Effect of carbohydrate ingestion on adipose tissue lipolysis during long-lasting exercise in trained men

To study whether sucrose administration acts on lipid mobilization during prolonged exercise, we used subcutaneous abdominal adipose tissue microdialysis in eight well-trained subjects submitted at random to two 100-min exercises (50% maximal aerobic power) on separate days. After 50 min of exercise, the subjects ingested either a sucrose solution (0.75 g/kg body wt) or water. By using a microdialysis probe, dialysate was obtained every 10 min from the subjects at rest, during exercise, and during a 30-min recovery period. During exercise without sucrose, plasma and dialysate glycerol increased significantly. With sucrose, the response was significantly lower for dialysate glycerol (P < 0.05). Plasma free fatty acid level was lower after sucrose than after water ingestion (P < 0.05). With water ingestion, plasma catecholamines increased significantly, whereas insulin fell (P < 0.05). With sucrose ingestion, the epinephrine response was blunted, whereas the insulin level was significantly increased. In conclusion, the use of adipose tissue microdialysis directly supports a lower lipid mobilization during exercise when sucrose is supplied, which confirms that the availability of carbohydrate influences lipid mobilization.     

Adipose tissue leptin production and plasma leptin kinetics in humans

Abdominal adipose tissue leptin production was determined in vivo by arteriovenous balance in 14 lean and obese men (mean BMI 27.0 +/- 1.9, range 21.4-45.2). Blood samples were taken simultaneously from an abdominal vein that drains subcutaneous adipose tissue and from a radial artery. Adipose tissue blood flow was measured by xenon washout. Abdominal vein leptin concentrations (mean 8.9 +/- 2.4 ng/ml, range 2.1-36.5 ng/ml) were consistently greater than arterial values (mean 6.6 +/- 1.9 ng/ml, range 1.7-28.2 ng/ml) (P < 0.001). The net rate of abdominal adipose tissue leptin production (mean 3.2 +/- 0.5 ng x 100 g(-1) x min(-1)) correlated directly with percentage body fat (rs = 0.59, P = 0.016). Estimated whole-body leptin production rate (797 +/- 283 ng x person(-1) x min(-1)) correlated directly with percent body fat (rs = 0.93, P < 0.0001) and with regional leptin production (rs = 0.81, P < 0.001). In contrast, the rate of leptin clearance from plasma (mean 1.50 +/- 0.23 ml x kg(-1) x min(-1)) and plasma leptin half-life (mean 24.9 +/- 4.4 min) was unrelated to adiposity (rs = 0.06, P = 0.30; rs = 0.16, P = 0.30, respectively). These results provide direct evidence that leptin is produced by adipose tissue in humans and that the rate of production is directly related to adiposity. A combination of greater leptin production per unit of body fat and increased production from expanded total body fat mass, rather than alterations in leptin clearance, account for the increase in plasma leptin concentrations observed in obese humans.     

Right atrial pressure and forearm blood flow during prolonged exercise in a hot environment

Right atrial pressure (RAP) at rest is known to be reduced by an increase in skin blood flow (SkBF) in a hot environment. However, there is no clear evidence that this is so during exercise. To clarify the effect of the increase in SkBF on RAP during exercise, we measured forearm blood flow (FBF) (as an index of SkBF) and RAP continuously using a Swan-Ganz catheter in five male volunteers exercising on a cycle ergometer at 60% of peak aerobic power for 50 min in a hot environment (30 degrees C, relative humidity 20%). Cardiac output increased from 5.5 +/- 0.2 l/min at rest to 17.9 +/- 1.2 l/min (mean +/- SE, P < 0.01) in the first 10 min of exercise and then remained steady until the end of exercise. FBF did not change significantly during the first 5 min, but then increased from 2.7 +/- 0.5 ml/100 ml per min at rest to 10.8 +/- 1.7 ml/100 ml per min (P < 0.001) by 25 min as pulmonary arterial blood temperature (Tb) rose from 37.0 +/- 0.1 degrees C to 38.1 +/- 0.1 degrees C (P < 0.001). FBF then reached a plateau, despite a continuing increase in Tb. RAP increased significantly from 4.3 +/- 0.8 to 7.6 +/- 1.2 mm Hg (P < 0.001) during the first 5 min of exercise and then gradually declined to 6.1 +/- 1.0 mm Hg by 25 min (P < 0.001 vs. 5 min) and further to 5.7 +/- 1.0 mm Hg by 50 min, a value not significantly higher than at rest.(ABSTRACT TRUNCATED AT 250 WORDS)     

Computer analysis system of blood oxygen saturation in an animal hypoxia model

Forearm blood flow (ml/min/100 ml) was determined with strain-gauge venous occlusion plethysmography at rest and in response to handgrip exercise in 7 patients with congestive heart failure and in 9 normal subjects before and after regional administration of endothelin-1 in the brachial artery. Administration of endothelin-1 significantly decreased forearm blood flow at rest and during exercise in normal subjects but did not change it at rest or during exercise in patients with congestive heart failure.     

