Effect of different cooling methods on cardiac valves cryopreserved in liquid nitrogen with chondroitin sulfate

【Objective】 To estimate the effect of different cooling methods on the histological structure and cytoactive of cryopreserved homograft cardiac valves in liquid nitrogen with chondroitin sulfate(CS).【Methods】 32 rabbit aortic valves were randomly divided into control and experiment groups(Ⅰ-Ⅲ)(n =8).All the valves were germicidal treated.Then,the activity of endothelial cells in control group was immediately examined and the tissues were observed under light and electron microscopes.In the experiment groups,valves were cryopreserved in liquid nitrogen contained CS by three different cooling protocols.In group I,valves were immediately frozen to-196 degrees C.In group II,valves were firstly frozen to 4 degrees C,then-80 degrees C after 2 h,and finally into liquid nitrogen after 8 h.In group III,valves were frozen with programmed freezing at a controlled rate of-1 degrees C/min to-196 degrees C prior to liquid nitrogen.All valves in experiment groups were cryopreserved for 1 month.Then,the activities of endothelial cells in different groups were examined and the tissues were observed under light and electron microscopes.【Results】 Compared with control,cytoactive in GroupⅠwas significantly declined(P 0.05) and severe morphologic changes occurred.In Group Ⅱ,cytoactive was also significantly declined(P 0.05),but morphologic changes were slight.In group Ⅲ,cytoactive was slightly declined(P 0.05) and there were almost no morphologic changes.【Conclusion】 Among all cooling protocols,the programmed cooling method is best,since the histological structure and cytoactive were both cryopreserved well.