Oxygen Consumption, Body Temperature and Heart Rate of Woodchucks Entering Hibernation

¹ From the Department of Anatomy, Harvard Medical School, Boston, and the Museum of Comparative Zoology, Harvard University, Cambridge, Massachusetts

Oxygen consumption, heart rate and temperatures from various parts of the body were measured in woodchucks (Marmota monax) entering hibernation. Comparisons were made with the chilling of woodchucks anesthetized with sodium pentobarbital, with and without the ganglionic blocking agent bis(trimethylammonium)hexane dibromide. Heart rate and oxygen consumption began to decline before any drop in body temperature as animals entered hibernation. The process was usually not continuous, for periodically the heart speeded, oxygen consumption and muscle action potentials increased and, shortly thereafter, the temperature rose transiently with the anterior portion of the body warming faster than the posterior. These partial rewarmings were less and less frequent as the total period of hibernation became longer. As hibernators chilled, the heart was the warmest area, with the thorax warmer than the abdomen. Dead woodchucks curled in the hibernating position chilled faster than the hibernators with the central portion of the abdomen chilling the slowest. In the supine, anesthetized animal, with or without the ganglionic blocking agent, the flow of blood altered the chilling so that the area near the heart remained slightly warmer than the abdomen. If curled in the hibernating position, the heart region remained much warmer than the abdomen because blood flow was curtailed by the restricted position. Chilling of the hibernator was identical to the curled, anesthetized animal except that the thoracic region of the former remained warmer due to periodic rewarmings, and also shivering in this well-muscled area. It is concluded that entrance into hibernation is not strictly temperature-dependent and that the animal is vasodilated during this process.

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