Abstract
Summary
The repeated systemic infusion of TRH (200 μg, twice daily) was effective in repeatedly elevating plasma T4 levels (20-40 min postinfusion) for the 3 experimental days. The post-TRH treatment (saline infusion) exhibited a depression of plasma thyroxine levels, possibly explained by previous high thyroxine levels exerting a sup-pressive effect on the hypothalamic-pitui-tary-thyroid axis. A depression of plasma glucocorticoid levels was shown within 1 hr in both experiments after TRH administration. The results indicate that TRH administration (systemic) is effective in temporarily elevating thyroxine levels and simultaneously lowering plasma glucocorticoids in cattle.
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