Autonomic Control of Thermogenic Capacity is Optimized in Deer Mice Native to High or Low Altitudes

The North American deer mouse ( Peromyscus maniculatus ) ranges from below sea level to above 4,300 m elevation. To survive the cold hypoxic conditions at altitude, highland populations must sustain high rates of aerobic thermogenesis in an oxygen scarce environment. Here, we investigated whether differences in autonomic control of the cardiovascular system contributes to the increased thermogenic capacity ( V̇ O 2 max) of deer mice native to high altitudes. We compared captive breeding colonies derived from wild populations at high and low altitudes, and measured V̇ O 2 max in cold hypoxia following intraperitoneal (i.p.) injection of adrenergic agonists/antagonists. Following control saline injection, highland mice had higher mass‐specific V̇ O 2 max than lowland mice. Both α ‐adrenergic agonist and antagonist reduced V̇ O 2 max by a similar magnitude in both populations, indicating that α ‐adrenergic vascular tone is naturally optimized to enhance blood flow to tissues responsible for thermogenic V̇ O 2 max, and that functional sympatholysis does not contribute to population differences in V̇ O 2 max. β 2 ‐adrenergic tone had no effects on V̇ O 2 max, suggesting that these receptors are not required to achieve thermogenic V̇ O 2 max. β 1 ‐adrenergic tone appears to be maximized to achieve V̇ O 2 max in both populations, because β 1 ‐agonist (dobutamine) had no effect on V̇ O 2 max whereas β 1 ‐antagonist (metoprolol) reduced V̇ O 2 max . Preliminary experiments in anaesthetized mice confirmed that pharmacological agents entered the circulation after i.p. injection and had predictable effects on heart rate and blood pressure. Our results therefore suggest that autonomic control of the cardiovascular system is optimized during thermogenesis in hypoxia, such that population differences in V̇ O 2 max do not arise from evolved changes in autonomic control. Support or Funding Information Supported by NSERC of Canada