Inhibition of shivering in hypothermic seals during diving

• Published in: American journal of physiology. Regulatory, integrative and comparative physiology integrative and comparative physiology, 2005-08, Vol.289 (2), p.R326-R331
• Main Authors: Kvadsheim, Petter H, Folkow, Lars P, Blix, Arnoldus Schytte
• Format: Article
• Language: English
• Subjects: Air; Animals; Body Temperature - physiology; Brain - physiology; Cold Temperature; Diving - physiology; Electromyography; Male; Muscle, Skeletal - physiology; Rectum - physiology; Seals, Earless - physiology; Shivering - physiology
• ISSN: 0363-6119; 1522-1490
• DOI: 10.1152/ajpregu.00708.2004

Department of Arctic Biology and Institute of Medical Biology, University of Tromsø, Tromsø, Norway Submitted 18 October 2004 ; accepted in final form 3 March 2005 The mammalian response to hypothermia is increased metabolic heat production, usually by way of muscular activity, such as shivering. Seals, however, have been reported to respond to diving with hypothermia, which in other mammals under other circumstances would have elicited vigorous shivering. In the diving situation, shivering could be counterproductive, because it obviously would increase oxygen consumption and therefore reduce diving capacity. We have measured the electromyographic (EMG) activity of three different muscles and the rectal and brain temperature of hooded seals ( Cystophora cristata ) while they were exposed to low ambient temperatures in a climatic chamber and while they performed a series of experimental dives in cold water. In air, the seals had a normal mammalian shivering response to cold. Muscles were recruited in a sequential manner until body temperature stopped dropping. Shivering was initiated when rectal temperature fell below 35.3 ± 0.6°C ( n = 6). In the hypothermic diving seal, however, the EMG activity in all of the muscles that had been shivering vigorously before submergence was much reduced, or stopped altogether, whereas it increased again upon emergence but was again reduced if diving was repeated. We conclude that shivering is inhibited during diving to allow a decrease in body temperature whereby oxygen consumption is decreased and diving capacity is extended. hooded seal Cystophora cristata ; shivering electromyogram; body core temperature; thermoregulation Address for reprint requests and other correspondence: P. H. Kvadsheim, Norwegian Defence Research Establishment, PO Box 115, NO-3191 Horten, Norway (E-mail: phk{at}ffi.no )