Myocardial hibernation: another view

In the following, three newer concepts are brought together: myocardial hib ernation, 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 ma intain myocardial integrity and viability by down-regulating contractile fu nction 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 clos e correlation between regional flow and regional metabolism. In low-flow/lo w-metabolism areas, myocardial function must be reduced, since the myocardi um would otherwise undergo necrosis. Thus, others and we hypothesize that f unction must be down-regulated to induce hibernation in low-flow areas. Bec ause no regional histologic differences exist (the mitochondria are uniform ly distributed within the myocardium), the pattern of heterogeneity seems t o shift over time. Hence, we hypothesize that such very regional hibernatio n presents an evolutionary, protective mechanism, permitting subsequent myo cardial areas to rest within the ceaselessly working heart. We also hypothe size 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 myoca rdial oxygen consumption. Thus, we lastly hypothesize that myocardial hiber nation is a remnant of the early stages of evolution and is closer to physi ologic hibernation than traditionally viewed.