Effects of L-tryptophan on blood pressure in normotensive and hypertensive rats.

The effects of L-tryptophan on blood pressure and brain serotonin have been investigated in normotensive and spontaneously hypertensive rats. Doses of L-tryptophan from 25 to 100 mg/kg increased the blood pressure of normotensive rats by 10 to 15 mm Hg. The lower doses of L-tryptophan also increased blood pressure in hypertensive rats but, in contrast, the highest dose (100 mg/kg) lowered blood pressure by 30 to 35 mm Hg. Blood pressure effects of L-tryptophan were evident within 30 min of treatment and reached maximal response by 60 min. L-Tryptophan-induced changes in serotonin neurochemistry were correlated on a temporal basis with changes in blood pressure. However, the dose-response relationship between blood pressure changes and increases in brain serotonin and 5-hydroxyindoleacetic acid content produced by L-tryptophan was not related. The effects of L-tryptophan on blood pressure in normotensive and spontaneously hypertensive rats cannot be explained entirely by its effects on brain serotonin.