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 reduces blood pressure. The effect is maximal within 2 hr of injection. In spontaneously hypertensive rats, a dose of 50 mg/kg, intraperitoneally, reduces blood pressure by about 12 mm Hg (1 mm Hg = 1.33 x 10(2) pascals); a dose of 200 mg/kg produces the maximal effect, a reduction of about 40 mm Hg. Tryptophan injection (225 mg/kg) also lowers blood pressure in spontaneously hypertensive rats, but only by about half as much as an equivalent dose 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 central nervous system, since the effect can be blocked by co-administering other large neutral amino acids that reduce tyrosine's uptake into the brain. That tyrosine's antihypertensive action is mediated by an acceleration in norepinephrine or epinephrine release within the central nervous system is suggested by the concurrent increase that its injection produces in brain levels of methoxyhydroxyphenylethylglycol sulfate.