Influence of circulating NE and Epi on adipose tissue vascular resistance and lipolysis in humans

Abstract

The effects of circulating norepinephrine (NE) and epinephrine (Epi) on vascular resistance in subcutaneous adipose tissue and the calf as well as on plasma glycerol, an indicator of lipolysis, were studied in healthy volunteers. Adipose tissue blood flow was determined by the local clearance of 99mTcO-4 or 133Xe. The two isotopes gave similar results. Calf blood flow was determined by venous occlusion plethysmography. Intravenous infusion of NE caused increases in systolic and diastolic blood pressures, adipose tissue and calf vascular resistances, and plasma glycerol and a decrease in plasma insulin and heart rate, all of which were significant when arterial plasma NE was elevated from 1.17 +/- 0.14 to 8.38 +/- 0.30 nM (n = 16). Epi reduced diastolic and mean arterial pressures and adipose tissue and calf vascular resistances and increased plasma glycerol without affecting systolic blood pressure or plasma insulin. An increase of arterial plasma Epi from 0.20 +/- 0.03 to 1.15 +/- 0.05 nM (n = 6) was sufficient to induce vasodilatation in adipose tissue and lipolysis. Human adipose tissue differs from canine adipose tissue inasmuch as Epi causes vasodilatation in humans (present results) but vasoconstriction in the dog (previous results), presumably due to a predominance of vascular beta 2-adrenoceptors in human and beta 1-adrenoceptors in canine adipose tissue. Furthermore, Epi is a considerably more potent lipolytic hormone than NE in humans but not in the dog. Our results indicate that both NE and Epi may influence human adipose tissue blood flow and lipolysis as circulating hormones.

The effect on adipose tissue blood flow of isoenergetic meals containing different amounts and types of fat

“…28 -30 Noradrenaline infusion has been shown to cause adipose tissue vasoconstriction. 31 However, the noradrenaline concentrations required to produce this effect were 7-fold the concentrations seen in our study. The fact that, especially after the high-fat meals, the peak noradrenaline concentration occurred later than the peak in ATBF suggests that physiologically, noradrenaline is less important that insulin in this respect.…”

Major differences in noradrenaline action on lipolysis and blood flow rates in skeletal muscle and adipose tissue in vivo

“…Studies where the 133 Xe clearance methods have been used in adipose tissue and plethysmography in skeletal muscle have given divergent results. Vasoconstriction in both adipose tissue and muscle tissue, as well as vasodilatation in adipose tissue coupled with no vascular reaction in the muscle, has been described [25,29]. Dose-related blood flow responses to noradrenaline in skeletal muscle have been registered using forearm plethysmography.…”

Lipolytic and nutritive blood flow response to β-adrenoceptor stimulation in situ in subcutaneous abdominal adipose tissue in obese men

“…6 On the other hand, the release of glycerol from the interstitial fluid into the systemic circulation may be reduced because of a lowered adipose tissue blood flow response, as measured by xenon-clearance technique. 4,8,12 Local nutritive blood flow, as assessed by the microdialysis technique by determining the ethanol out/in ratio, increases in lean subjects during local administration of isoprenaline, 13-15 terbutaline 13,16 or dobutamine. 13 However, little is known on whether badrenoceptor changes in local nutritive blood flow are altered in obesity.…”

“…Adipose tissue blood flow, as measured by the 133 xenon-clearance technique, is significantly lower in obese compared to lean subjects, both at rest [7][8][9][10][11] and during i.v. epinephrine 4,12 and isoprenaline infusion. 8 The aim of the present study was to investigate subcutaneous adipose tissue lipolysis during local administration of b-agonists through a microdialysis probe to differentiate between local tissue events and systemic blood flow effects.…”