Activation of alpha 1-adrenoceptors, protein kinase C, or treatment with intracellular free Ca2+ elevating agents increases pineal phospholipase A2 activity. Evidence that protein kinase C may participate in Ca2+-dependent alpha 1-adrenergic stimulation of pineal phospholipase A2 activity.
The regulation of pineal phospholipase A2 activity was studied indirectly by measuring the release of [3H]arachidonic acid from [3H]arachidonic acid-labeled tissue in organ culture and the formation of radiolabeled lysophosphatidylcholine by glands labeled with 32Pi or [14C]choline. Glands were transferred sequentially through a series of 10-min incubations in label-free medium. Norepinephrine (10(-5) M) stimulated [3H]arachidonic acid release by 2-fold; release peaked during the first 10 min and returned to basal levels during the third incubation period. Studies with selective alpha 1-, alpha 2-, and beta-adrenergic agents indicated that norepinephrine was acting through alpha 1-adrenergic receptors. Ca2+ appears to play a critical role because the effects of norepinephrine were mimicked by treatment with the Ca2+ ionophore A23187 and inhibited by inorganic Ca2+ channel blockers or EGTA; other [Ca2+]i elevating treatments also stimulated [3H]arachidonic acid release. The possibility that protein kinase C may be involved was studied because it is activated by the alpha 1-adrenergic agonist phenylephrine in the pineal gland (Sugden, D., Vanecek, J., Klein, D. C., Thomas, T. P., and Anderson, W. B. (1985) Nature 314, 359-361). Three protein kinase C activators stimulated [3H]arachidonic acid release with the same relative potency as that established for activation of protein kinase C (4 beta-phorbol 12-myristate 13-acetate greater than 4 beta-phorbol 12,13-dibutyrate greater than 1-oleoyl 2-acetylglycerol). The effects of norepinephrine, A23187, and protein kinase C activators appear to be mediated by phospholipase A2 because the effects of these compounds on [3H]arachidonic acid release are blocked by an established inhibitor of this enzyme, mepacrine, and because these compounds stimulate the formation of 32P- and 14C-labeled lysophosphatidylcholine by glands incubated with 32Pi or [14C]choline. In addition, an inhibitor of diacylglycerol lipase, another enzyme which generates arachidonic acid, did not inhibit the stimulation of [3H]arachidonic acid release by norepinephrine, A23187, or a phorbol ester. Cyclic nucleotides do not appear to play an important role in the regulation of phospholipase A2 activity because dibutyryl cyclic AMP does not alter [3H]arachidonic acid release and also because the amounts of cAMP and cGMP in the culture medium are not consistently associated with [3H]arachidonic acid release. These findings suggest that pineal phospholipase A2 activity is controlled by norepinephrine acting via an alpha 1-adrenergic mechanism which might involve Ca2+ and protein kinase C.
D000316:Adrenergic alpha-Agonists / Q000494:pharmacology*; D000818:Animals; D016718:Arachidonic Acid; D001095:Arachidonic Acids / Q000378:metabolism; D003994:Bucladesine / Q000494:pharmacology; D000001:Calcimycin / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D004075:Diglycerides / Q000494:pharmacology; D008244:Lysophosphatidylcholines / Q000378:metabolism; D008297:Male; D009638:Norepinephrine / Q000494:pharmacology; D009924:Organ Culture Techniques; D010042:Ouabain / Q000494:pharmacology; D010052:Ovariectomy; D010656:Phenylephrine / Q000494:pharmacology; D010740:Phospholipases / Q000378:metabolism*; D010741:Phospholipases A / Q000378:metabolism*; D054467:Phospholipases A2; D010870:Pineal Gland / Q000187:drug effects / Q000201:enzymology*; D011188:Potassium / Q000494:pharmacology; D011493:Protein Kinase C / Q000378:metabolism*; D011796:Quinacrine / Q000494:pharmacology; D051381:Rats; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology
D000316:Adrenergic alpha-Agonists; D001095:Arachidonic Acids; D004075:Diglycerides; D008244:Lysophosphatidylcholines; D010656:Phenylephrine; D016718:Arachidonic Acid; D000001:Calcimycin; D010042:Ouabain; D003994:Bucladesine; C038237:1-oleoyl-2-acetylglycerol; D011493:Protein Kinase C; D010740:Phospholipases; D010741:Phospholipases A; D054467:Phospholipases A2; D011796:Quinacrine; D013755:Tetradecanoylphorbol Acetate; D011188:Potassium; D002118:Calcium; D009638:Norepinephrine