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R. E. SMITH, BARBARA A. HORWITZ, and Y. IMAI
weighed animals. Since this study was done in the latter part of the hibernating season (February and March), it is likely that the relative amounts of
brown fat in the squirrels were considerably less at this time than would be
seen at the beginning of the hibernating season (cf. A. T. RASMUSSEN, J. Morpho!. 38, 147, (1924)). (2) We did not measure the loss in brown fat weight
during the course of arousal. JOEL, however (Handbook of PhysioI., Selt. 5,
Adipose Tissue, Amer. PhysioI. Soc., Washington, D. c., 1965, p.59) has
reported that during the arousal of the 13-lined ground squirrel (C. tridecemlineatus), the brown fat loses about 0.95 gm of lipid.
ARLEY:
Can you measure the phenomenon of shivering in a quantitative way? And if SO,
could it be used to observe the metabolic processes of your hibernating
animals visually and thus without interfering with their normal life processes?
It seems to me that avoiding such interference would be one of the most
important problems encountered in biological experimentation.
SMITH:
In answer to your question, let me try to clarify an apparent misunderstanding.
Since we sought to evaluate the brown fat thermogenesis relative to that of the
whole animal, there was no necessity to determine the quantity of heat resulting solely from shivering. Mention was made, however, of the fact that
shivering usually occurred during some stage of the experimental procedure.
This observation was reported to emphasize that the total caloric output of
both the rats and squirrels included the thermal contributions from both
shivering and non-shivering activities. Therefore, the percentages calculated
for the brown fat thermal contributions are lower than would be obtained if
the heat production of the tissue had been compared only to the non-shivering
thermogenesis of the animal. On the other hand, I entirely agree with you
that the optimal conditions for any experimentation are those which interfere
least with the normal physiological status of the animal.
R. E. SMITH, BARBARA A. HORWITZ, and Y. IMAI
weighed animals. Since this study was done in the latter part of the hibernating season (February and March), it is likely that the relative amounts of
brown fat in the squirrels were considerably less at this time than would be
seen at the beginning of the hibernating season (cf. A. T. RASMUSSEN, J. Morpho!. 38, 147, (1924)). (2) We did not measure the loss in brown fat weight
during the course of arousal. JOEL, however (Handbook of PhysioI., Selt. 5,
Adipose Tissue, Amer. PhysioI. Soc., Washington, D. c., 1965, p.59) has
reported that during the arousal of the 13-lined ground squirrel (C. tridecemlineatus), the brown fat loses about 0.95 gm of lipid.
ARLEY:
Can you measure the phenomenon of shivering in a quantitative way? And if SO,
could it be used to observe the metabolic processes of your hibernating
animals visually and thus without interfering with their normal life processes?
It seems to me that avoiding such interference would be one of the most
important problems encountered in biological experimentation.
SMITH:
In answer to your question, let me try to clarify an apparent misunderstanding.
Since we sought to evaluate the brown fat thermogenesis relative to that of the
whole animal, there was no necessity to determine the quantity of heat resulting solely from shivering. Mention was made, however, of the fact that
shivering usually occurred during some stage of the experimental procedure.
This observation was reported to emphasize that the total caloric output of
both the rats and squirrels included the thermal contributions from both
shivering and non-shivering activities. Therefore, the percentages calculated
for the brown fat thermal contributions are lower than would be obtained if
the heat production of the tissue had been compared only to the non-shivering
thermogenesis of the animal. On the other hand, I entirely agree with you
that the optimal conditions for any experimentation are those which interfere
least with the normal physiological status of the animal.