The Concentration of Gonad-Stimulating Hormone in Blood Serum and of Oestrin in the Urine Throughout Pregnancy in the Mare*

Cole and Hart (1930 and 1930a) have shown that the blood serum of mares contains a gonad-stimulating hormone between the 45th and the 150th days and small amounts of oestrin during the last half of pregnancy. According to Zondek (1930), tremendous amounts of oestrin are present in the urine of the mare between the 74th and 260th days. The concentration of these hormones at the various stages of pregnancy has not, however, been systematically studied. Many problems might be more easily solved if exact information on this point were available. For example, one question concerns the sources of these hormones. Does the fetus with its attending membranes initiate an unusual activity of the hypophysis and ovary or are the hormones in question vicariously produced during this phase of reproduction? Another problem concerns the fate of the gonad-stimulating hormone. It is not excreted in the urine unchanged for only rarely can it be detected there. Thus it must be eliminated with other body excretions or destroyed within the mare. In addition, several interesting gonadal phenomena characteristic of this species may be partly explained by a study of hormonal concentrations. Another objective in our experiments was to ascertain in what period of gestation these hormones are most abundant.