GESTATOON 



963 



Monge (1942) reported a lack of repro- 

 duction in the Spaniards for more than 50 

 years after residence in certain areas of 

 Bolivia (14,000 feet or more above sea 

 level). Many malformations have also been 

 observed in the progency of mice, rats, and 

 rabbits exposed to low atmosperic pres- 

 sures. Exposure of mice on the 10th day 

 of pregnancy for 2 hours to a 6 per cent 

 oxygen-94 per cent nitrogen mixture at 

 normal atmospheric pressure gave mal- 

 formations in the young comparable with 

 those found after exposure to a low at- 

 mospheric pressure which was equivalent 

 to the above with respect to the number of 

 oxygen molecules per unit of air (Curley 

 and Ingalls, 1957). Although these mal- 

 formations involved the ribs and vertebrae, 

 it is conceivable that more extensive mal- 

 formations could result in death of the 

 fetuses leading to resorption or abortion of 

 the young. 



Vidovic (1952, 1956) made a very com- 

 plete study of the effect of lowered body 

 temperature on gestation in the rat using 

 the technique of Giaja (1940) in which an 

 hypoxic hypothermia is induced by cool- 

 ing under reduced oxygen tension. The 

 animal is placed in a sealed container 

 which is surrounded by ice for a period of 

 approximately 10 hours. Under these con- 

 ditions a hypothermia of 3 to 4 hours' 

 duration and body temperature of 14 to 

 18°C. can be induced. No deleterious ef- 

 fects were noted in the rats cooled on or 

 before the 13th day of pregnancy. However, 

 the induction of hypothermia after the 

 13th day resulted in a marked increase 

 in the disturbance of gestation. These dis- 

 turbances consisted of an increased number 

 of resorbed fetuses, an increased ratio be- 

 tween stillborn and live young in that 

 more stillborn occurred, a decreased body 

 weight in the progency, and a delay in the 

 onset of parturition. In addition, a marked 

 increase in sensitivity to hypothermia was 

 noted in the animals as pregnancy pro- 

 gressed. Courrier and Marois (1953) cooled 

 pregnant rats by exposure to a temperature 

 of 0°C. for 2 hours. Thereafter the rats 

 were placed in cold water for 3 to 4 hours 

 and a body temperature of 15.5 to 17°C. 

 was obtained. Exposure to the above treat- 

 ment on the 7th to the 11th day of preg- 



nancy had no effect on the fetuses or the 

 pregnancy. Treatment on the 12th to the 

 18th day of pregnancy led to resorption 

 and abortion of the young. The authors 

 concluded that the degree of deleterious 

 effects following exposure to cold varied 

 with the length of the pregnancy. 



Recently, Fernandez-Cano (1958a) ex- 

 posed pregnant rats for 5 hours on 2 con- 

 secutive days to one of the following three 

 experimental procedures: (1) an environ- 

 mental temperature of 103°F. that led to 

 an increase in body temperature to 104°F.; 

 (2) an environmental temperature of 26°F. 

 that led to a decrease in body temperature 

 to 94°F.; and (3) barometric pressure of 

 410 mm. Hg. Both temperature changes led 

 to a marked decrease in the number of 

 implantations and, to a lesser extent, to 

 some embryonic degeneration after implan- 

 tation (Table 16.3). Although some dele- 

 terious action was seen before implantation, 

 hyi^oxia was more harmful after implan- 

 tation. Whereas these results are not in 

 full agreement with Vidovic 's report, it 

 must be remembered that Vidovic used a 

 combination of cold and hypoxia to induce 

 the effects that he observed. Adrenalectomy 

 failed to increase embryonic degenerations 

 in rats treated as above (Fernandez-Cano, 

 1958b). Inasmuch as adrenocorticotrophic 

 hormone (ACTH) causes degeneration of 

 the embryos in intact pregnant rats and not 

 in adrenalectomized rats (Velardo, 1957 1 , 

 it is apparent that these results are explain- 

 able on the basis of an increased release 

 of adrenal corticoids due to the stressor 

 and/or a direct action of the corticoids on 

 the development of the embryo. 



V. Maternal Hormone Levels 

 during Gestation 



Proof that certain hormones are neces- 

 sary for a successful pregnancy came from 

 evidence involving ablation of the source 

 of the hormone and replacement therapy. 

 This was followed by quantitative analyses 

 of the concentration of the hormone in the 

 blood and urine throughout gestation. The 

 increasing concentrations of the hormones 

 as pregnancy advances can be used as a 

 second argument for the role of hormones 

 in the development and maintenance of 

 pregnancy (Zarrow, 1957). Changes of this 



