Effect of Local Metabolic Factors on Vascular Smooth Muscle

1,067

905

SUMMARY1. Five subjects exercised with the knee extensor of one limb at work loads ranging from 10 to 60 W. Measurements of pulmonary oxygen uptake, heart rate, leg blood flow, blood pressure and femoral arterial-venous differences for oxygen and lactate were made between 5 and 10 min of the exercise.2. Flow in the femoral vein was measured using constant infusion of saline near 0 'C. Since a cuff was inflated just below the knee during the measurements and because the hamstrings were inactive, the measured flow represented primarily the perfusion of the knee extensors.3. Blood flow increased linearly with work load right up to an average value of 57 1 min-. Mean arterial pressure was unchanged up to a work load of 30 W, but increased thereafter from 100 to 130 mmHg. The femoral arterial-venous oxygen difference at maximum work averaged 14-6 % (v/v), resulting in an oxygen uptake of 0-80 1 min-. With a mean estimated weight of the knee extensors of 2-30 kg the perfusion of maximally exercising skeletal muscle of man is thus in the order of 2-5 1 kg-' min', and the oxygen uptake 0-35 1 kg-' min-. 4. Limitations in the methods used previously to determine flow and/or the characteristics ofthe exercise model used may explain why earlier studies in man have failed to demonstrate the high perfusion of muscle reported here.5. It is concluded that muscle blood flow is closely related to the oxygen demand of the exercising muscles. The hyperaemia at low work intensities is due to vasodilatation, and an elevated mean arterial blood pressure only contributes to the linear increase in flow at high work rates. The magnitude of perfusion observed during intense exercise indicates that the vascular bed of skeletal muscle is not a limiting factor for oxygen transport.

Section: Discussionmentioning

confidence: 99%

Maximal perfusion of skeletal muscle in man.

Andersen¹,

Saltin²

1985

1,067

905

“…Oxygen availability is considered to one of the most important local factors influencing vascular contractility (Sparks, 1980). However, the effect of a decrease in oxygen tension is not uniform throughout the vascular system.…”

Section: Introductionmentioning

confidence: 99%

Effects of hypoxia upon contractions evoked in isolated rabbit pulmonary artery by potassium and noradrenaline.

Marriott¹,

Marshall²

1990

SUMMARY1. Comparisons have been made between rabbit thoracic aorta and main pulmonary artery of the effects of hypoxia upon contractions evoked by noradrenaline (NA) and KCl (K+).2. Contractions were evoked in cylindrical sections of pulmonary artery and aorta, mounted for isometric recording of tension, by NA and K+ (at ED80) in normoxia (PO2 110 mmHg) and hypoxia (Po2 23 or 7 mmHg). Contractions were also evoked in Ca2+-free conditions with EGTA to prevent influx of extracellular Ca2+. All contractions are expressed as a percentage of normoxic response in the presence of Ca2+. 3. Potassium-evoked contractions of aorta and pulmonary artery were reduced to a similar extent by both levels of hypoxia, to 85 and 92 % respectively. As expected K+-evoked contractions were virtually abolished by Ca2+-free conditions. It is proposed that hypoxia has a small inhibitory effect upon contraction mediated by Ca2+ influx via voltage-operated Ca2+ channels.4. In the aorta in the presence of Ca2+, hypoxia reduced NA-evoked contractions to 84 % at Po2 23 mmHg and 34 % at Po2 7 mmHg. In the absence of Ca2+, NA-

“…Blood oxygen content is known to be an important local factor in the regulation of circulation (for reviews see Sparks, 1980;Wadsworth, 1994). In systemic arteries a decrease in local 02 tension (Po2) normally leads to vasodilatation whereas hypoxia predominantly evokes the opposite response (vasoconstriction) in the pulmonary circulation (Dawson, 1984;Harder, Madden & Dawson, 1985a;Madden, Vadula & Kurup, 1992).…”

mentioning

confidence: 99%

Differential oxygen sensitivity of calcium channels in rabbit smooth muscle cells of conduit and resistance pulmonary arteries.

Franco‐Obregón

López‐Barneo

1996

115

1. Calcium currents were recorded from smooth muscle cells dispersed from conduit and resistance rabbit pulmonary arteries. We tested the hypothesis that Ca2+ channel activity was regulated by environmental 02 tension.2. Conduit (proximal) and resistance (distal) myocytes differ in their Ca2P channel density and responses to low Po2. Ca2P current density in distal myocytes (20'7 + 7-4 pA pFY, n = 10)is almost twice the value in proximal myocytes (12-6 + 5-5 pA pF', n = 39). In proximal myocytes, the predominant response to reductions in P02 is inhibition of the calcium current (n = 12) at membrane potentials below 0 mV, whereas potentiation of current amplitude is observed in distal myocytes (n = 24). 3. Hypoxia also produces opposite shifts in the conductance-voltage relationships along the voltage axis. The average displacements induced by low P02 are +5 05 + 2-98 mV (n = 5) in proximal myocytes and -6-06 + 2-45 (n = 10) in distal myocytes.4. These findings demonstrate longitudinal differences in Ca2P channel density and 02 sensitivity in myocytes along the pulmonary arterial tree. These results may help to understand the differential reactivity to hypoxia of the pulmonary vasculature: vasodilatation in conduit arteries and vasoconstriction in resistance vessels.