following a reference compound, the compound of interest can be tested 1 dose per tissue, and curves constructed from the individual results, across multiple experiments. This allows more successful determination of potency for compounds with slow onset, particularly where pKB analysis is to be performed as some agonists equilibrate slower still in the presence of antagonist. The table below compares data obtained for the fast-onset β2 agonist Formoterol, profiled within (intra-) and across (inter-) tissues, to validate the new method:

TestEC50 nM (95% CI)Potency relative to isoprenaline (ISO) referencepKB for 300nM ICI-118551
Formoterol (intra-tissue, n=4 geometric mean)¹1.87 (1.46-2.41)0.011 (ISO curve constructed on same tissue)8.17
Formoterol (inter-tissue n=4 ~EC50)2.78 (1.50-5.13)0.013 (ISO curve constructed across tissues)8.14

The results show that data for the two methods correlate well. Data for the fast onset β agonist Isoprenaline and the very slow onset β2 agonist Salmeterol will also be presented.
¹Shepherd, C. et. al. European Respiratory Journal, 22, 104s.