Detraining differentially preserved beneficial effects of exercise on hypertension: effects on blood pressure, cardiac function, brain inflammatory cytokines and oxidative stress

Abstract

Aims: This study sought to investigate the effects of physical detraining on blood pressure (BP) and cardiac morphology and function in hypertension, and on pro- and anti-inflammatory cytokines (PICs and AIC) and oxidative stress within the brain of hypertensive rats.

Methods and results: Hypertension was induced in male Sprague-Dawley rats by delivering AngiotensinII for 42 days using implanted osmotic minipumps. Rats were randomized into sedentary, trained, and detrained groups. Trained rats underwent moderate-intensity exercise (ExT) for 42 days, whereas, detrained groups underwent 28 days of exercise followed by 14 days of detraining. BP and cardiac function were evaluated by radio-telemetry and echocardiography, respectively. At the end, the paraventricular nucleus (PVN) was analyzed by Real-time RT-PCR and Western blot. ExT in AngII-infused rats caused delayed progression of hypertension, reduced cardiac hypertrophy, and improved diastolic function. These results were associated with significantly reduced PICs, increased AIC (interleukin (IL)-10), and attenuated oxidative stress in the PVN. Detraining did not abolish the exercise-induced attenuation in MAP in hypertensive rats; however, detraining failed to completely preserve exercise-mediated improvement in cardiac hypertrophy and function. Additionally, detraining did not reverse exercise-induced improvement in PICs in the PVN of hypertensive rats; however, the improvements in IL-10 were abolished.

Conclusion: These results indicate that although 2 weeks of detraining is not long enough to completely abolish the beneficial effects of regular exercise, continuing cessation of exercise may lead to detrimental effects.

Figure 1. Experimental protocol.

The rats were first acclimatized to the treadmill for 14 days before the start of the experiment. After 7 days of acclimation, the rats were implanted with radio-telemetry probes for continuous recording of MAP and then were allowed to recover for next 7 days. Then miniosmotic pumps (42 days) filled with AngII or saline were subcutaneously implanted. Before AngII pump implantation, animals were weighed and a baseline echocardiogram was performed. Animals in exercise groups were allowed to run for 42 days, whereas, animals in sedentary groups were placed on non-running treadmill for the exercise sessions. Animals in detraining groups underwent exercise for 28 days and were kept sedentary for the rest of the14 days. 24 hours after the last exercise session, animals were weighed and the final echocardiogram was performed. The animals were then euthanized and the brains were collected for real-time RT-PCR and Western blot analysis.

Figure 2. Time course of mean arterial pressure (MAP, in millimeters of mercury) in normotensive and hypertensive rats.

MAP was significantly increased in AngII+Sed compared with Sal+Sed rats from day 8 of AngII infusion (empty arrow). MAP was significantly reduced in AngII+Ex compared with AngII+Sed rats from day 16 of exercise (filled arrow). 2 weeks of detraining did not abolish the exercise-induced reduction in MAP in AngII-infused rats. Values are mean±SE; n = 6 per group. *p<0.05 Sal+Sed versus AngII+Sed; ^#p<0.05 AngII+Sed versus AngII+Ex; ^$p<0.05 AngII+Sed versus AngII+Det.

Figure 3. Effect of exercise and detraining on cardiac hypertrophy and cardiac function in normotensive and hypertensive rats as measured by M-mode and Doppler echocardiography.

AngII+Sed rats had significantly higher levels of IVSTd, LVPWTd, and Tei index when compared to Sal+Sed. Exercise caused significant reduction in these variables in AngII+Sed rats. 2 weeks of detraining resulted in significantly increased LVPWTd in comparison with AngII+Ex; whereas, IVSTd and Tei index values were considerably but insignificantly increased in AngII+Det versus AngII+Ex. These data suggest that detraining caused partial reversal of exercise-induced changes in hypertensive rats. Values are mean±SE. n = 8 per group. *p<0.05 Sal+Sed versus AngII+Sed; ^#p<0.05 AngII+Sed versus AngII+Ex; ^@p<0.05 AngII+Ex versus AngII+Det.

Figure 4. Effects of exercise on TNF-α, IL-1β, and IL-10 in the PVN of normotensive and hypertensive rats.

A, mRNA expression of TNF-α. B, mRNA expression of IL-1β. C, mRNA expression of IL-10. D, a representative Western blot. E, densitometric analysis of protein expression. Detraining did not alter exercise-induced reduction in TNF-α and IL-1β levels in the PVN of AngII-infused animals; whereas, it did abolish exercise-mediated increase in IL-10 levels.Values are mean±SE. n = 9 per group for mRNA and n = 6 per group for protein analysis. *p<0.05 Sal+Sed versus AngII+Sed; ^#p<0.05 AngII+Sed versus AngII+Ex and AngII+Sed versus AngII+Det; ^@p<0.05 AngII+Ex versus AngII+Det.

Figure 5. Effects of exercise on iNOS and gp91^phox in the PVN of normotensive and hypertensive rats.

A, mRNA expression of iNOS. B, mRNA expression of gp91^phox. C, a representative Western blot. D, densitometric analysis of protein expression. Detraining did not alter exercise-induced reduction in gp91^phox levels in the PVN of AngII-infused animals; whereas, it partially abolished exercise-mediated reduction in iNOS levels.Values are mean±SE. n = 9 per group for mRNA and n = 6 per group for protein analysis. *p<0.05 Sal+Sed versus AngII+Sed; ^#p<0.05 AngII+Sed versus AngII+Ex and AngII+Sed versus AngII+Det; ^@p<0.05 AngII+Ex versus AngII+Det; ^$AngII+Sed versus AngII+Det.

Figure 6. Effects of exercise on Cu/ZnSOD in the PVN of normotensive and hypertensive rats.

Densitometric analysis of protein expression (upper panel) and a representative Western blot (lower panel) showed that detraining completely abolished exercise-mediated increase in Cu/ZnSOD levels.Values are mean±SE. n = 6 per group. *p<0.05 Sal+Sed versus AngII+Sed; ^#p<0.05 AngII+Sed versus AngII+Ex and AngII+Sed versus AngII+Det; ^@p<0.05 AngII+Ex versus AngII+Det; ^$AngII+Sed versus AngII+Det.

Figure 7. A schematic depicting the proposed pathways of effects of exercise training and detraining on AngII-induced hypertensive response.

Lines with arrow represent ‘activation’ and lines with no arrow represent ‘inhibition’. It has become clear from the past several years of research that an increased production of PICs in response to overactivated RAS within the cardiovascular regulatory centers of the brain (such as paraventricular nucleus) causes increased sympathetic outflow leading to increased arterial pressure and cardiac remodeling in experimental models of hypertension. At the cellular level, PICs activate reactive oxygen species which in turn can activate various intracellular signaling pathways, including that of NFκB. Activation of NFκB induces gene transcription of PICs fostering a positive feedback mechanism, and eventually leading to the progression of hypertension. A growing body of evidence suggests that the beneficial effects of exercise in hypertension could be attributed to reduced PICs, improved cellular redox homeostasis, and downregulation of NFκB activity. A step further, in the present study, we demonstrated that transient cessation of exercise (2 weeks of detraining) abolishes the exercise-induced improvements in cardiac hypertrophy, cardiac function, anti-inflammatory cytokine (IL-10) and oxidative stress in the PVN of hypertensive rats, although, positive effects in MAP and PICs remains unchanged. Further studies are still warranted to unravel the effects of exercise and detraining on other components of the AngII-induced signaling pathway such as downstream transcription factors and sympathetic activity.