REGIONAL SYMPATHETIC NERVOUS ACTIVATION AFTER A LARGE MEAL IN HUMANS

1. To investigate the link between post-prandial thermogenesis and sym pathetic nervous activation we have studied the effects of a single la rge meal on regional sympathetic nervous activity in healthy, lean sub jects. 2. In nine male subjects, noradrenaline spillover was measured from the heart, kidney and liver using isotope dilution, both while fa sting and after consumption of a high-energy liquid meal of compositio n 53% carbohydrate, 32% fat and 15% protein (energy value 2.64-3.51 MJ ). Regional oxygen consumption, whole-body oxygen consumption and, in a subset of subjects, muscle sympathetic nerve firing (microneurograph y) were also measured. 3. Both whole-body oxygen consumption (P<0.03) and total body spillover of noradrenaline (P<0.01) rose after the meal , with peak increases of 24% and 56% respectively. Spillover of noradr enaline from the heart was unchanged, that from the hepatosplanchnic c irculation increased marginally (0.377 nmol/min to 0.480 nmol/min, P=0 .09), while renal noradrenaline spillover more than doubled (0.440 nmo l/min to 0.937 nmol/min, P<0.05). Skeletal muscle sympathetic nerve ac tivity (peroneal nerve) increased from 7.7 bursts/min at rest to peak at 17.9 bursts/min 60 min after the meal in the three subjects in whom stable recordings were obtained. 4. The meal increased oxygen consump tion in the kidneys and liver significantly, from 11.5 +/- 1.6 ml/min to 14.5 +/- 1.1 ml/min and from 46 +/- 7 ml/min to 57 +/- 6 ml/min res pectively (P<0.05), but not in the heart. 5. Consumption of a large me al produces a substantial and relatively selective increase in sympath etic outflow to the kidneys and skeletal muscle. While resting regiona l oxygen consumptions and noradrenaline spillovers were related, the c hanges that occurred in each were unrelated, so that no direct relatio nship could be demonstrated between postprandial thermogenesis and sym pathetic activity.