272 ADVENTURES IN RADIOISOTOPE RESEARCH 



1 — e-^' 

 From X — 0.69 hour"', and / — 4 hours, it follows that 



y = 3. 



The value obtained for Y is too high, as the decrease of the labelled 

 phosphatide content of the plasma takes place in the later stages of the 

 experiment at a slower rate than according to the equation mentioned 

 above. By taking into account this deviation we arrive at the values 



Y = 2.6 and X ^ 81 . 



From the fact that the phosphatide content of the plasma of the rabbit 

 amounted to 60 mgm it follows that, from the phosphatide molecules 

 present in the liver after the lapse of 4 hours, 52 mgm were such as migra- 

 ted from the plasma into the liver during the experiment. 



Summary 



Plasma of rabbits containing labelled phosphatides was injected to other 

 rabbits. Plasma samples of the last mentioned rabbits were taken at intervals 

 and their labelled phosphatide content determined. The labelled phosphatide 

 content of the organs was determined as well. The labelled phosphatides were 

 found to disappear at a fairly rapid rate from the circulation. Half of those origi- 

 nally present left the circulation in the course of about 2 hours. 



The labelled phosphatide molecules penetrate at a fast rate into the interspaces 

 of the liver, at a much slower rate into that of other organs: the sequence of the 

 decreasing rate of penetration being lungs, kidneys, spleen, heart, small intestine, 

 brain, and muscles. 



The accumulation of labelled phosphatides in the Uver in the course of 4 hours 

 was ten times larger- than expected in the case that the interspaces alone contained 

 these phosphatides. From this fact follows a very great permeability of the cell 

 walls of the liver to phosphatides. This is not the case for the other organs investi- 

 gated. In view of the small amounts of phosphatides which penetrate, in the 

 course of 4 hours, from the plasma into the muscles and the brain, we can conclude 

 that the exchange of phosphatides between the cells of these orgarrs and the 

 circulation is almost negligible. 



The total amount of phosphatides taken up from the plasma by the liver in 

 the course of 4 hours was found to be 52 mgm. This uptake is accompanied by a 

 migration of a similar amount in the opposite direction. Not only is the rate of 

 turnover of phosphatides in the liver very high, the exchange of phosphatide mole- 

 cules betweeir the liver cells and the plasma takes place at a much higher rate 

 than the corresponding process between other organs and the circulation. 



In the course of 17 min, about 65 per cent of the labelled phosphatides origin- 

 ally present in the plasma of the chicks left the circulation. 



Administration of large doses of histamin had no striking effect on the 

 rate of penetration of phosphatides through the capillaries of the chick. 



