ORAL TRIIODOTHYRONINE ADMINISTRATION LOWERS PLASMA FIBRONECTIN LEVELS IN HUMANS

Both serum triiodothyronine (T3) and plasma fibronectin values declined with fasting and increased with treatment of diabetic ketoacidosis in parallel manner. To evaluate the mechanism responsible for these changes, the effects of both oral T3 administration and fasting were examined in 6 healty, adult subjects. Initial plasma fibronectin values were normal in both groups. Despite a substantial rise in serum T3 values with oral T3 administration, plasma fibronectin fell in group 1 subjects. Fasting caused a significant decline in serum T3 levels, but only a small further decline of plasma fibronectin concentrations. Serum T3 levels rose after 1 wk of refeeding, whereas plasma fibronectin levels in group 1 did not return toward normal. Plasma fibronectin values did not change in group 2 subjects with oral T3, fasting, or refeeding. There is not simple cause-and-effect relationship between previously observed changes in plasma fibronectin and serum T3 concentrations. High doses of oral T3 will lower plasma fibronectin levels in subjects with initially normal plasma fibronectin values and a normal caloric intake.