Effect of TRH, and Short‐term Exposure to Experimental Stress or Cold on the Serum Immunoassayable TSH Concentration in the Rat

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Abstract
The influence of TRH, transfer and sampling stress and cold on the blood TSH level was studied in female rats using a specific radioimmunoassay for rat TSH. The maximum response to TRH increased with the dose of TRH and occurred at 5 min with 10 and 50 ng. With a TRH dose of 250 ng the niaxirnum response occurred at 10 min. Transfer stress caused a significant rise in serum TSH level at 5 min. After this, the serum TSH level gradually decreased and the decrease at 30 min was significant compared with 5 min value. Sampling stress caused a slight increase in the serum TSH level at 5 min, and at 30 and 60 min the serum TSH level was significantly lower than ir. controls. The maximum effect of cold on the blocd TSH level was seen in animals kept for 30 min at 5° C. These studies clearly demonstrate the effect of TRH on the serum TSH level in rats. The activation of the secretion of TSH in the cold is physiologically relevant, and the inhibition of TSH secretion in response to stress refutes the hypothesis that stressful stimuli activate the thyroid gland.