Abstract
Evans et al. 1 have shown that there is a wide distribution of a substance in the urine and blood serum of mammals which resembles prolan, in that when it is mixed in vitro with the pituitary synergist the effect upon the ovary of the immature rat is enhanced. Evidence that a similar prolan-like substance is present in the blood serum of the non-pregnant and pregnant mare is given in Table 1.∗ Further the data indicate that the prolan-like substance is distinct from the substance in the blood serum of the pregnant mare which is so highly effective in stimulating the gonads when given alone. Following our nomenclature in previous publications we will term the latter substance the gonad-stimulating hormone.
Referring to Table 1 it may be seen that equivalent amounts of non-pregnant and mid-pregnancy mare serum are equally effective in stimulating the gonads of immature rats when combined with the pituitary synergist. The amount of gonad-stimulating hormone present in the 2 types of sera differs greatly. Two cc. of the mid-pregnancy serum when given alone induces follicular development and luteinization whereas 10 cc. of the non-pregnant serum produces no response. In fact, we have shown previously that doses of 60 cc. of non-pregnant serum are without response on the immature rat. Thus it is clear that there is no relationship between the response of the serum when given alone and the response of serum plus synergist. This fact is further demonstrated when the response of early pregnancy blood serum highly potent in gonad-stimulating hormone is compared to non-pregnant serum. The amount of early pregnancy serum injected contained 2 to 4 rat units of gonad-stimulating hormone while the non-pregnant serum contained none. Still the response of the early pregnancy serum plus synergist was less than the non-pregnant serum plus synergist.
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