Abstract
To clarify the endocrinological characteristics of the mares with granulosa theca cell tumor (GTCT), peripheral plasma samples from the 6 mares affected with GTCT were collected before and after the surgical removal of the affected ovary. Concentrations of testosterone (T), follicle stimulating hormone (FSH), luteinizing hormone (LH), immunoreactive-inhibin (ir-INH), progesterone (P) and estradiol-17beta (E(2)) in the plasma samples were measured by radioimmunoassay. Before removal of GTCT in all cases, the concentrations of T were significantly higher than those of normal mares at the breeding and non-breeding seasons, whereas plasma concentrations of FSH, LH, ir-INH, P and E(2) were lower. After surgical removal of the affected ovary, the circulatory concentrations of T was declined, but the concentrations of other hormones were constantly low as compared with those of normal mares. The present study suggests that 1) the source of higher T may be due to the abnormal follicles in ovary of GTCT, 2) in the case of GTCT the elevated level of T is observed due to the lack of aromatase, and 3) the high level of T is a typical characteristics for GTCT in mares. It is also suggested 4) due to the elevated levels of T the concentrations of gonadotropins may be suppressed.