COMPARATIVE ACTIVITIES OF A NUMBER OF OESTROGENS WHEN ADMINISTERED INTRAVENOUSLY AND INTRAMUSCULARLY IN THE SHEEP

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Abstract
The activities of six oestrogenic substances were compared when given as a single injection, intravenously (i/v) or intramuscularly (i/m), to spayed progesterone-primed ewes. The following values for the ED50 for oestrous behaviour, with associated 95% fiducial limits, were obtained Oestradiol-17[beta] (i/v) 16[long dash] 25[long dash] 39; (i/m) 3[long dash] 7[long dash] 16 Oestradiol benzoate (i/v) 30[long dash] 45[long dash] 69; (i/m) 5[long dash] 11[long dash] 23 Oestrone (i/v) 48[long dash] 96[long dash]194; (i/m) No data Diethylstilboestrol (i/v) 6[long dash] 10[long dash] 18; (i/m) 6[long dash] 10[long dash] 18 Hexoestrol (i/v) 46[long dash] 103[long dash]234; (i/m) 46[long dash]103[long dash] 234 Methylethylstilboestrol (i/v) CO[long dash]; (i/m) 130[long dash]279[long dash] 600 They fell into three groups, with the following i/v : i/m ratios: natural oestrogens; oestradiol-17[beta], oestradiol benzoate, 4:1: synthetic oestrogens; diethylstilboestrol and hexoestrol, 1 : 1: pro-oestrogen; methylethylstilboestrol, : 1. True oestrogens are presumed to accumulate in the reacting tissues with variable efficiencies. Pro-oestrogens, given i/v, are probably ineffective because they are not converted to oestrogens in a manner or at a rate suitable for such accumulation.