Testosterone inhibits expression of inducible nitric oxide synthase in murine macrophages.

We investigated the effect of testosterone, the main sexual steroid hormone in men, upon inducible nitric oxide synthesis in murine macrophages. Incubation of murine macrophages (RAW 264.7 cells) stimulated by bacterial lipopolysaccharide (2 microg/ml) with increasing amounts of testosterone (0.1-40 microM) showed a dose dependent inhibition of inducible nitric oxide synthesis. Inducible nitric oxide synthase protein expression was reduced in a dose dependent manner as revealed by immunoblotting when cells were incubated with increasing amounts of testosterone. This was associated with a decline in iNOS mRNA-levels as determined by competitive semiquantitative PCR. As nitric oxide plays an important role in immune defense and atherosclerosis prevention, testosterone-induced iNOS inhibition could lead to an elevated risk of infection as well as to the development of atherosclerotic lesions.