THE TRH-TEST FOR THE DIAGNOSIS OF CANINE HYPOTHYROIDISM

The present paper describes a modified TRH stimulation test for the di agnosis of canine hypothyroidism. Thyroid function is difficult to ass ess with basal thyroid hormone levels, however bovine TSH is no longer available for stimulation tests, and there is considerable controvers y as to the validity acid practical aspects of a TRH test. Therefore w e studied in healthy animals the dose-response relationship and the ki netics of T4 release after TRH. We could show that the T4 maximum occu red 2-3 h after an optimal dose of 10 mu g TRH/kg intravenously. Using this method (blood samples at 0, 2, and 3h) we studied 65 dogs with c linical symptoms of hypothyroidism. We were able to define criteria to classify 66 % of the patients to be euthyroid, 23 % to be hypothyroid , and 11 % as ambigous. This diagnosis could be verified by the succes s of a levothyroxin substitution therapy: in 9 out of 10 dogs all clin ical signs of the disease were reversed after treatment. Sequential te sting with TSH and TRH of the thyroid function in another 9 patients r evealed good agreement of the two test procedures. From these data we conclude that the TRH stimulation test is both practicable and reliabl e in assessing thyroid function in the dog which will be particularly useful in view of the availability of canine TSH assays in the near fu ture.