Adrenergic modulation of astroglial phospholipase D activity and cell proliferation

As phospholipase D (PLD) activation has been associated with mitogenic sign alling in several cell types, we tested an association between adrenergic a ctivation of PLD and cellular proliferation in primary cultures of rat cort ical astrocytes. In 2-week old cultures, PLD activation by noradrenaline (E C50: 0.49 mu M) was inhibited by prazosin, a specific antagonist at alpha(1 )-adrenergic rcceptors (IC50: 0.23 mu M) Adrenergic PLD activation was not affected by genistein, an inhibitor of tyrosine kinases, or by Ro 31-8220, an inhibitor of protein kinase C (PKC), but was dose-dependently depressed in the presence of brefeldin A (1-100 mu g/ml), an inhibitor of ARF activat ion. In experiments measuring cell proliferation, noradrenaline potently (E C50: 20 nM) reduced [H-3]thymidine incorporation to 20-30% of basal values. This action was mimicked by the beta-specific agonist isoprenaline and was inhibited by the beta-antagonist propranolol in a concentration-dependent manner. The alpha(1)-adrenergic agonists, phenylephrine and methoxamine, al so reduced DNA synthesis. The adrenergic inhibition of astroglial DNA synth esis was not reduced, but further potentiated in the presence of brefeldin A, ethanol, and 1-and 2-butanol; 1-butanol, a substrate of PLD, was equally effective as 2-butanol, a non-substrate. We conclude that adrenergic PLD a ctivation in astrocytes is not involved in mitogenic signalling. The involv ement of ARF in the activation of PLD via alpha(1)-adrenoceptors indicates a role in protein trafficking. (C) 1999 Elsevier Science B.V. All rights re served.