Tyrosine administration reduces blood pressure and enhances brain norepinephrine release in spontaneously hypertensive rats.

Abstract

Administration of L-tyrosine to normotensive or spontaneously hypertensive rats [SHR] reduces blood pressure. The effect is maximal within 2 h of injection. In SHR, a dose of 50 mg/kg i.p. reduces blood pressure by .apprx. 12 mm Hg (1 mm Hg = 1.33 .times. 102 pascals); a dose of 200 mg/kg produces the maximal effect, a reduction of .apprx. 40 mm Hg. Tryptophan injection (225 mg/kg) also lowers blood pressure in SHR, but only by about 1/2 as much as an equivalent does of tyrosine. Other amino acids tested (leucine, isoleucine, valine, alanine, arginine and aspartate) do not affect blood pressure. Tyrosine injection appears to reduce blood pressure via an action within the CNS, since the effect can be blocked by co-administering other large neutral amino acids that reduce tyrosine''s uptake into the brain. Tyrosine''s antihypertensive action may be mediated by an acceleration in norepinephrine or epinephrine release within the CNS by the concurrent increase that its injection produces in brain levels of methoxyhydroxyphenylethylglycol sulfate.