Several reports have indicated that heparin has a bronchodilative effect in asthma patients, and that it enhances airway smooth muscle contraction in vitro, protamine is known to inhibit or enhance contraction of tracheal smooth muscle. Thus the effects of protamine and heparin on airway smooth muscle contraction are not consistent. However, no report is available on the effects of enflurane on heparin and protamine tracheal smooth muscle contraction. We performed this study to evaluate the effects of heparin or protamine on the carbachol induced contraction of tracheal smooth muscle in the guinea pig. And we also evaluated the effects of enflurane on heparin or protamine induced tracheal smooth muscle contraction.

Isolated tracheal rings of the guinea pig were suspended in Krebs solution. Contractions were recorded isometrically using a transducer. Contraction was induced by carbachol (10^-6 M) and then cumulative dose responses of heparin or protamine (0.006 mg/ml, 0.02 mg/ml, 0.06 mg/ml, 0.2 mg/ml, 0.4 mg/ml) and in heparin (E) group and protmine (E) group, enflurane (4.34%) was administered for 15 minute after carbachol adminstration.

Contraction by carbachol was inhibited by level of heparin or protamine at concentrations of 0.2 mg/ml and 0.4 mg/ml. At an enflurane (4.34%) contraction was inhibited, and no further inhibition of contraction by heparin or protamine was observed.

Heparin or protamine inhibited the tracheal smooth muscle contraction induced by carbachol at 0.2 mg/ml and 0.4 mg/ml, and no further significant inhibition of contraction by heparin or protamine was observed after enflurane administration (4.34%).