1,25 Dihydroxyvitamin D causes attenuation of cyclic AMP responses in monocyte-like cells

The U937 cell is a human monocyte-like line which possesses 1,25(OH)2D receptors. To study 1,25(OH)2D actions in these cells we have measured the cAMP produced by U937 cells during 10 minute stimulus by the beta-adrenergic agonist isoproterenol or by forskolin. cAMP produced by isoproterenol is 6 times that of forskolin. When cells are exposed to 1,25(OH)2D for at least 8 hours the cAMP produced is decreased up to 55%. This attenuative effect of 1,25(OH)2D is dose dependent with an EC50 of 10(-10)M. Other vitamin D metabolites are less than 1/100th as potent.