WATER AND ELECTROLYTE DISTRIBUTION IN RAT AND GUINEA-PIG THYROID GLANDS

Abstract

SUMMARY Procedures for the calculation of the volume of water and the Na+, K+ and Cl− concentrations in the three anatomical compartments of the thyroid (interstitium, follicular cells and lumen) are described. There was an excellent correlation between the volume of water of these three compartments calculated from the total water, [14C]inulin space and histometric measurements of the thyroid gland and the results obtained from 3H2O-uptake studies. Na+ and K+ concentrations in the luminal fluid of rat and guinea-pig thyroid glands were the same as those in the interstitial fluid which is an ultrafiltrate of plasma. Cl− concentration in the luminal fluid of thyroid gland was usually lower than that in the interstitial fluid. The concentration depends on the amount of colloid present in the follicular lumen. In the cellular fluid of the thyroid follicle, Na+ and Cl− concentrations were low and K+ concentration was high. The Cl− equilibrium potential between the interstitial and the cellular compartments, calculated from the corresponding Cl− concentrations by the Nernst equation, was the same as for previous values reported for the intracellular potentials determined by micro-electrode techniques in both rat and guinea-pig thyroid glands. In the rat thyroid, the calculated Cl− equilibrium potential between the interstitial and the luminal compartments was the same as the measured intra-luminal potential. However, in the guinea-pig thyroid the calculated Cl− equilibrium potential between the interstitial and the luminal fluids was considerably higher than the measured intra-luminal potential.