Possible Interaction: Thyroxine and Vitamin A

“In spite of the fact that elevated BMR increased the rate of depletion of the liver vitamin A in the rat, thyroxine so enhanced the storage of vitamin A from the diet that liver concentration rose above that of controls (Johnson and Baumann, '48).”

“Other evidence was presented supporting the hypothesis that thyroxin , or its physiologically active derivative, effects a change in vitamin A metabolism which results in a change in the type of chromophore on the visual protein.”

“However, retinol produced a decline in the concentration of thyroxine by 35% and 43% at 24 and 48 hr, respectively.”

“Following thyroidectomy, the total T4 levels were still decreased, suggesting that vitamin A produced its effects by increasing peripheral clearance of thyroxine.”

“In vitro, vitamin A enhanced T4 to T3 conversion in hepatic homogenates.”

“With vitamin A treatment, there was a marked increase in the percentage dialyzable T3 and T4 both in vivo and in vitro.”

“ Thyroxine treatment leads to a decrease in the level of vitamin A carrier proteins, retinol-binding protein and prealbumin-2 in plasma and liver.”

“The simultaneous administration of thyroxine decreased the accumulation of retinol and retinyl palmitate in liver tissue.”

“ Thyroxine increased both vitamin A storage and the fraction of the total vitamin A as retinol, this effect being dependent on dietary protein level.”

“ Thyroxine increased both vitamin A depletion from the liver and the percentage of vitamin A in the alcohol form, whereas thiouracil had the opposite effect.”