358 



ADVENTURES IN RADIOISOTOPE RESEARCH 



Kidney Phosphatides 



The ratio of the specific activities of kidney phosphatide P and inor- 

 ganic P is appreciably higher than the corresponding spleen values, 

 though it falls below the liver values. We found the mean value of the 

 specific activity of the kidney inorganic P to be 1.35 times the end value 

 and, consequently, we have to divide the figures of column 3 of Table 6, 

 which denote data of experiments, taking 2 hours, by 2x1.35 in order 

 to arrive at an estimate of the lower limit of the percentage turnover 

 per hour. 



The pronounced decrease in the phosphatide turnover with age shown 

 by the liver phosphatides is not exhibited by the kidney phosphatides. 



Turnover of Lecithin and Cephahn 



In the investigations described above the rate of incorporation of 

 22P into the total liver phosphatides was determined. Lecithin and 

 cephalin are renewed at a not very different rate. Platt and Porter 

 (1947) found, for example, 6 hours after administration of labelled 

 phosphate to full-grown rats kept in usual diet the ratio of specific 

 activities of lecithin P and cephalin P to be 1.5, while in the fasting rat 

 1.3 was found. These authors state, furthermore, that administration 

 of choline increases the turnover rate of lecithin while ethanolamine 

 promotes the turnover of cephalin formation. In the first mentioned 

 case a maximum increase of 33 per cent, in the latter case a maximum 

 increase of 87 per cent of the turnover rate was observed. They inter- 

 pret the increased formation of labelled phosphatides following admi- 

 nistration of choline and ethanolamine, respectively, as a mass action, 

 the assembly of the phosphatide molecule being promoted by an increase 

 in the choline and ethanolamine concentration, respectively. 



In experiments on dogs, Zilversmit and assoc. (1948) recently found 

 the mean specific activity ratio of lecithin P and cephalin P to be 1.2. 



Table 7. — Specific Activities 



' Activity of 1 mgm I' in percentage of tlie activity administered to tlie rat. 



