Figure 1

The in vivo electron spin resonance (ESR) method. (a) The ESR spectrum in the head of an anesthetized rat after intravenous injection of methoxycarbonyl (MC)-PROXYL into the tail vein showed a characteristic triplet set of peaks; the pattern was unchanged during measurement, whereas signal intensity, defined as the top-to-bottom height of the center peak of the triplet, decreased with time. (b) The natural logarithmic values of 60-s averages of signal intensity were consecutively plotted as a function of time for 5 min; the signal decay rate was defined as the negative slope (−Δ) of the linear regression of these plots, which had good linearity. The signal decay rate in stroke-prone spontaneously hypertensive rats (SHRSP) was increased compared with that in age-matched Wistar–Kyoto (WKY) rats; the difference was small, but statistically significant. ^**P<0.01, n=6 for each. (c) The effect of antioxidants on in vivo ESR signal decay rate. Increased signal decay rate in SHRSP (control) was decreased by pretreatment with apocynin (apocynin), or by coadministration of MC-PROXYL with dimethylthiourea (DMTU), to comparable levels of those of WKY. Pharmacological intervention in combination with apocynin and DMTU (Apo/DMTU) resulted in no further decrease from respective single treatment. Pretreatment with allopurinol did not affect the increased in vivo ESR signal decay rate in SHRSP (allopurinol). ^**P<0.01.