448 



Prof. E. A. Schafer. 



[July 22, 



separated from the anterior lobe — has a specific action both upon the renal 

 vessels and upon the kidney cells. For whereas this extract produces 

 contraction of most of the arteries in the body, it has the opposite effect upon 

 those of the kidney, causing them to dilate, although this dilatation, which 

 is very marked and lasting, may be preceded by a short period of contraction. 

 The increase in flow of urine, although no doubt greatly assisted by the 

 dilatation of the kidney vessels, which is coincident with a rise in general 

 blood-pressure caused by contraction of other arteries, is not entirely produced 

 by the vascular changes. For it may occur without them, as in the case 

 when a repeated dose of the] extract is administered intravenously within a 

 short interval. In such cases, as we have seen, the rise of blood-pressure may 

 fail altogether, or even be replaced by a temporary fall, and there may also 

 be no further dilatation of the kidney produced ; nevertheless, the diuretic 

 effect may still occur, and this can only be explained by supposing that there 

 is some substance in the extract which acts by directly stimulating the 

 secretory activity of the cells. Moreover, I have had occasion to observe 

 that the converse of this experiment may occasionally be obtained, and this 

 with a first dose ; the normal effects of rise of blood-pressure and dilata- 

 tion of kidney being produced without any increase in flow of urine (see 

 fig. 1). 



It is further noticeable that in a large proportion of experiments 

 a common phenomenon is a temporary diminution or cessation of urine 

 flow, even although the blood-pressure is raised to a considerable extent and 

 the kidney volume markedly increased ; conditions which — on the mechanical 

 or filtration theory of urine secretion — should inevitably produce diuresis. 

 There is, in fact, very often at first an inhibition of secretion (followed in the 

 majority of cases by the characteristic secretory activity), even although the 

 vascular conditions are throughout favourable to the occurrence of free 

 secretion.* The extract is therefore liable to cause two effects which are 

 antagonistic to one another. The most reasonable explanation of this is 

 afforded by the supposition that the gland contains not only a substance 

 which stimulates the kidney cells to activity but also another substance 

 which depresses their activity, and this to so great an extent in certain 

 cases that the kidney ceases to secrete, although all the vascular conditions 

 for urine secretion are of the most favourable character. Nevertheless, the 

 secretory substance usually ultimately proves the more potent : or it may be 

 that the kidney cells are more susceptible to its influence. 



* These facts are illustrated by several of the tracings given in the paper in the 

 ' Phil. Trans. ' for 1906 by Herring and myself. This paper deals exclusively with the 

 effects upon the kidney and urine-flow of extracts of pituitary. 



