In-vitro and in-vivo use of vasoactive agents in characterising aortic stiffness in rats: testing the assumptions

Background: Arterial properties are studied in-vitro and in-vivo in rodents using vasoactive agents. In-vitro aortic ring experiments show a 1-2 fold change in active smooth muscle tension while the in-vivo use of the same agents assumes a singular action at the periphery, with minimal affect on aortic smooth muscle tension. This study investigates the validity of this assumption.

Methods: Arterial stiffness was measured as pulse wave velocity (PWV) in anaesthetised (urethane) Sprague Dawley rats (12 weeks, n=6) using 1.6F pressure catheters. Sodium nitroprusside (SNP) and phenylephrine, (30 microg/kg/min i.v), lowered and raised mean arterial pressure (MAP). Partial occlusion of the inferior vena cava reduced venous return to lower pressure passively for comparison to the MAP range achieved with SNP. This was repeated during continuous infusion of phenylephrine to assess effect of phenylephrine on the aorta

Results: No significant difference was found in arterial stiffness achieved with the vasoactive agents or with the venous occlusion methods of blood pressure manipulation. For MAP range 60–90 mmHg, PWV for SNP did not differ from PWV for venous occlusion (4.05±0.55 m/s, 4.05±0.51 m/s, p=0.99). For MAP 120–150 mmHg, PWV for phenylephrine did not differ from PWV with concurrent venous occlusion (6.37±0.87 m/s, 6.71±0.72 m/s, p=0.62).

Conclusions: The results indicate the concentration of SNP and phenylephrine infused did not significantly affect aortic smooth muscle in-vivo and all pressure dependent changes in PWV were mediated through effects on total peripheral resistance and not via active effects on the smooth muscle in the aortic wall.