Seasonal thermogenic capacity in a hibernator,Spermophilus richardsonii

Seasonal changes in thermoregulation and maximum metabolism in the yellow-necked field mouse

“…During the experiments carried out in helium-oxygen mixture, a decrease in body temperature to as much as 15 and 12 °C was noted, without lethal effect. The maximum thermogenesis values extrapolated to -20 °C in summer reached 11.6±0.8 ccm CteXg-iXhr- 1 and extrapolated to-30 °C in winter reached 13.4+1.6 ccm OzXg-iXhr-i. BMR in summer (2.9±0.3 ccm OaXg-iXhr" 1 ) did not differ significantly from that determined in winter (3.0±0.4 ccm ChXg-iXhr -1 ).…”

“…The rate of it changes allometrically with body weight (Pasquis et al, 1970, Weiner, unpubl. data) and undergoes seasonal acclimatization though it usually falls into the range between three times and eight times the BMR value (Pasquis et al, 1970, Rosenmann & Morrison, 1974, Rosenmann et al, 1975, Abbotts & Wang, 1980. The maximum metabolism in A. flavicollis do fall within this range.…”

“…The thermal conductivity of helium is about six times higher than that of nitrogen (Rosenmann & Morrison, 1974). Thus the helium-oxygen mixture helped to simulate temperature condition mudh below 0 °C and hence incurring corresponding huge heat loss that made possible measuring the maximum thermogenesis (Wickler, 1980;Abbotts & Wang, 1980). The measurements in the helium-oxygen mixture lasted not less than 15 minutes but never exceeded 70 minutes.…”

Mammalian Hibernation: An Escape from the Cold

“…This study, however, provides the cellular evidence for our in vivo observations in the Richardson's ground squirrel on seasonal changes of NST and weight cycle, namely: (1) during the weight-gain phase, the NE-stimulated NST is comparable to that seen in the weight-stable phase, suggesting patency of sympathetically stimulated thermogenesis of the BAT (Wang and Lee, unpubl. observations); and (2) that in the hibernation phase, the NE-NST is highest, suggesting hypertrophy of the BAT (Abbotts and Wang 1980). Taken together, these observations indicate that during the weight-gain phase, BAT hypertrophy occurs but thermogenesis is apparently not activated to dissipate the excess caloric intake following hyperphagia.…”

“…However, since peak heat production during arousal from hibernation in some ground squirrels is only about 60 -70070 of their maximum thermogenic capability elicited by severe cold (Wang and Abbotts 1981), there remains the possibility that shivering thermogenesis could have increased to compensate for the heat deficit created by the removal of the BAT. 1n this regard it is interesting to note that in the Richardson's ground squirrel, the maximum thermogenic capacity does not vary seasonally but the NST is, however, significantly elevated from 20.6% of total thermogenesis in animals sampled in June to 45.6070 sampled in the hibernating phase (Abbotts and Wang 1980). The significance of this seasonal shift is presumably to aid heat production during the early stages of arousal when conditions for shivering thermogenesis may not have been fully optimized due to low muscle temperature and restriction of blood flow to some of the large muscle masses in the posterior part of the body.…”