Abstract
Tyrosine and tryptophan contents in the plasma and brain, and noradrenaline and serotonin contents in the brain were measured in spontaneously hypertensive rats (SHR) and two normotensive strains, Wistar/Kyoto rats (WKR) and Wistar/Carworth rats (WCR) to investigate the quantitative relationship between monoamines and their precursor amino acids in the brain of SHR. WKR is the parent strain of SHR. Tyrosine level in the plasma and brain of SHR was significantly lower than that in WCR, whereas tryptophan level in the plasma and brain of SHR was higher than that of WCR. The levels of these amino acids were the same in SHR and WKR. Noradrenaline and serotonin contents in the brain stem of SHR and WKR were lower than the respective contents of WCR, while no difference was found in noradrenaline and serotonin contents in the telencephalon of these 3 strains. In SHR, 1.0% L-tyrosine ingestion for 5 days produced a slight but significant fall of the blood pressure accompanied by an increase of tyrosine in the plasma and brain. However, noradrenaline in the brain stem did not change following the L-tyrosinc feeding. These results suggest that differences in contents of the monoamines and their precursor amino acids in SHR and WKR could be due to genetic factors in a specific closed colony.
