Abstract
Objective: We investigated the effects of exercise training starting after emergence of hypertension (15-week-old) on nitrative stress and protein levels and activities of nitrative stress-related enzymes in the hearts of spontaneously hypertensive rats (SHR).
Material and Methods: We examined the hearts of 25-week old (wk) SHR that performed either 10 wk of voluntary exercise training (Ex) or remained intact (Cont). We also analyzed 5 wk and 15 wk SHR in order to determine basal alterations of nitrative stress and enzymes. Starting at 15 weeks old, 25 wk Ex SHR exercised by voluntary running in a wheel-cage for 10 weeks. At the end of the breeding or training period, rats were anesthetized and hearts were collected. We measured the level of nitrotyrosine by the time-resolved fluoroimmunoassay method, the amount of manganese-containing (Mn-) and copper/zinc-containing (Cu, Zn-) superoxide dismutase (SOD), and endothelial nitric oxide synthase (eNOS) in the heart by the western blotting method. Furthermore Mn- and Cu, Zn-SOD and total NOS activity were measured by the spectrometry method.
Result: Systolic blood pressure was elevated at 15 wk and remained high until 25 wk Cont SHR. Exercise did not affect the blood pressure. Although there was no significant increase in 3-nitrotyrosine (3-NT) concentration in 100,000g precipitate fractions (P2) of heart homogenate of 15 wk SHR, a significant in crease in 3-NT concentration was observed in that of 25 wk Cont SHR. This increase in 3-NT concentration was significantly attenuated in that of 25 wk Ex SHR. The same alterations of 3-NT levels were observed by immunohistochemical analysis using specific antibody for 3-NT. Protein levels of endothelial nitric oxide synthase (eNOS) in the membrane fractions were reduced in 15 wk and 25 wk Cont SHR compared with those of 5 wk SHR, but not affected by Ex. This evidence was supported by the measurements of total NOS activity in the same fractions. Protein levels of Cu, Zn-SOD were reduced to a greater degree in 25 wk Ex and Cont SHR than in those of 5 wk and 15 wk SHR, but there was no significant effect observed by Ex. The same results were obtained upon measurement of Cu, Zn-SOD activity. However, protein of Mn-SOD increased significantly in 15 wk SHR, compared to that of 5 wk SHR. Although there was no significant difference in Mn-SOD levels between 25 wk Cont SHR and 15 wk SHR, significant increases in Mn-SOD levels and activity were observed in 25 wk Ex SHR, compared with those of 25 wk Cont SHR. This evidence accounts for the significant attenuation of 3-NT formation in the P2 fraction of 25 wk Ex SHR.
Conclusion: We conclude that 10 weeks of exercise training after the emergence of hypertension could reduce nitrative stress in the organelle fractions of the heart as a result of the increase in Mn-SOD.