What is the blood flow to resting human muscle?

1. An investigation was carried out in five healthy lean adults to assess whether forearm and calf plethysmography largely reflect muscle blood flow as measured by 133Xe and whether there is substantial variability in the blood flow to muscles located at different sites in the body. 2. Blood flow to forearm and calf flexors and extensors, biceps, triceps and quadriceps was assessed using the 133Xe clearance technique. Blood flow to forearm skin and subcutaneous adipose tissue was also measured using the 133Xe clearance technique, whereas blood flow to the forearm and calf was measured using strain gauge plethysmography. 3. The mean blood flow to different muscles ranged from 1.4 +/- 0.6 (gastrocnemius) to 1.8 +/- 0.7 (forearm extensor) ml min-1 100 g-1 muscle (1.4 +/- 0.6 and 1.9 +/- 0.8 ml min-1 100 ml-1 muscle, respectively) but there were no significant differences between them. Forearm and calf blood flows (2.7 +/- 0.3 and 3.0 +/- 0.7 ml min-1 100 ml-1 limb tissue, respectively) were about 50% to more than 100% greater (P < 0.025) than blood flow to the muscles within them (1.7 +/- 0.5 and 1.4 +/- 0.5 ml min-1 100 g-1 muscle, respectively, or 1.8 +/- 0.6 and 1.5 +/- 0.5 ml min-1 100 ml-1 muscle, respectively). In contrast, the blood flows to 100 g of forearm skin (9.1 +/- 2.6 ml min-1 100 g-1) and adipose tissue (3.8 +/- 1.1 ml min-1 100 g-1) were higher than the blood flow to 100 g of forearm (P < 0.01 and not significant, respectively).(ABSTRACT TRUNCATED AT 250 WORDS)     

Intrinsic regulation of blood flow in adipose tissue

Previous studies on intact human subcutaneous tissue have shown, that blood flow remains constant during minor changes in perfusion pressure. This so-called autoregulatory response has not been demonstrable in isolated preparations of adipose tissue. In the present study on isolated, denervated subcutaneous tissue in female rabbits only 2 of 12 expts. revealed an autoregulatory response during reduction in arterial perfusion pressure. Effluent blood flow from the tissue in the control state was 15.5 ml/100 g-min (S.D. 6.4, n = 12) corresponding to slight vasodilatation of the exposed tissue. Following total ischemia all experiments showed a period with reactive hyperemia, and both duration of hyperemia and excess flow was related to the duration of the ischemia. This response therefore seems more resistant to the experimental procedure, while autoregulation of blood flow to lowered pressure is more susceptible to surgical exposure of the tissue. During elevation of arterial perfusion pressure blood flow in the isolated tissue showed a transient increase and then almost returned to the level during normotension, indicating an elevated vascular resistance. Raising of venous pressure elicited vasoconstriction with pronounced flow reduction. These two reactions may be important for local regulation of blood flow in subcutaneous tissue during orthostatic changes in arterial and venous pressure. It is concluded that the response in adipose tissue to changes in arterial pressure (autoregulation), venous pressure and total ischemia appear to be elicited by different mechanisms.     

