Guanidinoethane sulfonate and the disposition of dietary taurine in the rat.

Guanidinoethane sulfonate, a transport antagonist of taurine in brain synaptosomes and isolated perfused hearts, causes profound and rapid depletion of tissue taurine levels when given to rats as a 1% solution. In tissues outside of the central nervous system, guanidinoethane sulfonate on average decreased by half the absolute amount of taurine obtained from the diet. However, the percent of taurine derived from the diet increased from an average of 36% to an average of 58%. In the brain, guanidinoethane sulfonate had little effect on the absolute amount of taurine obtained from the diet, but increased the percent contribution of diet from an average of 60% to an average of 80%. Guanidinoethane sulfonate had no effect on the tissue:serum ratio of radioactivity in brain, thymus, muscle or pancrease 24 hours after an injection of [3H]taurine. However, other tissues showed significant decreases in tissue:serum ratio, ranging from 67% of control in the small intestine to 36% of control in the liver. In its taurine-depleting action, therefore, guanidinoethane sulfonate discriminates between taurine derived from diet and taurine derived from biosynthesis. I conclude that the taurine-depleting action of guanidinoethane sulfonate is complex in mechanism, being a combination of inhibition of transport and interference with synthesis.