Effects of storage temperature and fetal calf serum on the endothelium of porcine aortic valves

Endothelial integrity and function may be an important determinant for long-term success of allograft heart valves. To determine the optimal storage temperatures for preservation of long-term endothelial function in porcine aortic valves, different storage temperatures and times were investigated, Fresh valves were either (1) stored at 4 degrees C, with or without 10% fetal calf serum supplement, for 1, 2, 4, 7, 14, 21, or 28 days; (2) cryopreserved for 2, 4, or 8 weeks at -80 degrees C or -170 degrees C; (3) cryopreserved in long-term storage (as long as 1 year),,vith or without fetal calf serum, at -170 degrees C. Viability of endothelial cells was assessed through measurement of the production of prostacyclin in basal and bradykinin-stimulated conditions, during in vitro incubation of the valve cusps at 37 degrees C. Endothelial morphologic variations in valves stored at 4 degrees C were evaluated by scanning electron microscopy. With storage at 4 degrees C, after 4 days the valves already produced significantly less (p < 0.05) prostacyclin than fresh preparations in both basal (0.21 +/- 0.01 versus 3.56 +/- 0.03 ng . ml(-1) . cm(-2)) and stimulated conditions (4.17 +/- 0.36 vs 24.23 +/- 1.83). Morphologic changes could not yet be distinguished with scanning electron microscopy at that time. When the storage period was extended, the levels of prostacyclin further diminished; after 14 days, prostacyclin release could no longer be detected. In cryopreserved valves, prostacyclin production was similar for as long as 2 weeks of storage either at -80 degrees C or at -170 degrees C in basal (2.69 +/- 0.63 vs 2.93 +/- 0.51) and stimulated (16.43 +/- 3.19 vs 16.50 +/- 2.57, = 6) conditions, After 8 weeks, no prostacyclin release could be detected in valves stored at -80 degrees C. After 6 months storage at -170 degrees C, the prostacyclin production was significantly (p < 0.05) reduced compared with fresh valves; it then remained constant for as long as 1 year, The valves stored with fetal calf serum produced significantly (p < 0.05) less prostacyclin than did those without fetal calf serum. For longer cryopreserved banking, we recommend storing heart valves at -170 degrees C instead of at -80 degrees C to maintain viability of endothelial cells. Fetal calf serum would harm endothelial viability during long-term cryopreservation.