Effects of PGE₂ and a thromboxane A₂ analogue on uptake of IgG complexes and LDL by mesangial cells

Vasoactive agents such as angiotensin (ANG) and eicosanoids can influence macromolecular deposition in the glomerular mesangium. We studied whether prostaglandin E₂ (PGE₂) and U-46619 (a stable analogue of thromboxane A₂) could directly affect the uptake of immunoglobulin G (IgG) complexes or low-density lipoprotein (LDL) by cultured rat mesangial cells (MC). Preincubation of MC with PGE₂ (10^-6 M) resulted in decreased uptake (in counts·min^-1·well^-1) of IgG complexes (PGE₂, 2,589 ± 72; control, 3,840 ± 114; P < 0.001) and LDL particles (PGE₂, 23,176 ± 1,145; control, 37,216 ± 4,520; P < 0.05). MC preincubated with forskolin (10^-5 M) also showed decreased uptake of IgG complexes (forskolin, 2,896 ± 196; control, 3,840 ± 114; P < 0.005) and LDL particles (forskolin, 23,176 ± 1,145; control, 37,216 ± 4,520; P < 0.05). In contrast, preincubation with ANG II (5 X 10^-7 M) showed significantly higher uptake of IgG complexes (ANG II, 4,475 ± 282; control, 3,787 ± 277; P < 0.05) and LDL (ANG II, 48,573 ± 1,079; control, 44,697 ± 770; P < 0.05). Similarly, preincubation with U-46619 (10^-6 M) resulted in significantly higher uptake of IgG complexes (U-46619, 5,370 ± 300; control, 3,659 ± 307; P < 0.02) and LDL (U-46619, 48,298 ± 1,418; control, 44,697 ± 770; P < 0.05). After preincubation with cyclooxygenase inhibitor meclofenamate (10^-6 M), ANG II (5 X 10^-7 M) resulted in a significantly higher uptake of IgG complexes compared with uptake by MC treated with ANG II alone (P < 0.05). Similarly, MC preincubated with meclofenamate (10^-6 M) enhanced uptake of LDL (53,328 ± 1,334, P < 0.005) in response to U-46619 compared with U-46619 alone (48,298 ± 1,418). This suggests that inhibition of PGE₂ synthesis by meclofenamate enhances the effect of ANG II and U-46619 on macromolecular uptake. Because both forskolin and PGE₂ activate adenylate cyclase in MC, it appears that the action of these agents on MC uptake of macromolecules may be mediated via generation of adenosine 3',5'-cyclic monophosphate.