ACTIVE PRINCIPLES OF PARS NEURALIS 



Long (1931) stated that the lethal dose of the vasopressor 

 fraction administered to rabbits intravenously is 25 units per 

 kilogram body-weight; 3-15 units intravenously per kilogram 

 per hour killed some rabbits within 2-3 hours. 



THE PREPARATION AND THE CHEMICAL PROPERTIES OF 

 THE ACTIVE PRINCIPLES OF THE PARS NEURALIS 



How many active principles can be extracted from the pars 

 neuralis? — Although Abel and his collaborators have main- 

 tained that the pars neuralis contains only one active prin- 

 ciple from which are derived the oxytocic and the vaso- 

 pressor fractions, this single, complete hormone has never 

 been secured in pure form. Until this has been accomplished, 

 it is just as reasonable and more convenient to consider that 

 the two fractions represent two different substances not pre- 

 viously combined in one molecule. None of the active prin- 

 ciples has been prepared in pure form. Histamine certainly 

 is not the oxytocic principle (Guggenheim, 1912; Dudley, 

 1919; Hanke and Koessler, 1920; and Dale and Dudley, 

 1 921). Thus far only two fractions have been secured: the 

 oxytocic fraction (oxytocin, a hypophamine, "Pitocin," 

 "Orasthin") and the vasopressor fraction (vasopressin, ^ 

 hypophamine, "Pitressin," "Tonephin"). Although it has 

 been suggested that the substance inhibiting water diuresis 

 is not identical with the oxytocic or the vasopressor sub- 

 stance (Bijlsma, Burn, and Gaddum, 1928), and although 

 Kamm, Grote, and Rowe (1931) stated that they had ob- 

 tained a "derived hormone" with powerful antidiuretic ef- 

 fects but without any pressor action, most investigators be- 

 Heve that the most potent preparations with vasopressor 

 effects are similarly the most potent preparations with anti- 

 diuretic effects. 



Dudley (191 9, 1923), followed by Schlapp (1925) and 

 Draper (1927) who confirmed and extended Dudley's obser- 

 vations, was clearly able partly to separate the oxytocic and 



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