1346 HANDBOOK OF PHYSIOLOGY -^ CIRCULATION II 



fig. 15. The effect on forearm and 

 hand blood flow of various doses of 

 acetylcholine and histamine injected 

 over i-min periods into the brachial 

 artery of four normal subjects. Con- 

 tinuous line: injected side; dotted lines: 

 control side. Doses in jig. [From Duff 

 et al. (65).] 



40 



E 

 § 



R.B.C. 



5 M - 10 



Minutes 



Minutes 



tion, and the skin becomes flushed and petechial 

 hemorrhages appear; thus the vessels controlling 

 flow are constricted, and those responsible for color 

 are dilated (169). On the other hand, the low pressure 

 capacity vessels as a whole are rendered less disten- 

 sible (93), so the reaction of those responsible for color 

 appears not to be typical of the low pressure vessels 

 as a whole. 



Adenosine Triphosphate 



Injected intra-arterially in man, magnesium 

 adenosine triphosphate causes a great increase in the 

 blood flow through the hand, and is nearly as ef- 

 fective as an equal weight of histamine (68). A dose 

 of 1 mg per min into the brachial artery raises the 

 blood flow in the hand to an average value of 34 ml 

 per 100 ml of hand per min. Adenosine triphosphate 

 may be the transmitter substance released from 

 sensory nerve endings causing antidromic vaso- 

 dilatation (122). 



Bradykinin 



Detailed information is not yet published but it 

 appears that, per molecule of injected substance, 

 bradvkinin has a more potent vasodilator effect than 

 any other tested substance (80). 



Carbon Dioxide 



Breathing mixtures containing high concentrations 

 of carbon dioxide has a complex effect on the circu- 

 lation, with great disturbance of vasomotor regulation. 

 The local effect of carbon dioxide, as seen when a 

 hand is immersed in a saturated solution of the gas 

 (60) or when carbon dioxide mixtures are injected 

 subcutaneously (61), is entirely vasodilator. The 

 effect has not, however, been quantitatively defined 

 in terms of the response to various tensions of the 

 gas in the tissues. 



Vasopressin 



Infused intravenously this causes an initial vaso- 

 constriction in the hands, which diminishes as the 

 infusion continues ( 1 33)- 



Oxytocin 



Injected intravenously in man this may cause 

 flushing. Injections of 500 units intravenously or 

 50 units into the brachial artery cause the blood 

 flow through the hand to double for a few minutes. 

 With repeated doses, by either route, the response 

 diminishes (134). The vasodilator effect of oxytocin 

 is balanced by one-twentieth of the number of units 

 of vasopressin. 



