Development of hypertension in spontaneously hypertensive rats fed L-tyrosine-supplemented diets.

The blood pressure of spontaneously hypertensive rats (SHR) was measured by tail-plethysmography. Feeding SHR a diet supplemented with 0.6 g% L-tyrosine, for 15 weeks after weaning, resulted in a slower increase of blood pressure than in rats fed the control diet (no tyrosine added). The blood pressure stabilized, after about 8 weeks, at values lower by about 10 mm Hg than in the control SHR group. Diets with a higher content of free L-tyrosine (1.2 or 2.4 g%) produced no greater hypotensive effects, despite the fact that the plasma level of the amino acid, at the time of blood pressure measurements, was related to the tyrosine content of the diet. In addition, providing 2.4 g% free L-tyrosine to the diet of SHR with established hypertension, produced within a few days a decrease of blood pressure similar to the one recorded in rats fed the tyrosine-supplemented diet during the whole period of development of hypertension. A maximal effect of L-tyrosine, in decreasing the blood pressure of SHR, is thus obtained at relatively low concentrations of the amino acid in the diet, and after a short period of consumption. However, this effect is rather small, and rapidly reversed upon removing free L-tyrosine from the diet.