ENDOTHELIUM AND VASCULAR SMOOTH-MUSCLE FUNCTION IN INTERNAL MAMMARY ARTERY AFTER CRYOPRESERVATION

An optimal cryopreserved arterial conduit should have anatomic and phy siologic characteristics similar to those of the fresh artery. We have cryopreserved canine internal mammary artery (IMA) with intact, prost acyclin (PGI(2))-producing endothelial cells, but the underlying vascu lar smooth muscle appeared nonfunctional. Thus the aim of this study w as to evaluate which steps of the cryopreservation method compromise v ascular smooth muscle function in cryopreserved IMA. Isometric tension recording responses to vasoconstrictor agonists were used to evaluate the level of vascular muscle integrity, while endothelial function wa s assessed by relaxation responses to acetylcholine and by PGI(2) prod uction. These variables were measured in vessels rewarmed to 37 degree s C, following initial exposure to different stages of an eight-step c omputerized cryopreservation protocol (n = 10). In this protocol, tiss ue temperature was lowered to -10 degrees C (steps 1-2), rapidly reduc ed to -12 degrees C (steps 3-4), reduced further to -40 degrees C at a rate of -0.5 degrees C/min (steps 5-6),lowered to -70 degrees C (step 7), and finally equilibrated at -196 degrees C by immersion in liquid nitrogen (step 8). Compared to fresh IMA, the amplitude of dose-depen dent contractions to norepinephrine (NE 10(-9) to 10(-4) M) was step-w ise depressed after cooling to less than or equal to 12 degrees C (ste ps 3-4), showing only 75 and 19% of maximal contraction after steps 3- 4 and step 7, respectively. Similarly, depolarization-induced contract ions to KCI (10 to 60 mM) also were progressively depressed after step -wise cryopreservation, showing reduced contractile amplitudes even af ter steps 1-2 (-10 degrees C). Vascular muscle agonist sensitivity was unchanged (KCl) or only mildly influenced (NE) by these same temperat ure reductions. In contrast, endothelial-dependent relaxation to acety lcholine and PGI(2) production were maintained after all steps in the cryopreservation process, and baseline PGI(2) production was higher in cryopreserved IMA. These data indicate that IMA smooth muscle cell vi ability is poorly-preserved after cooling to below -10 to -12 degrees C of the cryopreservation process, whereas endothelial cell function a ppears intact after profound cooling to -196 degrees C. The loss of va scular smooth muscle responsiveness coupled with the protection afford ed by an intact endothelium may provide an arterial conduit less susce ptible to vasospasm. Such a graft, however, would lack. the dynamic pr operties of flow regulation in response to the metabolic needs of the myocardium. (C) 1996 Academic Press, Inc.