GESTATION 



965 



TABLE 16.4 

 Maximal hormone levels in the blood during pregnancy 



" Expressed as equivalents of progesterone. 



'' Guinea pig units. 



"■ Protein-bound iodine. 



'Vg. equivalent of a purified bovine growth-promoting substance. 



the corpus luteum is necessary for the 

 maintenance of pregnancy. Fraenkel dem- 

 onstrated at the turn of the century that 

 the corpus luteum of the rabbit is essential 

 for the maintenance of pregnancy in the 

 rabbit (Fraenkel and Cohn, 1901; Fraen- 

 kel, 1903; Fraenkel, 1910). These observa- 

 tions were confirmed by Hammond and 

 Marshall (1925.) who found that castration 

 before the 20th day of pregnancy led to the 

 termination of pregnancy in 24 hours. Cas- 

 tration later in pregnancy resulted in abor- 

 tion approximately 2 days after the opera- 

 tion. In 1928, Corner showed that an extract 

 of the corpus luteum could induce a proges- 

 tational endometrium in the castrated rab- 

 bit. This was soon followed by the demon- 

 stration that this extract could induce 

 implantation of the fertilized egg in the 



rabbit and maintain pregnancy in the cas- 

 trated animal (Allen and Corner, 1929; 

 1930). Purification of the extract of the 

 corpus luteum led to the chemical identifica- 

 tion of the active substance by Butenandt, 

 Westphal and Cobler in 1934, and in the 

 following year Allen, Butenandt, Corner 

 and Slotta (1935) agreed to the name pi^o- 

 gesterone for this hormone of the corpus 

 luteum. 



These events were soon followed by tlu' 

 discovery that progesterone is excreted in 

 the urine as tlie glucuronide of pregnane- 

 diol and i)regnanolone, metabolites of pro- 

 gesterone. Studies of urinary products of 

 progesterone were immediately undertaken 

 and a marked increase in urinary preg- 

 nancdiol was observed in the human female 



