DOCOSAHEXAENOIC ACID REDUCES BOTH CYCLIC-NUCLEOTIDE AND MELATONIN SYNTHESIS IN RAT PINEALOCYTES

The effect of docosahexaenoic acid (22:6n-3) on melatonin (MT) product ion in rat pinealocytes was measured. In pinealocytes, supplementation with 50 mu M 22:6n-3 for 48 h decreased MT production after a norepin ephrine (NE)-stimulation (2 and 10 mu M). Using co-treatment with IBMX (1 mM), a cyclic nucleotide phosphodiesterase inhibitor known to incr ease NE-stimulated cAMP and prazosin (1 mu M), an alpha 1 antagonist, the results indicate that a) 22:6n-3 did not act on cyclic nucleotide phosphodiesterase activities to decrease both cAMP (-64%) and cGMP (-4 5%) levels and b) the inhibition of cGMP was higher (-70%) in presence of prazosin. These results confirm that in rat pinealocytes the lower ing effect of 22:6n-3 supplementation on cAMP is likely to be dependen t on alpha 1-adrenoceptor modulation whereas the decrease of cGMP seem s to involve other intracellular mechanisms. The absence of 22:6n-3 ef fect on serotonin metabolites suggest that the lowering effect on MT m ay be also correlated with alterations of O-methylation step.