RELATION OF TSH CONCENTRATION IN BLOOD TO THE RADIOACTIVE RUBIDIUM 86Rb UPTAKE IN THE THYROID GLAND OF RATS: EVIDENCE OF TSH REGULATORY EFFECT ON THYROID GLAND BLOOD FLOW

Abstract

ABSTRACT To study the relations between thyroid gland blood flow and the concentration of thyroid-stimulating hormone (TSH) in rats, a graded concentration of endogenous TSH was induced: for a period of 10 days, methylthiouracil was added to the food (Alkiron, Spofa, 0.2%) and in addition, in the respective groups, dried thyroid gland preparation (Thyreoidin, Spofa) in concentrations of 0.01, 0.02, 0.03, 0.04 and 0.05%. The concentration of TSH was estimated by means of the McKenzie bioassay (results are given in the percentile response index). In addition, the relative weight of the thyroid gland (in mg per 100 g of body weight) was followed and the tissue uptake of radioactive rubidium 86Rb (in % of dose per 1 g of tissue) was recorded as an indicator of changes in the thyroid gland blood flow. The experiment was repeated 3 times in exactly the same way. The course of the changes in groups fed dried thyroid from 0.01 up to 0.05 % was evaluated by means of a regression analysis. Regression lines for the same index (i. e. concentration of TSH, relative weight of the thyroid gland and uptake of 86Rb) in each particular experiment were parallel, i. e. the course of the changes for all 3 repeated experiments was identical. Regression coefficients for all the 3 indices were significantly different from zero. The values for all 3 indices then showed a statistically significant decrease concomitantly with the rising concentration of dried thyroid gland in the food, the course of the changes being very similar. Changes in the uptake of 86Rb in the thyroid gland that are in agreement with changes in the concentration of endogenous TSH are considered as further evidence of a TSH regulatory effect on the thyroid gland blood flow.