Dimeric inhibin concentrations in mares with granulosa-theca cell tumors

Objective-To determine whether concentrations of dimeric inhibin (alpha bet a(A)) are greater in plasma and tumor fluid from mares with granulosa-theca cell tumors (GTCT), compared with concentrations in plasma and equine foll icular fluid (eFF) from control mares. Animals-6 mares with GTCT and 12 clinically normal mares. Procedure-The alpha beta(A) immunoradiometric assay used 2 antibodies, one against each subunit of inhibin (alpha and beta(A) subunits). Tumor tissue, tumor fluid, and a single blood sample were collected at the time of surgi cal removal of the GTCT. A single blood sample was collected from 7 control mares during various stages of the estrous cycle. Five other control mares were ovariectomized when their ovaries contained growing follicles of 25 t o 35 mm in diameter. A blood sample and eFF from the largest follicle were collected at the time of ovariectomy. Results-Mares with GTCT had significantly greater plasma concentrations of alpha beta(A) (mean +/- SEM, 0.86 +/- 0.53 ng of recombinant human-alpha be ta(A)/ml), compared with control mares (0.14 +/- 0.02 ng/ml). Concentration s of alpha beta(A) in tumor fluid and eFF were similar. Concentrations of a lpha beta(A) were significantly lower after ovariectomy. Conclusions and Clinical Relevance-Dimeric inhibin concentration was higher in plasma from mares with GTCT than in plasma from control mares. Increase d granulosa cell mass and loss of mechanisms regulating alpha beta(A) relea se in mares with GTCT likely accounted for the increase in plasma concentra tions. Measurement of alpha beta(A) concentrations may be useful for identi fying mares with GTCT.