Tyrosine's vasoactive effect in the dog shock model depends on the animal's starting blood pressure

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Abstract
We examined the effect of tyrosine (10–200 mg/kg given intravenously) or placebo on blood pressure (BP) in dogs made hypotensive (systolic BP=50 mm Hg) by bleeding one hour previously. Animals which, prior to induction of hypotension, had been normotensive (mean arterial pressures, [MAP]≦145 mm Hg) subsequently exhibited a dose-related increase in BP after tyrosine administration. In contrast, dogs which had beenhypertensive prior to bleeding exhibited afall in BP after tyrosine. These observations indicated that prior cardiovascular status may be an important factor influencing responses to exogenous tyrosine, and to endogenous catecholamines produced from the tyrosine.