2000 Volume 11 Issue 2 Pages 35-43
To clarify the endocrinological characteristics of mares with granulosa-theca cell tumor (GTCT), 2 mares with GTCT and a long estrous period were investigated. Before removal of the GTCT in both cases, the concentrations of testosterone, immunoreactive (ir-) inhibin and follicle stimulating hormone (FSH) in the peripheral blood were higher than those of normal mares at the follicular phase, whereas the plasma concentrations of progesterone were constantly low. In Case 1 mare, the plasma concentrations of testosterone, ir-inhibin and follicle stimulating hormone (FSH) changed to significantly high levels. In Case 2 mare, plasma concentrations of all hormones except for progesterone changed to significantly high levels. After surgical removal of the GTCT, the circulating concentration of ir-inhibin decreased rapidly to the basal level. The ir-inhibin levels in GTCT tumor fluid were similar to the follicular fluid in healthy follicles 3.5-5.0 cm in diameter. Concentrations of estradiol in the GTCT tumor fluid were low, but testosterone levels were higher than those in healthy follicles 3.5-5.0 cm in diameter. These results suggest that high levels of circulating inhibin in addition to high levels of testosterone and low levels of progesterone may be used as a clinical sign in the diagnosis of GTCT in mares.
