Absorption, distribution and elimination of creatinine and urea in hyperthyroid mice.

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Abstract
The absorption, distribution and elimination of creatinine and urea, which pass through the water-filled pores of biological membranes easily, were investigated in hyperthyroid mice to clarify the effects of enhanced blood circulation rate on drug behavior in the body. The elimination rate constant in hyperthyroid mice was significantly and considerably larger than that in the control in both creatinine and urea (P < 0.01). This result might be based on the increased urinary excretion rate of these 2 chemicals in hyperthyroid mice. Autoradiographic study indicated that creatinine was distributed more homogeneously in hyperthyroid mice than the control at 30 s and 2 min following i.v. administration. It was probably caused by the enhanced membrane permeability to creatinine due to some physiological changes (e.g., blood flow rate and pressure) or to a change of membrane itself. The gastrointestinal absorption of these 2 chemicals were also evaluated by the expiratory excretion of 14CO2 following oral administration. Creatinine might be absorbed more slowly in hyperthyroid mice than in the control, and in the case of urea such a difference in absorption might not exist.