NOREPINEPHRINE-INDUCED PHOSPHATIDYLCHOLINE HYDROLYSIS BY PHOSPHOLIPASE-D AND PHOSPHOLIPASE-C IN RAT TAIL ARTERY

Rat tail arterial segments were incubated with [H-3]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, [H-3]choline, and [H-3]phosphocholine. The release of [H-3]choline and [H-3]phosphocholine from the segments was NE dose dependent (10(-6)-10(-3) M). NE also increased the formation of [H-3]phosphatidylethanol in [H-3]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 [H-3]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.