1016 



SPERM, OVA, AND PREGNANCY 



duces uterine contractions and induces labor 

 and delivery of the young. It is apparent, 

 however, that a mass of contradictory data 

 exist and the hypothesis is still in need of 

 better evidence before it can be fully ac- 

 cepted (for review of early literature see 

 Reynolds, 1949) . 



Some of the evidence supporting the 

 above hypothesis is the fact of the presence, 

 to a limited degree, of a deficiency syn- 

 drome in parturition following removal of 

 the posterior pituitary gland. The data, 

 however, are still equivocal. Labor is ap- 

 parently prolonged in the monkey (Smith, 

 1946) and guinea pig (Dey, Fisher and 

 Ranson, 1941 ) after total hypophysectomy. 

 Nevertheless, parturition will occur nor- 

 mally after removal of the pituitary gland 

 in the rabbit (Robson, 1936), cat (Allen 

 and Wiles, 1932), mouse (Gardner and Al- 

 len, 1942), and rat (Smith, 1932). Even 

 where there is some indication of interfer- 

 ence with labor, delivery occurs. However, 

 the lack of consistent results and species 

 differences may be due to the recent finding 

 that the posterior pituitary hormones are 

 synthesized in the hypothalamus and that 

 removal of the posterior pituitary is only 

 effective under limited conditions because 

 the source of the hormone is still present. 

 These experiments have also been criti- 

 cized on the ground that the anterior pitui- 

 tary was also removed and hence inter- 

 ference with many other hormones occurred. 



Additional evidence in favor of a role 

 for the neurohypophysis in the delivery of 

 the young is the increase in uterine motility 

 following stimuli that bring about release 

 of the posterior pituitary hormones, and the 

 lack of an effect on the uterus when release 

 of the hormone is blocked. 



Positive evidence for the release of oxy- 

 tocin at the time of parturition is still lack- 

 ing as are measurements of the concentra- 

 tion in the blood. Fitzpatrick (1957) takes 

 the view that oxytocin is liberated as an es- 

 sential part of normal parturition and cites 

 the following evidence. (1) A superficial 

 similarity exists between spontaneous labor 

 and that induced by oxytocin. Harris (1955) 

 also stresses the similarity in the uterine re- 

 sponse to oxytocin and to electrical stimula- 

 tion of the supraoptic hypophyseal nucleus. 

 (2) Mechanical dilation of the uterus or 



cervix evokes an increase in uterine con- 

 tractions presumably by way of a nervous 

 reflex release of oxytocin (Ferguson, 1941). 

 (3) Oxytocin is decreased in the posterior 

 pituitary gland of the rat and the dog after 

 labor (Dicker and Tyler, 1953). 



Evidence from the attempts to measure 

 the concentration of oxytocin in body fluids 

 at the time of parturition is inadequate. The 

 early reports of higher concentrations in 

 the urine (Cockrill, Miller and Kurzrok, 

 1934) and blood (Bell and Morris, 1934; 

 Bell and Robson, 1935) during parturition 

 are questioned because of the inadequate 

 methods of extraction and lack of specificity 

 in the assay. Recently, Hawker and Robert- 

 son (1957, 1958) reinvestigated the problem 

 and concluded that two oxytocic substances 

 are present in the blood and hypothalamus 

 of cats, cows, and rats and blood of women. 

 However, they found that the concentration 

 of oxytocin in the blood fell during labor 

 from a high during pregnancy. It is ap- 

 parent that this presents a paradoxical situ- 

 ation in view of the fact that the concentra- 

 tion of oxytocin is low at the time of 

 parturition; a time when the hormone is 

 supposedly exerting its greatest effect. The 

 situation is further complicated by the pres- 

 ence of two oxytocic factors and the pres- 

 ence of an oxytocinase in the blood and 

 l)lacenta (von Fekete, 1930; Page, 1946; 

 Woodbury, Ahlquist, Abreu, Torpin and 

 Watson, 1946; Hawker, 1956). Although 

 more work is required on this problem and 

 esi)ecially with regard to the specificity and 

 concentration of the oxytocinase, there is 

 some indication of a fall in enzyme level 

 before parturition. Tyler (1955) reported a 

 decrease in the blood level of the enzyme 

 towards the end of pregnancy and Sawyer 

 (1954) reported a decrease in oxytocinase 

 activity in rat tissues at the end of preg- 

 nancy. 



C. RELAXIN 



Recently, the discovery of the action of 

 relaxin on the pubic symphysis, uterine 

 cervix, and uterine motility has raised the 

 question of the role of this hormone in par- 

 turition. Certainly in the species that nor- 

 mally show pubic relaxation, relaxin would 

 appear to play a significant role. However, 

 this phenomenon is a special adaptation and 



