[DEPENDENCE OF FUNCTIONAL PARAMETERS OF RAT SKELETAL MUSCLE CONTRACTION FROM LEVEL CIRCULATING TRIIODOTHYRONINE].

Abstract

In experiments on white rats with different thyroid status (thyroidectomy, euthyroidism, hyper- and a thyrotoxicosis) in conditions in situ the relationship between the severity of functional parameters of the tibialis anterior muscle and individual level of circulating free triiodothyronine was learnt. The latent period of muscle contraction, the average and maximum speed of its contraction were determined. A comparative quantitative analysis of the values of indicators of the contractile function of the tibialis anterior muscle in euthyroid and thyroidectomy rats allowed to evaluate the «thyroid contribution) of free triiodothyronine in the functional state of the native skeletal muscle, which formed to 15% for the latency reduction period, 12 % for the average speed of contractile act and 8% for of the maximum speed of muscle contraction. It is shown that in rats if the control group at the beginning of the scale of triiodothyronine concentration (2.2-4.9 pmol/L) hormone activity is expressed weakly, and in the range of 5.2-7.6 pmol/L is greatly increased (up to 11 times). It was established that the positive effect of triiodothyronine is preserved far beyond of the physiological norm of hormone concentration. It is allowed to speak about the existence of an extended corridor of hormone activity. On the base of the analysis of the degree of severity of the physiological parameters of the muscle contraction curve from circulating level of triiodothyronine in rats with different thyroid status (0.1-45 pmol/L) constructed of functional activity of free triiodothyronine. This curve consists of 7 different zones which are located in different sectors of the scale of concentration.