Blood flow in canine adipose tissue during intravenous infusion of norepinephrine

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

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 CO2 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.

Subcutaneous adipose tissue blood flow and triacylglycerol-mobilization during prolonged exercise in dogs

In 6 dogs concentration differences for glycerol and FFA were measured between the aorta and the external pudendal vein, a vein which mainly drains subcutaneous adipose tissue in dogs, during prolonged exercise. It was found that the a-v differences increased about 2-fold for both glycerol and FFA, however great interindividual differences were found. In 4 dogs adipose tissue blood flow, glycerol and FFA a-v differences were measured simultaneously, and the mobilizations of glycerol and FFA as well as the re-esterification of FFA were calculated. After 2 h of exercise the values were in the range of 1-7 umol/(100 g.min) for FFA and glycerol mobilizations while the FFA re-esterification was in the range of 2-14 umol/(100 g.min). It was found that the FFA/albumin ratio in adipose venous blood, on average 3.6 was at a level at which the FFA mobilization has been shown to depend on the adipose tissue blood flow in isolated fat pads. In 11 dogs subcutaneous adipose tissue blood flow rose 2-fold during exercise from about 5-10 ml/(100 g.min). It is concluded that the subcutaneous adipose tissue blood flow response to exercise is equal in man and dog, that lipolysis, FFA mobilization and FFA re-esterification are increased in subcutaneous adipose tissue during exercise, and that the increase in blood flows is of importance for the enhanced FFA mobilization during exercise.

Comparison of beta-adrenoceptors mediating vasodilatation in canine subcutaneous adipose tissue and skeletal muscle

Blood flow changes in response to various drugs in simulataneously autoperfused canine subcutaneous adipose tissue and gracilis muscle were compared to study the vascular beta-adrenoceptors. Compared to isoprenaline the beta 2-selective agonist salbutamol was 4--6 times more potent as a vasodilator in the muscle than in adipose tissue. Furthermore two beta 1-selective agonists (Tazolol and H80/62) caused vasodilatation in adipose tissue but not in the gracilis muscle. When given by close i.a. injection after beta-adrenoceptor blockade, adrenaline was a more potent vasoconstrictor than noradrenaline in both tissues. Before beta-blockade, however, noradrenaline was the more potent vasoconstrictor in the gracilis muscle whereas adrenaline was more potent in adipose tissue. Intravenous infusion of adrenaline in doses causing vasodilatation in the muscle caused vasoconstriction in adipose tissue whereas intravenous infusion of noradrenaline caused vasoconstriction in both tissues. The present findings suggest that the beta-adrenoceptors mediating vasodilatation in skeletal muscle are mainly ose tissue. Since adrenaline is a much more potent beta2- than beta1-agonist, these differences point to different roles of intravascular adrenaline in the two sites. In skeletal muscle circulating adrenaline is mainly a vasodilator whereas in subcutaneous adipose tissue it mainly acts as a vasoconstrictor.

Noradrenaline reversal in canine subcutaneous adipose tissue

Although adrenaline reversal is a well known phenomenon, fewer investigations have demonstrated reversal of the vascular response to noradrenaline (NA). The present studies compared subcutaneous adipose tissue vascular responses to intra-arterial NA with those of sympathetic nerve stimulation. Both NA and electrical stimulation produced vasoconstriction in adipose tissue which was reversed to beta-adrenergically mediated vasodilation following local alpha-adrenergic block.

Influence of acidosis on noradrenaline-induced vasoconstriction in adipose tissue and skeletal muscle

Vasoconstriction due to parallel i.a. injections of NA were studied in subcutaneous adipose tissue and gracilis muscle preparations in dogs. The vasoconstrictor response to NA was significantly lower in adipose tissue than in muscle. Only in muscle did acidosis inhibit NA-induced vasoconstriction. The beta-receptor antagonist propranolol increased the vasoconstrictor response in adipose tissue to the level of skeletal muscle. The lack of significant inhibition of NA-induced vasoconstriction in adipose tissue may be due to the simultaneous inhibition of two opposing mechanisms-alpha-adrenergic vasoconstriction and beta-adrenergic vasodilatation. After propranolol acidosis inhibited NA-induced vasoconstriction equally in adipose tissue and muscle. The difference between adipose tissue and muscle may thus be due to a greater importance of a beta-adrenergic vasodilator mechanism in the former tissue. The metabolic response to isoprenaline was inhibited by acidosis, while the direct vasodilatation was unaffected. It is suggested that the beta-adrenergic vasodilator mechanism that is inhibited by acidosis is related to the metabolism of the tissue.

The distribution of blood flow between individual muscles and non-muscular tissues in the hind limb of the young ox (Bos taurus): values at thermoneurality and during exposuer to cold

1. The radioactive microspheres method was used to measure the distribution of blood flow in the hind leg in conscious young steers exposed to thermoneutral and moderately cold environments. Simultaneous measurement of total leg blood flow allowed calculation of blood flow (ml. 100 g tissue-1 min-1) to individual muscles and the major non-muscular tissues in the leg. 2. In the thermoneutral environment, leg blood flow was distributed approximately according to tissue weight, so that about 65% went to muscle and the remainder to bone, skin, connective tissue and fat; 1-7-11-5% of the injected dose of microspheres was found in the lungs, indicating the presence of functioning arteriovenous anastomoses in the leg. 3. During cold exposure leg blood flow increased two-and-a-half fold and 91% of this increase was due to increased blood flow in muscle. This was accompanied by substantial decreases in both total and capillary blood flow in leg skin in three of the four animals. 4. Values for resting tissue blood flow to the six largest individual leg muscles were compared, as well as that for tissue blood flow to the remaining leg muscle. Blood flow in the three large upper thigh muscles (biceps femoris, semimembranosus and semitendinosus) was about half that in muscles in the rest of the leg. 5. Cold exposure caused a threefold increase in total leg muscle blood flow, but the only individual muscles to respond substantially in all four animals were the vastus lateralis and the rectus femoris. Comparison of results from individual animals suggested a relation between total leg blood flow and the number of muscles (apart from vastus lateralis and rectus femoris) involved in shivering. Leg adipose tissue blood flow also increased significantly in the cold.