Sensitivity of the PGF2 alpha-versus carbachol-contracted trachea to relaxation by salbutamol, forskolin and prenalterol.

A comparison has been made of the abilities of salbutamol, forskolin and prenalterol to relax guinea-pig tracheal rings contracted equivalently with either prostaglandin F2 alpha (PGF2 alpha) or carbachol. In the absence of spontaneous tension, 10(-6) M PGF2 alpha and 4 X 10(-7) M carbachol induced equivalent contractions of tracheal rings. Tracheal contractions induced by PGF2 alpha were more sensitive to the relaxant effects of salbutamol, forskolin or prenalterol than were contractions induced by carbachol. Each tracheal relaxant had a lower IC50 value for inhibiting PGF2 alpha-induced contractions, and prenalterol (a beta-adrenoceptor partial agonist) induced more complete relaxation of PGF2 alpha- than carbachol-induced tracheal tension. It is concluded that the tracheal relaxant activity of these compounds is in part dependent upon the contractile agent which induces tension, and that the variable sensitivity of different isolated tracheal muscle preparations to the actions of tracheal relaxants may result from differences in the contracting stimulus being antagonized in each of these models.