Acadesine increases blood flow in the collateralized heart during exercise

Acadesine, an adenosine-regulating agent, has been shown to increase coronary flow and exert cardioprotective effects in acutely ischemic myocardium, but a beneficial effect on coronary collateral flow during exercise has not been demonstrated. We examined the effect of acadesine, 100 micromol/min, i.v., on myocardial blood flow during treadmill exercise in six normal dogs and seven dogs with moderately well-developed coronary collateral vessels. Collateral vessel growth was produced with 2-min intermittent occlusions of the left circumflex coronary artery followed by permanent occlusion. During resting conditions, myocardial blood flow in the collateral zone was not significantly less than in the normal zone, but during exercise, blood flow increased by only 79 +/- 21% (from 0.98 +/- 0.29 ml/min/g to 1.64 +/- 0.19 ml/min/g; p < 0.05) in the collateral zone as compared with 118 +/- 32% (from 1.09 +/- 0.28 ml/min/g to 2.14 +/- 0.2 ml/min/g; p < 0.01) in the normal zone. During exercise, acadesine further increased mean blood flow in the collateral-dependent region by 24 +/- 5% (to 2.04 +/- 0.26 ml/min/g; p < 0.05) with no change in the transmural distribution of perfusion. The increase in collateral zone blood flow in response to acadesine resulted from a decrease in both transcollateral resistance from 25.1 +/- 2.7 mm Hg/min/g/ml to 18.8 +/- 8 mm Hg/min/g/ml (p < 0.05) and small-vessel resistance in the collateral-dependent myocardium from 45.3 +/- 6.6 mm Hg/min/g/ml to 36.4 +/- 5.8 mm Hg/min/g/ml (p < 0.05). Acadesine also significantly increased normal-zone flow in the collateralized dogs (to 2.62 +/- 0.33 ml/min/g; p < 0.05). In contrast, acadesine had no effect on coronary blood flow in normal dogs. In dogs with moderately well-developed collateral vessels, acadesine increased blood flow in both the collateral-dependent and normal myocardial zones during exercise. In contrast, acadesine did not increase blood flow in normal dogs. These findings suggest that adenosine metabolism is altered not only in the collateral-dependent region but also in the normal region of hearts with a coronary artery occlusion.     

Renal and intrarenal blood flow distribution in swine during severe exercise

It is known that a compensatory reduction and diversion of renal flow occurs in severe exercise in humans but not in dogs. We investigated this in miniature swine by measuring changes in total renal blood flow (TRF) and intra-renal blood flow (IRBF) distribution with tracer microspheres (15 +/- 5 mum) at rest and during steady-state exercise at 4.8-7.2 kph and 0% grade, and during severe exercise at 4.8-7.2 kph and 10% grade. We measured heart rate and cardiac output (Q) via implanted probes. TRF was determined as a percent of Q and as ml/100 g per min. IRBF was determined for the outer cortex, inner cortex, outer medulla, and inner medulla. Our results show that renal blood flow is significantly (P less than 0.05) reduced in pigs with exercise. Steady-state exercise reduced flow to about 66% of control and severe exercise reduced renal flow to 30% of control. IRBF was unchanged throughout. These results show that the exercising pig augments blood flow to skeletal muscle by reducing blood flow to kidneys, a response known to occur in man.     

Continuous measurement of subcutaneous lactate concentration during exercise by combining open-flow microperfusion and thin-film lactate sensors

The present study was carried out to investigate in vivo in healthy humans the method of open-flow microperfusion for monitoring of the subcutaneous (s.c.) lactate concentration during rest and cycle ergometer exercise. Using open-flow microperfusion, a perforated double lumen catheter with an inflow and an outflow connection is inserted into the s.c. adipose tissue and perfused with a sterile, isotonic, ionfree fluid. Due to the low flow rate, the fluid partially equilibrates with the surrounding tissue. The equilibrated perfusate passes a sensor flow chamber where the substance of interest and the rate of recovery (i.e. the ratio of sampled concentration to interstitial concentration) are continuously monitored. Within this study, the method was evaluated in four healthy volunteers during cycle ergometer exercise. The relative increase of the lactate concentration was approximately a third in the s.c. tissue compared to the capillary blood and the peak time was delayed on average by 10 min. The correlation coefficient between blood and s.c. tissue lactate concentration ranged from r = 0.41 to r = 0.90 (n = 29) in the individual experiments. The combination of open-flow microperfusion and lactate and conductivity sensors enables on-line monitoring of the s.c. lactate concentration without in vivo calibration during steady-state and cycle ergometer exercise.     

