Haemodynamic responses in muscle and adipose tissue and whole body metabolic responses during norepinephrine infusions in man

Abstract

Circulatory metabolic and cardiovascular responses to 1-h-long infusions of norepinephrine (NE) (approx. 0.2 and 0.4 nmol/kg body weight per min) were measured on two separate occasions in six subjects. The infusions increased circulating NE concentrations 6- and 13-fold, respectively. Blood flow to adipose tissue, measured with the 133Xe clearance technique, increased from a basal value of about 3 ml/100 g per min, to about twice this value at 60 min with both doses of NE. In contrast muscle blood flow was unaffected. The higher dose of NE produced significant increments at 60 min in whole body oxygen consumption (approx. 9%), and circulating concentrations of glucose (approx. 18%), non-esterified fatty acids (approx. 200%) and glycerol (approx. 32%) which were greater than those observed with the low-dose infusion. Changes in blood pressure, pulse and CO 2 exchange were observed within 5–10 min after the start of the infusion, whilst changes in adipose tissue blood flow were observed after 15–30 min. It is concluded that in humans ( i) a dose of NE as low as 0.2 nmol/kg per min is sufficient to evoke both circulatory and metabolic responses; ( ii) the pattern in the adipose tissue blood flow response to NE may help explain some of the conflicting reports about the haemodynamic effects of this hormone in adipose tissue; and ( iii) blood flow and vascular resistance in different tissues may be affected in different ways by norepinephrine.