Abstract-The relationship between the onset of hypertension and changes in monoamine oxidase (MAO) activity in the brains and hearts of spontaneously hypertensive rats (SHR) were studied. After 7-weeks-old, blood pressure of SHR increased rapidly and reached a level of 170 to 180 mmHg; but following 4 weeks of propranolol treatment (10 mg/kg/day), blood pressure decreased significantly compared to that of untreated SHR. Heart/body weights ratio of SHR was higher than that of normotensive Wistar Kyoto rats (WKY). MAO activities in the brain stem, the medulla oblongata and pons of the SHR were significantly higher than those in WKY at 7 weeks of age, and MAO activity in the brain stem of the propranolol-treated SHR was significantly lower than that in the untreated SHR. Propranolol inhibited MAO activity in brain tissue in vitro, and the 150 values of propranolol were identical (1 X10-4 M) in SHR and WKY. In both the WKY strain and the SHR, the Vmax values of heart MAO increased with age, and the Vmax values of SHR were twice those of WKY. Km values for tyramine of heart MAO in WKY and SHR were approx. 100 PM and 140 ,iM, respectively; however, these values were not age-dependent. It was concluded that an increase in MAO activity in SHR brain stem may trigger a reduction in noradrenaline content and that propranolol may be responsible for its restoration, thus reducing peripheral sympathetic activity; moreover, the increase in MAO activity in the hearts of SHR may be of genetic origin.
Abstract-The effects of various local anesthetics on rat brain and liver monoamine oxidase (MAO) and their antihemolytic and local anesthetic effects were studied.All local anesthetics tested at 1 X 10-7 M to 1 X 10-3 M inhibited MAO activity in rat liver mitochondria with 5-hydroxytryptamine (5-HT) as substrate.The order of potency was tetracaine>procaine> dibucaine>lidocaine>prilocaine.Tetracaine and procaine inhibited 5-HT oxidation much more than 13-phenylethylamine (PEA) oxidation. Dibucaine inhibited PEA oxidation as much as 5-HT oxidation.Inhibition of MAO by local anesthetics other than dibucaine was reversible. Tetracaine and procaine inhibited 5-HT oxidation competitively, whereas dibucaine inhibited it non-competitively.Antihemolytic effects were observed with dibucaine and tetracaine at concentrations of 6 x 10-5 M and 1 X 10-4 M, respectively. The order of surface anesthetic potencies was dibucaine>tetracaine> prilocaine>lidocaine>procaine.These results suggest that the inhibition of MAO activities by local anesthetics depends on both electrostatic and hydrophobic interactions between these drugs and enzyme-associated phospholipids or the hydrophobic regions of proteins.
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