Renal excretion of 8-oxo-7,8-dihydro-2'-deoxyguanosine in Wistar rats with increased O(2) consumption due to cold stress.

DNA damage by reactive oxygen species is of special interest in the development of cancer and in aging. The renally excreted amount of 8-oxo-7,8-dihydro-2'-deoxyguanosine (oxo(8)dG) is a potential noninvasive marker of oxidative DNA damage. The respiratory chain of mitochondria is one source for the formation of reactive oxygen species. In the present study we investigated in Wistar rats (n = 7; mean body weight at start, 307.4 +/- 11 g) the effect of an increased O(2) consumption, i.e., energy expenditure, due to cold stress on the renally excreted amount of oxo(8)dG. First, the rats were housed for 4 days at 23.5 degrees C (basic period, BP), and then for 6 days at 10 degrees C (cold stress period, CSP), and finally for 3 days at 23.5 degrees C (recovery period, RP). The O(2) consumption (L O(2)/day/kg weight) was significantly (P < 0.0001) on average 50% higher in CSP (69.0 +/- 3.9) than in BP (45.8 +/- 4.8), and similar in BP and RP (44.3 +/- 5.4). The average renal excretion of oxo(8)dG (pmol/day/kg weight) was significantly (P < 0.025) on average 13% higher in CSP (375.5 +/- 27.7) than in BP (333.2 +/- 47. 4) and similar in BP and RP (331.8 +/- 34.3). Maximum increase in oxo(8)dG excretion of on average 17% was on the third to fifth day of the CSP. This study reveals that an increase in O(2) consumption of 50% resulted in a much lower increase in the renal excretion of oxo(8)dG.

Non-invasive temperature imaging of muscles with magnetic resonance imaging using spin-echo sequences.

The application of spin-echo magnetic resonance imaging sequences on non-invasive temperature imaging for temperature mapping of human limbs is investigated. In an in vitro experiment performed on a meat sample, the equilibrium magnetisation P and the spin-lattice relaxation time T1 are calculated from the values for the repetition time TR and the signal intensities obtained by a spin-echo sequence at different tissue temperatures as measured by a fibre-optic probe. T1 is linearly correlated to the tissue temperature, and P is linearly correlated to the reciprocal value of the absolute temperature. Both effects, taken together, lead to a non-linear dependency of the signal intensity on temperature. Therefore a TR leading to maximum temperature dependency of the signal intensity is calculated and used in the further experiments. In the in vivo experiments, the lower legs of two volunteers are cooled from outside. Images are acquired with a spin-echo sequence (1.5 T, TR = 1200 ms, TE = 10 ms). A rise in signal intensity in the muscle with falling skin temperature is observed, particularly in more peripheral muscle layers. This study shows that spin-echo sequences can be used to monitor temperature changes and temperature differences in living muscle tissue.

Thermographic studies on patterns of skin temperature after exercise.

In six subjects thermograms of the thighs and the forearms were taken before, during and after 10 min ergometer exercise at 100 W at an ambient temperature of 23 degrees C. During exercise, an intra-individually constant and reproducible skin temperature pattern with local temperature differences exceeding 3 degrees C evolved. Reactions after external local cooling or after occlusion of blood flow and measurements with a laser Doppler-flowmeter showed dispersed convective heat transport to be the source of this irregular pattern. Temperature differences of 3.6 degrees C and deviations of blood flow in the skin microcirculation of 300% within a distance of a few centimetres reduce the value of single-spot measurements of skin temperature with reference to the whole extremity.