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SUMMARY
Single injections of oestriol were partially effective in sensitizing the uterus to a decidual stimulus and inducing ovum-implantation in progesterone-treated spayed mice, whereas two injections (6 h apart) were fully effective. It seems that in the progestational uterus, as in the non-progestational organ, oestriol can induce a full oestrogenic response provided that its level in the target organ is maintained. It is also concluded that ovum-implantation is not triggered by some transient early effect of oestrogen, but requires about 12 h of sustained oestrogen action for its successful completion.
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An extensive description is given of the techniques and schedules used in the tetrazolium assay for oestrogens. Among the variables studied, volume of tetrazolium solution, dissection speed and the use of albumen solution were without effect. Priming of mice increased overall formazan production and reduced variability, but did not increase sensitivity or slope of the dose response line for oestrone. Other possible variables affecting the assay are discussed. Three randomly bred strains of mice were comparable in sensitivity and precision, while a single inbred strain (CBA) was so variable as to be unsatisfactory for routine use.
Oestradiol-3:17β was 3·7 times as active as oestrone, and oestriol approximately half as active. The slope of the dose-response line for oestriol was significantly lower than those for oestrone and oestradiol. Diethylstilboestrol was slightly less active than oestradiol-3:17β and equal in slope.
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Locally applied [6:7-3H]oestradiol was taken up rapidly by the vagina, at a rate similar to that of oestrone. Levels of radioactivity in the tissue reached their highest value 1–3 min. after application, and thereafter dropped slowly to reach 20% of the injected dose at 12 hr. This is in contrast to the behaviour of oestrone, the tissue levels of which fell rapidly over the first ½ hr. It is suggested that this difference accounts for the relative biological activity of the two hormones in the vagina, and results from varying affinities for receptor sites associated with the initiation of vaginal growth. Evidence is presented that oestrone, oestradiol and oestriol have a common site of action. Dimethylstilboestrol (DMS) converted the retention pattern of oestradiol to one resembling that of oestrone, and it is suggested that this involves blocking of receptor sites. The results are discussed in relation to the mode of action of oestrogens.
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Progesterone and various nor-steroids did not prevent oestrogenic interruption of early pregnancy in the mouse, although they inhibited other oestrogen-induced changes in the uterus and vagina. It is suggested that the relationship between oestrogen and progesterone is not one of simple molecular competition.
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Histamine dihydrochloride, administered intravaginally, was similar in action to oestrone, causing increased tetrazolium reduction, epithelial growth and cornification in the vagina. However, massive doses were required, and the ineffectiveness of histamine releasers and of various antihistamines indicated that histamine release is not involved in the response of the vagina to oestrogens. The inhibition of histamine dihydrochloride by dimethylstilboestrol indicates that oestrogenic activity is involved. However, the inactivity of the diphosphate excludes histamine itself as a weak oestrogen and suggests that histamine dihydrochloride contains minute amounts of oestrogenic contaminants.
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The reduction of 2-3-5-triphenyltetrazolium chloride in the vaginal epithelium of the mouse is shown to form a suitable basis for a highly sensitive assay of oestrogens. The method is as sensitive and precise as those utilizing mitosis and epithelial thickness, with the added advantage of extreme simplicity.
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The differing sensitivities of two lines of mice, selected on the basis of vaginal cornification for high and low sensitivity to oestrogens, were not reflected in early responses to oestrogen, nor in differential rates of loss of oestrogen from the vagina.
The relation of vaginal cornification to the initial action of oestrogens is discussed.
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A dose of tamoxifen (ICI 46,474), which has been found to inhibit the vaginal smear response to oestrogens, exerted prolonged oestrogenic effects in mice and increased the rate of cell proliferation in both the vagina and uterus. The vaginal epithelium became multilayered with stratified or cornified surface layers and the uterus developed gross cystic glandular hyperplasia. This demonstrates that ICI 46,474 is simply a weak oestrogen in the mouse.
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SUMMARY
The rate at which oestrogens reached their sites of action was investigated by the local application of dimethylstilboestrol at short intervals after the local application of each oestrogen. Receptor occupation appeared to be complete within 2–4 min. of the application of oestradiol-17β and of oestrone and in some cases with oestradiol within 1 min. However, such was the degree of variability between experiments that more precise estimates were not possible. These findings are discussed in relation to the mode of action of the oestrogens.
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SUMMARY
Locally applied [6:7-3H]oestrone was rapidly taken up by the vagina. The hormone content of the tissue reached a peak 1 min. after application, and thereafter dropped rapidly to a level of 20–30% of the administered dose at 27 min., and more slowly to a level of 6% at 16 hr. The hormone content of the lumen decreased rapidly to near zero at the end of 27 min.
Simultaneous application of dimethylstilboestrol (DMS) had little effect on tissue levels at 1 min., but significantly reduced the fraction retained for longer periods. Progesterone was without effect.
It is suggested that, after its rapid passage into the vagina, a small proportion of the hormone is bound at the site of action, where it is retained for some hours. Any unbound hormone is lost to the general circulation within 30 min. The results are discussed in relation to the mode of action of oestrogens and anti-oestrogens.
