Exercise- and hypertension-induced collagen changes are related to left ventricular function in rat hearts

Abstract

Chronic hypertension, known to affect the collagen profile of the heart, and exercise result in impaired or improved heart function, respectively. Collagen types I [alpha 1(I)2 and alpha 2(I)] and III [alpha 1(III)3] are the predominant interstitial collagens thought to influence cardiac function, and the ratio of type III to I (collagen III/I) is thought to be a significant factor in the altered relaxation observed in hypertrophy. The present study tested the hypothesis that the myocardial structure and function are different in chronically exercise-trained vs. hypertensive rat hearts. Male rats were either chronically exercised (XTr) or submitted to experimental hypertension by coarctation of the abdominal aorta (Hyp) for 10 wks. Heart rate, blood pressure, and maximal rate of fall of the left ventricular pressure (-dp/dt) were recorded during isoproterenol stimulation. Results showed that both Hyp and XTr had higher heart weight and left ventricular weight-to-body weight ratios (P < 0.05). Mean arterial pressure (MAP) was higher in Hyp and lower in XTr (P < 0.05), whereas (-dP/dt)/MAP was diminished in Hyp but enhanced in XTr. Left ventricular collagen was higher in Hyp than XTr, whereas collagen III/I was reduced in Hyp compared with XTr (P < 0.05). Scanning and transmission electron microscopy also supported an accumulation of left ventricular collagen in Hyp compared with XTr. A negative correlation was observed between collagen III/I and (-dP/dt)/ MAP (r = -0.91; P < 0.05). These results suggest an important relationship between adaptations in left ventricular collagen and the changes in diastolic function observed in both chronic hypertension and exercise cardiac stress.

Reduced cardiac stiffness following exercise is associated with preserved myocardial collagen characteristics in the rat

“…Conversely, attenuation of end-diastolic stiness has been associated with a reduction in myocardial collagen content and cross-linking (Bing et al 1978;Kato et al 1995). With regard to exercise-induced alterations in cardiac diastolic function, only one study has investigated the potential contribution of alterations in the properties of myocardial collagen towards changes in LV diastolic performance (Burgess et al 1996). Contrary to our results, the latter authors concluded that a relationship exists between adaptations in LV collagen and changes in diastolic performance following an exercise training programme.…”

“…However, the goal of the latter study was to examine the eects of physical stress on myocardial collagen. Hence, an intensive treadmill running regimen (3 h Á day À1 Y 7 days Á week À1 ), as opposed to a regular 1 h Á day À1 , 5 days Á week À1 programme, utilised by others (Burgess et al 1996;Thomas et al 1992) and by ourselves, was employed by Bartosova et al (1969). Our data con®rm the inability of moderate habitual exercise, commenced in young rats, to aect collagen concentrations in the LV.…”

“…Both running training (Burgess et al 1996) and swimming training (Medugorac and Jacob 1983) are unable to alter myocardial collagen types I/III. Similarly, many studies demonstrate that myocardial collagen concentrations remain unchanged following exercise programmes (Burgess et al 1996;Kiiskinen and Heikkinen 1976;Medugorac 1980;Takala et al 1991;Tomanek et al 1972). In contrast, Hickson et al (1979) and Masumura et al (1983) showed that a decrease in myocardial total hydroxyproline concentration occurs following an exercise programme.…”

“…Contrary to our results, the latter authors concluded that a relationship exists between adaptations in LV collagen and changes in diastolic performance following an exercise training programme. However, a negative correlation between the ratio of collagen phenotypes III to I (III/I) and an index of diastolic function was observed in the absence of any dierences in collagen types III/I in the exercised rats (Burgess et al 1996). Also, although the index of diastolic function used by these authors was potentially corrected for afterload dierences Àd adt Á MAP À1 , no attempt was made to correct for dierences in heart rate and Àd adt is a heart-rate-dependent measure of cardiac performance.…”

Physical Exercise, Aortic Blood Pressure, and Aortic Wall Elasticity and Composition in Rats

“…Some authors have reported an increase in cardiac or left ventricular mass, or both, relative to body weight after physical training. 25,26 This has not been confirmed by others. 24 It has been suggested that this may be due to a substantial decrease in body weight with relatively little change in cardiac mass.…”