Inhibin concentrations in mares with granulosa cell tumors

M. T. Bailey, M. H.T. Troedsson, J. E. Wheaton

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61 Scopus citations

Abstract

The hormone-producing equine granulosa cell tumor (GCT) may secrete high levels of inhibin. Measurement of inhibin concentrations may be useful in the diagnosis and conformation of mares with GCT. Inhibin may be measured using RIA, which recognizes dimeric αβA-inhibin as well as the monomeric (free) inhibin α-subunit, or using a two-site immunoradiometric assay (IRMA) specific for αβA-inhibin. The objective of this study was to examine concurrent relationships among α-inhibin (as measured using RIA), αβA-inhibin (as measured using IRMA), and other hormones (testosterone, estradiol, LH, FSH) in mares with GCT. Hormone concentrations were measured in single serum or plasma samples obtained from 22 mares with GCT and from 31 normal cycling mares. One GCT mare had blood samples collected at 12-h intervals for 21 days, and at 15-min intervals for two 6-h periods during that time. Results showed that in GCT mares α-inhibin was increased to a greater extent, was more uniformly elevated, and had a less variable secretory pattern than did αβA-inhibin. Concentrations of α-inhibin and tumor mass were positively correlated (P < 0.01). Concentrations of LH were higher (P < 0.02) in GCT mares than control mares and were positively associated with testosterone concentrations (P = 0.05). Concentrations of FSH tended to be lower in GCT than control mares and were inversely related with αβA-inhibin in GCT mares. Testosterone and estradiol concentrations were variable. It was concluded that immunoreactive <-inhibin reflected detection of both αβA-inhibin and free α-subunit. Free α-subunit was evidently secreted at a relatively steady rate dependent upon mass of the GCT, whereas secretion of αβA-inhibin was more responsive to FSH regulation. Determination of α-inhibin using RIA appeared to be a more reliable indicator of the presence of a GCT than specific measurement of αβA-inhibin using IRMA.

Original languageEnglish
Pages (from-to)1885-1895
Number of pages11
JournalTheriogenology
Volume57
Issue number7
DOIs
StatePublished - 2002

Bibliographical note

Funding Information:
We thank the National Hormone and Pituitary Program, the National Institute of Diabetes and Digestive and Kidney Diseases and Dr. A. F. Parlow for purified hormones and antisera. Appreciation is expressed to Drs. T. O’Brien, C. O’Dell and C. Carlson for histological consultation; and to J. Bultman, C. Bailey, M. Ababneh, S. Madill and N. Vetscher for technical assistance and veterinary care. The study was supported by the Minnesota Equine Research Center and the Minnesota Agricultural Experiment Station and published as paper no. 011167501 of the scientific journal series on research conducted under Project 16-75.

Keywords

  • Granulosa cell tumor
  • Hormones
  • Inhibin
  • Mares

ASJC Scopus subject areas

  • Small Animals
  • Food Animals
  • Animal Science and Zoology
  • Equine

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