78 Physiology of the Kidney 



In passing, may I comment on the effect of adrenin upon 

 the blood pressure. It is still frequently stated that adrenin 

 raises the systolic pressure because it is a vasoconstrictor drug. 

 Admittedly it constricts the efferent arterioles of the kidneys, 

 as shown here, as well as the arterioles of the skin; it probably 

 also constricts the spleen and some of the venous reservoirs. 

 But it dilates the arterioles in the skeletal muscles and possibly 

 in some of the viscera, and because of the larger fraction of 

 the vascular bed involved in these regions the net effect of 

 this dilatation is quantitatively preponderant over such vaso- 

 constriction as may occur. Consequently the mean peri- 

 pheral resistance is substantially reduced, as has been ade- 

 quately demonstrated by several groups of investigators.^^'^^'^^ 

 So far as the net effect of relatively large doses in man is con- 

 cerned, adrenin must be considered as a vasodilator drug, 

 this vasodilatation being evidenced typically by a fall in the 

 diastolic pressure. In this particular experiment the diastolic 

 pressure fell to undeterminable levels. The rise in systolic 

 pressure must be attributed to increased cardiac output in 

 consequence of increased heart rate and increased stroke vol- 

 ume, the increased stroke volume in part being attributable 

 to increased venous pressure. If the cardiac output is suf- 

 ficiently increased the diastolic pressure may be maintained 

 at its control level or even momentarily increased. 



There is included in this experiment a series of measure- 

 ments of glucose-Tm (G-Tm) obtained by maintaining the 

 plasma glucose at 380-445 mgm. per cent. During the four 

 control periods this value averaged 306 mgm. per minute; 

 during the action of adrenin it averaged 325 mgm. per min- 

 ute, i.e., it increased by 6 per cent, an increase of doubtful 

 significance. Glucose-Tm, you will recall, is a measure of 

 the number of active nephrons which are reabsorbing glucose. 



