Hyperresponse to Thyrotropin-Releasing Hormone Accompanying Small Decreases in Serum Thyroid Hormone Concentrations

Abstract

A B S T R A C

Effect of amiodarone on serum triiodothyronine, reverse triiodothyronine, thyroxin, and thyrotropin. A drug influencing peripheral metabolism of thyroid hormones.

“…As in earlier experiments with iodine treatment, there was a transient rise in serum TSH, and the response of TSH to TRH was increased when compared to a control period (21). Nevertheless, there was one difference between these experiments and the present study: the response of T3 in the TRH test was previously observed to be inhibited by iodine treatment, while in the present study serum T3 increased nearly twice as much as in the control TRH test, excluding any important blocking effect of this drug on thyroid hormone secretion.…”

Augmentation of thyrotropin responses to thyrotropin-releasing hormone following inorganic iodide.

“…Similar results were obtained from experiments in which normal volunteers were given 50mg or 250mg of inorganic iodide daily for 13 days (Saberi and Utiger, 1975 T3 levels were observed after iodide administration in the earlier studies (Vagenakis et al, 1974;Saberi and Utiger, 1975). Saberi and Utiger (1975) observed a significant decrease in basal serum T4 and T3 concentrations on several days during iodide treatment only when the results were analyzed by the paired t test, using the mean of the 5 pretreatment days as control.…”

“…It has been demonstrated by Vagenakis and coworkers (Vagenakis et al, 1974) that small decreases in serum thyroid hormone concentrations in response to treatment with 190mg of inorganic iodide daily for 10 days, were associated with slight increases in basal serum thyrotropin (TSH) concentrations and pronounced increases in the TSH response to thyrotropin-releasing hormone (TRH). Similar results were obtained from experiments in which normal volunteers were given 50mg or 250mg of inorganic iodide daily for 13 days (Saberi and Utiger, 1975 T3 levels were observed after iodide administration in the earlier studies (Vagenakis et al, 1974;Saberi and Utiger, 1975).…”

Comparison between the thyrotropin response to thyrotropin-releasing hormone in summer and that in winter in normal subjects.

“…December 1978 an increase of serum T3 concentration but not T4 (Snyder and Utiger, 1973;Rabello et al, 1974), it would be possible that the elevation of T3 in winter might be produced by the minor and gradual increase in serum TSH which was unassessable by the present radioimmunoassay method. It has been shown that only minimum changes in serum thyroid hormone concentration, still within the normal range, sensitively affect the TSH response to TRH (Synder and Utiger, 1972;Vagenakis et al, 1974). Hefco et al, in their studies on the effect of acute exposure of rats to cold, suggested that in vivo pituitary responsiveness to TRH was determined by the serum thyroid hormone concentration rather than the pituitary TSH content (Hefco et al, 1975).…”