THE INTERACTION OF OESTROGEN AND PROGESTERONE ON THE VAGINAL CYCLE OF THE EWE

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Abstract
SUMMARY: The vaginal smear pattern of the intact ewe experiencing normal oestrous cycles was compared with that of the spayed untreated ewe, and with the spayed ewe injected with a physiological dose-level of oestradiol benzoate (ODB) administered either alone or alternating with progesterone (Prog.) injected in a time-dose relationship closely approximating that of the intact animal. Normal vaginal cornification appeared to be a result of oestrogen stimulation. The normal manifestation of leucocytic invasion and changes in the viscosity of mucus appeared to be dependent on an interaction between oestrogen and progesterone. Some vaginal cornification was apparent on the day of oestrus, or 48 hr after the injection of ODB, but maximum cornification occurred 2 days later. For a maximum response, as measured by the number of ewes which yielded one or more cornified smears, it was necessary to take smears daily for 4 days commencing on the day of oestrus. By relating the smear pattern of the ODB-injected spayed ewe to that of the normal intact ewe a standard method of appraisal of vaginal smears has been evolved. This is considered suitable for quantitative assay work. A positive vaginal smear is one which is virtually free of leucocytes but contains appreciable numbers of cornified cells either alone or in association with squamous and/or nucleated epithelial cells. The various types of typical cornified smears are illustrated.