Cardiovascular effects of dopexamine HCl in conscious and halothane-anaesthetised horses.

The study investigates the cardiovascular effects of dopexamine HCl on conscious and halothane-anaesthetised horses, finding potential benefits for its use in treating low cardiac output states.

Methodology of the Study

• The study involved an evaluation of the cardiovascular effects of gradually increasing infusions of dopexamine HCl on horses. This was investigated in two test groups consisting of six conscious horses and eight halothane-anesthetised horses.
• The conscious horses were given 1, 2, 4, 6, 10 micrograms/kg body weight (bwt) of dopexamine per minute, while the anaesthetised ones were given dosages of 0.5, 1, 5, 10, 20 micrograms/kg bwt/min.

Findings of the Study

• Dopexamine led to dose-dependent increases in heart rate, +dP/dtmax’ -dP/dtmax (which are indicators of the rate of pressure change in the ventricles) and the cardiac output (the volume of blood pumped by the heart per minute).
• It also resulted in a decrease in systemic vascular resistance (resistance that the heart must overcome to pump blood through the body’s circulatory system) in both the test groups. This implies that dopexamine acts by dilating blood vessels, thus decreasing the pressure or resistance the heart experiences while pumping blood.
• Mean arterial blood pressure remained constant in conscious horses but increased to a peak at a dosage of 10 micrograms/kg bwt/min in halothane-anesthetised horses. After reaching this peak, the median arterial blood flow decreased.
• The drug produced ventricular arrhythmias (irregular heartbeats originating from the lower chambers of the heart) in two conscious horses at the dosage of 10 micrograms/kg bwt/min. However, in anaesthetised horses, no cardiac arrhythmias other than sinus tachycardia (a fast, but regular, heartbeat) were observed.
• Administration of propranolol, a beta-blocker that affects the heart and circulation, combated the cardiac effects of dopexamine HCl at a dosage of 5 and 10 micrograms/kg bwt/min in anaesthetised horses, suggesting that these effects are through the stimulation of beta-adrenoceptors.

Implications of the Findings

• The results from this study suggest that dopexamine HCl may offer particular advantages over dopamine and dobutamine for treating conditions associated with low cardiac output in horses. This could be due to the way it affects heart rate, systemic vascular resistance and cardiac output.
• Further research is needed to fully understand the scope of these findings, the mechanisms involved, and their applications in the veterinary field.