EFFECT OF THYROIDECTOMY AND LOW ENVIRONMENTAL TEMPERATURE (4.4° C) UPON PLASMA AND PITUITARY THYROTROPHIN IN THE RAT

Abstract

The content of thyrotrophin (TSH) in rat plasma and hypophyses was determined by means of the haemagglutination inhibition reaction. Mature female rats maintained at 26 [degree] C had a plasma TSH level of 0.94 mU/ml and a mean pituitary TSH level of 68.26 mU/mg. After 10 days of thyroidectomy the plasma TSH increased to 2.15 mU/ml, and to 2.81 mU/ml after 20 days. The TSH/mg of the pituitary glands was reduced to 40.4 mU after 10 days and to 35.0 mU after 20 days. After 25 days of thyroidectomy, L-Thyroxine (L-T4) at level of 2.5 [mu]g/100 g body weight was injected for 1, 3 and 5 days. The plasma TSH level was reduced to 1.59, to 1.48 and 1.06 mU/ml, respectively. The pituitary TSH/mg was 37.5, 38.6 and 77.9 mU, respectively. When rats held at 26[degree]C were exposed to a temperature at 4.4[degree] C for 10 and 20 days, the plasma TSH increased to 2.15 and 2.69 mU/ml, respectively. The pituitary TSH increased to 108.04 and to 240.9 mU/mg, respectively. The combined effect of thyroidectomy and 4.4 [degree]C for 10 and 20 days, caused the plasma TSH to increase to 4.37 mU/ml after 10 days then decline to 2.4 mU/ml after 20 days. The pituitary TSH declined to 43.79 and 37.58 mU/mg, respectively. When thyroidectomized rats held at 4.4[degree] C for 20 days were returned to 26[degree] C for 4 days, the plasma level declined to 1.44 mU/ml and the pituitary remained low, 34.90 mU/mg.