A method for galactose-1-phosphate uridyltransferase assay and the separation of its isozymes by DEAE-cellulose column chromatography

The resistance to coronary blood flow in various parts of the myocardium was studied with the tracer microspheres technique before and immediately after an acute coronary occlusion and several weeks after a more slowly occurring coronary occlusion by Ameroid constrictor. All experiments were carried out in the isolated, metabolically supported, empty, beating dog heart at maximal coronary vasodilation induced with adenosine. Coronary resistance of the normal empty beating heart at maximal coronary vasodilation was 0.20 mm mm Hg/(ml/min) per 100 g of tissue (subepicardium) and 0.16 mm Hg/(ml/min) per 100 g of tissue (subendocardium). After acute coronary occlusion the perfusion of the subtended myocardium was maintained at a much lower level by way of collateral vessels, which showed a resistance to flow of 3.52 mm Hg/(ml/min) per 100 g. If coronary artery occlusion proceeded more slowly the collateral vessels became more functional and myocardial infarction was avoided. During collateral enlargement collateral resistance fell from 3.52 to 0.22 mm Hg/(ml/min) per 100 g within a period of 8 weeks after implantation of the constricting device. The degree of compensation by collaterals for the loss of the occluded native coronary artery was 33% of its former conductance.     

In situ assessment of the role of the beta 1-, beta 2- and beta 3-adrenoceptors in the control of lipolysis and nutritive blood flow in human subcutaneous adipose tissue

1. The involvement of beta 1-, beta 2- and beta 3-adrenoceptors in the control of lipolysis and nutritive blood flow was investigated in abdominal subcutaneous adipose tissue of healthy young adults by use of an in situ microdialysis technique. 2. Dialysis probes were infused either with isoprenaline (non-selective beta-adrenoceptor agonist), CGP 12,177 (selective beta 3-adrenoceptor agonist having beta 1-/beta 2-antagonist properties), dobutamine (selective beta 1-adrenoceptor agonist) or terbutaline (selective beta 2-adrenoceptor agonist). The recovery of each probe used for perfusion was calculated by an in vivo calibration method. The local blood flow was estimated through the measurement of the escape of ethanol infused simultaneously with the drugs included in the probe. 3. Isoprenaline infusion at 0.01 microM had a weak effect while higher concentrations of isoprenaline (0.1 and 1 microM) caused a rapid, sustained and concentration-dependent increase of glycerol outflow; the maximum increase was 306 +/- 34% with 1 microM. Isoprenaline also increased the nutritive blood flow in adipose tissue; a significant effect appeared at 0.1 microM isoprenaline and was greater at 1 microM. 4. CGP 12,177 (10 and 100 microM) increased the glycerol concentration in the dialysate (128 +/- 8 and 149 +/- 12%, respectively) and nutritive blood flow. Terbutaline and dobutamine (100 microM) both provoked rapid and similar increases in glycerol outflow (252 +/- 18 and 249 +/- 18%, respectively). Both, terbutaline and dobutamine increased nutritive blood flow. 5. It is concluded that beta 1- and beta 2-adrenoceptor subtypes are both mainly involved in the mobilization of lipids and in the control of nutritive blood flow. beta 3-Adrenoceptors play a weaker role in the control of lipolysis and nutritive blood flow in human subcutaneous abdominal adipose tissue.     

Regional variation in adipose tissue insulin action and GLUT4 glucose transporter expression in severely obese premenopausal women

Insulin action and GLUT4 expression were examined in adipose tissue of severely obese premenopausal women undergoing gastrointestinal surgery. Fat samples were taken from three different anatomical regions: the subcutaneous abdominal site, the round ligament (deep abdominal properitoneal fat), and the greater omentum (deep abdominal intraperitoneal fat). The stimulatory effect of insulin on glucose transport and the ability of the hormone to inhibit lipolysis were determined in adipocytes isolated from these three adipose depots. Insulin stimulated glucose transport 2-3 times over basal rates in all adipocytes. However, round ligament adipose cells showed a significantly greater responsiveness to insulin when compared to subcutaneous and omental adipocytes. Round ligament fat cells also displayed the greatest sensitivity and maximal antilipolytic response to insulin. We also investigated whether regional differences in fat cell insulin-stimulated glucose transport were linked to a differential expression of the GLUT4 glucose transporter. GLUT4 protein content in total membranes was 5 and 2.2 times greater in round ligament adipose tissue than in subcutaneous and omental fat depots, respectively. Moreover, GLUT4 mRNA levels were 2.1 and 3 times higher in round ligament than in subcutaneous or omental adipose tissues, respectively. Adipose tissue GLUT4 protein content was strongly and negatively associated (r = -0.79 to -0.89, p < 0.01) with the waist-to-hip ratio but not with total adiposity. In conclusion, these results demonstrate the existence of site differences in adipose tissue insulin action in morbidly obese women. The greater insulin effect on glucose transport in round ligament adipocytes was associated with a higher expression of GLUT4 when compared to subcutaneous abdominal and omental fat cells. Moreover, despite the regional variation in GLUT4 expression, an increased proportion of abdominal fat was found to be associated with lower levels of GLUT4 in all adipose regions investigated.     

