α-1 adrenergic receptor agonists modulate ductal secretion of BDL rats via Ca2+- and PKC-dependent stimulation of cAMP

Acetylcholine potentiates secretin-stimulated ductal secretion by Ca2+-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 IP3 and Ca2+ levels in normal and BDL rats. We measured the effect of phenylephrine on lumen expansion in intrahepatic bile duct units (IB-DUs) and cyclic adenosine monophosphate (CAMP) levels in cholangiocytes from BDL rats in the absence or presence of BAPTA/AM and Go6976 (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 IP3 and Ca2+ 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 Ca2+/ PKC) induces maximal ductal bicarbonate secretion in liver diseases.