Turnover and Synthesis of Norepinephrine in Experimental Hypertension in Rats

Abstract

The turnover of norepinephrine and the enzymes responsible for the synthesis of catecholamines were studied in various organs of rats made hypertensive by DOCA and NaCl. After inhibition of tyrosine hydroxylase by α-methyl-p-tyrosine, an increase in the rate of disappearance of endogenous norepinephrine in the heart, intestine, and spleen of hypertensive rats indicated an increased norepinephrine turnover rate in these organs: Similarly, the rate of decline of ³H-norepinephrine endogenously formed from ³H-dopamine seemed to be increased in the same organs from hypertensive animals. In contrast, the salivary glands showed no change in turnover of norepinephrine. The conversion of tyrosine to catecholamines was normal in the hearts of the hypertensive rats but it was increased in the adrenal glands. The β-hydroxylation of dopamine to norepinephrine was normal or slightly increased in the heart, spleen, intestine, and salivary glands of hypertensive animals. The phenylethanolamine N-methyl transferase activity was normal in the adrenal glands. It thus seems that in hypertension produced by DOCA and NaCl the turnover of norepinephrine is increased in various organs without any detectable change in the synthesis rate, with the exception of the adrenal gland, in which it was increased. This might explain the reduction of the endogenous norepinephrine levels observed in many tissues of animals made hypertensive by DOCA and sodium.