1. The presence of histamine and tryptase in serum during and after coronary artery bypass grafting may be an indication of the induction of inflammation.
2. One group of patients received no glucocorticoids and a second group received methylprednisolone before extracorporeal circulation. In the steroid group no effects were seen on the basal levels of histamine (2.84 + 0.12 ng/ml) and tryptase (030 + 0.05 ng/ml) during and after surgery. In the other group two peak levels of histamine were observed: one at 10 min after starting extracorporeal circulation (4.19 +1.79 ng/ml) and another at 4h after surgery (8.26 +4.85 ng/ml). In this group tryptase was only elevated during the period of extracorporeal circulation (1.54+ 0.16 ng/ml).
3. There were no differences between the two groups in complement activation. C3a levels rose to 170 +8% and 180 +10% of the initial value in the steroid and non-steroid group, respectively.
4. It was concluded that during surgery mast cells were activated, but since tryptase levels decreased in the post-operative period, the second increase in the histamine level can be explained by activation of basophils or by an unknown mechanism for the release of histamine but not tryptase by mast cells.
5. In the bronchoalveolar lavage fluid the levels of histamine and tryptase showed no differences between the two groups of patients, but histamine was enhanced compared with normal levels.