Hypertensive effects of methoxamine on arterial mechanics in rats: analysis based on exponentially tapered T-tube model

Methoxamine, a specific alpha1-selective adrenoceptor agonist, has proven to be useful in the treatment of hypotension, especially hypotension due to failure of the sympathetic nervous system. This study is to explore the vascular dynamic response to methoxamine in Wistar-Kyoto rats, based on the exponentially tapered T-tube model. The pulsatile aortic pressure and flow signals before and after the administration of methoxamine (0.025 mg/kg) were measured by a high-fidelity pressure sensor and electromagnetic flow probe, respectively. Hemodynamic parameters, such as aortic characteristic impedance, wave transit time, and arterial load compliance, were inferred from the aortic pressure and flow signals to describe the pulsatile nature of blood flow in the vasculature. The hypertensive effects of methoxamine on the static components of ventricular afterload were characterized by (1) little change in cardiac output, (2) a decrease in heart rate and (3) an increase in aortic pressure and total peripheral resistance. As for the pulsatile components of ventricular afterload, no significant changes in aortic characteristic impedance and wave transit time were observed, suggesting that the distensibility of the aorta was not altered in rats after the administration of methoxamine. In contrast, there was a significant drop in arterial load compliance mainly due to the elevated arterial blood pressure in methoxamine-treated rats. In conclusion, methoxamine at the dose of 0.025 mg/kg has a greater effect on peripheral resistance vessels than on Winkessel vessels in the rat systemic circulation.