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COMPARATIVE AND EVOLUTIONARY PHYSIOLOGY

AMP does not induce torpor

Department of Biology, Williams College, Williamstown, Massachusetts

Submitted 20 December 2006 ; accepted in final form 31 March 2007

Torpor, a state characterized by a well-orchestrated reduction of metabolic rate and body temperature (T_b), is employed for energetic savings by organisms throughout the animal kingdom. The nucleotide AMP has recently been purported to be a primary regulator of torpor in mice, as circulating AMP is elevated in the fasted state, and administration of AMP causes severe hypothermia. However, we have found that the characteristics and parameters of the hypothermia induced by AMP were dissimilar to those of fasting-induced torpor bouts in mice. Although administration of AMP induced hypothermia (minimum T_b = 25.2 ± 0.6°C) similar to the depth of fasting-induced torpor (24.9 ± 1.5°C), ADP and ATP were equally effective in lowering T_b (minimum T_b: 24.8 ± 0.9°C and 24.0 ± 0.5°C, respectively). The maximum rate of T_b fall into hypothermia was significantly faster with injection of adenine nucleotides (AMP: –0.24 ± 0.03; ADP: –0.24 ± 0.02; ATP: –0.25 ± 0.03°C/min) than during fasting-induced torpor (–0.13 ± 0.02°C/min). Heart rate decreased from 755 ± 15 to 268 ± 17 beats per minute (bpm) within 1 min of AMP administration, unlike that observed during torpor (from 646 ± 21 to 294 ± 19 bpm over 35 min). Finally, the hypothermic effect of AMP was blunted with preadministration of an adenosine receptor blocker, suggesting that AMP action on T_b is mediated via the adenosine receptor. These data suggest that injection of adenine nucleotides into mice induces a reversible hypothermic state that is unrelated to fasting-induced torpor.

core body temperature; adenosine; hibernation; heart rate

This article has been cited by other articles:

				S. J. Swoap Why one enters torpor: focus on "NPY Y1 receptor antagonist prevents NPY-induced torpor-like hypothermia in cold-acclimated Siberian hamsters" Am J Physiol Regulatory Integrative Comp Physiol, January 1, 2008; 294(1): R234 - R235. [Full Text] [PDF]