Effects of chronic β-blockers treatment on catecholamine synthesizing enzymes in spontaneously hypertensive rats

Abstract

In the present work the effects of two β-blocking agents (Propranolol: 40 mg/kg/day and S 2395: 20 mg/kg/day) on the activity of central and peripheral catecholaminergic (CA) structures were studied in SHR after 55 days of oral treatment. These effects were assessed by measuring the activity of tyrosine hydroxylase (TH), dopamine-β-hydroxylase (DBH) and phenylethanolamine- N-methyl-transferase (PNMT) in different structures dissected out from treated and control SHR. At the peripheral level, the only significant change was a decrease in the DBH activity of the adrenal medulla in propranolol-treated SHR. The plasma DBH activity was not altered. In the pons medulla, propranolol and S 2395 increased the TH activity of the A 6, C 1 and C 2 region, and propranolol decreased the DBH activity in the A 6 and the C 2 region. The PNMT activity of these 3 neuronal groups remained unchanged. In the hypothalamus, TH and DBH activity exhibited no consistent changes. On the other hand, the PNMT activity was significantly reduced by propranolol in the anterior hypothalamus and in the median eminence but not in the posterior hypothalamus. The effects of β-blockers on the activity of central and peripheral CA structures were markedly different from those observed in similar conditions after chronic treatment with hydralazine, a peripheral vasodilator. Therefore, it was concluded that the enzymatic changes observed were not a consequence of the treatment induced decrease in blood pressure, but might more probably reflect a specific action of β-blockers on the central and peripheral CA structures of the SHR.