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17 beta-Estradiol (E2) and progesterone (P) concentrations in blood and in the myometrium of human pregnancy at term (n=33) and in a few samples (n=5) around midterm of pregnancy were determined. E2 concentration in the myometrium (per g wet wt) at midterm was lower than the concentration in the plasma (per ml) so that the myometrium to plasma (My:Pl) ratio was 0.7. Relative to plasma concentration, the myometrial E2 increased little from midterm to term so that My:Pl was only 0.2 at term. Although P concentration in the myometrium was much greater than that in the plasma at midterm, My:Pl ratio being 2.2, it was lower than that in plasma at term so that My:Pl ratio was only 0.6. A fairly good correlation between plasma steroids and the myometrial steroids was observed at midterm but was distorted at term, probably due to saturation of the tissue-binding capacity. Steroid concentrations determined on the basis of protein showed a good correlation to the values expressed on the basis of wet weight. Whereas myometrial E2 concentration was significantly influenced by the distance from placenta, P concentration was not.

The effect of vasopressin on the flow of blood through the uterus and placenta in the rabbit has been investigated by an angiographic technique, with contrast injection through a catheter inserted in the external iliac artery or selectively in the urogenital artery. It was found that the drug markedly reduced contrast filling of the vessels in the placentae and uterine wall including the placental sinuses. It is suggested that this effect was produced by constriction of the venules in the uterine vascular bed. The possible operation of a shunt mechanism in the uterus is discussed.

A technique is described for studying endometrial or decidual blood flow by introducing a thermistor, mounted in a flexible catheter, into the uterus. The technique was first tested in model experiments and in the pregnant rabbit and was then used to study the blood flow of the human uterus. In pregnant women, the thermistor was introduced between the decidua and fetal membranes, and in non-pregnant women, it was applied to the endometrium of the fundus. Intra-uterine pressure was recorded simultaneously. No complications were encountered in either pregnant or non-pregnant patients. Decidual or endometrial blood flow remained steady over long periods. There were transient fluctuations about the mean level, usually associated with myometrial contractions, but these could easily be distinguished from changes in the level of blood flow evoked by administration of vasoactive drugs.

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