Alpha-1 adrenergic receptor agonists modulate ductal secretion of BDL rats via Ca(2+)- and PKC-dependent stimulation of cAMP.
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abstract
Acetylcholine potentiates secretin-stimulated ductal secretion by Ca(2+)-calcineurin-mediated modulation of adenylyl cyclase. D2 dopaminergic receptor agonists inhibit secretin-stimulated ductal secretion via activation of protein kinase C (PKC)-gamma. No information exists regarding the effect of adrenergic receptor agonists on ductal secretion in a model of cholestasis induced by bile duct ligation (BDL). We evaluated the expression of alpha-1A/1C, -1beta and beta-1 adrenergic receptors in liver sections and cholangiocytes from normal and BDL rats. We evaluated the effects of the alpha-1 and beta-1 adrenergic receptor agonists (phenylephrine and dobutamine, respectively) on bile and bicarbonate secretion and cholangiocyte IP(3) and Ca(2+) levels in normal and BDL rats. We measured the effect of phenylephrine on lumen expansion in intrahepatic bile duct units (IBDUs) and cyclic adenosine monophosphate (cAMP) levels in cholangiocytes from BDL rats in the absence or presence of BAPTA/AM and G6976 (a PKC-alpha inhibitor). We evaluated if the effects of phenylephrine on ductal secretion were associated with translocation of PKC isoforms leading to increased protein kinase A activity. Alpha-1 and beta-1 adrenergic receptors were present mostly in the basolateral domain of cholangiocytes and, following BDL, their expression increased. Phenylephrine, but not dobutamine, increased secretin-stimulated choleresis in BDL rats. Phenylephrine did not alter basal but increased secretin-stimulated IBDU lumen expansion and cAMP levels, which were blocked by BAPTA/AM and Go6976. Phenylephrine increased IP(3) and Ca(2+) levels and activated PKC-alpha and PKC-beta-II. In conclusion, coordinated regulation of ductal secretion by secretin (through cAMP) and adrenergic receptor agonist activation (through Ca(2+)/PKC) induces maximal ductal bicarbonate secretion in liver diseases. (Supplementary material for this article can be found on the HEPATOLOGY website (http://interscience.wiley.com/jpages/0270-9139/suppmat/index.html).
