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Friday 01 October 2004

Norepinephrine increases alveolar fluid reabsorption and Na,K-ATPase activity.

By: Azzam ZS, Adir Y, Crespo A, Comellas A, Lecuona E, Dada LA, Krivoy N, Rutschman DH, Sznajder JI, Ridge KM.

Am J Respir Crit Care Med 2004 Oct 1;170(7):730-6

The purpose of this study was to determine whether alpha-adrenergic receptor agonists have a role in alveolar fluid reabsorption, via Na,K-ATPase, in the alveolar epithelium. Alveolar fluid reabsorption increased approximately twofold with increasing concentrations of norepinephrine (NE) as compared with control rats. Treatment with the nonselective alpha-adrenergic receptor agonist, octopamine, and the specific alpha(1) agonist, phenylephrine, increased alveolar fluid reabsorption by 54 and 40%, respectively, as compared with control. The specific alpha(1)-adrenergic receptor antagonist, prazosin, inhibited the stimulatory effects of NE by approximately 30%, whereas alpha(2)-adrenergic antagonist, yohimbine, did not prevent the stimulatory effects of NE. The administration of ouabain, Na,K-ATPase inhibitor, prevented the NE-mediated increase in alveolar fluid reabsorption. In parallel with these changes, NE increased Na,K-ATPase activity and protein abundance in alveolar epithelial type II cells via the alpha(1)- and beta-adrenergic receptor. We report here that NE increased alveolar fluid reabsorption via the activation of both alpha(1)- and beta-adrenergic receptors, but not alpha(2)-adrenergic receptors. These effects are due to increased activity and abundance of the Na,K-ATPase in the basolateral membrane of ATII cells.

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