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

in Reproduction

Summary.

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-17β (i/v) 16 —, 25 — 39; (i/m) 3 — 7 — 16

Oestradiol benzoate (i/v) 30 — 45 — 69; (i/m) 5 — 11 — 23

Oestrone (i/v) 48 — 96 — 194; (i/m) No data

Diethylstilboestrol (i/v) 6 — 10 — 18; (i/m) 6 — 10 — 18

Hexoestrol (i/v) 46 — 103 — 234; (i/m) 46 — 103 — 234

Methylethylstilboestrol (i/v) ∞ — ; (i/m) 130 — 279 — 600

They fell into three groups, with the following i/v : i/m ratios: natural oestrogens; oestradiol- 17β, 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.

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