Metabolic correlates of selection for swim stress-induced analgesia in laboratory mice
Konarzewski, M.; Sadowski, B.; Jóźwik, I.
American Journal of Physiology 273(1 Pt 2): R337-R343
1997
ISSN/ISBN: 0002-9513 PMID: 9249569 Document Number: 471687
The upper limits of metabolic rates and the links between maximal and resting metabolic rates in vertebrates have recently received a lot of attention, mainly due to their possible relationship to the evolution of endothermy. We measured peak metabolic rates during 3 min swimming in 20 degree C water ( ovrhdot VO-2s-wim), maximal metabolic rate ( ovrhdot VO-2max) in -2.5 degree C Helox, and basal metabolic rate (BMR) in two lines of mice selected for high (HA) and low (LA) swim stress-induced analgesia (SSIA). We found that exercise combined with heat loss used for producing SSIA also acted as a selection agent, resulting in a 15% HA/LA line difference in ovrhdot VO-2swim. Core body temperature of HA mice (characterized by lower ovrhdot VO-2swim) was also on average 3.2 degree C lower than that of LA mice. Furthermore, ovrhdot VO-2max of HA mice was lower than that of LA mice by 8% and accompanied by larger hypothermia. Thus mice with exceptionally high (or low) ovrhdot VO-2max tended to have exceptionally high (or low) ovrhdot VO-2swim, resulting in a positive correlation between ovrhdot VO-2swim and ovrhdot VO-2max. All these suggest that selection for SSIA produced genetically correlated responses in both ovrhdot VO-2swim and ovrhdot VO-2max. However, we did not observe HA/LA differences in BMR. Hence, changes in resting and maximum metabolic rates are not necessarily correlated. We hypothesize that the lack of such a correlation was partially due to the modulation of metabolic responses by SSIA.