Thyroid hormone status influences the Zn²⁺ and metallothionein levels in intestine, liver, and kidney. To evaluate the impact of thyroid hormones on Zn²⁺ metabolism, Zn²⁺ uptake studies were carried out in intestinal and renal brush-border membrane vesicles (BBMV). Steady-state Zn²⁺ transport in intestinal and renal cortical BBMV was increased in hyperthyroid (Hyper-T) rats and decreased in the hypothyroid (Hypo-T) rats relative to euthyroid (Eu-T) rats. In both the intestinal and renal BBMV, Hyper-T rats showed a significant increase in maximal velocity compared with Eu-T and Hypo-T rats. Apparent Michaelis constant was unaltered in intestinal and renal BBMV prepared from the three groups. Fluorescence anisotropy of diphenyl hexatriene was decreased significantly in intestinal and renal brush-border membrane (BBM) isolated from Hyper-T rats compared with Hypo-T and Eu-T rats. A significant reduction in the microviscosity and transition temperature for Zn²⁺ uptake in intestinal and renal BBM from Hyper-T rats is in accordance with the increased fluidity of these BBMs. These findings suggest that the increased rate of Zn²⁺ transport in response to thyroid hormone status could be associated with either an increase in the number of Zn²⁺ transporters or an increase in the active transporters due to alteration in the membrane fluidity. Thus the thyroid hormone-mediated change in membrane fluidity might play an important role in modulating Zn²⁺ transport activity of intestinal and renal BBM.

zinc metabolism; fluorescence polarization studies; metallothionein; Arrhenius plot