Cardiac metabolism in the hypothermic ground squirrel and rat

¹ Department of Anatomy, Louisiana State University School of Medicine, New Orleans, Louisiana

A biochemical and electrocardiographic study of cardiac function during hypothermia in the ground squirrel (7–17 C) and the rat (11–19 C) revealed that, in the ground squirrel heart, adenosine triphosphate (ATP) and phosphocreatine (PC) each decreased significantly 60% thus maintaining their ratio (2.6/1), whereas in the rat heart ATP decreased 61%, PC decreased 48%, and lactate increased 194%. Histochemical studies demonstrated an increase in succinic dehydrogenase and a decrease in triphosphopyridine nucleotide diaphorase in the rat heart. As rectal temperature decreased in the ground squirrel the components of the electrocardiogram lengthened and voltage was maintained. In the rat, voltage decreased with decreasing rectal temperature and the electrocardiographic pattern reflected myocardial anoxia. The metabolic integrity of cardiac muscle cells and the membrane potential are apparently maintained in the ground squirrel during hypothermia. In the rat, however, this is not so and conduction difficulties become evident at 20–15 C. Disruption of mitochondrial morphology, presently being investigated, is thought to be responsible for the metabolic and conduction problems which occur in the rat heart during hypothermia.

Key Words: hypothermia • hypothermia and the EKG • myocardial phosphates • myocardial lactate • hibernator vs. nonhibernator • nonhibernator • heart function in a hibernator vs. a nonhibernator

Submitted on November 30, 1964