You have no items in your shopping cart.
ABSTRACT Numerous studies have demonstrated the link between the aging process and cardiovascular dysfunction. Arginase action reduces substrate (L-arginine) availability for the formation of nitric oxide. Also, enhanced vascular arginase activity contributes to endothelial dysfunction in Dahl-S rats with salt-induced hypertension. There is, however, a paucity of information on vascular arginase activity of aged normotensive and spontaneously hypertensive rats (SHR). This study tests the hypothesis that the agedependent vascular dysfunction in SHRs is mediated by arginase. Young (12-14 weeks) and old (11-12 months) male Wistar and spontaneously hypertensive rats (SHR) were used for this study. On the day of the experiment, each rat was weighed after which mean arterial pressure (MAP) was measured in the rats using the invasive method. The rats were then euthanized and 5mL of blood was drawn from the heart to obtain serum for the assay of arginase activity. Mesenteric resistant arteries (MRAs) and thoracic aortae were excised and placed in ice-cold Physiological salt solution (PSS). They were cleaned of adhering tissues. Thereafter, a portion was snap-frozen in liquid nitrogen and stored for immunoblotting studies, while a second portion was cut into 2mm rings for vascular reactivity studies. Cumulative concentration-response tests to (PE; 10-9 -3x10-5M), Acetylcholine (ACH; 10-9 – 3x10-5M) and Sodium nitroprusside (SNP; 10-12 – 3x10-5 M) were performed. Thirty minutes prior to the concentration-response tests, some arterial rings were incubated separately with the following agents: L-arginase, 0.05U/ML (MRA) or 0.5U/ML (aorta); Rho kinase inhibitor, Y27632 - 10-5mmol/L; or 0.5U/ML L-arginase + 10-5mmol/L Y27632 (aorta). All the chemicals were obtained from Sigma-Aldrich MO, USA. Force development in response to a Ca2+ handling experimental protocol was evaluated in MRAs from young and old Wistar and spontaneously hypertensive rats. Data are expressed as mean ± S.E.M. of 6 rats per group; statistical differences were calculated using Student‘s t-test and two-way ANOVA with repeated measures followed by Bonferroni post hoc test. Significance was set at p<0.05. All statistical tests were performed using Graphpad Prism (v. 6.0 Graphpad Software). Results from this study showed: Aging increased blood pressure in the SHRs but not in the wistar rats. Arginase impaired the endothelium-dependent relaxation responses of thoracic aortic and MRA rings to ACH in the old Wistar rats and SHRs whereas the arginase induced impairment of endothelium independent-relaxation response to SNP was observed in the old SHRs only. Correspondingly, arginase potentiated the contractile responses of thoracic aortic and MRA arterial rings to PE in the old SHR; this potentiation was attenuated by Rho Kinase inhibitor (Y26732) in the presence or absence of arginase. It was also observed that there were no significant differences in the serum arginase activity in the four groups of rats. On the contrary, arginase activity in the thoracic aorta of old Wistar; young and old SHR were increased compared to the young Wistar. Arginase expression was also increased in the old Wistars and SHRs. Arginase increased the transient caffeine-induced contraction due to Ca2+ release from the intracellular stores in mesenteric resistance arterial rings from old SHRs.In conclusion, the results of this study suggest that arginase impairs both endothelium-dependent and -independent vasorelaxation; this could be through the NO downstream signaling pathway. The results also suggest that increased arginase activity mediates vascular dysfunction in the old SHR through a mechanism that involves activation of the RhoA-Rho Kinase pathway and abnormalities in cellular Ca2+ handling
