Abstract

SUMMARY A flock of 135 ovariectomized ewes was used in five tests designed to investigate the ability of three 9α-halogenated steroids to condition the spayed ewe to exhibit oestrus after a single injection of oestradiol benzoate (ODB). The experimental steroids (9α-fluoro-11β-hydroxypregn-4-ene-3,20-dione, 9α-chloro-11β-hydroxypregn-4-ene-3,20-dione and 9α-bromo-11β-hydroxypregn-4-ene-3,20 dione) were tested against a progestagen of known characteristics (17α-acetoxy-9α-fluoro-11β-hydroxypregn-4-ene-3,20-dione = SC-9880, G. D. Searle) and against each other. The steroids were injected intramuscularly, daily for 12 days and ODB was given at one of three doses as a single intramuscular injection 48 or 96 hr. after the final steroid injection. The effects of the three experimental steroids, as indicated by the oestrous responses to ODB, differed little from that of SC-9880, thus proving them to be highly potent progestagens; 0·4 mg./day appeared to be about the minimum daily effective dose of all three experimental steroids indicating a potency about 15–20 times that of progesterone.

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