CHAPTER X 

 THE SUPRARENAL CAPSULES (continued) 



Evidences of the Passage of Adrenalin into the Blood 



That the passage of adrenalin into the blood is always proceeding in 

 sufficient amount appreciably to raise the tone of the blood-vessels seems 

 somewhat doubtful. It was found by Oliver and myself that even in the 

 blood of the suprarenal vein there is not always enough of the autacoid 

 to cause a rise of blood-pressure when a few cubic centimetres are injected 

 into a vein. But it is possible by employing more delicate physiological 

 tests — e.g. the dilatation of the pupil which occurs in the enucleated eye of 

 the frog, or by passing extracts of dried and deproteinised mammalian 

 blood through the vessels of the frog — to obtain evidence in some animals 

 of its presence not only in the blood of the suprarenal vein, but to a less 

 degree in the blood generally. The amount is, however, normally very 

 small, even in the suprarenal vein : not more than about one part in a 

 million, according to Hoskins, M'Clure, and O'Connor, whilst Fraenckel 

 estimates it at very much less. This indicates that the rate of passage 

 into the blood is usually slow : probably it varies at different times. If 

 only a very small percentage is present, the blood-pressure may be lowered 

 instead of raised : we cannot, therefore, assume that the normal tone of 

 the vascular system depends on the presence of adrenalin in the blood, 

 although, that the maintenance of vascular tone is in some animals assisted 

 in this manner, is shown by the experiment of compressing the suprarenal 

 vein. Such compression is followed by a gradual fall of blood-pressure, 

 which quickly recovers, and, indeed, more than recovers, its former height 

 on relieving the compression. Temporarily compressing the abdominal 

 aorta produces somewhat similar results. It is possible that the partially 

 resumed tone of peripheral vessels which comes on after section of their 

 nerves may be due to a compensatory increase of adrenalin in the blood, 

 perhaps assisted by an increase of the pressor autacoid of the posterior lobe 

 of the pituitary. The circumstance that after section of its nerves plain 

 muscular tissue becomes more sensitive to the influence of adrenalin must 

 be borne in mind in considering this question. 



Trendelenburg estimated the amount of adrenalin in the blood of the supra- 

 renal vein of a cat, and found that on the average "003 mg. was passed out of the 

 two organs per minute. From the data thus obtained he reckons that about 5 mg. 

 per kilo, body weight is formed in twenty-four hours. After draining oft' a large 

 quantity of blood and thus causing a considerable fall of blood-pressure, the amount of 



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