HYPERTHERMIA STIMULATES NITRIC-OXIDE FORMATION - ELECTRON-PARAMAGNETIC-RESONANCE DETECTION OF CENTER-DOT-NO-HEME IN BLOOD

Previous experiments from our laboratory have demonstrated that severe hyperthermia results in a selective loss of splanchnic vasoconstricti on. Using electron paramagnetic resonance spectroscopy to scan whole b lood samples collected in vivo from the portal vein and femoral artery of conscious unrestrained rats, we observed an increase in the concen tration of spectroscopy-detectable species in portal venous blood of a ll heat-stressed animals. These spectra consisted of at least three di stinct species: one with a broad feature having an effective g factor for the unpaired electron (g) of 2.06 assigned to the copper-binding a cute phase protein ceruloplasmin, and two with narrower features that evolved at core temperatures >39 degrees C representing a semiquinone radical and .NO-heme. This heat-induced signal displays the classic ni trogen triplet hyperfine structure (nitrogen hyperfine splitting const ant = 17.5 gauss, centered at g = 2.012) that is consistent with a fiv e-coordinate heme complex and is characteristic of an unpaired electro n coupled to nitrogen in the ferrous .NO-heme adduct [(alpha(2+)NO)bet a(3+)](2). The intensity of this signal increased approximately twofol d as core temperature rose to >39 degrees C, peaking 1 h post-heat exp osure at greater than threefold basal concentration. This species was not seen in corresponding arterial blood samples. This is the first de monstration that whole body hyperthermia produces increased concentrat ions of radicals and metal binding proteins in the venous blood of the rat and suggests that severe hyperthermia stimulates an enhanced loca l release of NO within the splanchnic circulation.