Dimeric inhibin concentrations in mares with granulosa-theca cell tumors

Abstract

Abstract Objective To determine whether concentrations of dimeric inhibin (αβA) are greater in plasma and tumor fluid from mares with granulosa-theca cell tumors (GTCT), compared with concentrations in plasma and equine follicular fluid (eFF) from control mares. Animals 6 mares with GTCT and 12 clinically normal mares. Procedure The αβA immunoradiometric assay used 2 antibodies, one against each subunit of inhibin (α and βA subunits). Tumor tissue, tumor fluid, and a single blood sample were collected at the time of surgical 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 to 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 αβA (mean ± SEM, 0.86 ± 0.53 ng of recombinant human-αβA/ml), compared with control mares (0.14 ± 0.02 ng/ml). Concentrations of αβA in tumor fluid and eFF were similar. Concentrations of αβA 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. Increased granulosa cell mass and loss of mechanisms regulating αβA release in mares with GTCT likely accounted for the increase in plasma concentrations. Measurement of αβA concentrations may be useful for identifying mares with GTCT. (Am J Vet Res 1999;60:1407–1410)