Abstract

Serum levels of thyrotrophin (TSH), prolactin (PRL), free thyroxine (FT4) and free triiodothyronine (FT3) were determined before and after physical exercise in 21 normal male subjects. The subjects were divided into 3 groups as follows: group I - light exercise (exercise on the Mijnhardt bicycle ergometer at 100 Watts for 15 min); group II - moderate exercise (a 5 km marathon); group III - heavy exercise (a 10 km marathon). In group I, TSH level rose from 1.96 +/- 42 micro-u/ml to 2.52 +/- 0.30 micro-u/ml, and PRL levels rose from 11.0 +/- 2.0 ng/ml to 19.0 +/- 5.2 ng/ml. In group II, TSH rose from 2.11 +/- 0.51 micro-u/ml to 2.62 +/- 0.56 micro-u/ml, and PRL rose from 11.2 +/- 1.6 ng/ml to 24.0 +/- 5.2 ng/ml. In group III, TSH rose from 2.01 +/- 0.41 micro-u/ml to 2.36 +/- 0.45 micro-u/ml, and PRL rose from 12.1 +/- 2.0 ng/ml to 47.7 +/- 9.3 ng/ml. The serum levels of FT4 showed different results among the three groups: Group I showed an increased response from 1.60 +/- 0.12 ng/dl to 1.72 +/- 0.12 ng/dl; group II showed no significant difference; and group III demonstrated a diminished response from 1.61 +/- 0.14 ng/dl to 1.45 +/- 0.16 ng/dl. FT3 levels increased in group I from 4.50 +/- 0.16 ng/dl to 4.77 +/- 0.22 ng/dl, but no statistically significant change was observed in groups II and III. The present investigation demonstrates that physical exercise leads to increased TSH and PRL, whereas short-term continued light exercise results in rises in FT3 and FT4 levels, but long-term continued heavy exercise results in the damping of FT4 levels. TBG levels did not change during the experiment. The results indicate that the change in the TSH level is not regulated by the feedback mechanism of the hypothalamo-pituitary-thyroid axis alone but that a more complex, but as yet unidentified, mechanism is involved. Verf.-Referat