The effect of alpha-, beta adrenergic receptor agonists and antagonists on the efflux of 22Na and uptake of 42K by rat brain cortical slices

Preconditioning prevents the inhibition of Na+,K+-ATPase activity after brain ischemia

Application of single transient forebrain ischemia (ISC) in adult Wistar rats, lasting 2 or 10 min, caused inhibition of Na+,K+-ATPase activity in cytoplasmic membrane fractions of hippocampus and cerebral cortex immediately after the event. In the 2-min ISC group followed by 60 min of reperfusion, the enzyme inhibition was maintained in the cortex, while there was an increase in hippocampal enzyme activity; both effects were over 1 day after the event. However, in the 10-min ISC group enzyme inhibition had been maintained for 7 days in both cerebral structures. Interestingly, ischemic preconditioning (2-min plus 10-min ISC, with a 24-hour interval in between) prevented the inhibitory effect of ischemia/reperfusion on Na+,K+-ATPase activity observed either after a single insult of 2 min or 10 min ischemia. We suggest that the maintenance of Na+,K+-ATPase activity afforded by preconditioning be related to cellular neuroprotection.

Subacute noradrenergic agonist infusions in vivo increase Na+, K+-ATPase and ouabain binding in rat cerebral cortex

In order to investigate the specificity of noradrenergic effects on Na+, K+-ATPase, we infused noradrenergic agonists into the cerebral ventricles of rats, with or without depletion of forebrain norepinephrine. Infusion of norepinephrine, isoproterenol, or phenylephrine increased ouabain binding in intact rats, whereas clonidine infusion decreased binding. Depletion of forebrain norepinephrine by destruction of the dorsal noradrenergic bundle reduced ouabain binding. Norepinephrine infusion reversed the effect of dorsal bundle lesion; isoproterenol and phenylephrine increased ouabain binding in lesioned rats, but did not restore the effect of the lesions. Clonidine had no effect in lesioned rats. Effects on Na+, K+-ATPase activity were similar, but smaller. These results suggest that stimulation of both alpha 1- and beta-noradrenergic receptors may be necessary for optimal Na+, K+-ATPase, and that clonidine reduces Na+, K+-ATPase indirectly through decreased norepinephrine release.

Stimulation of brain Na+, K+-ATPase by norepinephrine in vivo: prevention by receptor antagonists and enhancement by repeated stimulation

The role of alpha 1- and beta-noradrenergic receptors in the stimulation of the K+-p-nitrophenylphosphatase activity and ouabain binding associated with rat brain Na+, K+-ATPase by acute or repeated yohimbine were examined. Repeated yohimbine increased enzyme activity and ouabain binding by about 25%; this was prevented by the alpha 1-receptor antagonist prazosin and decreased by the beta-antagonist propranolol. Pretreatment with repeated yohimbine increased the stimulation of enzyme activity by acute yohimbine while the stimulation was prevented by prazosin pretreatment.