The effect of different adrenoceptor agonists on Na, K-ATPase activity and lipid peroxidation of rat brain homogenate was studied. Drugs which enhanced Na, K-ATPase activity-noradrenaline, adrenaline and oxymethazoline-were found to inhibit endogenous membrane lipid peroxidation. Other drugs-phenylephrine, xylazine and clonidine-which did not cause any change in the enzyme activity did not influence lipid peroxidation either. No increase of Na, K-ATPase activity by noradrenaline could be detected after preincubation of the homogenate for 5 min at 37°. During this time endogenous lipid peroxidation of considerable extent could be observed. It is concluded that there is no correlation between the adrenoceptor agonist feature of noradrenaline and its stimulatory effect on Na,K-ATPase activity of rat brain homogenate. However, it seems likely that in rat brain homogenate the increase of Na, K-ATPase activity and inhibition of endogenous lipid peroxidation by noradrenaline are related.
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