Equine thyroid function assessment with the thyrotropin-releasing hormone response test

Abstract
SUMMARY: The effect of thyrotropin-releasing hormone (trh) on equine thyroid function was determined by quantifying serum thyroxine (T4) and 3,5,3′-triiodothyronine (T3) before and after trh administration. Thyrotropin-releasing hormone was administered iv to adult horses (n = 5) and ponies (n = 6) at a dose of 1 mg or 0.5 mg, respectively. Serum T4 and T3 concentrations were determined before and 0.25, 0.5, 1, 2, 4, 6, 8, 12, and 24 hours after trh administration. Serum T4 increased from a basal concentration of 24.4 ± 8.7 ng/ml (mean ± sd) to a maximum value of 48.2 ± 10.2 by 4 hours after trh administration. Serum T3 increased from a basal concentration of 0.44 ± 0.18 ng/ml to a maximum value of 1.31 ± 0.37 ng/ml by 2 hours after trh administration. Seemingly, trh increases serum concentrations of T4 and T3 and may be useful as a test of equine hypophysis-thyroid function.

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