THE PITUITARY BODY 



be assumed that there is only one) produces effects different 

 from those characteristic of prolan but resembling those of 

 the anterior pituitary. Like the pregnant woman, the preg- 

 nant mare also excretes oestrin-like hormones, but in much 

 larger quantities, particularly in the latter part of pregnancy. 

 The gonadotropic hormone peculiar to the blood and 

 tissues of the pregnant mare appears not to be as readily 

 excreted by the kidneys as prolan. Ordinarily, but not in- 

 variably, the concentration of prolan in the urine of pregnant 

 women resembles that in the blood; the gonadotropic hor- 

 mone of pregnant mares, however, is found in a much higher 

 concentration in the blood than in the urine. Moreover, 

 when it is injected into other animals for assay, a single dose 

 in comparison with repeated doses is about as effective or 

 even more effective (Cole, Guilbert, and Goss, 1932; Catch- 

 pole and Lyons, 1934). Cole and Hart pointed out that the 

 hormone did not appear in the blood until about the time 

 of nidation (about the thirty-seventh day). The maximum 

 concentrations were found between the forty-third and 

 eightieth days. "Oestrin," on the other hand, appeared in 

 the blood later, and unlike the gonadotropic hormone per- 

 sisted throughout the remainder of pregnancy. -^^ The period 

 between the fortieth and one hundred and fiftieth days, when 

 gonadotropic hormone could be found in the blood, was also 

 the only period in which new corpora lutea (presumably fol- 

 lowing ovulation) were formed in the ovaries of pregnant 

 horses (Cole, Howell, and Hart, 1931). Catchpole and Lyons 

 (1934) determined the presence or the approximate amounts 

 of the hormone in blood, chorion, and endometrium at differ- 

 ent stages of pregnancy (different fetal lengths). The endo- 

 metrium of the fertile horn was found, at appropriate stages, 

 to contain the most hormone (in fact it appeared to be richer 

 in gonadotropic hormone than any other tissue so far investi- 



^9 Also see Cole and Saunders (1935). 



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