Adipose tissue blood flow during prolonged, heavy exercise

Subcutaneous adipose tissue blood flow (ATBF) was examined in 8 subjects during 6 h exercise on a bicycle ergometer. The initial work load was 118 W corresponding to about 50% of maximal work capacity. The oxygen uptake increased from 0.261 - min-1 at rest to about 1.61-min-1 during work. In 7 subjects ATBF increased, in 1 it remained constant. After 3 h exercise ATBF at an average reached values 3--4 times the control value. This increase was maintained for the remaining work periods. The increase was significant at the 5% level. Plasma free fatty acids increased 7-, plasma glycerol 10-fold during work.     

Rat hindlimb muscle blood flow during level and downhill locomotion

During eccentrically biased exercise (e.g., downhill locomotion), whole body oxygen consumption and blood lactate concentrations are lower than during level locomotion. These general systemic measurements indicate that muscle metabolism is lower during downhill exercise. This study was designed to test the hypothesis that hindlimb muscle blood flow is correspondingly lower during downhill vs. level exercise. Muscle blood flow (determined by using radioactive microspheres) was measured in rats after 15 min of treadmill exercise at 15 m/min on the level (L, 0 degrees) or downhill (D, -17 degrees). Blood flow to ankle extensor muscles was either lower (e.g., white gastrocnemius muscle: D, 9 +/- 2; L, 15 +/- 1 ml. min-1. 100 g-1) or not different (e.g., soleus muscle: D, 250 +/- 35; L, 230 +/- 21 ml. min-1. 100 g-1) in downhill vs. level exercise. In contrast, blood flow to ankle flexor muscles was higher (e.g., extensor digitorum longus muscle: D, 53 +/- 5; L, 31 +/- 6 ml. min-1. 100 g-1) during downhill vs. level exercise. When individual extensor and flexor muscle flows were summed, total flow to the leg was lower during downhill exercise (D, 3.24 +/- 0.08; L, 3.47 +/- 0. 05 ml/min). These data indicate that muscle blood flow and metabolism are lower during eccentrically biased exercise but are not uniformly reduced in all active muscles; i.e., flows are equivalent in several ankle extensor muscles and higher in ankle flexor muscles.     

Strain gauge plethysmography and Doppler ultrasound in the measurement of limb blood flow

The maintenance of adequate oxygen delivery (DO2) and tissue uptake (VO2) has become central dogma in the management of the critically ill. However, these parameters are derived using gas tensions measured in mixed venous blood and may not reflect changes in regional blood flow. Therefore, it has become necessary to provide estimates of blood flow to specific organs and to evaluate the most adequate techniques available. In order to define the best means of assessing blood flow to the lower limb noninvasively in normal subjects, measurements of superficial femoral arterial blood flow using Doppler ultrasound (DU) and strain gauge plethysmography (SGP) were compared in 10 normal volunteers at rest and during exercise. To evaluate the effect of strain gauge positioning, results of measurements made under four different combinations of cuff/strain gauge placement were compared in 15 other volunteers. The correlation of the limb blood flow obtained using the two methods at rest and exercise was 0.57 and 0.62 and the limits of agreement (d +/- 2SD) were 0.40 +/- 2.49 and -0.86 +/- 5.22 ml 100 ml-1 tissue min-1 at rest and on exercise, respectively. Results obtained using SGP were more reproducible (Coef. repeat. 0.45 vs. 0.94 ml 100 ml-1 tissue min-1, for SGP and DU, respectively). The various combinations of cuff/strain gauge positioning showed a tendency to over-read when the latter was placed on the thigh, but were not significantly different (P > 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)     

Effect of sympathetic nerve stimulation on net transvascular movement of fluid in canine adipose tissue

