thermogenesis resulting from the effects of the sympathetic nervous system neurotransmitters, epinephrine, and norepinephrine, acting to increase the cellular metabolic rate in skeletal muscle and other tissues, thereby increasing heat production. In a specialized form of adipose tissue, brown fat, the effect of the sympathetic neurotransmitters is to increase the rate of uncoupled oxidative phosphorylation by the mitochondria, which results in heat production without formation of adenosine 5'-triphosphate.