The Development of a Plasma Volume Expander 65 



of peptide and especially on methods of peptide production in deep 

 culture. 



When the possibility arose in 1950 that replacement of blood or 

 plasma might again become an urgent problem, and this time on a 

 scale far exceeding the practical supply of whole blood or its com- 

 ponents, it seemed that once again expediency must prevail over inter- 

 est, and our work on glutamyl peptide as a plasma volume expander 

 was resumed. 



At the same time we proposed the use of the straight-chain peptide 

 as a sedimenting agent to be used in the low gravity centrifugal sepa- 

 ration of red cells from plasma in the project on blood fractionation 

 and preservation that was underway at Harvard. In connection with 

 this activity testing of the straight-chain peptide in humans was begun. 

 (The material had been thoroughly tested in animals and found satis- 

 factory, in 1941.) No unacceptable properties manifested themselves 

 in these tests, and these findings provided further encouragement to 

 proceed with preparation and testing of conjugates as plasma volume 

 expanders. With increasing promise of eventual usefulness of the 

 conjugate as an extender, the problem of peptide production in deep 

 culture had become more and more important as the available shallow- 

 culture method of production was economically unsatisfactory. In 

 preliminary experiments we had recently determined that peptide could 

 be produced in deep culture by aeration with COo-air mixtures, but 

 results in different batches were irregular and generally not too satis- 

 factory. With the aid of the group at Detrick peptide production by 

 the deep-culture methods soon reached a highly satisfactory status. 

 One of the first findings with this deep-culture peptide was that its 

 molecular weight was much higher than that produced in shallow 

 culture. The highest number average molecular weight we ever ob- 

 served in the latter was approximately 28,000, whereas the former 

 frequently ran as high as 100,000 or over. The availability of this 

 material greatly increased our range and flexibility with respect to 

 size and shape of conjugates, and the ease of production * of peptide 

 in large quantity greatly increased the impetus of the project. 



With the availability of straight-chain peptide of molecular weight 

 120,000, which was presumably about 10 times as long as that previ- 

 ously used, the question immediately arose and was put to the test 

 as to whether this material would show increased retention in the blood 

 stream. The results are of considerable interest in that they demon- 



* The collaboration of Merck & Co. in the production of peptide is gratefully 

 acknowledged. 