Net transvascular movement of fluid has been studied in the isolated, autoperfused subcutaneous adipose tissue of the dog, during and after sympathetic nerve stimulation (1-15 Hz) and during infusion of 50% glucose i.a. Net fluid movement was calculated as the difference between change in tissue volume and change in blood volume. Tissue volume was measured by plethysmography and blood volume by external monitoring of circulating 131I-albumin. No net fluid movement of statistical significance was found during or after nerve stimulation except during the first minute of stimulation at 15 Hz when a small net absorption (p less than 0.05) was obtained. In contrast, infusion of glucose at 25-75 mOsm/kg H2O produced a dose-dependent net absorption lasting several minutes, amounting maximally to 0.30 ml x min-1 x 100 g-1. The absence of prolonged net absorption in subcutaneous adipose tissue during nerve stimulation as well as the absence of net filtration after stimulation may be explained by an essentially unaltered mean hydrostatic capillary pressure. The results indicate that adipose tissue does not contribute to the fluid homeostasis of the body via sympathetic resetting of the pre-postcapillary resistance ratio. Thus, mobilisation of fluid from the interstitial space in adipose tissue into the blood does not seem to occur by nerve activity.     

Scintigraphic assessment of regionalized defects in myocardial sympathetic innervation and blood flow regulation in diabetic patients with autonomic neuropathy

OBJECTIVES: This study sought to evaluate whether regional sympathetic myocardial denervation in diabetes is associated with abnormal myocardial blood flow under rest and adenosine-stimulated conditions. BACKGROUND: Diabetic autonomic neuropathy (DAN) has been invoked as a cause of unexplained sudden cardiac death, potentially by altering electrical stability or impairing myocardial blood flow, or both. The effects of denervation on cardiac blood flow in diabetes are unknown. METHODS: We studied 14 diabetic subjects (7 without DAN, 7 with advanced DAN) and 13 nondiabetic control subjects without known coronary artery disease. Positron emission tomography using carbon-11 hydroxyephedrine was used to characterize left ventricular cardiac sympathetic innervation and nitrogen-13 ammonia to measure myocardial blood flow at rest and after intravenous administration of adenosine (140 microg/kg body weight per min). RESULTS: Persistent sympathetic left ventricular proximal wall innervation was observed, even in advanced neuropathy. Rest myocardial blood flow was higher in the neuropathic subjects (109 +/- 29 ml/100 g per min) than in either the nondiabetic (69 +/- 8 ml/100 g per min, p < 0.01) or the nonneuropathic diabetic subjects (79 +/- 23 ml/100 g per min, p < 0.05). During adenosine infusion, global left ventricular myocardial blood flow was significantly less in the neuropathic subjects (204 +/- 73 ml/100 g per min) than in the nonneuropathic diabetic group (324 +/- 135 ml/100 g per min, p < 0.05). Coronary flow reserve was also decreased in the neuropathic subjects, who achieved only 46% (p < 0.01) and 44% (p < 0.01) of the values measured in nondiabetic and nonneuropathic diabetic subjects, respectively. Assessment of the myocardial innervation/blood flow relation during adenosine infusion showed that myocardial blood flow in neuropathic subjects was virtually identical to that in nonneuropathic diabetic subjects in the distal denervated myocardium but was 43% (p < 0.05) lower than that in the nonneuropathic diabetic subjects in the proximal innervated segments. CONCLUSIONS: DAN is associated with altered myocardial blood flow, with regions of persistent sympathetic innervation exhibiting the greatest deficits of vasodilator reserve. Future studies are required to evaluate the etiology of these abnormalities and to evaluate the contribution of the persistent islands of innervation to sudden cardiac death complicating diabetes.     

Experience with the Cryosurgical treatment of the prostatic diseases in 100 patients (author''s transl)]

The semitendinosus muscle of the dog is supplied by two separate arteries and drained by two corresponding veins. In the muscles used in this study no blood entering via the distal artery was found to leave via the proximal vein during perfusion through both arteries (orthograde perfusion). Therefore, collateral flow (CF) could be determined as proximal venous outflow during occlusion of the proximal artery. During orthograde perfusion total blood flow averaged 12 ml x min-1 x 100 g-1 at rest and 58.4 ml x min-1 x 100 g-1 during exercise. CF was found to average 6.2 ml x min-1 x 100 g-1 at rest and increased to 9.2 ml x min-1 x 100 g-1 during exercise. CF was sufficient to cover the metabolic demand of resting muscle. During exercise the O2-uptake (VO2) of the distal muscle portion was increased 13.4 fold in comparison to a 3.1 fold increase in the proximal muscle portion. The average contractile power decreased by 46%. Additional infusion of adenosine into the distal artery resulted in an increase of CF to 11.4 ml x min-1 x 100 g-1 and of orthograde flow to 71 ml x min-1 x 100 g-1. The average contractile power of the muscle increased by 13%. Both orthograde flow and CF were found to decrease with increasing muscle load. But this decrease was significantly more pronounced in the case of CF especially at a lower range of loads. It is concluded that after acute occlusion of orthograde flow, CF is limited by the number, the size and the dilatory capacity of precapillary network vessels. Furthermore, CF is influenced considerably by changes of extravascular support.     

