Obesity and precursor availability affect urinary catecholamine metabolite production in women

The effect of obesity and tyrosine (tyr) supplements on catecholamine metabolism in 12 normal weight and nine obese adult women was studied. Protein intake was maintained at 1.4 g protein/kg fat-free mass daily for 4 days with tyr added (0.26 g/kg fat-free mass) to the liquid diet on the last 2 days. In the 12 normal subjects, but not the obese, base-line urinary excretion of the norepinephrine metabolite, 3-methoxy-4-hydroxy phenylethyleneglycol was related to body fat whereas excretion of the norepinephrine metabolite vanilmandelic acid was related to fat-free mass and to total energy intake. Normal subjects responded to tyr with elevations in plasma tyr/neutral amino acid, plasma 3-methoxy-4-hydroxy phenylethyleneglycol, urinary vanilmandelic acid, and homovanillic acid, a dopamine metabolite, but not the norepinephrine metabolite, dihydroxy phenylethyleneglycol. The obese showed no increase in plasma or urinary 3-methoxy-4-hydroxy phenylethyleneglycol during tyr supplementation, although vanilmandelic acid and homovanillic acid increased. We conclude that urinary catecholamine metabolite production is related to body composition and to tyr intake in normal weight women. These relationships however, are altered in the obese, suggesting an association of obesity with abnormal catecholamine metabolism.