Ionizing radiation at clinical dose levels activates both pro-and anti-proliferative signal
transduction pathways, the balance of which determines cell fate. The initiating and
amplifying mechanisms involved in the activation are poorly understood. We demonstrate
that one mechanism involves stimulation of constitutive nitric-oxide synthase (NOS) activity.
NOS activity of Chinese hamster ovary cells was measured by the arginine→ citrulline
conversion assay. Irradiation stimulated a transient activation of NOS with maximal activity at …