Comparison of exogenous adenosine and voluntary exercise on human skeletal muscle perfusion and perfusion heterogeneity

Abstract

Adenosine is a widely used pharmacological agent to induce a "high-flow" control condition to study the mechanisms of exercise hyperemia, but it is not known how well an adenosine infusion depicts exercise-induced hyperemia, especially in terms of blood flow distribution at the capillary level in human muscle. Additionally, it remains to be determined what proportion of the adenosine-induced flow elevation is specifically directed to muscle only. In the present study, we measured thigh muscle capillary nutritive blood flow in nine healthy young men using PET at rest and during the femoral artery infusion of adenosine (1 mg min(-1) l thigh volume(-1)), which has previously been shown to induce a maximal whole thigh blood flow of approximately 8 l/min. This response was compared with the blood flow induced by moderate- to high-intensity one-leg dynamic knee extension exercise. Adenosine increased muscle blood flow on average to 40 +/- 7 ml x min(-1) x 100 g muscle(-1) with an aggregate value of 2.3 +/- 0.6 l/min for the whole thigh musculature. Adenosine also induced a substantial change in blood flow distribution within individuals. Muscle blood flow during the adenosine infusion was comparable with blood flow in moderate- to high-intensity exercise (36 +/- 9 ml x min(-1) x 100 g muscle(-1)), but flow heterogeneity was significantly higher during the adenosine infusion than during voluntary exercise. In conclusion, a substantial part of the flow increase in the whole limb blood flow induced by a high-dose adenosine infusion is conducted through the physiological non-nutritive shunt in muscle and/or also through tissues of the limb other than muscle. Additionally, an intra-arterial adenosine infusion does not mimic exercise hyperemia, especially in terms of muscle capillary flow heterogeneity, while the often-observed exercise-induced changes in capillary blood flow heterogeneity likely reflect true changes in nutritive flow linked to muscle fiber and vascular unit recruitment.

Inhibition of α-adrenergic tone disturbs the distribution of blood flow in the exercising human limb

“…Arterial blood radioactivity was monitored continuously with a radioactivity detector. Exercise consisted of low-to-moderate intensity dynamic one-leg exercise at 40 rpm with an average work load of 4 kg (20,22,23). Local muscle blood flow was measured from the whole thigh muscles of the right leg: from the quadriceps femoris muscle and from its four heads [vastus intermedius (VI), rectus femoris (RF), vastus Fig.…”

Local heating, but not indirect whole body heating, increases human skeletal muscle blood flow

“…Scanning began simultaneously with the bolus infusion of the tracer and scanning consisted of the following frames; 6 ϫ 5 s, 12 ϫ 10 s and 7 ϫ 30 s. Arterial blood radioactivity was also sampled continuously with a detector during imaging for blood flow quantification. The data analysis was performed using standard models (14) and methods (11)(12)(13)32). Blood flow was analyzed from calf musculature, with specific regions of interest including the soleus and gastrocnemius muscles, but avoided all apparent blood vessels and bone structures ( Fig.…”

The effect of nitric oxide synthase inhibition with and without inhibition of prostaglandins on blood flow in different human skeletal muscles

“…Additionally, a cannula was placed under local anaesthesia in the femoral artery for local drug infusions. Subjects were then moved to the PET scanner with the femoral region in the gantry and the right leg was positioned in an in-house designed leg exercise dynamometer (Heinonen et al 2007(Heinonen et al , 2010a(Heinonen et al , b, 2012c(Heinonen et al , 2013bRuotsalainen et al 1997). Subjects were laying supine both during resting and exercising measurements.…”

“…Local muscle blood flow was measured separately in the four different muscle parts of the m. quadriceps femoris. All of the experiments and the data analysis were performed using the standard models and methods (Heinonen et al 2007(Heinonen et al , 2010a(Heinonen et al , b, 2012b(Heinonen et al , 2013bRuotsalainen et al 1997).…”

“…Structural magnetic resonance imaging (MRI) was performed about one week before the PET study as described earlier (Heinonen et al 2010a), when subjects were also accustomed to the one-leg knee extension exercise model in a PET scanner. MRI scanning was performed to obtain total leg volume of the working leg since NOS inhibiting drug infusions were based on effective concentrations per litre leg volume (Heinonen et al 2011;Mortensen et al 2007).…”