CIRCULATION THROUGH THE SKIN 



1345 



40 -S 



20 



64 



16 



_1_ 

 64 



16 



fig. 14. The mean percentage 

 reduction in the rate of blood flow in 1 3 

 hands, tested before and after sym- 

 pathectomy, in response to infusions of 

 adrenaline and noradrenaline at various 

 rates into the brachial artery. The 

 effects of general disturbance of the 

 circulation have been eliminated by 

 referring the blood flow to the simul- 

 taneously measured blood flow in the 

 opposite hand. Noradrenaline has a 

 greater constrictor effect than adrena- 

 line in normally innervated hands. After 

 sympathectomy the response to both 

 substances is augmented. [From Duff 

 (6 4 )0 



general circulation is tested by intravenous infusion. 

 The rate should ideally follow the normal pattern of 

 secretion but, in the general absence of exact knowl- 

 edge of this, steady infusion is best employed (g) and 

 is much superior to a sudden injection. The effect 

 on the skin or any other part of the peripheral circu- 

 lation depends on a combination of direct local 

 action and of general circulatory disturbance involv- 

 ing changes in arterial pressure and vasomotor 

 control, and probably changes in the concentration 

 of other humoral agents in the arterial blood. 



Adrenaline and Noradrenaline 



subcutaneously both substances cause 

 1 pallor, and iontophoresis of adrenaline 

 virtually to arrest the circulation through 

 . Injected into the brachial artery in very 

 both substances (22) cause a reduction in 

 through the hand (fig. 14). There is 

 of the low pressure capacity vessels, 

 veins, as well as of the resistance vessels 



Injected 

 intense loca 

 can be used 

 the skin ( 7 1 

 small doses, 

 blood flow 

 constriction 

 presumably 



(93)- 



During the infusion of either substance intra- 

 venously at 20 fig per min there is a severe reduction, 

 and sometimes nearly complete arrest, of the blood 

 flow through the hands. After adrenaline injection, 

 the flow usually increases for a time to above the 

 resting level (182) and there is often a flushing of the 

 face (17, 103). No such increase is seen in sym- 

 pathectomized hands, or after intravenous nor- 

 adrenaline, or either substance given intra-arterially 

 (182). 



Histamine 



Pricked into the skin histamine causes a local wheal 

 and a reddening of the skin or flare extending for a 

 radius of 3 to 4 cm (139). The temperature of the skin 

 is only slightly increased in the region of the flare 

 (61, 139) and, although the content of blood is greatly 

 increased, the increase in the flow is modest. Infused 

 into the brachial artery, histamine has a dilator 

 effect at all doses tested (fig. 15) and the skin becomes 

 deeply flushed. The flush does not always cover all 

 parts of the hand, and this illustrates a general 

 difficulty with intra-arterial infusions. The injected 

 material may not become thoroughly mixed with the 

 arterial blood at the site of injection, and the artery 

 may not be the exclusive supply to the area of tissue 

 examined. Further, the pattern of distribution may 

 varv with changes in the circulation. 



Acetylcholine 



This acts as a powerful dilator to the blood vessels 

 of the hand (fig. 15), but so rapid is its destruction in 

 the blood stream that for equal effect on the blood 

 flow through the hand the dose into the brachial 

 artery must be about one thousand times as great 

 as that into the radial artery (65). 



5-Hydroxytryptamine ( Serotonin ) 



When infused into the brachial artery at the rate 

 of 1 fig per min or more, this causes a reduction in 

 the rate of flow of blood through the hand, but the 

 volume of the part increases because of edema forma- 



