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Norepinephrine-induced Phosphatidylcholine Hydrolysis By Phospholipases D And C In Rat Tail Artery

H. Gu, S. Trajkovic, E. F. LaBelle

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Rat tail arterial segments were incubated with [3H]choline to selectively label endogenous phosphatidylcholine. Norepinephrine (NE; 10(-5) M) addition for periods of 10 s to 30 min significantly increased the concentration of extracellular phosphatidylcholine metabolites, [3H]choline, and [3H]phosphocholine. The release of [3H]choline and [3H]phosphocholine from the segments was NE dose dependent (10(-6)-10(-3) M). NE also increased the formation of [3H]phosphatidylethanol in [3H]myristate-labeled tail artery in the presence of ethanol, characteristic of phospholipase D activity. NE-induced phosphatidylcholine hydrolysis was blocked by pretreatment with prazosin (10(-5) M) and was unchanged by pretreatment with propranolol (10(-5) M). 4 beta-phorbol 12,13-dibutyrate (PDBu, 10(-6) M) stimulated the release of [3H]choline, which was inhibited by pretreatment with staurosporine (10(-5) M). The stimulatory effect of NE on phosphatidylcholine metabolism was not altered by either pretreatment with staurosporine (10(-5) M) or calcium-free buffer. In summary, we have demonstrated NE-stimulated phosphatidylcholine hydrolysis by phospholipase D and C in intact vascular smooth muscle. This effect of NE was dose dependent and was mediated through the alpha 1-adrenergic receptor. Norepinephrine and PDBu stimulated phosphatidylcholine hydrolysis through different mechanism(s), and the stimulatory effect of NE did not seem to require protein kinase C and calcium influx.