[Myocardial hibernation: another view]

In the following, three newer concepts are brought together: myocardial hibernation, heterogeneity in myocardial blood flow and oxidative metabolism, and effects of hibernating animal serum on non-hibernators. Myocardial hibernation is viewed as a protective mechanism that helps to maintain myocardial integrity and viability by down-regulating contractile function as an adaptation to reduced blood flow. Myocardial flow is considerably heterogeneous. Consequently, oxygen supply to the myocardium is also heterogeneous. Many lines of evidence show a close correlation between regional flow and regional metabolism. In low-flow/low-metabolism areas, myocardial function must be reduced, since the myocardium would otherwise undergo necrosis. Thus, others and we hypothesize that function must be down-regulated to induce hibernation in low-flow areas. Because no regional histologic differences exist (the mitochondria are uniformly distributed within the myocardium), the pattern of heterogeneity seems to shift over time. Hence, we hypothesize that such very regional hibernation presents an evolutionary, protective mechanism, permitting subsequent myocardial areas to rest within the ceaselessly working heart. We also hypothesize that this mechanism ensures the down-regulation of function following myocardial ischemia in order to induce myocardial hibernation on a broader level. Surprisingly, a substance (opioid in nature) contained in hibernator serum both induced hibernation-like state in non-hibernators and suppressed myocardial oxygen consumption. Thus, we lastly hypothesize that myocardial hibernation is a remnant of the early stages of evolution and is closer to physiologic hibernation than traditionally viewed.