362 



ADVENTURES IN RADIOISOTOPE RESEARCH 



activity of the plasma ortliophosphate, liver inorganic P, liver ATP Pg^g and 

 phosphatide P determined. Some of the resuhs obtained are listed in Table 10. 

 The phosphatides were purified according to Levin's method as modified by 

 Hahn and Tyren (1946). The above results do not indicate the presence of a 

 rapidly renewed phosphatide fraction. 



Experiments of Long Duration 



As observed at an early date (Hevesy and Aten, 1938: Zilversmit et al., 

 1943, 1948) in experiments of long duration the specific activity of phosphatide 

 P exceeds the corresponding value of orthophosphate P, the last mentioned magni- 

 tude decreasing at a slower rate than the orthophosphate P. As seen in Table 11 

 the specific activity of orthophosphate P resp. labile ATP phosphorus declines 

 between 1/12 day and 84 days (the maximum value is observed about V12 day after 

 subcutaneous injection) from 0.546 to 0.000603. Thus, out of 900 ^ap atoms in the 



Table 11. — Specific Activity of Liver Fractions at Different Dates Following 



Administration of ^-P 



1 Activity of 1 mg P in percentage of the dose administered, obtained by comparing tlie radioactivity 

 oi a known aliquot of the solution injected with that of a known amount of phosphorus of the fraction 

 mvestigated. 



nitial maximum state, only 1 is present after the lapse of 84 days (beside the loss 

 due to radioactive decay). During the same interval, the beginning of which 

 does not correspond, however, to the maximum value of ^ap content of phosphati- 

 des, the 32P content of phosphatides decreases to Viio of their initial value. 



The decline of the ^sp of liver orthophosphate, which in view of the highperme- 

 abihty of liver cells corresponds closely to the fall of ^ap content of plasma 

 orthophosphate, is due partly to incorporation of ^ap into the tissues and partly 

 to its excretion. With increasing time excretion becomes more and more the sole 

 way of escape of ^sp from the circulation. While on the first day, the ^ap content 

 of orthophosphate decreases to V5 oi its 2-hour-value, a decline to V7 of the first 

 day's value takes 12 days, a decline to V3 of the 12 day- value 9 days, the decrease 

 of the 21st day value to almost 1/4 takes not less than 28 days, while a decrease 

 of half the 44 day- value requires 35 days. 



The renewal of the phosphatides takes place at a slower rate than the escape 

 of 32p from the plasma, however, after a long sequence of days this difference 

 diminishes due to the reduced loss of ^ap by the circulation. 



The values were obtained from pooled organs of 4—6 rats weighing about 

 160 gm. In the 84-day experiment 0.1 miUicurie was administered to each rat, 

 in the experiments of shorter duration correspondingly less. The administration 

 of 0.1 millicurie or more involves risks in experiments of long duration as to bio- 

 logical action of the radiation emitted by the administered P, as the radiation 

 dose to which the rats are exposed during the experiment may amount to a few 

 hundred rep. 



