96 THE SIMPLER NATURAL BASES 



Physiological Action of Adrenaline. 



A. Action on the Circulatory System. 



Oliver and Schafer [1894, 1895, i] and soon afterwards Cybulski 

 [1895] and Szymonovicz [1895] found that intravenous injection 

 of supra-renal extracts causes a very marked rise of arterial blood pres- 

 sure ; this effect is due to the adrenaline contained in such extracts. 

 Oliver and Schafer showed that the rise of blood pressure is mainly 

 due to the constriction of the arterioles, but that the action of the 

 mammalian heart is also accelerated and augmented in a remarkable 

 manner, the acceleration being most prominent when the vagi have 

 been cut (cf. Gottlieb [1897]). The vaso-constriction is chiefly of 

 peripheral origin, due to the action of the drug on the walls of the 

 arterioles, but some authors have asserted that the vaso-motor centre 

 also plays a part. Oliver and Schafer [1895, 2] further showed that 

 the activity is confined to extracts of the supra-renal medulla, those of 

 the cortex being inactive or nearly so ; the extracts of the gland in two 

 cases of Addison's disease were also found by them to be inactive. 



Cybulski [1895] detected the pressor action of the blood from 

 the supra-renal vein. 



Very minute doses of adrenaline are sufficient to produce a distinct 

 effect; according to Cameron [1906] 0*0003 mg. per kilo, is enough 

 in rabbits. The latent period is short and the rise of blood pressure 

 begins a few seconds after intravenous injection. The rise is very 

 transitory and the blood pressure soon falls again to the normal level, 

 at first rapidly, then more slowly. In Oliver and Schafer's experi- 

 ments, the rise lasted in dogs for at most 4 minutes, and in rabbits 

 for at most 6 minutes. This rapid cessation of the pressor action, 

 which is very characteristic of adrenaline, was first attributed to a dis- 

 appearance of the base from the blood, but Weiss and Harris [1904] 

 were able to show that after the blood pressure has returned to the 

 normal, the blood still contains adrenaline, capable of raising the blood 

 pressure when injected into another animal (cat), and of producing 

 vaso-constriction, when allowed to flow into a previously ligatured 

 limb of the animal experimented upon (hind limb of frog). 



In man a rise of blood pressure may be produced by subcutaneous 

 injection of adrenaline, but the effect is much less marked than with 

 intravenous doses, since the local vaso-constriction, set up at the site of 

 injection, does not allow a sufficiently rapid absorption of the drug. 

 This prevents the maintenance of a sufficiently steep gradient of con- 

 centration between the adrenaline in the blood and that in the arterial 





