Inhibin localization in equine granulosa-theca cell tumours and inhibin forms in tumour fluid

The aim of this study was to examine inhibin production in granulosa-theca cell tumours (GTCT). The experimental aims were: (i) to determine GTCT cell types that produce inhibin alpha- and betaA-subunits; (ii) to determine whether alpha- and betaA-subunit forms differ in GTCT fluid and normal equine follicular fluid (eFF); and (iii) to determine whether dimeric inhibin (alpha betaA) is present in GTCT plasma and tumour fluid. Plasma, tumour fluid and tumour tissue were collected from mares (n=6) with GTCT. Plasma and eFF were collected during the follicular phase from mares (n=4) undergoing normal cycles. Immunohistochemical examination of GTCT tumour sections showed strong inhibin alpha- and betaA-Subunit immunostaining in granulosa cells and polyhedral-shaped cells in the thecal-stromal layer. The presence of polyhedral-shaped cells was related to testosterone concentration in tumour fluid. Low molecular weight alpha-subunit forms were less abundant in tumour fluid than in eFF, whereas the amounts of betaA-subunit forms were similar in tumour fluid and eFF. Concentrations of betaA were increased in plasma from mares with GTCT and similar in tumour fluid and eFF. In summary, lower molecular weight alpha-subunit forms were less prominent in GTCT fluid than in eFF and concentrations of betaA were higher in GTCT plasma than in control plasma.