Biosynthetic enzyme activities and catecholamines in adrenal glands of genetic and experimental hypertensive rats

Abstract

The activities of catecholamine-synthesizing enzymes in adrenal glands have been investigated during the development of high blood pressure in spontaneously hypertensive rats (SHR) and in rats made hypertensive by administration of DOCA and saline. There was a significant decrease in the activity of tyrosine hydroxylase, dopamine-β-hydroxylase, and phenylethanolamine N-methyltransferase in young spontaneously hypertensive rats at the age of 2 and 4 weeks, when compared with the activity in adrenals of the Wistar-Kyoto substrain. Tyrosine hydroxylase activity was not different between normotensive and hypertensive animals at 8 weeks of age, but was increased in adult SHR. Both dopamine-β-hydroxylase and phenylethanolamine N-methyltransferase activity were still decreased at the age of 8 weeks in SHR, but were not significantly different from the controls at the age of 14 weeks. Blood pressure in SHR was slightly but significantly higher at 4 weeks of age and rose steadily during maturation. In rats made hypertensive by administration of deoxycorticosterone-sodium chloride (DOCA-saline hypertensive rats), tyrosine hydroxylase activity in adrenals was increased after only 1 week of treatment and remained increased after 2 and 4 weeks of treatment. Adrenal epinephrine was increased after 4 weeks of treatment, whereas dopamine-β-hydroxylase, phenylethanolamine N-methyltransferase, and norepinephrine levels were unchanged. Our findings of increased tyrosine hydroxylase in adrenal glands of adult genetically hypertensive and chronic experimentally hypertensive rats indicate a sympathoadrenal activation during the established phase of hypertension in both models. Whereas, in DOCA-saline hypertensive rats, the sympathoadrenal synthesis of catecholamine parallels the development of high blood pressure, in genetically hypertensive rats, the activity of the catecholamine-synthesizing enzymes is decreased early in development. These results suggest the existence of different mechanisms regulating the participation of adrenal catecholamines in both the spontaneously (genetic) and the experimentally induced (DOCA-saline) hypertension in rats.