Taurine transport rates between plasma and tissues in adult and 7-day-old mice

Transport rates for taurine from plasma to liver, kidney, heart, spleen and femoral muscle were evaluated in adult and 7-day-old mice in vivo. The mice were injected with [35S]taurine and the specific radioactivity of taurine was determined in the above tissues at varying intervals from 10 min up to 48 hr after the injection. A multicompartment model was fitted to the data and the transport rates with their confidence limits were estimated using a digital computer. The tissue-plasma exchange rate was generally faster in adult mice than in 7-day-old mice. The transport rates between the plasma and the brain or muscle were low, while taurine penetrated into the liver and kidneys very rapidly. There was no distinct correlation between the calculated transport rates and the tissue taurine concentrations. The metabolic breakdown of taurine in the tissues was slow, since only negligible amounts of radioactivity were recovered in the metabolites of taurine, isethionic acid and inorganic sulphate. It seems unlikely that either the magnitudes of the transport rates between the plasma and the tissues or taurine breakdown rates in situ act as the primary factor determining the taurine levels in tissues.