Mechanisms of the vasodilator response in skeletal muscles during emotional stress

Abstract

The sympathetic system can induce cholinergic vasodilatation in the vessels of skeletal muscles [1][2][3]. This vasodilatation is one of the autonomic components of the state of rage or anxiety [4][5][6]. Cholinergic vasodilatation arises in man during emotional stress (intensive mental arithmetic, fright, and so on). Experiments on cats have shown that this form of increase in the velocity of blood flow is connected with the activation of glyeolysis in the muscle, with an increase in phosphorylase activity and in the production of lactic acid [7, 8]. The sympathetic system is considered to act primarily on the muscle fiber, in which it activates t:he enzyme phosphorylase. The activation of glycolysis thereby produced induces vasodilatation secondarily, through the action of metabolites on the smooth muscle of the vessel [7][8][9][10][11][12].To establish a relationship of cause and effect between the activation of glycolysis and dilatation of the muscle, vessels in emotional stress in man, the vasodilatation in nonworking muscles was investigated in patients with muscular glycogen disease. Muscular glycogen disease is a rare hereditary disease caused by deficient activity of myophosphorylase or of some other enzymes (amylo-l,6-glucosidase, phosphofructokinase, phosphoglucomutase, acid maltase), leading to the development of a partial or total block of glycogenolysis and to the accumulation of large masses of unsplit glycogen in the skeletal muscles [13]. If the above hypothesis is correct, cholinergic dilatation of the muscle vessels in this disease ought to be reduced or absent altogether because of disturbance of the processes of glycogenolysis.Cholinergic vasodilatation in animals is stronger in white than in red muscles [14][15][16]. In the writers' opinio n, tl~[s difference may be connected with the fact that ~4aite muscle fibers are distinguished by a very intensive course of glycolysis, whereas red muscle fibers satisfy their energy requirements mainly by aerobic metabolism. In this investigation emotional vascular responses were studied in the red soleus and mixed tibialis anterior muscles of healthy persons. EXPERIMENTAL METHODThe ,volume velocity of the blood flow in the forearm of 23 healthy subjects (aged 17-30 years) and in nine patients (20-50 years) was determined by venous occlusion plethysmography [12]. Changes in the limb volume in :response to temporary cessation of the venous drainage were measured with a flexible plethysmographic sensor and, after conversion into electrical'signals by means of the ]~M'PD-2 electromedical pressure transducer of the model 064 Krasnogvardeets sphygmograph, there were recorded as arterial inflow curve,s on the KSP-4 automatic writer. The pulse rate was calculated from the ECG, recorded on the 060 electrocardiograph.The blood supply to the soleus muscle (SM) and to the tibialis-anterior muscle (rAM) in ten healthy subjects was determined from the rate of elimination of radioactive isotope 133Xe from the intramuscular depot. A sterile solution of 133Xe was inject...