EXTRACTS OF THE PARS NEURALIS 



Nearly all the other observations on the pharmacology of 

 the oxytocic principle were made to ascertain the uterine re- 

 sponse after the secretion or injection of oestrogen or pro- 

 gesterone or both. For example, under the influence of oes- 

 trogen the uterus of some species of animals may exhibit a 

 heightened sensitivity toward the oxytocic principle. Abor- 

 tion, as shown by Parkes in the pregnant mouse, may occur 

 after the administration of oestrogen followed by oxytocic 

 principle, although either substance by itself does not inter- 

 rupt pregnancy. To some authors (e.g., Druckrey and Bach- 

 mann, 1937) it has seemed that these and related observa- 

 tions satisfactorily explain the initiation of parturition and 

 perhaps its continuation. However, the experimental basis 

 for such a belief is far from satisfactory.^ The later experi- 

 ments of Marrian and Newton (1935) and of Robson (1935) 

 in pregnant mice fully confirm Parkes's findings. The in- 

 creased sensitivity to oxytocic principle after the administra- 

 tion of oestrogen can also be observed in the isolated uterus.-* 

 From experiments in other animals^ such as the rabbit and 

 man there is also evidence that both spontaneous activity of 

 the uterus and its sensitivity toward the oxytocic principle 

 are increased when follicular hormone (oestradiol) is pre- 

 dominantly affecting the uterus. The specificity of this in- 

 creased sensitivity has not been proved. For example, ergot- 

 amine, like posterior-lobe extract, has been found to elicit 

 uterine contraction more readily during ovarian follicular 

 growth. 



Undoubtedly, the uterus of the rabbit is less sensitive 

 toward the oxytocic principle during pseudopregnancy or 



•i The reader is particularly referred to the articles of Marrian and Newton (1935), 

 D'Amour and Dumont (1937), and Robson (1937). 



■"The isolated pregnant uterus of the mouse or rabbit is more sensitive toward 

 the oxytocic principle after ovariectomy but not if the uterine contents also have 

 been removed (Robson, 1936). 



5 Robson and Henderson (1936) reported that the oxytocin-sensitivity of the 

 uterus of the hypophysectomized dog is, if anything, reduced after the administra- 

 tion of oestrin. 



[261I 



