28 



RADIOISOTOPES IN BIOLOGY AND AGRICULTURE 



10,000 

 9000 



8000 

 7000 - 



6000 — 



5000 



1 



S. 4000 



'a. 

 "o 



■§■ 3000 



2000 



1000 



P/jose 1 

 Plasma 

 A 



Exponential 

 removal with rate 

 constant P/a 



Removal and 

 return with rate 

 constant P/a 



tVi = 324 min 

 tf- 466 min 

 P/a ^0.002f 



300 



100 200 



Time /, min 



Fig. 1-5. Simple turnover — no return of labeled substance. Disappearance of injected 

 labeled phospholipids from plasma of dog. [From I. L. Chaikoff and D. B. Zilversrnit, 

 Radioactive Phosphorus: Its Application to the Study of Phospholipid Metabolism, 

 Advances in Biol, and Med. Phys., 1: 321-352 (1948).] 



found. The half-time value as determined graphically or by Eq. (1-17) 

 was about 324 min, which gave a turnover time of 466 min, as calculated 

 by Eq. (1-25). Thus it was shown that, in dogs weighing from 6.6 to 

 8.5 kg, an amount of plasma phospholipid equal to that contained in their 

 plasma was completely renewed in 8 to 9 hr. 



Turnover or Exchange — Return of Labeled Substance. As indicated pre- 

 viously (page 8), there are many biological processes in which ions move 



