EFFECT OF TRIIODOTHYRONINE ON NITRIC OXIDE PRODUCTION IN MESANGIAL CELLS AND RENAL TUBULAR EPITHELIAL CELLS

: Nitric oxide (NO) is a signalling molecule that is produced by mesangial cells and renal tubular epithelial (RTE) cells. It plays a role in the regulation of glomerular and tubular function. In renal cells, NO is synthesized by the inducible isoform of the enzyme nitric oxide synthase (NOS). Thyroid hormone modulates the activity of neuronal NOS; therefore, we examined whether triiodothyronine (T3) stimulated the activity of inducible iNOS in mesangial cells, LLC-PK1 cells (analogue of the proximal tubule) and MDCK cells (analogue of the distal tubule). T3 (concentration range: 10(-10)-10(-7) M) had no effect on NO synthesis or iNOS protein expression by the three renal cell types. In addition, T3 did not modulate NO production in RAW 264.7 cells, a murine macrophage cell line, confirming that the hormone had no effect on iNOS activity. We conclude that, unlike its effect on neuronal NOS, T3 does not regulate iNOS activity in mesangial cells, RTE cells, or macrophages, and that the effects of T3 on renal cell growth and function are not mediated by inducible increases in NO synthesis.