The mouse placenta possesses a soluble oestrogen sulphotransferase activity which increases markedly from at least 12 days of gestation until term. At about 16 days of gestation, a similar activity is found in the uterus. This activity also increases until term and disappears rapidly post partum. The uterine enzyme activity appears to require the presence of the foetal unit for its onset, since unoccupied horns, whether their endometrial stromal cells are differentiated to decidual cells or not, are essentially devoid of it. Uterine cytosols from non-pregnant mice are also inactive in this respect. In late gestation, the uterine sulphotransferase is confined to the decidua basalis, the areas to which the placentas are attached. The sulphotransferase(s) of placenta and uterus has an absolute requirement for 3'-phosphoadenosine 5'-phosphosulphate, and possesses little activity in the absence of exogenous thiol groups. Stimulation is also seen in the presence of Mn2+, Mg2+ or Ca2+. Oestrone and oestradiol, and to a lesser degree oestriol, are substrates for the enzyme(s), whereas testosterone, cortisol and dehydroepiandrosterone are not. Oestrone and oestradiol at higher concentrations (1.0-1.5 microM) completely inhibit the enzyme(s). These enzymes could play a role in altering tissue concentrations of active oestrogens during gestation in the mouse. Oestrogen sulphotransferase activity is low or absent in reproductive tissues of the pregnant rat.

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Incubation of nanomolar concentrations of [3H]estrone with ovine liver slices from adult and fetal animals demonstrated, in particular, the production of estrogen sulfates together with smaller amounts of glucuronides, even although microsomal estrogen glucuronyltransferase (GT) and sulfatase activities were high, especially in adult tissue. [3H]Estriol was conjugated almost exclusively as sulfate under the same experimental conditions. Slices of maternal and fetal kidney medulla were also strikingly active in promoting estrogen sulfate production as were slices of fetal kidney cortex. Adult kidney cortex conjugated estrogen only in the glucuronide form. These data indicate the possibility that maternal and fetal liver and kidney might contribute to the high circulating level of estrone sulfate in the pregnant sheep. Through the use of [3H]estrone and [3H]estrone sulfate as substrates, it was possible to demonstrate that adult slices of kidney medulla possessed relatively low sulfatase, considerable sulfotransferase (ST), and virtually no GT activity, whereas cortex had high sulfatase, little or no ST, and low, though demonstrable, GT activity. The ST activity of kidney high-speed supernatants was stimulated by the presence of sulfhydryl groups, whereas that in liver was not. Enzymic reduction of estrone and (or) estrone sulfate by liver and kidney slices indicated that, in the former, 17 alpha-reduction prevailed and, in the latter with the exception of the maternal medulla, 17 beta-reduction was the main pathway, particularly in the fetus.

Glutathione-insulin trandhydrogenase (GIT) activity has been shown to be stimulated in culture of explants of pregnant mouse mammary gland by a mixture of insulin, cortisol, and prolactin. Since this hormone mixture stimulates lactogenesis in vitro it is possible that the increase in GIT activity is functionally related to one of the processes of milk secretion or ejection. Oxytocin is degraded by GIT and the interaction of this hormone with its mammary gland receptors may be influenced by the change in enzyme activity. The increase in GIT activity caused by insulin, cortisol, and prolactin in vitro can be prevented by the addition of progesterone or oxytocin to the culture medium.