Characteristics of oestrogen-induced refractoriness in ovine cervical secretion.

Ovariectomized ewes treated with oestradiol benzoate (OB) had a reduced cervical mucus response to subsequent treatment with OB. This refractory effect was observed 48 h after a single dose of OB, but could be postponed until 72 h by a second dose of OB at 24 h. This postponement did not occur in animals which were recovering from previously induced refractoriness. Less mucus was recovered from refractory ewes, and it had an increased proportion of dry matter and normal Spinnbarkeit. Pretreatment of ewes with 10 mg progesterone for 10 days decreased the proportion of dry matter and increased the Spinnbarkeit of mucus collected after stimulation with OB. This change was different from that produced by increasing the dose of OB. Progesterone given to ewes after 10 days treatment with OB had a detectable effect on cervical mucus, but it did not specifically decrease refractoriness. The cervix provides a convenient site for studying oestrogen-induced refractoriness in the ewe, without possible confusion by an effects of progesterone.