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

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.

Human thyroid blood flow response to endogenous, exogenous human, and bovine thyrotrophin measured by electromagnetic flowmetry

“…Close correlation has been shown between TBF and serum TSH concentra¬ tions in rats after 10 days' methimazole administra¬ tion (Kapitola et al 1974). In contrast, we found no correlation between TSH and TBF response.…”

“…Some investigators have shown a stimulatory effect of bovine TSH on TBF (Söderberg 1958;Solomon et al 1963;Clayton & Szego 1967;Varga et al 1971;Kapitola et al 1974), whereas others (Rosenberg et al 1965;Dumont 1971;Rocmans et al 1978) have observed no significant changes in TBF; decreased TBF values have also been re¬ ported (Goldsmith et al 1965;Ahn et al 1969). These studies used less appropriate techniques for blood flow measurement, however, as pointed out previously (Söderberg 1959).…”

Thyroid Steal Syndrome Secondary to Active Hyperthyroid State

“…After cessation of antithyroid medications, the patient was rendered euthyroid and the symptoms of TIA ceased [ 1 ]. In this case, it was theorized that the increased thyroid blood flow was stimulated by the high levels of TSH (>100 mIU/ml) [ 1 , 4 ]. The other three documented cases of TSS were all in patients who presented with recurrent TIAs and were found to have a voluminous thyroid goiter [ 2 , 3 ].…”

Thyroid Vascular Conductance: Differential Effects of Elevated Plasma Thyrotropin (TSH) Induced by Treatment with Thioamides or TSH-Releasing Hormone*

“…TSH-induced alterations in the metabolic activity and structure of the thyroid gland may be accompanied by alterations in thyroid blood flow (1,(3)(4)(5)(6)(7)(8)(9)(10)(11)(12). We reported recently (1) that the vascular C/mass (and blood flow) of the thyroid gland is decreased at very low plasma TSH levels and increased at very high plasma TSH levels, but is unchanged over a broad intermediate range of plasma TSH, encompassing normal.…”

“…Thyroid blood flow per mass of tissue is decreased 6 (1) or 30 (9) days after hypophysectomy, while replacement with bovine TSH can normalize thyroid blood flow (1). Chronic treatment with thioamides, which induce hypothyroidism and elevate endogenous plasma TSH levels, results in increased thyroid blood flow (1,(10)(11)(12). We reported recently (1) that thyroid vascular conductance (C) or blood flow per mass of gland is increased only at very high levels of plasma TSH.…”