BODY TISSUES 321 



experiments provided the impetus for the isolation of the peptides, 

 oxytocin (pitocin) and vasopressin (pitressin). These peptides were 

 fust separated in electrophoretic studies. 



Oxytocin contains a ring of five amino acids linked to a side chain 

 of three amino acids with all carboxyl groups in amide forms. The 

 structure has been established not only by sequential amino acid 

 determinations but also by synthesis. Oxytocin stimulates the con- 

 traction of the uterus and is useful in instigating the removal of the 

 by-products of partinition. Oxytocin also functions in milk ejection 

 from lactating mammary glands by stimulating contractions of the 

 smooth muscles of those organs. 



Vasopressin is also peptide in nature, containing eiglit amino acids, 

 and is very similar t(j oxytocin except that phenylalanine replaces 

 isoleucine in the cyclic portion of the molecule and arginine replaces 

 leucine in the side chain in beef vasopressin. Lysine replaces leucine 

 in the side chain of hog vasopressin. 



Vasopressin causes arterial constriction (pressor action) with a rise 

 in blood pressure. Administration of this hormone has been used to 

 combat low blood pressure in treating shock. Vasopressin may also 

 be ftmctional in the constriction of renal tubes and thus prevent ex- 

 cessive water excretion, although some workers believe that a third 

 peptide in pituitary extract is more effective for this ptirpose. 



There is some evidence that the above hormones exist in the pitui- 

 tary as one unit, and that the active principles isolated are the result 

 of breakdown of that constituent. A protein, apparently pure, has 

 been isolated which possesses activities associated with the above two 

 (or three) peptides, that is, pressor action, uterine contraction, and 

 renal action. 



Placenta. Placental tissue contains a gonadotropic hormone, known 

 as chorionic gonadotropin. This hormone is produced by the placenta 

 and is excreted into the urine soon after pregnancy occurs. When 

 pregnancy urine is injected into immature female mice, it causes 

 hemorrhage of an ovarian follicle within a period of 4 days. This 

 effect has become the basis of the Ascheim-Zondek pregnancy test, 

 which has achieved real success in human medicine. The Friedman 

 )3regnancy test is based on the same principle. Human pregnancy 

 urine is injected into mature unmated female rabbits. If the placental 

 hormone is present in the urine, follicular rupture and corpus kiteum 

 formation occur within 1 or 2 days. The hormone is a glycoprotein 

 containing galactose. 



Reproductive glands. The organs of reproduction responsible for 

 the production of sex hormones are the ovaries and the testes. 



