Effect of chronic dietary treatment with 1-tryptophan on spontaneous salt appetite of rats.

Chronic dietary treatment with 1-tryptophan (2.5 and 5.0% in food) reduced the exaggerated spontaneous NaCl intake induced by deoxycorticosterone acetate (DOCA) in rats. In the absence of DOCA, chronic (4-week) dietary treatment with 1-tryptophan (5.0% in food) failed to affect significantly spontaneous NaCl intake. In addition, treatment with tryptophan in the absence of DOCA failed to affect significantly systolic blood pressure, plasma renin activity, plasma aldosterone concentration, and the weights of the heart, kidneys, adrenals, and thyroid gland. It also failed to affect the specific binding of [125I]-Ang II to neuronal membranes isolated from the diencephalon of the rats. However, the contents of both serotonin and 5-hydroxyindoleacetic acid in the lower brain stem were increased significantly by chronic treatment with tryptophan. These results suggest that the effect of chronic treatment with tryptophan to reduce the salt appetite of DOCA-treated rats is a specific effect of this amino acid under these conditions and may be related to the ability of tryptophan to prevent the upregulation of specific Ang II receptors induced by DOCA.