Role of lipid peroxidation and the glutathione-dependent antioxidant system in the impairment of endothelium-dependent relaxations with age.
1. Age-related changes in the blood prooxidant-antioxidant state, as well as its influence on the relaxant responses to acetylcholine (ACh) were studied in the tail artery from 6-, 24- and 30-month-old Sprague-Dawley (SD) rats. 2. Malondialdehyde (MDA) plasma levels increased 2 and 3 times in 24- and 30-month-old rats, respectively, when compared with 6-month-old rats (0.43+/-0.09 microM). This increase was accompanied by an induction of 6-phosphogluconate dehydrogenase (6PG-DH) and glutathione reductase (GR) activities in red blood cells from 24-month-old rats. In 30-month-old rats, a further induction of these enzymatic activities, as well as glucose-6-phosphate dehydrogenase (G6P-DH) and glutathione peroxidase (GPx) activities was observed. 3. No differences with age were found in the concentration-response curves to ACh in isolated tail artery segments from 6- and 24-month-old rats precontracted with 0.3 microM noradrenaline (NA). However, a decrease in sensitivity to ACh-induced relaxation was observed in 30-month-old rats; EC30 values were 3.5 (1.3-8.0) x 10(-7) M and 18.1 (8.9-30.1) x 10(-7) M for 6- and 30-month-old rats, respectively. Moreover, a decrease in maximum ACh relaxation (10 microM) was found in 30-month-old rats in comparison with that obtained in 6-month-old rats (58.5+/-3.9% and 42.5+/-3.4% of previous NA contraction, respectively). 4. Incubation of tail artery segments with MDA (0.5, 1 or 10 microM) caused a reduction of ACh-induced relaxations that was different in the three ages. Thus, the reduction of ACh-induced relaxations became significant with 0.5 microM MDA in 6-, with 1 microM MDA in 24-, and with 10 microM MDA in 30-month-old rats. In addition, MDA did not cause a shift in the concentration-response curve to ACh, but a decrease in the maximum response. 5. Superoxide dismutase (SOD; 150 u ml(-1), a superoxide anion scavenger) reversed the inhibitory effect of MDA on ACh-induced relaxations at all ages studied. 6. We conclude that: (1) ageing produces an increase in lipid peroxidation process, as indicated by the increase in MDA plasma levels, that is accompanied by an induction of lipid peroxide detoxification enzymes: (2) the changes in prooxidant-antioxidant equilibrium with age contribute, at least partially, to the impairment of the relaxant responses evoked by ACh; and (3) the effect of MDA appears to be mediated by superoxide anion at all ages studied.
Rodríguez-Martínez
M A
MA
Departamento de Farmacología y Terapéutica, Facultad de Medicina, Universidad Autónoma, Madrid, Spain.
Alonso
M J
MJ
Redondo
J
J
Salaíces
M
M
Marín
J
J
D000109:Acetylcholine / Q000378:metabolism; D000375:Aging / Q000502:physiology*; D000818:Animals; D000975:Antioxidants / Q000378:metabolism*; D001794:Blood Pressure / Q000502:physiology; D004730:Endothelium, Vascular / Q000502:physiology*; D004912:Erythrocytes / Q000378:metabolism; D005978:Glutathione / Q000502:physiology*; D006339:Heart Rate / Q000502:physiology; D066298:In Vitro Techniques; D015227:Lipid Peroxidation / Q000502:physiology*; D008297:Male; D008315:Malondialdehyde / Q000378:metabolism; D009119:Muscle Contraction / Q000502:physiology; D009126:Muscle Relaxation / Q000502:physiology; D009131:Muscle, Smooth, Vascular / Q000502:physiology; D010084:Oxidation-Reduction; D051381:Rats; D017207:Rats, Sprague-Dawley; D013482:Superoxide Dismutase / Q000378:metabolism
D000975:Antioxidants; D008315:Malondialdehyde; D013482:Superoxide Dismutase; D005978:Glutathione; D000109:Acetylcholine