Effects of moderate-continuous and high-intensity interval aerobic training on cardiac function of spontaneously hypertensive rats

Abstract

The aim of this study was to verify the effects of moderate-intensity continuous (MICT) and high-intensity interval (HIIT) aerobic training on cardiac morphology and function and the mechanical properties of single cardiomyocytes in spontaneously hypertensive rats (SHR) in the compensated phase of hypertension. Sixteen-week-old male SHR and normotensive Wistar (WIS) rats were allocated to six groups of six animals each: SHR CONT or WIS CONT (control); SHR MICT or WIS MICT (underwent MICT, 30 min/day, five days per week for eight weeks); and SHR HIIT or WIS HIIT (underwent HIIT, 30 min/day, five days per week for eight weeks). Total exercise time until fatigue and maximum running speed were determined using a maximal running test before and after the experimental period. Systolic (SAP), diastolic (DAP), and mean (MAP) blood pressures were measured using tail plethysmography before and after the experimental period. Echocardiographic evaluations were performed at the end of the experimental period. The rats were euthanized after in vivo assessments, and left ventricular myocytes were isolated to evaluate global intracellular Ca²⁺ transient ([Ca²⁺]_i) and contractile function. Cellular measurements were performed at basal temperature (~37°C) at 3, 5, and 7 Hz. The results showed that both training programs increased total exercise time until fatigue and, consequently, maximum running speed. In hypertensive rats, MICT decreased SAP, DAP, MAP, interventricular septal thickness during systole and diastole, and the contraction amplitude at 5 Hz. HIIT increased heart weight and left ventricular wall thickness during systole and diastole and reduced SAP, MAP, and the time to peak [Ca²⁺]_i at all pacing frequencies. In conclusion, both aerobic training protocols promoted beneficial adaptations to cardiac morphology, function, and mechanical properties of single cardiomyocytes in SHR.

Keywords: Cardiomyocytes; aerobic training; calcium transient; cardiac function; hypertension; spontaneously hypertensive rats.

Figure 1.

Intracellular calcium transient in single left ventricular myocytes. (A) Amplitude. (B) Time to peak (ms). (C) Time to 50% decay (ms). Data are mean ± SEM of six animals in each group. WIS CONT, normotensive control rats. WIS MICT, normotensive rats that performed MICT. WIS HIIT, normotensive rats that performed HIIT. SHR CONT, hypertensive control rats. SHR MICT, hypertensive rats that performed MICT. SHR HIIT, hypertensive rats that performed HIIT. ANOVA (P < 0.05): ^aversus WIS CONT; ^bversus WIS MICT; ^cversus WIS HIIT; ^dversus SHR CONT. (A color version of this figure is available in the online journal.)

Figure 2.

Contractility in single left ventricular myocytes. (A) Shortening (% r.c.l.: percentage of resting cell length). (B) Time to peak (ms). (C) Time to 50% relaxation (ms). Data are mean ± SEM of 6 animals in each group. WIS CONT, normotensive control rats. WIS MICT, normotensive rats that performed MICT. WIS HIIT, normotensive rats that performed HIIT. SHR CONT, hypertensive control rats. SHR MICT, hypertensive rats that performed MICT. SHR HIIT, hypertensive rats that performed HIIT. ANOVA (P < 0.05): ^aSHR CONT versus WIS CONT; ^bSHR MICT versus WIS MICT; ^cSHR HIIT versus WIS HIIT; ^dWIS CONT versus WIS MICT; ^eSHR MICT versus SHR CONT and SHR HIIT; ^fWIS CON versus WIS HIIT. (A color version of this figure is available in the online journal.)