Effect of Altered Thyroid Status Induced by Thyroid Hormones, Goitrogens and Diet on Intestinal Electrogenic Valine Transfer

The kinetics of the electrogenic transfer of valine across rat jejunum was studied in vitro with an electrical technique. The operational kinetic parameters of ‘apparent Km’ and the p. d. max (maximum transfer potential difference generated) were calculated and used to characterize the effects of diet and thyroid status on the electrogenic valine transfer mechanism. Hypothyroidism induced by 6-propyl-2-thiouracil (PTU), potassium thiocyanate, surgery or diet significantly increased the p. d. max but not the ‘apparent Km’. Triiodothyronine (T3) treatment reduced the elevated p. d. max in both the PTU-treated and thyroidectomized rats but thyroxine (T4) was ineffective in the PTU group. The p. d. max and ‘apparent Km’ in euthyroid rats were decreased by T3 and T4 but were unaltered by a 3-day fast. Fasting hypothyroid rats, however, did prevent the enhancement of p. d. max observed in hypothyroidism. Significant differences were observed in the p. d. max, the percentage 131I protein bound in the serum and percentage 131I uptake by the thyroid in rats fed notionally similar diets manufactured by two different suppliers but no differences were observed in total body O2 uptake. The results obtained on giving supplemental iodine indicated that one of the diets altered thyroid function which significantly affected electrogenic valine transfer but not total body oxygen uptake. Thus electrogenic valine transfer is a more sensitive index of change in thyroid status than its conventional measure by total body oxygen uptake.