1372 



HANDBOOK OF PHYSIOLOGY 



CIRCULATION II 



fig. 1 8. Results show the effect of an intravenous infusion of 

 adrenaline in man on forearm blood flow. The initial large 

 transient and later smaller sustained vasodilatation are due to 

 the action of adrenaline on the blood vessels in the skeletal 

 muscles. 



constant and conspicuous response of the vessels 

 in the muscles of the calf and forearm. 



During the initial vasodilatation blood flow in- 

 creases about fivefold. The main resistance vessels, 

 the arterioles and precapillary sphincters must be 

 widely dilated. This is in accordance with micro- 

 scopic observations made by Hartman & Walker 

 ( 1 1 8) on the tibialis anticus of the cat. Small doses of 

 adrenaline dilated arterioles, capillaries, and venules. 

 In man this dilatation is not dependent on nervous 

 connections. It occurs after nerve block, after sympa- 

 thectomy, and in completely denervated limbs (29, 

 177). It must be due to the local action of adrenaline 

 in the skeletal muscles. This might be a direct action 

 on the plain muscle of the arterioles or a metabolic 

 action due to products of carbohydrate metabolism 

 released by the action of adrenaline on the skeletal 

 muscle fibers. That the action of adrenaline is direct 

 rather than metabolic is shown by the following ob- 

 servations. In the first place, the initial vasodilatation 

 is not accompanied by any rise in venous blood 

 lactate, which may even fall, so it is not likely that 

 there is a rise in the concentration of anv other 



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MINUTES 



fig. 19. Simultaneous records of the changes in blood flow in calf of the leg (plethysmograph) and 

 in the muscles of the calf of the leg iHensel needle) recorded in six experiments before, during, and 

 after the intravenous infusion of adrenaline. [After Barcroft el al. (26).] 



