Proceedings of The Physiological Society

Europhysiology 2018 (London, UK) (2018) Proc Physiol Soc 41, PCA352

Poster Communications

The effects of ageing on the biomechanical properties of the rat middle cerebral artery

F. G. Ewbank1, C. Torrens1

1. Human Development & Physiology, Faculty of Medicine, University of Southampton, Southampton, United Kingdom.

Ageing has a well characterised impact on systemic arteries, including remodelling and increasing arterial stiffness. However, cerebral vasculature has a number of unique properties making it structurally and functionally distinct from systemic arteries. With these in mind, it is likely that cerebral arteries have a distinctive ageing process. While the age-related properties of large systemic elastic arteries have been well characterised, the effects of ageing on the biomechanical properties of resistance- sized cerebral arteries has been relatively overlooked. These biomechanical properties have important implications for cerebral autoregulation, as well as the perivascular drainage of extracellular solutes. The aim of this study was to assess the effects of ageing on the structure and biomechanical properties of the rat middle cerebral artery. Male Wistar rats aged between 14-16 weeks (young) and 56-58 weeks (old) were euthanised by CO2 inhalation and cervical dislocation. Middle cerebral arteries were dissected and mounted on a wire myograph, bathed in PSS at 37°C and continually gassed with 95% O2 and 5% CO2 (n=5 per group). Passive properties were assessed by incremental stretches of 0.05 mm every 2 minutes. For each incremental stretch, the peak force and plateau force were measured. In a subgroup, additional segments were fixed in formalin and stained using Miller's method for elastin and collagen (n=4 per group). Wall thickness and composition were analysed using ImageJ software. Biomechanical relationships were assessed by two-way ANOVA, while histological data was assessed by independent sample t-test with significance accepted as p<0.05. Arteries from old rats showed a significant reduction in the tension generated in response to stretch compared with arteries from young rats (p<0.05). This was true whether measured at the peak or plateau of the tension- length curve. This equated to a reduced Youngs modulus in the arteries from old rats (p<0.01). However, there was no significant difference in arterial compliance or internal circumference measured at 100 mmHg (p>0.05). Histological analysis showed that wall thickness and elastin: collagen ratio were similar between the two age groups (p>0.05). Large systemic arteries have been shown to demonstrate an age-related increase in arterial stiffness, as well as changes in arterial structure and composition. However, this data suggests that this is not the case for cerebral arteries. Instead, cerebral arteries become less stiff with age and produce no obvious change in composition or structure. These findings have important implications for the autoregulatory maintenance of cerebral blood flow in the aged brain. Moreover, this data may influence our current understanding of many cerebrovascular conditions, including Alzheimer's disease and aneurysm.

Where applicable, experiments conform with Society ethical requirements