Effects of chronic and acute aminoguanidine treatment on tail artery vasomotion in ageing rats

Abstract

1. This study was designed to evaluate the effects of aminoguanidine, a selective inhibitor of the inducible isoform of nitric oxide synthase (iNOS), on the reactivity and intracellular calcium ([Ca(2+)](i)) mobilization induced by noradrenaline in the perfused tail artery from aged WAG/Rij rats. Global mean internal diameter was 350+/-15 microns and wall thickness 161+/-3 microns. The influence of the endothelium on these responses was also analysed. The intracellular dye fura-2 for [Ca(2+)](i) measurements was used. 2. Noradrenaline-induced vasoconstriction decreased progressively from 3 to 20 and 30 months. Removal of the endothelium attenuated vasoconstriction in 20 and 30 month-old rats (P<0.05) but not in young rats. 3. Chronic administration of aminoguanidine (50 mg kg(-1) day(-1), p.o.) to WAG/Rij rats from 20 to 30 months enhanced (P<0. 01) the [Ca(2+)](i)-sensitivity of noradrenaline-induced vasoconstriction. 4. Aminoguanidine (300 microM) in vitro significantly shifted the concentration-vasoconstriction curve to noradrenaline to the left (P<0.01) in denuded vessels from both 20 and 30 month-old rats. The acute inhibitory effect of aminoguanidine was also observed after chronic aminoguanidine treatment. Aminoguanidine failed to modify vasoconstriction in the presence of the endothelium. 5. Acute aminoguanidine (300 microM) treatment did not modify vasoconstriction induced by noradrenaline in young rats. 6. Quantification of iNOS mRNA expression in tail arteries from 3 and 20 month-old WAG/Rij rats showed that expression was enhanced (x2.1, P<0.01) with age. 7. These results suggest that an inflammatory process develops in the media of the rat tail artery with age and that the subsequent increase in non-endothelial iNOS activity attenuates noradrenaline-induced vasoconstriction.

Figure 1

Concentration-response curves for noradrenaline-induced vasoconstriction in intact and endothelium-denuded tail artery segments from WAG/Rij rats. Results are expressed as increases in perfusion pressure (ΔP, mmHg). The lines drawn through the data were obtained by logistic curve fitting (see Methods). Results are the mean of 5–6 experiments; vertical lines show s.e.mean. ANOVA: P_age<0.001; P_endothelium<0.05; P_{age×endothelium}<0.05.

Figure 2

Effect of acute aminoguanidine treatment on noradrenaline-induced vasoconstriction in perfused tail artery segments with or without endothelium from WAG/Rij rats. Results are expressed as increases in perfusion pressure (ΔP, mmHg). The lines drawn through the data were obtained by pragmatic logistic curve fitting (see Methods). Results are the mean of 6–7 experiments; vertical lines show s.e.mean. ANOVA: P_age<0.001; P_AGacute<0.001; P_endothelium> 0.05; P_age×AGacute<0.001; P_{age×endothelium}>0.05; P_{AGacute×endothelium} < 0.001.

Figure 3

Noradrenaline-elicited contractions in intact and denuded tail arteries from 30 month-old WAG/Rij rats. Results are expressed as increases in perfusion pressure (ΔP, mmHg). The lines drawn through the data were obtained by pragmatic logistic curve fitting (see Methods). Results are the mean of 6–7 experiments; vertical lines show s.e.mean. ANOVA: P_AGchron<0.05; P_AGacute<0.001; P_endothelium>0.05; P_{AGchron x AGacute}<0.05; P_{AGchron x endothelium}>0.05; P_{AGacute x endothelium}<0.001.

Figure 4

Concentration-response curves for noradrenaline-induced vasoconstriction in endothelium-denuded tail artery segments from young and old WAG/Rij rats in the absence or presence of L-NAME (10 μM). Results are expressed as increases in perfusion pressure (ΔP, mmHg). The lines drawn through the data were obtained by logistic curve fitting (see Methods). Results are the mean of 5–6 experiments; vertical lines show s.e.mean. Two-way ANOVA (20 months): P_L-NAME<0.001.

Figure 5

mRNA levels of inducible nitric oxide synthase (iNOS) in tail arteries from 3 (left) and 20 (right) month-old WAG/Rij rats.