RESTORATION OF THE CAMP 2ND MESSENGER PATHWAY ENHANCES CARDIAC PRESERVATION FOR TRANSPLANTATION IN A HETEROTOPIC RAT MODEL

Current organ preservation strategies subject graft vasculature to sev ere hypoxia (PO2 approximately 20 Torr), potentially compromising vasc ular function and limiting successful transplantation. Previous work h as shown that cAMP modulates endothelial cell (EC) antithrombogenicity , barrier function, and leukocyte/EC interactions, and that hypoxia su ppresses EC cAMP levels. To explore the possible benefits of cAMP anal ogs/agonists in organ preservation, we used a rat heterotopic cardiac transplant model; dibutyryl cAMP added to preservation solutions was a ssociated with a time- and dose-dependent increase in the duration of cold storage associated with successful graft function. Preservation w as also enhanced by 8-bromo-cAMP, the S(p) isomer of adenosine 3',5'mo nophosphorothioate, and types III (indolidan) and IV (rolipram) phosph odiesterase inhibitors. Neither butyrate alone nor 8-bromoadenosine we re effective, and the cAMP-dependent protein kinase antagonist R(p) is omer of adenosine 3',5'monophosphorothioate prevented preservation enh ancement induced by 8-bromo-cAMP. Grafts stored with dibutyryl cAMP de monstrated a 5.5-fold increase in blood flow and a 3.2-fold decreased neutrophil infiltration after transplantation. To explore the role of cAMP in another cell type critical for vascular homeostasis, vascular smooth muscle cells were subjected to hypoxia, causing a time-dependen t decline in cAMP levels. Although adenylate cyclase activity was unch anged, diminished oxygen tensions were associated with enhanced phosph odiesterase activity (59 and 30% increase in soluble types III and IV activity, respectively). These data suggest that hypoxia or graft isch emia disrupt vascular homeostasis, at least in part, by perturbing the cAMP second messenger pathway. Supplementation of this pathway provid es a new approach for enhancing cardiac preservation, promoting myocar dial function, and maintaining vascular homeostatic properties.