Pituitary-thyroid interrelationship in rats exposed to different environmental temperatures.
The present work intended to show interrelationships between triiodothyronine (T3), thyroxine (T4), thyroid stimulating hormone (TSH) and cyclic adenosine 3'5'-monophosphate (cyclic AMP) in both the pituitary and the thyroid. Experiments were carried out on animals exposed to 0 and 37 degrees C for 4 days and to 34 degrees C for 21 days. Control animals were maintained at 22 degrees C. T4 serum levels of 2.6, 4.0 1.1 and 0.42 mug/100 ml serum, and T3 levels of 95, 135, 65 and 36 ng/100 ml serum were recorded at 22, 0, 34 and 37 degrees C, respectively. The observed serum TSH levels were 265, 192, 237 and 182 mug/100 ml serum in rats exposed to 22, 0, 34 and 37 degrees C, respectively. Pituitary TSH content was similar at 22, 0 and 34 degrees C whereas the content in the 37 degrees C exposed rats was twice that of controls. Thyroid cyclic AMP levels were not significantly different among the various experimental groups. The content of cyclic AMP in the pituitary was higher at 34 degrees C by 125% and 37 degrees C by 240%, and lower at 0 degress C by 56% with regard to the control. These results suggest that the 0 and 34 degrees C exposed rats reach a new steady state in the control of thyroid hormones secretion rate. However, at 37 degrees C, the TSH-Thyroxine interrelationships seem to break down.
D000818:Animals; D000242:Cyclic AMP / Q000097:blood / Q000378:metabolism*; D004781:Environmental Exposure; D008297:Male; D010902:Pituitary Gland / Q000378:metabolism / Q000502:physiology*; D051381:Rats; D012636:Secretory Rate; D013696:Temperature; D013961:Thyroid Gland / Q000378:metabolism / Q000502:physiology*; D013972:Thyrotropin / Q000097:blood / Q000378:metabolism*; D013974:Thyroxine / Q000097:blood / Q000378:metabolism*
D013972:Thyrotropin; D000242:Cyclic AMP; D013974:Thyroxine