1124 



SUBMAMMALIAN VERTEBRATES 



TABLE 18.6 

 Effect uf progesterone on estrogen-induced increase in oviduct weight of immature Jowl 



* Average body weight of groups. 



t Weight estimated from age of birds from Table 9, Nutritional Requirements of Poultry, Nat. Res. 

 Council, Publ. 301, 1954. 



1949a). The observation that j)rogesterone 

 alone can inhibit this response to estrogen 

 has been confirmed by some workers, but 

 others have noted a definite synergistic ac- 

 tion. Some of these experiments have been 

 summarized in Table 18.6. The list of ex- 

 periments is not complete, for in some cases 

 no quantitative data were published (Gard- 

 iner, Phillips, Maw and Common, 1952). 

 The difi"erent results are difficult to evalu- 

 ate because of differences in body weight 

 and the uncertainty concerning the amount 

 of estrogen absorbed from implanted pellets. 

 It is possible, however, that an antagonism 

 occurs at the higher doses of estrogen. This 

 is somewhat similar to the inhibition ob- 

 served between some combinations of es- 

 tradiol, estriol, and estrone in immature 

 rats. At lower doses, estrone + estradiol and 

 estradiol + estriol acted synergistically in 



stimulating uterine weight, but estradiol 

 inhibited the eftect of estriol when estradiol 

 + estriol were given in higher doses 

 (Grauer, Saier, Strickler and Cutuly, 1958). 

 More detailed studies on the dose relation- 

 ship and the ratio of estrogens to progester- 

 one are required in order to determine 

 whether the present variations in results 

 can be explained by competitive inhibition. 

 It is notew^orthy that Brant and Nalban- 

 dov (1956) observed no antagonism between 

 estrogen and progesterone W'hen oviduct 

 weight, tubular gland development, and al- 

 bumen secretion were measured. When es- 

 trogen plus 2 to 3 mg. of testosterone were 

 administered, an optical stimulation oc- 

 curred, but W'hen a larger amount of testos- 

 terone (4 mg. per day) was given with estro- 

 gen an antagonism was indicated by the 

 low^er oviduct weight, the lesser develop- 



