Torpidity in Mammals

Seasonal pattern and energetics of short daily torpor in the Djungarian hamster, Phodopus sungorus

“…On the other hand it should be kept in mind that the estimate was based on comparisons of resting metabolic rate, and it is difficult to appraise the extent to which this assumption is in accordance with conditions in nature. This difficulty will arise from the extra energy expenditure for foraging and other energy" consuming behavioural activities which should be taken into account, and will include the problem whether frequency, length and depth of torpor observed experimentally will be representative of their occurrence in nature, as discussed by Hudson (1973) andHill (1975). For example if torpor would actually replace periods of activity instead of rest, the amount of energy saved by torpor will be higher than suggested above.…”

Mammalian Hibernation: An Escape from the Cold

“…The blood pressure is typically maintained at 90/30 mm Hg in comparison to the 130/80 mmHg seen in euthermia. These and other impressive cardiovascular modifications related to hibernation have been extensively reviewed (e.g., South et al 1972;Hudson 1973;Lyman 1984) and only selected highlights will be presented here. Studies on the isolated, perfused heart indicate that hearts from species which hibernate (body temperature = 2 0 -7 °C typically, e. g., woodchuck, ground squirrel, chipmunk, and hamster) continue to beat at -0.5 0 to 7°C, whereas hearts from those which do not hibernate (tree squirrel, white rat, cotton rat, and mountain beaver) stop beating at 10 0 to 16°C (Lyman and Blinks 1959).…”

“…Earlier literature has been summarized by Lyman and Chatfield (1955), Kayser (1961), Hoffman (1964), Hudson (1973) and more recently, Raths and Kulzer (1976), Davis (1976), , Lyman (1984), and Wang (1985and Wang ( , 1986a. Specific aspects of hibernation have also been reviewed, for instance on neural (Beckman 1978;Beckman and Stanton 1982;HelIer 1979), endocrinological (Hudson and Wang 1979;Wang 1982Wang , 1987b, ionic (Willis 1979), and membrane aspects (Willis et al 1981).…”

“…Such diversities in torpor pattern no doubt represent the heterogeneity in selection pressure which different ecological niches exemplify. Extensive studies on the evolutionary, biochemical, physiological, neurophysiological, and neuroendocrinological aspects have firmly established that torpor in mammals is polyphyletic in origin and is an advanced form of thermoregulation rather than a reversion to primitive poikilothermy (see Hudson 1973;Lyman et al 1982, for reviews).…”

Control of sex steroid-binding protein (SBP) in the male little brown bat: relationship of plasma thyroxine levels to the induction of plasma SBP in immature males

“…Although the factors that control these seasonal fluctuations are not known precisely, a recent study has indicated that the increases in plasma SBP levels which occur following arousal from hibernation may be modulated by the thyroid gland (Damassa, Gustafson, Kwiecinski & Pratt, 1985). In addition, thyroid function in bats (Sadler & Tyler, 1960; Azzali, 1967;Nunez & Becker, 1970;Fujita, 1971;Velicky & Titlbach, 1972;Nunez, Wallis & Gershon, 1974), as in other mammalian hibernators (Hoffman, 1964;Hudson, 1973;Maurel, Joffre & Boissin 1977;Demeneix & Henderson, 1978;Saboureau & Boissin, 1978;Hudson & Wang, 1979;Young, Danforth, Vagenakis et al 1979;Jallageas & Ässenmacher, 1984), exhibits marked seasonal fluctuations. In general, thyroid activity has been found to increase in the spring, decrease in the autumn and remain quiescent throughout most of hibernation.…”