Another view of myocardial hibernation

This manuscript brings together three newer concepts: myocardial hibernatio n, heterogeneity in myocardial blood Row and oxidative metabolism, and effe cts of hibernating animal serum on non-hibernators. Myocardial hibernation is viewed as a protective mechanism that helps to maintain myocardial integ rity and viability by down-regulating contractile function as an adaptation to reduced blood flow. Myocardial flow is considerably heterogeneous. Cons equently, oxygen supply to the myocardium is also heterogeneous. Many lines of evidence show a close correlation between regional flow and regional me tabolism. In low-flow/low-metabolism areas, myocardial function must be red uced, since the myocardium would otherwise undergo necrosis. Because no reg ional histological differences exist, the pattern of heterogeneity seems to shift over time. Hence, we hypothesize that such very regional hibernation presents an evolutionary, protective mechanism, permitting subsequent myoc ardial areas to rest within the ceaselessly working heart. We also hypothes ize that a similar mechanism ensures the down-regulation of function follow ing myocardial ischemia in order to induce myocardial hibernation on a broa der level. Surprisingly, a substance (opioid in nature) contained in hibern ator serum both induced hibernation-like state in non-hibernators and suppr essed myocardial oxygen consumption. Thus, we lastly hypothesize that myoca rdial hibernation is a remnant of the early stages of evolution and is clos er to physiological hibernation than traditionally viewed. (C) 2001 Elsevie r Science Ireland Ltd. All rights reserved.