998 



SPERM, OVA, AND PREGNANCY 



tions or stillbirthsrtf one eliminates the 

 sterile woman from the group, the figure for 

 women showing abortion or stillborn rises 

 to approximately 35 per cent. However, the 

 results are still controversial both with 

 regard to data obtained within a single 

 species and from different species. 



Hypothyroidism in the rat induced by 

 the prolonged administration of thiouracil 

 resulted in a resorption of the fetus in 100 

 per cent of the cases (Jones, Delfs and 

 Foote, 1946). Rogers (1947) reported a re- 

 duction in litter size following sulfaguani- 

 dine and Krohn and White (1950) reported 

 a reduction in litter size following thyroidec- 

 tomy in the rat. Thyroidectomy early in 

 pregnancy caused a resorption of the 

 fetuses and if performed at a later stage 

 in pregnancy resulted in the birth of still- 

 born young (Chu, 1945). Following the in- 

 duction of pregnancy in thyroidectomized 

 rabbits, either a resorption of the young or 

 abortion or prolongation of gestation was 

 noted and the newborn young were usually 

 dead. Chu concluded that the thyroid hor- 

 mone was concerned with the vitality and 

 growth of the embryos during gestation. In 

 the pig the average duration of pregnancy 

 was 114 days for normal gilts and 124.5 

 days for thiouracil-treated animals. In ad- 

 dition, the controls farrowed an average of 

 8.67 pigs per litter compared with 3.25 per 

 litter for the thiouracil-treated .sows ( Lucas, 

 Brunstad and Fowler, 1958 ) . The difference 

 was significant in both instances. Bruce and 



Fio. 16.31. Tlie effect of tliyioid deficiency on 

 litter size. O, 422 litters from tliyroid-defieient 

 mice; •, 423 litters from normal control mothers. 

 (From H. M. Bruce and H. A. Sloviter, J. En- 

 docrinol., 15, 72. 1957.) 



Sloviter (1957) pointed out that part of 

 the conflicting reports on the role of the 

 thyroid in gestation might be due to the 

 different methods used in producing a 

 thyroid-deficient state. Surgical removal of 

 the gland generally results in the loss of 

 the parathyroids which may be also im- 

 portant in the maintenance of gestation 

 (Krichesky, 1939), although adequate in- 

 formation is lacking. The use of antithy- 

 roidal substances offers more serious ob- 

 jections because these drugs not only pass 

 through the placenta but they are non- 

 specific and interfere with other glands such 

 as the adrenal cortex (Zarrow and Money, 

 1949; McCarthy, Corley and Zarrow, 1958), 

 with nutrition, and with the general status 

 of the animal. Consequently, Bruce and 

 Sloviter preferred to establish a thyroidec- 

 tomized state in mice by the use of radio- 

 active iodine after establishing the dose 

 necessary to induce total destruction of the 

 thyroid without damage to the jiarathyroid 

 or ganiete.s. 



Although ( lorbman ( 1950 ) rei)orted a 

 complete loss of reproductive activity in the 

 mouse following treatment with P'*\ Bruce 

 and Sloviter (1957) reported no effect on 

 the ability of the mouse to conceive or bear 

 young. This discrepancy could be due in 

 part to the strain differences in the sensi- 

 tivity of the ovary to the I^^^. Bruce and 

 Sloviter (1957), however, noted a decrease 

 in the average litter size of thyroid-deficient 

 mice (Fig. 16.31 ). The data indicate a max- 

 imum of 6 young per litter in thyroid-de- 

 ficient mice versus 10 young per litter for 

 the normal mice. It is apparent that the 

 entire curve for the litter size of thyroid- 

 deficient mice is shifted toward a smaller 

 size. This has also been observed in the rat 

 following thyroidectomy (Nelson and To- 

 bin, 1937). The thyroid-deficient mice also 

 showed a prolongation of gestation as re- 

 ported in rats, guinea pigs, and sows. Of 

 the thyroid-deficient rats, 46 per cent 

 showed a gestation period of more than 19 

 days whereas only 15 per cent of the normal 

 controls showed a gestation period of more 

 than 19 days whereas only 15 per cent of 

 the normal controls showed a gestation pe- 

 riod of more than 19 days (Table 16.9). 

 Analysis of the data based on grouping 

 according to litter size showed clearly an 



