IN-VITRO TOLERANCE TO ANOXIA AND ISCHEMIA IN ISOLATED HEARTS FROM HYPOXIA SENSITIVE AND HYPOXIA TOLERANT TURTLES

Although freshwater turtles as a group are highly anoxia tolerant, dra matic interspecific differences in the degree of anoxia tolerance have been demonstrated in vivo. Painted turtles (Chrysemys picta bellii) a ppear to be the most hypoxia-tolerant species thus far studied, while softshelled turtles (Trionyx spinifer) are the most hypoxia-sensitive. We have assumed that this dichotomy persists in vitro but have not, u ntil now, directly tested this assumption. We, therefore, directly com pared the responses of isolated, perfused, working hearts from these t wo species to either 240 min of anoxia, 90 min of global ischemia, or 240 min of global ischemia followed by reoxygenation/reperfusion. Isol ated hearts were perfused at 20 degrees C and monitored continuously f or phosphocreatine (PCr), adenosine triphosphate (ATP), inorganic phos phate (P-i), and intracellular pH (pH(i)) by P-31-nuclear magnetic res onance spectroscopy as well as for ventricular developed pressure and heart rate. Contrary to our expectations, we observed few significant differences in any of these parameters between painted and softshelled turtle hearts. Hearts from both species tolerated 240 min of anoxia e qually well and both restored PCr, pH(i), and Pi contents to control l evels during reoxygenation. We did observe some significant interspeci fic differences in the 90 min (pH(i) and P-i) and 240 min (PCr) ischem ia protocols although these seemed to suggest that Trionyx hearts migh t be more tolerant to these stresses than Chrysemys hearts. We conclud e that: (a) the observed in vivo differences in anoxia tolerance betwe en painted and softshelled turtles must either be due to differences i n organ metabolism in organs other than the heart (e.g., brain) or to some integrative physiologic differences between the species; and (b) isolated hearts from a species known to be relatively anoxia sensitive in vivo can exhibit an apparent high degree of anoxia and ischemia to lerance in vitro. (C) 1997 Elsevier Science Inc.