Tryptophan-induced lowering of blood pressure and changes of serotonin uptake by platelets in patients with essential hypertension.

Oral tryptophan loading and serotonin (5-HT) uptake by platelets were investigated as an approach to the study of central serotonergic mechanisms in patients with essential hypertension. Single oral doses of L-tryptophan (50 mg/kg body weight) lowered blood pressure significantly 90-120 min after administration in 14 patients with essential hypertension, but not in normotensive controls. Baseline measurements (without tryptophan loading) of 5-HT uptake by platelets did not differ between hypertensive and normotensive persons. Whereas L-tryptophan changed the uptake kinetics and increased 5-HT uptake in normal controls, these effects were not observed--or occurred to a much lesser degree--in hypertensive patients. It is suggested that in human essential hypertension central serotonergic mechanisms are involved in pathogenetic mechanisms. The tryptophan-induced lowering of blood pressure could be attributable to the enhancement of central 5-HT synthesis.