1008 



SPERM, OVA, AND PREGNANCY 



(1955) who noted that hypophysectomy of 

 the mother prevented the fetal adrenal 

 weight increase observed following adrenal- 

 ectomy of the pregnant mother. However, 

 complete atrophy of the adrenal gland was 

 not observed in the pregnant mother if the 

 conceptus was present. It was concluded 

 that ACTH can cross the placental barrier 

 and that the fetus or placenta or both pro- 

 duce a sufficient amount of ACTH, to influ- 

 ence the maternal adrenal gland in the 

 absence of the maternal hypophysis. It is 

 still questionable, however, whether these 

 sources, i.e., placenta and fetal pituitary, 

 are of sufficient magnitude to account for 

 the increased release of adrenal corticoids. 

 Hofmann, Knobil and Caton (1954) showed 

 that the ability of the hypophysectomized 

 nonpregnant rat to secrete a water load is 

 not greater than that of the hypophysecto- 

 mized pregnant rat. Hence the contribution 

 of the fetal pituitary or j^lacenta to the 

 corticoid pool is not of sufficient magnitude 

 to influence water balance. 



As with the gonadotrophins, the increased 

 amounts of estrogen ancl pregnanediol dur- 

 ing pregnancy were thought to be derived 

 from the placenta. In 1933, Selye, Collip 

 and Thompson presented evidence to indi- 

 cate that the placentas of rats jiroduce both 

 estrogen and gestagen. Many physiologic 

 data have been accumulated to prove this 

 point, but completely convincing evidence 

 was obtained only when these hormones 

 were identified in placental extracts and in 

 fluid perfused through the placenta. Dicz- 

 falusy and Lindkvist (1956) identified es- 

 tradiol in the placenta and the presence of 

 progesterone was described by Salhanick, 

 Noall, Zarrow and Samuels (1952) and by 

 Pearlman and Cerceo (1952). 



Perfusion experiments on human placen- 

 tas have revealed that this organ secretes a 

 number of steroids (Pincus, 1956). These 

 include progesterone, desoxycorticosterone 

 Cortisol, and a number of unidentified ster- 

 oids. Addition of ACTH to the perfusate 

 had no effect on the concentration of Corti- 

 sol, but it did increase the concentration of 

 the reduced corticosteroids, namely, the 

 tetrahydro derivatives of cortisone and Cor- 

 tisol. This was interpreted as a stimulation 

 of the placenta by ACTH resulting in an in- 

 creased release of the corticoid as demon- 



strated by the increase in the degradation 

 products. 



The identification of the placenta as a 

 source of both sex steroids and certain gon- 

 adotrophins clarifies the manner by which 

 jiregnancy can be maintained in certain 

 species in the absence of the pituitary 

 gland or ovary (see sections above on ovary 

 and pituitary gland). Newton and Beck 

 (1939) and others showed the hypophy- 

 sectomy of the pregnant mouse does not pre- 

 cipitate abortion. Studies of the ovary re- 

 veal that, if the placentas are retained, the 

 corpora lutea remain normal but removal 

 of the placentas causes immediate degenera- 

 tion of the corpora lutea (Deanesly and 

 Newton, 1940). A comparable situation ap- 

 pears to exist in the rabbit and rat ; it is as- 

 sumed, therefore, that the placenta takes 

 over control of the corpus luteum in preg- 

 nancy in those species that require the 

 ovary for successful gestation. In other spe- 

 cies, such as man, sheep, cattle, and guinea 

 pig, it seems that the placenta can supplant 

 the ovary after pregnancy has progressed 

 to a certain stage. 



G. PELVIC ADAPTATION 



The discovery that pelvic changes are 

 under hormonal control in certain species 

 was the result of extensive studies on pelvic 

 adaptations associated with parturition (see 

 reviews by Allen, Hisaw and Gardner, 1939; 

 Hisaw and Zarrow, 1951). It has been ar- 

 gued that, in general, a narrow pelvis is 

 present in mammals living in burrows. This 

 would have the advantage of permitting an 

 animal to turn within narrow confines, but 

 a narrow pelvis would also interfere with 

 the delivery of the young at parturition. As 

 Hisaw pointed out in his extensive studies, 

 this problem has been met by special adap- 

 tations on the part of different species. This 

 has varied from a resorption of the carti- 

 laginous pubic arch in the male and female 

 mole iScalopiis aquaticus machrinus, Raf.) 

 which is independent of the endocrine sys- 

 tem (Hisaw and Zilley, 1927) to elongation 

 of the pubic ligament which is directly un- 

 der hormonal control (Hisaw and Zarrow, 

 1951). 



The symphysis pubis of the pocket go- 

 pher, Geomys bursarius (Shaw), behaves as 

 a female secondary sexual character so that 



