Abstract
Inhibin activity and concentrations of sex steroid hormones were determined in normal follicular fluid and ovarian cystic fluid of individual dairy cows. Inhibin activity was measured using the primary monolayer culture system of rat anterior pituitary cells and expressed as potencies relative to the working standard solution of our laboratory by the parallel line assay. A pooled bovine folli-cular fluid after removal of steroids by charcoal treatment (working standard) was divided into small aliquots and kept frozen until use. One unit was defined as the potency of FSH-inhibiting activity of 1 ml working solution. Estradiol-17β (E2), progesterone (P) and testosterone (T) were measured by radioimmunoassay. The results were given in Table 1.
1) Inhibin activity in almost all the luteal cysts and cystic corpora lutea was below the sensi-tivity of the assay and the concentration of E2 was low, whereas huge amounts of P were found. Histological examinations of the luteal cyst showed no granulosa cell around the wall of antrum and extensive formation of fibroid tissue with the luteinized theca interna.
2) Inhibin activity was still noted in the follicular fluid of a silent heat cow with low concen-trations of E2 and T, suggesting that granulosa cells may wane the activity of estrogen secretion earlier than that of inhibin secretion.
3) Follicular cysts can be divided into three groups. One is the cystic follicle with hyper-func-tion of granulosa cells. Second is the follicles with rather degenerating granulosa cells with higher amounts of P. Third is the one with little endocrine function.
The presence of inhibin activity in some of the cystic follicles may be responsible for the low levels of FSH in the plasma of cows with follicular cysts.
