Further studies on catecholamine synthesis in the spontaneously hypertensive rat: catecholamine synthesis in the central nervous system

Catecholamine levels, turnover rates and in vivo synthesis rates were measured in the brainstems of spontaneously hypertensive rats (SHR) and two normotensive strains, Wistar/NIH and Wistar/Kyoto. All these parameters of catecholamine metabolism were lower in SHR than in the Wistar/NIH but similar to those in the Wistar/Kyoto, the parent strain of SHR. Examination of the three biosynthetic enzymes in the conversion of tyrosine to norepinephrine indicated that all three strains had similar levels of tyrosine hydroxylase and dopamine-β-hydroxylase activity but that the SHR and the Wistar/Kyoto had markedly reduced dopa decarboxylase activity. In vivo synthesis studies using labeled tyrosine and dopa, however, indicated that the decreased synthesis rate in the SHR as compared to Wistar/NIH is the result of decreased amounts of tyrosine entering the catecholamine pool.