Lynestrenol is a potent oral pregestagen. The oral activities in the Clauberg and Corner & Allen tests are of the same order as that of subcutaneously administered progesterone. No effect was found in the tests for deciduomagenic activity in the mouse and for the maintenance of pregnancy in the rat. Lynestrenol has a marked inhibitory action on ovulation in the rat. This effect can be enhanced by low doses of oestrogen, which themselves are inactive in this respect. The main cause of this effect seems to be an inhibition of the development of the follicles. Lynestrenol is a weak oestrogen with an activity of about 1–2% of that of ethinyloestradiol. Its effects on fertilized ova in the rat are in agreement with what could be expected from its oestrogenic activity. There is little or no effect on nidation. Lynestrenol is a weak androgen, the oral activity in the rat amounting to 1/3–1/4 of that of methyltestosterone. 5. Acute and chronic toxicity studies demonstrate the absence of any general toxicity.

In the search for a pregnancy maintaining steroid allylestrenol has been found orally active in the Clauberg assay, the mouse deciduoma test and in maintaining pregnancy in spayed rats. It has been shown to be practically devoid of androgenic, oestrogenic and gonad-and adrenal-inhibiting properties; no impairment of pregnancy and no influence on the external genitalia of foetuses were observed. Some antioestrogenic activity is present. In chronic toxicity studies in rats and dogs no signs of general toxicity were observed. Allylestrenol can thus be considered as a pure and complete oral gestagen.The preparation of a new series of steroids, the 17-alkylated 3-deoxo-19-nortestosterones (or estrenóles) was described last year (de Winter et al. 1959). The authors mentioned that these compounds have a marked progestational activity. In this paper various properties of the 17a-allyl compound will be described.CH,-CH = CHi allylestrenol 1. Allylestrenol is the generic name of 17u-allyl-17/:¿-hydroxy-estr-4-ene, the active principle of the preparation Gestanon (N. V. Organon, Oss, the Netherlands). 2. A preliminary communication was presented to the sixth symposium of the Deutsche Gesellschaft für Endokrinologie at Kiel, April 28-30, 1959.

Compared with the uteri of other species, the uteri of mice showed a rather high carbonic anhydrase activity, with values ranging from 25 to 110 enzyme units per gram of uterine tissue (E. U./g) under various experimental conditions. In dioestrus, prooestrus and metoestrus the carbonic anhydrase activity of the mouse uterus was almost the same (about 60 E. U./g); during oestrus it was significantly increased (98 E. U./g). Eight days after castration, uterine carbonic anhydrase activity was not significantly altered (47 E. U./g). Treatment of spayed mice with 0.25 mg progesterone (pregn-4-ene-3,20-dione) daily s. c. did not have any significant effect upon uterine carbonic anhydrase (49 E. U./g). Treatment with oestradiol monobenzoate (0.025 μg and 0.1 μg daily s. c. for 7 days) significantly increased the carbonic anhydrase activity (to 109 and 86 E. U./g, respectively). This effect of oestrogen was counteracted by simultaneous administration of progesterone. These results differ markedly from the results obtained in similar experiments with rats and rabbits. Deciduomatous uterine horns showed significantly less carbonic anhydrase activity (26 E. U./g) than the control horns without deciduoma (48 E. U./g).

To test the usefulness of a recently described bioassay of progestational activity (Madjerek, 1972), based on the production of traumatic decidual reaction in immature female rats, a series of agents, known to have some progestational effects in other tests, was investigated for their short-and long-lasting activities.Immature female rats of an inbred commercial Wistar strain were used. Daily administration of a substance was begun 1 day before uterine traumatization and continued once daily for 5 days. To test prolonged activity, the substance was given in one single injection 1 day before traumatization. On the 5th day after traumatization, the rats were killed and the uteri removed.The decidual reaction (DR) was scored macro-and microscopically according to an arbitrary scale (1-4) and expressed as the deciduoma index (DI), arrived at by dividing the sum of all individual values in one experimental group by the number of animals in that group. The DI values from 2 to 4 are taken as characteristic of marked progestational activity in this test.The substances tested and the results are summarized in Table 1. As reference standard, a daily subcutaneous dose of 0-25 mg progesterone regularly induced a distinct decidual reaction, while a single subcutaneous dose of 12-5 mg progesterone showed a marked prolonged activity and the lower dose levels (7-5 mg and less) were ineffective. Table 1. The activities of a series of progestational steroids in the production of traumatic decidual reaction (DR) in immature female rats Substance Progesterone 0-25 mg daily 1x12-5 mg 1 7-5 mg

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