Pattern of activin A and follistatin release in a sheep model of cardiopulmonary bypass

Objective: Activin A, a member of transforming growth factor-β superfamily, has been established as a critical cytokine released early in endotoxemia and other inflammatory syndromes. The release of activin A and its binding protein, follistatin during cardiopulmonary bypass (CPB) has not been previously reported. Our study aimed to define the pattern of activin A and follistatin release in a sheep CPB model.

Methods: Control group consisted of left thoractomy alone (n=6). CPB was performed using either unfractionated heparin (n=6) or lepirudin (n=6) as anticoagulant. Unlike heparin, lepirudin does not cause activin A and follistatin release on its own. Serum samples were assayed for activin A, follistatin, tumour necrosis factor-α and interleukin-6.

Results: Compared with the control group, CPB using lepirudin was associated with a biphasic release of activin A. The first peak occurred within the first hour of CPB and a second peak occurred within the early post-operative period, coincident with a large release of follistatin. Close correlation was found between follistatin and IL-6 in the control and lepirudin groups, indicative of a role for follistatin in the acute phase response. In contrast to the control and lepirudin groups, CPB using heparin resulted in a concurrent release of activin A and follistatin.

Conclusions: CPB is a trigger for the release of biologically-active free activin A into the circulation, at levels considerably greater than that induced by surgery alone. Triggering release of this critical inflammatory cytokine suggests that activin A may contribute to the adverse outcomes associated with systemic inflammation in cardiac surgery.