Observations on the Conjugated Oestrogens in the Urine of Pregnant Mares

Abstract

Recently in this laboratory it was shown 1 2 that during the last few days of pregnancy in women, immediately before and during labor, there occurs a rapid fall in the total amount of oestrogen excreted, simultaneously with a very great increase in the ratio of “free” ether-soluble oestrogen to conjugated ether-insoluble oestrogen. It was tentatively suggested that this conversion of the less physiologically potent conjugated hormones to the free hormones might be a factor in the initiation of labor. In order to obtain further evidence to support this theory, attempts were made to carry out similar investigations on other species, so that the research could be extended along more experimental lines. In this paper we report the results of colorimetric determinations 3 of the free and conjugated oestrogen in the urine of several mares at different stages of pregnancy. Previous work from this laboratory and elsewhere 4 , 5 , 6 has shown that the colorimetric procedure is applicable to pregnant mares' urine.

The estimations were carried out as follows: 100 cc. of fresh urine were adjusted to pH 6.0 after saturation with NaCl, and extracted several times with toluene. The combined toluene extracts were washed with saturated aqueous Na₂CO₃ and then extracted repeatedly with N. NaOH. The NaOH extract was made faintly acid with HCl, then alkaline with Na₂CO₃ and finally extracted with ether. The ethereal extract after washing with water was evaporated to dryness and the “free” oestrogen estimated colorimetrically in an aliquot portion of the residue. The oestrogen present in such a fraction is presumably a mixture of oestrone, equilin, hippulin, equilenin and oestradiol. At the present time no methods for the quantitative separation of these oestrogens from one another are available and few data are available on their relative chromogenic powers.