234 



METABOLIC HORMONES 



or Other colloids. The top curve (Ccr) in Fig. 5-23 shows the 

 effect of the pressor action of frog ADH in reducing the volume of 

 the filtrate by constricting the blood flow to the glomerulus. It can 

 also reduce the number of glomeruli which are active. After 

 injection of antidiuretin the kidney tubules, therefore, receive a 

 reduced volume of isosmotic filtrate, containing salts, sugar and 

 urea. 



lOOr ^°"^ catesbicna 500g 

 I /ICO frog ADH 



(0007 Oxytocic unit/ kg) 



50 



20 



10 



n50 



20 



10 



Hours 



Fig. 5-23. Responses of the bullfrog, Rmia catesbiana, during 

 2 hr after an injection of the antidiuretic hormone from the 

 NEUROHYPOPHYSIS. Frog ADH reduces G.F.R., the filtration rate 

 (shown by creatinine clearance, ^^-^i, on ordinate scale on left) 

 but not sufficiently to account for the large reduction in volume 

 (V on same scale) of excreted urine. This is chiefly due to the reduc- 



tion in the ratio (shown as 



on percentage scale on right) of 



clearance of "free water" to that of creatinine, due to reabsorption 

 of water in the kidney tubules. Control injections caused no signifi- 

 cant changes (from Sawyer, 1957). 



