THE ACTIVITY OF A NUMBER OF OESTROGENS AS TESTED IN THE SPAYED EWE

Abstract

SUMMARY Eight oestrogens were tested for potency in spayed ewes. A. The estimated m.e.d.'s (μg.) for (a) vaginal and (b) behavioural oestrus, with associated 95% fiducial limits were: (1) Natural oestrogens (free). β-Oestradiol: (a) 9·2-11·7-14·6, (b) 9·7-11·2-12·8; oestrone: (a) 39·5-54·1-74·0, (b) 71·1–81·7-93·7; oestriol: (a) 745-961-1241, (b) 877-985-1108. (2) Natural oestrogens (conjugated). Oestradiol benzoate: (a) 3·7-6·6-11·6, (b) 13·5-14·9-16·4; oestrone benzoate: (a) 17·0-33·3-65·3, (b) 90·0-100·3-111·9. (3) Synthetic oestrogens. Stilboestrol: (a) 3·6-8·2-18·6, (b) 23·2-27·5-32·7; hexoestrol: (a) 6·5-12·7-25·9, (b) 21·0-30·5-44·5; dienoestrol: (a) 22·4-40·1-68·8, (b) 80·4-95·3-112·7. B. Relative potencies on the basis of free oestrogen, and related to β-oestradiol = 100, were: (1) Vaginal oestrus: oestradiol benzoate 234, stilboestrol 143, β-oestradiol 100, hexoestrol 92, oestrone benzoate 47, dienoestrol 29, oestrone 22, oestriol 1. There was no clear pattern of seasonal change of ewe sensitivity as measured by vaginal changes. (2) Behavioural oestrus. (a) Uncorrected for seasonal variation in sensitivity of ewes: oestradiol benzoate 100, β-oestradiol 100, stilboestrol 41, hexoestrol 37, oestrone benzoate 15, oestrone 14, dienoestrol 12, oestriol 1. (b) Corrected for seasonal variation: oestradiol benzoate 128, β-oestradiol 100, stilboestrol 71, hexoestrol 66, dienoestrol 21, oestrone 17, oestrone benzoate 15, oestriol 1. Oestradiol and dienoestrol were more effective when the dose was given as three injections than when given as a single injection. Oestrone was less effective when given as a divided dose. Other oestrogens were unaffected by frequency of injection, but the slope of response to stilboestrol was increased by dividing the dose.