HYPERTENSIVE EFFECTS OF METHOXAMINE ON ARTERIAL MECHANICS IN RATS - ANALYSIS BASED ON EXPONENTIALLY TAPERED T-TUBE MODEL

Methoxamine, a specific alpha(1)-selective adrenoceptor agonist, has p roven to be useful in the treatment of hypotension, especially hypoten sion due to failure of the sympathetic nervous system. This study is t o explore the vascular dynamic response to methoxamine in Wistar-Kyoto rats, based on the exponentially tapered T-tube model. The pulsatile aortic pressure and Row signals before and after the administration of methoxamine (0.025 mg/kg) were measured by a high-fidelity pressure s ensor and electromagnetic flow probe, respectively. Hemodynamic parame ters, such as aortic characteristic impedance, wave transit time, and arterial load compliance, were inferred from the aortic pressure and f low signals to describe the pulsatile nature of blood flow in the vasc ulature. The hypertensive effects of methoxamine on the static compone nts of ventricular afterload were characterized by (1) little change i n 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, suggesti ng that the distensibility of the aorta was not altered in rats after the administration of methoxamine. In contrast, there was a significan t drop in arterial load compliance mainly due to the elevated arterial blood pressure in methoxamine-treated rats. In conclusion, methoxamin e at the dose of 0.025 mg/kg has a greater effect on peripheral resist ance vessels than on Winkessel vessels in the rat systemic circulation . (C) 1998 Elsevier Science B.V. All rights reserved.