EXTRACTS OF THE PARS NEURALTS 



most of the depressor action to histamine. This organic base, 

 of course, was isolated from the posterior lobe years age.' 



Gulland and others (1935) have particularly studied the 

 oxytocic principle. They were unsuccessful in attempts to 

 employ adsorbents to effect a high degree of purification. 

 Electrodialysis also was found not to be of value. At pH 

 6.0-6.5 °^ ^^^^ ^^^ hormone migrated toward the cathode; 

 at a higher pH (8 or greater) the hormone remained in the 

 central cell. No ultraviolet absorption spectrum characteris- 

 tic of the hormone could be detected. 



Gulland and Randall, Freudenberg, Weiss, and Biller, and 

 Sealock and Du Vigneaud all published in the same year 

 (1935) evidence that posterior-lobe hormone(s) contain an 

 oxidation-reduction system probably dependent upon a di- 

 sulphide linkage. According to Gulland and Randall, the 

 E'o of the oxytocic principle is —0.025 volts at pH 6. They 

 found the activity of the principle to be 100 per cent in the 

 oxidized state and 50 per cent in the reduced state and of- 

 fered an interpretation of this finding. Also, they suggested 

 that there may be a second oxidation-reduction system in 

 the molecule of the oxytocic hormone. Sealock and Du 

 Vigneaud concluded that an -SH group, real or potential 

 (-S-S-group), must be present in active extracts of either 

 oxytocic or vasopressor hormone. Activity was preserved 

 after reduction by cysteine or after reoxidation following such 

 reduction but not after benzylation or methylation of the re- 

 duced compounds. The activity of the oxidized forms was 

 not affected by treatment with methyl iodide or benzyl 

 chloride. The activity of the oxytocic and vasopressor prin- 

 ciples seems to be less dependent on the state of their oxida- 

 tion-reduction systems than is the case with insulin. 



The assay of the active principles of the pars neuralis. — In 

 addition to the procedures reviewed previously, a few new 

 methods have been employed for the assay of the hormones. 



' It is not clear whether the chenical studies of Downes and Richards (1935) are 

 of any significance, 



[^59] 



