THE PITUITARY BODY 



during much of pregnancy — an effect which is usually attrib- 

 uted to the internal secretion of the corpus luteum, proges- 

 terone. The effect can be produced in rabbits, spayed im- 

 mediately after mating, by the injection of 4-5 mg. of natural 

 or synthetic progesterone distributed over 5 days (Make- 

 peace, Corner, and Allen, 1936). No corresponding decrease 

 in the sensitivity of the urinary bladder or colon was ob- 

 served by Podleschka and Dworzak (1936), who used pos- 

 terior-lobe extract; their results, therefore, have no apparent 

 significance. Robson (1935-36) found that it was difficult 

 to demonstrate any change in the activity of oxytocic hor- 

 mone on the uterus of pregnant or pseudopregnant rabbits 

 as a result of the administration of oestrogen. 



It is probable that the decreased oxytocin-sensitivity of 

 the pregnant or pseudopregnant rabbit's uterus has no gen- 

 eral significance. When the uterus of other animals is under 

 the influence of the corpus luteum, there may be no evidence 

 of diminished uterine sensitivity. This is true of the cat (van 

 Dyke and Li, 1938), guinea pig (Bell and Robson, 1936), 

 mouse and rat (Brooksby, 1937). From observations previ- 

 ously reviewed, as well as from new experiments, it may be 

 concluded that the human uterus likewise is not less sensi- 

 tive toward the oxytocic principle during the luteal phase of 

 ovarian secretion. Although Kraul (1935) and Podleschka 

 (1935) believed that the oxytocin-sensitivity of the uterus is 

 reduced in the latter part of the menstrual cycle, their find- 

 ings were not confirmed by the experiments of Kurzrok and 

 others (1937), Miller, Cockrill, and Kurzrok (1937), and 

 Robertson (1937). 



Androsterone appears not to affect the sensitivity of the 

 rabbit's uterus toward posterior-lobe extract (van Bokkum, 



1936). 



The pharmacology of the vasopressor hormone apart from its 

 metabolic effects.- — Following the intravenous injection of pos- 

 terior-lobe extract or of an extract containing principally the 

 vasopressor principle, a contraction of capillaries and arteri- 



[262] 



