The influence of body mass on thermoregulatory responses of newly born and adult guinea pigs to changes in ambient temperature, to hypoxia, and to hypercapnia
Farkas, M.; Donhoffer, S.Z.
Acta Physiologica Academiae Scientiarum Hungaricae 45(1-2): 15-21
1974
ISSN/ISBN: 0001-6756 PMID: 4470850 Document Number: 79430
The relationship between body weight (BW) and the changes in colonic temperature (.DELTA.Tc) was analyzed in guinea pigs aged less than 2 days, 3 to 6 days, 7 to 9 days and 10 to 20 days, and in adult animals, in response to transfer from a thermoneutral environment to a moderately cold one (newborn: 20.degree. C; adults: 20.degree. and 10.degree. C). Subsequently, the animals were exposed at these ambient temperatures (Ta) to 8% O2 and to 6% CO2. No correlation could be demonstrated between BW and .DELTA.Tc in response to transfer to the colder environment in any age-group with the exception of the group aged 10 to 20 days. In none of the groups was significant correlation observed between BW and the increase in heat production (.DELTA.O2) in response to transfer to the cold. In the newborn, no relationship was found between BW and .DELTA.Tc in hypoxia; in adult animals exposed to hypoxia at Ta 20.degree. C, the coefficient of correlation was significant statistically, but indicated that the reduction in Tc tended to increase with increasing BW. In hypercapnia, a statistically significant correlation was observed between BW and Tc in the group aged 7 to 9 days, and coefficients of similar magnitude were obtained with adult animals both at Ta 20.degree. C and at Ta 10.degree. C, showing that the fall in Tc tended to be greater in the smaller animal. Under conditions not leading to progressive hypothermia, BW, i.e., the mass-surface ratio is, at most, a minor determinant of the changes in Tc.