Antagonistic effects of vitamin D and parathyroid hormone on lipoprotein lipase in cultured adipocytes

The effects of 1,25-dihydroxyvitamin D3 (1,25(OH)(2)D-3) (calcitriol) and p arathyroid hormone (PTH) on synthesis and secretion of lipoprotein lipase ( LPL) were studied in 3T3-L1 adipocytes. Expression of the vitamin D recepto r was demonstrated by saturation kinetics with radiolabeled calcitriol. Inc ubation with calcitriol (10(-8) M) for up to 4 d resulted in a time-depende nt significant increase in heparin-releasable LPL activity (LPLa) accompani ed by a significant increase in LPL mRNA. In contrast, incubation with inta ct (1-84) PTH (10(-6) to 10(-9) M) produced a time- and dose- dependent sig nificant decrease in LPLa, but no change in LPL mRNA. The effect of PTH (24 -h incubation, 10(-8) M) could be prevented by the calcium channel blacker verapamil. Coincubation with both calcitriol and PTH at equimolar concentra tion (10-8 M) resulted in an increase in LPLa and LPL mRNA. These data indi cate an antagonistic role for calcitriol and PTH in the regulation of LPL, possibly mediated by intracellular calcium, which may contribute to the alt erations in lipoprotein metabolism occurring in uremia.