1118 



SUBMAMMALIAN VERTEBRATES 



TABLE 18.5 

 Changes in blood composition after estrogen administration 



Controls were nonlaying hens, treated were 11-week-old pullets. 



amounts of intramedullary bone whether 

 the birds were on a diet with enough calcium 

 or on one completely deficient in calcium. 



The Ca-deficient diet was also deficient in 

 vitamin D in order to further reduce the 

 intestinal absorption of Ca. Birds fed the 

 Ca-deficient diet deposited somewhat more 

 medullary bone after estrogen treatment 

 than did the estrogenized birds fed a Ca- 

 adequate diet. The bone cortex of the Ca- 

 deficient estrogen-treated birds showed re- 

 sorption cavities and osteoporosis (Urist, 

 1959). Apparently, the intramedullary bone 

 deposition occurs at the expense of the cal- 

 cium from the flat bones. Estrogen treatment 

 results in an increase in blood calcium, 

 mainly in nondiffusible Ca (Polin and Stur- 

 kie, 1958; Urist, 1959). Discussion of this 

 increase in blood calcium levels requires 



consideration of the role of the parathy- 

 roids on Ca metabolism. Estrogen adminis- 

 tration causes an increase in size of the 

 parathyroids (Landauer, 1954) and of ac- 

 tivity, as measured histologically (Benoit, 

 1950b; von Faber, 1954). Is this increase 

 coincidental or physiologic? The following 

 observations may allow the formulation of 

 a tentative explanation for the interaction 

 between estrogen and the parathyroid hor- 

 mone. 



a. Parathyroid hormone administration 

 results in greater increase in total blood 

 calcium in hens than in roosters (Polin, 

 Sturkic and Hunsaker, 1957). 



1). Parathyroidectomy results in a de- 

 crease in total calciimi (Clavert, 1948; 

 Polin and Sturkie, 1957) diffusible and non- 

 diffusible; the decrease in nondiffusible 