Skeletal muscle blood flow in humans and its regulation during exercise

Regional limb blood flow has been measured with dilution techniques (cardio-green or thermodilution) and ultrasound Doppler. When applied to the femoral artery and vein at rest and during dynamical exercise these methods give similar reproducible results. The blood flow in the femoral artery is approximately 0.3 L min(-1) at rest and increases linearly with dynamical knee-extensor exercise as a function of the power output to 6-10 L min[-1] (Q= 1.94 + 0.07 load). Considering the size of the knee-extensor muscles, perfusion during peak effort may amount to 2-3 L kg(-1) min(-1), i.e. approximately 100-fold elevation from rest. The onset of hyperaemia is very fast at the start of exercise with T 1/2 of 2-10 s related to the power output with the muscle pump bringing about the very first increase in blood flow. A steady level is reached within approximately 10-150 s of exercise. At all exercise intensities the blood flow fluctuates primarily due to the variation in intramuscular pressure, resulting in a phase shift with the pulse pressure as a superimposed minor influence. Among the many vasoactive compounds likely to contribute to the vasodilation after the first contraction adenosine is a primary candidate as it can be demonstrated to (1) cause a change in limb blood flow when infused i.a., that is similar in time and magnitude as observed in exercise, and (2) become elevated in the interstitial space (microdialysis technique) during exercise to levels inducing vasodilation. NO appears less likely since NOS blockade with L-NMMA causing a reduced blood flow at rest and during recovery, it has no effect during exercise. Muscle contraction causes with some delay (60 s) an elevation in muscle sympathetic nerve activity (MSNA), related to the exercise intensity. The compounds produced in the contracting muscle activating the group IIl-IV sensory nerves (the muscle reflex) are unknown. In small muscle group exercise an elevation in MSNA may not cause vasoconstriction (functional sympatholysis). The mechanism for functional sympatholysis is still unknown. However, when engaging a large fraction of the muscle mass more intensely during exercise, the MSNA has an important functional role in maintaining blood pressure by limiting blood flow also to exercising muscles.     

Lipoprotein lipase transport in plasma: role of muscle and adipose tissues in regulation of plasma lipoprotein lipase concentrations

Lipoprotein lipase (LPL) is synthesized in tissues involved in fatty acid metabolism such as muscle and adipose tissue. LPL is also found in the circulation, but is mostly lipolytically inactive. The proportion of active circulating LPL increases after a fatty meal. We investigated the release of active and inactive LPL from adipose tissue and muscle in the fasting and postprandial states. Arteriovenous concentration gradients of LPL across adipose tissue and forearm muscle were measured in male subjects before and after a fat-rich meal (n = 7) and before and during infusion of a triacylglycerol emulsion (Intralipid) (n = 6). Plasma LPL activity rose after the meal and more so during Intralipid infusion. Plasma LPL mass (>95% inactive LPL) increased after the meal but decreased after Intralipid infusion. In the fasting state (n = 13) muscle efflux of LPL activity was 0.263 +/- 0.098 mU/min per 100 ml of muscle tissue whereas there was an influx of LPL activity to adipose tissue of 0.085 +/- 0.100 mU/min per 100 g of adipose tissue (P < 0. 02 muscle vs. adipose tissue). Similarly in the postprandial state only muscle released LPL activity. Both tissues released LPL mass. In the fasting state efflux was 17.8 +/- 8.8 ng/min per 100 ml muscle and 55.2 +/- 21.3 ng/min per 100 g of adipose tissue (P < 0. 05 muscle vs. adipose tissue). Release of LPL, either active or inactive, was not correlated with levels of non-esterified fatty acids or plasma triacylglycerol. In conclusion, there is a substantial release of LPL from adipose tissue and muscle, most of which is inactive. A small proportion of active LPL seems to be redistributed from muscle to adipose tissue.