title: Physiological increments in epinephrine stimulate metabolic rate in humans.
abstract: Markedly elevated plasma epinephrine is known to increase metabolic rate (MR), but such levels of epinephrine are encountered infrequently in normal free-living subjects. We studied whether epinephrine levels common in usual daily activities can affect MR and thus possibly regulate caloric expenditure. To aid definition of a MR threshold, we first measured the hourly and daily variation in MR within individuals by measuring the MR of four individuals by indirect calorimetry for 6 h on six separate occasions without any intervention. We found that hour-to-hour variation (2.0 +/- 0.9%) and the day-to-day variation (2.7 +/- 0.9%) were low, thus allowing confident detection of small increments in metabolic rate during epinephrine infusion. To define a threshold for epinephrine's effect to increase MR, we studied five normal-weight postabsorptive young men on four separate occasions. During the 1st h of each 5-h study period, saline was infused intravenously. Then, during the subsequent 4 h, subjects received intravenous infusion of saline or epinephrine at 0.1, 0.5, and 1.0 microgram/min (randomized). A significant increase in MR (3.6 +/- 1.0% SE) was measured with the lowest epinephrine infusion rate (venous plasma concentration, 94 +/- 32 pg/ml). The increases in MR correlated (r = 0.85, P less than 0.001) with increases in plasma epinephrine. The threshold concentration (upper 95% confidence limit) of epinephrine to affect MR was 90 pg/ml, a concentration frequently occurring in daily life. Thus epinephrine may play an important role in weight maintenance by affecting energy expenditure.
mesh_terms: D000328:Adult; D002940:Circadian Rhythm; D004056:Differential Threshold; D004837:Epinephrine / Q000097:blood / Q000494:pharmacology*; D005230:Fatty Acids, Nonesterified / Q000097:blood; D006801:Humans; D007262:Infusions, Intravenous; D008297:Male; D008660:Metabolism / Q000187:drug effects*; D009994:Osmolar Concentration; D012119:Respiration / Q000187:drug effects; D013268:Stimulation, Chemical
chemical_list: D005230:Fatty Acids, Nonesterified; D004837:Epinephrine