Effect of Hypothyroidism on Intestinal Zinc Absorption and Renal Zinc Disposal in Five-Sixths Nephrectomized Rats

抄録

Both hypothyroid (Hypo) and hypozincemia are commonly observed in patients and animals with chronic renal failure (CRF). In CRF whether the hypothyroid plays a role in the pathogenesis of hypozincemia is unclear. This study is designed to investigate the effects of hypothyroid on intestinal zinc absorption and urinary zinc excretion in 5/6 nephrectomized (Nx) rats, because plasma zinc balance is attained through a controlled rate of intestinal uptake as well as renal reabsorption. Intestinal zinc absorption was carried out in jejunum and ileum segments by an in vivo perfusion technique and the renal zinc disposal was evaluated by a conventional method using a standard formula to calculate the zinc tubular reabsorption and the excretion of urinary zinc in 5/6 Nx rats with hypothyroidism. The Hypo-NxT rats showed a significant decrease in the rate of intestinal zinc absorption and in the response of plasma zinc levels during intestinal zinc perfusion compared with Eu-NxT rats. They also had significantly lower levels of mucosal zinc and MT as well as lower content of liver zinc than Eu-NxT rats after intestinal zinc perfusion for 80 min. Hypo-NxT rats showed low plasma zinc levels, but had a similar output of pancreaticobiliary zinc and excretion of 24-h urine zinc compared with the Eu-NxT rats. When 2% alcohol intestinal perfusion was used to produce water diuresis, the Hypo-NxT rats presented a higher excretion of urinary zinc than the Eu-NxT rats did, especially during 2% alcohol intestinal zinc perfusion. In the Hypo-NxT rats, the lower plasma zinc levels may thus result from the hypothyroid because it reduces intestinal zinc absorption. Increasing the urine flow rate may aggravate the reduction of plasma zinc level in Hypo-NxT rats because of the increased excretion of urinary zinc.