1000 



SPERM, OVA, AND PREGNANCY 



100 



40 



%(.._»( Thyroxin-injected females 

 C— ^Control females 92.2±2.2 



X — -XThyroidectomized 

 females _.- 



.^¥. 



63.4±0.9 



59.6+1.8 



o 5o[.53.3±i.4 Parturition 



Length of Gestation in Days 



10 



20 



30 



40 



50 



60 



70 



80 



Fig. 16.33. Oxygen con.suinption in the pregnant guinea pig treated with thyroxine or 

 thvroiclpctomized before mating. (From R. M. Hoar and W. C. Young, Am. J. PhysioL, 

 190, 425, 1957.) 



roid guinea pig!>, i.e., to a level !?een in the 

 untreated heterogeneous group. Treatment 

 of the heterogeneous group with thyroxine 

 not only failed to reduce the percentage 

 of stillborn but actually increased the abor- 

 tion rate particularly in the 2nd and 3rd 

 trimesters. The most consistent result, how- 

 ever, was a decrease in length of gestation 

 following treatment with thyroxine, and an 

 increase following thyroidectomy. From 

 these experiments it was concluded that 

 the thyroid hormone facilitates parturition 

 and need be present only late in gestation 

 to exert its action. 



It is apparent that in some species the 

 thyroid hormone is involved directly in 

 pregnancy. In the absence of the hormone, 

 certain species tend to resorb or to abort; 

 or if pregnancy is maintained gestation 

 tends to be lengthened. This is probably 

 due to an interference with the mechanism 

 of parturition. In certain species such as 

 the guinea pig only a parturitional problem 

 has been demonstrated; in others an entire 

 galaxy of symptoms may be present. Re- 

 duction in the size, number, and viability 

 of the young give added emphasis to an es- 

 sential role for thyroxine in the phenome- 

 non of gestation. 



B. ADRENAL CORTEX 



Removal of the adrenal cortex without 

 further treatment invariably leads to dis- 



turbances in rejM'oductive i)hysiology and 

 the termination of pregnancy. Although the 

 early results were controversial in that 

 some investigators reported that adrenal- 

 ectomy failed to affect gestation in the rat 

 (Lewis, 1923; Ingle and Fisher, 1938), 

 others reported that adrenalectomy led to 

 abortion (Wyman, 1928; Dessau, 1937) or 

 to some other disturbance of gestation (Mc- 

 Kcown and Spurrel, 1940). Davis and 

 Plotz (1954) adrenalectomized two groups 

 of pregnant rats on the 4th to 6th and the 

 14th to 16th day of pregnancy. Abortion 

 occurred in all 12 rats adrenalectomized 

 during the first half of pregnancy whereas 

 only 1 of the 12 adrenalectomized during 

 the second half of pregnancy aborted. How- 

 ever, even in those adrenalectomized during 

 the second half of gestation, an effect on 

 jiregnancy was observed. A significantly 

 higher incidence of stillborn and sickly 

 young (14.4 per cent) and a marked de- 

 crease in the weight of the fetuses were 

 noted (Table 16.10). 



Early results indicated that extracts of 

 the adrenal cortex could readily replace 

 the absent adrenal gland and maintain suc- 

 cessful pregnancies. Within recent years it 

 has been demonstrated that many steroids 

 such as cortisone and 9a-chlorohydrocorti- 

 sone at 10 /xg. per day (Llaurado, 1955) 

 permit fecundation and successful mainte- 

 nance of pregnancy. Successful maintenance 



