Date of Award

2001

Document Type

Thesis

Publisher

Edith Cowan University

Degree Name

Bachelor of Science Honours

Faculty

Faculty of Communications, Health and Science

First Supervisor

Dr Angus Stewart

Second Supervisor

Dr Peter Roberts

Abstract

Investigating the causes of ageing on the myocardium is especially important for the future health of Australia's ageing population, which is increasing due to increased life expectancy (AIHW, 1999). Cardiovascular disease is currently Australia's greatest health problem ( AIHW, 1999), and since the aged population is most commonly affected by this disease (HSVD, 1999), investigating the causes of ageing of the myocardium and the predisposing factors of cardiovascular disease is important for the future health of Australia's ageing population. In this study, male and female Wistar rats [young (11 = 8, aged 12-30 weeks old), middle aged (11 = 6, 1-1.5 years old) and senescent (11 = 7, 2-2.5 years old)] had cardiac tissue removed for contractile, histological and morphometric analysis. The data derived from the contractile investigations comparing young, middle-aged and senescent rats, do not demonstrate any major differences across the age spectrum. For the contractile analysis, mitochondria were inactivated and an exogenous energy supply was used. The results showed that the cardiomyocytes are able to develop the same levels of force regardless of age, suggesting that it is the mitochondria that exert an influence on ageing cardiomyocyte contractile function. Statistical analysis of one contractile parameter (pSr10, the pSr that produces 10% of maximum activated force) yielded a significant (P < 0.05) difference between young and middle-aged rats, and young and senescent rats. It was speculated that these results might reflect a developmental change in the Troponin C (TnC) protein that may only occur early in life ie. between young and middle-age in the rat. During the histological and morphometric analyses, significant (P < 0.05) changes were observed in the volume of mitochondria, cytoplasm and 'other' structures, in both sides of the heart, when comparing young, middle-aged and senescent rats. In the left side of the heart the volume of mitochondria significantly (P < 0.05) decreased whilst the volume of cytoplasm significantly (P < 0.05) increased with age. This provides further evidence of the influence of mitochondria on the functioning of the ageing heart. In the right side of the heart, the volume of mitochondria significantly decreased between young and middle-aged rats, then significantly (P < 0.05) increased between middle-aged and senescent rats. The volume of cytoplasm significantly (P < 0.05) increased between young and middle-aged rats whilst the volume of 'other' structures ie. connective tissue, vascular and interstitial space, significantly (P < 0.05) decreased between middle-aged and senescent rats. The knowledge gained from the current investigation will further the information already available on the effects of ageing on the myocardium. The results will be discussed in terms of human myocardial ageing.

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