Studies on sodium ion retention and antidiuretic effects after administration of L-tryptophan to rats.

Under certain conditions the i.p. injection of L-tryptophan leads to a reduction of elimination of Na+. At the same time, the fractional Na+ -reabsorption increases. No increase in the absolute tubular sodium transport rate was observed since the significantly reduced plasma-sodium concentration leads to a decreased sodium load. The most probable cause of a decreased plasma-sodium concentration seems to be a retention of sodium-free water under the chosen conditions of infusion. The water retention is compatible with the antidiuretic effect of 5-hydroxytryptamine.