[The effect of C-ring transformed estrogens on the reproductive system]

Comparative study of the effect of two groups of C-ring transformed oestrogens on the reproductive system was conducted in experiments on female rats. 11-Nitrate-9 alpha, 11 beta-dioxyethynylestadiols (I-IV), 11-nitrate-9 alpha-oxyesterons (V-VII), and 11 formiate-11 beta-oxyethynylstadiol (VIII) were given per os to the rats. As compared to ethynylestradiol (EE), compounds I-IV demonstrated 4-10 times higher oestrogenic activity and 11-23 times higher contraceptive activity. 11-Nitrate (V-VII) proved to be less active oestrogens (77-91% of EE activity) but its contraceptive effect was equal to or exceeded that of EE. The oestrogenic activity of 11-formiate (VIII) was three times higher than that of EE, but its contraceptive effect was only 50% of the effect of EE. The higher contraceptive effect of compounds I-IV in comparison to their oestrogenic activity allows these oestrogens to be considered perspective substituents of EE among the oral contraceptives. In oral administration of compound I alone or compounds I and IV together with gestagen acetomepregenol (AMP), inhibition of luteinizing hormone release was stronger and more prolonged than in administration of EE alone or in combination with AMP. This effect may be considered to be one of the possible mechanisms of the activity of 11-nitrate oestrogens.