Sympathetically mediated age related changes in abdominal aortic stiffness parameters in the rat

Background: Increased sympathetic activity is known as a driving factor behind increased blood pressure with age in spontaneously hypertensive rats (SHR). We have previously shown that sympathetic activity changes aortic stiffness. However, whether the increased sympathetic activity with age in the SHR invokes changes in aortic stiffness is unknown. Methods: SHR (10 weeks, n=7, 15 weeks, n=6, 20 weeks, n=5) were anaesthetized (urethane) and ventilated. Two high fidelity pressure transducers were introduced into the abdominal aorta via the carotid and femoral arteries for measurement of blood pressure and pulse wave velocity (PWV). Aortic diameters were measured via an ultrasound probe (6.2 Mhz) coupled with vessel tracking software (Art.Lab, Esaote). The recorded diameters and pulse pressures were used to calculate aortic compliance. Measurements were taken at basal blood pressure (138±3 mmHg) and again following sympathetic blockade with hexamathonium (i.v 20 mg/kg). Hexamethonium pressures were matched with basal blood pressures following a bolus of phenylephrine (i.v 0.3 ml 30 μg/ml). Results: Sympathetic blockade caused a greater change in compliance at 15 weeks (p<0.001) and 20 weeks (p<0.01) compared to the change induced at 10 weeks. There were no other significant differences between any measured changes in haemodynamic parameters with sympathetic blockade between ages. Conclusions: These data suggest that as SHR's age there is an increase in the contribution of sympathetic activity towards aortic compliance, though the effect on abdominal aortic PWV is not evident. This may be due to differential effects on aortic wall thickness and diameter changes.