[In vitro evaluation of mucolytic activities of some expectorants using porcine gastric mucin].

The measurement of viscoelasticity of airway secretions (sputum) has been very difficult, because the secretions, mainly consisting of high molecular weight glycoproteins, are heterogeneous and non-Newtonian viscous fluid. In the present study, a new in vitro method was devised for evaluating the effects of mucolytic expectorants, using porcine gastric mucin as a mucous fluid. Twenty percent porcine gastric mucin solution was prepared by dissolving it in tris-HCl buffer solution. The mucolytics tested were incubated with the mucin solution at pH 7.0 and 37 degrees C for 30 min. The viscoelasticity of mucous fluid was determined by the glass plate method and rheometer method. The two cysteine-mucolytics, acetylcysteine (10(-3)-10(-1) M) and ethylcysteine++ (10(-3)-10(-1) M) showed a marked viscoelasticity-lowering effect with either method. On the other hand, another cysteine-mucolytic, carbocysteine had no mucolytic effect at pH 7.0, but showed its effect at pH 6.0. A protease-mucolytic, alpha-chymotrypsin (0.1-10 mg/ml), remarkably lowered the viscoelasticity of mucin fluid with either method. Bromhexine (3 X 10(-4)-3 X 10(-3) M) had no mucolytic effect even at the range of pH 6-8. From the above findings, it is indicated that distinct evaluation of the mucolytic actions of expectorants is feasible using porcine gastric mucin. The glass plate method has many advantages over the rheometer method in terms of required sample volume, measurement time, inexpensive, and so on.