PARTURITION 



205 



earlier (see p. 202), has shown that the uterus of the rabbit is 

 practically insensitive to oxytocin during the first eighteen days 

 of pregnancy. During the second half of pregnancy the sensi- 

 tivity increases slowly, until just before parturition, when the 

 increase is very rapid. 



Fitiiitary 

 Eyctract 



oou. 



O'OSu 

 Otsttih. 



OO/u 



Fig. 69. — Action of CEstrin in sensitizing an isolated 



Uterus to Oxytocin. 



(From Bourne and Burn). 



On Knaus' view^, therefore, parturition is due, at least in part, 

 to the uterus developing a far greater sensitivity to oxytocin 

 towards the end than is found during the rest of pregnancy. 

 This insensitivity during the major part of pregnancy Knaus 

 ascribes to the action of the persistent corpora lutea of gestation. 



Effect of cestrin on sensitivitv of the uterus to oxytocin. In 

 comparison with Knaus's work on the effect of the corpus 

 luteum, interesting experiments have recently been performed 

 on the effect of oestrin on uterine sensitivity. Brouha and 

 Simonnet (102) and Miura (461) have show^n that the preliminary 

 injection of the animal wdth oestrin greatly increases the 

 sensitivity of the uterus to oxytocin. Bourne and Burn (79) 

 extended this result by showing that the initial treatment of the 

 uterus in vitro with oestrin greatly increases the response to 

 oxytocin. Actually a synergism exists between oestrin and 

 oxytocin. 



