| Summary: | The disposal of an infused dose of noradrenaline (NA) (0.42 nmol/kg/min for 60 min) was studied across subcutaneous abdominal adipose tissue and forearm muscle by measuring arteriovenous concentration differences and blood flows using the 133Xe technique. NA infusion increased its basal concentration from 0.9±0.3 nmol/l to a near steady-state value of about 13.7±3.9 nmol/l, (P<0.05) and significantly increased the blood flow to adipose tissue (26±3 vs 69±17 ml/kg/min, P<0.05) but not to muscle (21±2 vs 15±4 ml/kg/min). The mean whole body clearance of NA was found to be high at 2.5 l plasma/min corresponding to 4.6 l whole blood/min. The clearance by muscle and adipose tissue was about 50% of the volume of blood perfusing these tissues. Clearance by adipose tissue was three to four times greater than by an equivalent mass of muscle. Assuming no regional differences in clearance, both tissues combined were estimated to account for 17±6% of the total clearance of NA by the body, with adipose tissue being more important (11±15%) than muscle (6±3%) (P<0.01). It is concluded that subcutaneous abdominal adipose tissue is quantitatively more important than an equivalent mass of muscle in removing infused NA. The effect of NA in increasing blood flow to adipose tissue but not muscle is likely to be important in facilitating its clearance in adipose tissue. Neither muscle nor adipose tissue are likely to be the major sites for removing infused NA in the resting (non-exercising) state.
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