Nonshivering thermogenesis in skeletal muscle of seasonally acclimatized mice, Peromyscus

Abstract

Nonshivering thermogenesis (NST) is a major contributor to total heat production capabilities of Peromyscus and the magnitude of the NST response increases dramatically in winter-acclimatized animals. To directly assess the contribution from skeletal muscle to this NST, a hindlimb perfusion system was developed for Peromyscus. O2 consumption was then measured with and without norepinephrine (the mediator of NST) in freshly captured animals in summer and winter. Norepinephrine (NE) was infused at 0.001, 0.01 and 0.1 .mu.g/g hindlimb muscle per min. Vascular resistance (VR), calculated as arterial pressure divided by flow rate, increased during all NE infusions. At doses of 0.001 and 0.01, VR stabilized after approximately 10 min, but at 0.1 VR continued to rise. Resting O2 consumption was 0.817 .+-. 0.037 and 0.805 .+-. 0.049 .mu.mol O2/g per min in summer (n = 8) and winter (n = 7) animals, respectively. There was no apparent increase in O2 consumption with any dosage of NE. The increase in NST in winter animals is probably not due to an increased NST in skeletal muscle.