Activity -rest (circadian) rhythms were studied in two species of Arctic mammals living in Arctic continuous daylight with all human-induced regular environmental cues (zeitgebers) removed. The two Arctic species (porcupine and ground squirrel) lived outdoors in large enclosures while the Arctic summer sun circled overhead for 82 days. Would local animals maintained under natural continuous daylight demonstrate the Aschoff effect described in previously published laboratory experiments using continuous light, in which rats' circadian activity patterns changed systematically to a longer period, expressing a 26-hour day of activity and rest? The outdoor experiments reported here, however, showed that under natural continuous daylight, both species (porcupine and ground squirrel) had specific times of activity and rest on a nearly 24-hour scale, and their activity peaks did not come later each day. The daily rhythms of the two species were recorded using implanted physiological radio capsules, and from direct observation.

Small hibernating animals experience cycles of deep hypothermia followed by rewarming and feeding. This contrasts with bears, which remain in hibernation for four to seven months, experiencing large reductions in energy metabolism and heart rate, and small reductions in core temperature, and do not eat, drink, urinate, or defecate throughout. We measured the QT interval (QT) of the electrocardiogram (EKG) to determine whether the hearts of bears behave electrophysiologically more like classic hibernators or nonhibernators. We compared EKGs from grizzly and polar bears with small hibernators (marmots) and humans. Animal data were obtained using implanted radio capsules. EKGs of non-dormant marmots were characterized by a shortened QT (0.07-0.14 s); this held for grizzly and polar bears (0.14-0.23 s), but not for humans (0.39 s). Thus, the QT of bears resembles that of small hibernators. At the same heart rate, the QT of non-dormant bears and marmots differs in winter and summer.

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Blood from albino mice clots in glass tubes (Lee-White test) in approximately two minutes. The tube can be inverted and the coagulated blood does not move for hours. In contrast, blood from winter and summer deer mice (Peromyscus leucopus) from Iowa, and summer deer mice (N ¼ 89) from Connecticut, Georgia, and Texas (USA) either did not clot at all or formed a transient clot which became liquid within 1-5 minutes. A small (1/10 of specimen volume) clump remained in most specimens. The mechanism of the phenomenon is unknown, but may be an exceptionally enhanced spontaneous clot lysis.

Hearts of hibernators can resist lethal arrhythmias seen in hypothermic non‐hibernators. We present data on the effects of hypothermia on hearts of large hibernators, black bears. Hypothermia is used in cardiac surgery and survivors of cardiac arrest, but can also be fatal, leading to arrhythmias such as ventricular fibrillation and asystole. We compare electrophysiologic changes the heart undergoes in hypothermia between black bears and humans. Specifically, we compare heart rate and QT interval (QTi) with core body temperature. The last part of the QTi is the time during which the heart electrically repolarizes and mechanically relaxes. During this time the heart is vulnerable to fibrillation. Animal data was obtained from radio capsules implanted in 3 black bears that were made progressively hypothermic. Human data came from published literature. Black bears and humans show a direct relationship between heart rate and body temperature. Both bears and humans developed J (Osborne) waves, the amplitude of which correlated with the degree of hypothermia. As heart rate and body temperature decrease, QTi increases. However, 2 of the bears demonstrated a shortening of the QTi as their core temperature reached 21.8°C. After this point, the QTi began to prolong. This perturbation was not seen in human subjects, and was an unexpected finding. Does the hibernating heart attempt to resist hypothermia? Supported by ONR, NSF.