T3 regulates renal cell growth and tubular transport, NO is synthesized by MC and RTE using the enzyme inducible nitric oxide synthase (NOS) and may mediate the effects of T3. Therefore, we conducted experiments to ascertain the interaction between T3 and renal cell NO production.

Rat MC (2×105 cells/ml) and RTE (MDCK and LLC-PK1 cells, 2×106/ml), were placed in 96 well plates. They were maintained in control media, i.e., serum-free DME, or test media, i.e., serum-free DME supplemented with T3, 10-10 - 10-7 M, for 24 h. NO production was assessed with the Griess reaction to measure NO2- accumulation in conditioned media. Cell viability was determined with the MTT reagent. NO production was expressed per unit number of viable cells.

T3 had no effect on NO production by rat MC or either of the two RTE cell lines. To further exclude an effect of T3 on inducible NOS, RAW 264.7 cells, a macrophage cell line, were incubated in the absence or presence of 10-10 -10-7 M T3. T3 did not modulate NO production in cultured macrophages. Addition of L-arginine (10 mM) or L-NAME (1 mM) had a similar effect to stimulate and inhibit NO synthesis, respectively, under control and test conditions in all cells.

We conclude that, unlike its effect on neuronal NOS, T3 does not influence iNOS activity or NO production by MC, RTE, and monocyte-macrophages. This suggests that the effects of T3 on renal cell growth and function are not mediated by NO.