Reduced cervical mucus bioassay response to oestrogen by the ovariectomized ewe after oestrogen treatment during progesterone priming

Abstract

Ovariectomized ewes were treated with progesterone and oestrogen during a priming period, after which the mucus response of the cervix to trigger doses of 0, 5, 10 or 20 µg of diethylstilboestrol (DES) was determined. The ability of the cervix to respond to DES was diminished if the ewes had previously been given either 15 or 30 µg DES for 9 days during priming with 10 mg of progesterone daily, or if the ewes had been previously treated with 10 µg DES for 12 or 24 days during progesterone priming. Furthermore, the temporal pattern of cervical mucus response to oestrogenic pasture was altered when ewes were primed with progesterone while grazing that pasture. These phenomena made it impossible to measure accurately the oestrogenicity of a pasture when ewes were primed with progesterone for 10 days while on that pasture.

Failure to respond to the DES trigger doses was not due to the production and exhaustion of cervical mucus hring priming. There appeared to be two alternative responses by the ewe's cervix to oestrogen, one productive of cervical mucus and the other resulting in a refractory state.