Hemodynamic responses of the equine digit to intravenous and digital arterial infusion of dopamine.

This study investigates the impact of dopamine infusion on the blood flow dynamics (hemodynamic responses) of a horse’s digit (hoof). The main findings were that systemic dopamine infusion did not affect digital hemodynamics, but local infusion into the digital artery resulted in increased arterial pressure, digital vascular resistance, and capillary resistance ratio. These effects were mitigated by the use of phentolamine, a vasodilator.

Research Method

• The research involved six adult horses, each of whom was anesthetized using pentobarbital.
• An isolated extracorporeal pump was used to maintain a constant blood flow in the digit at a rate unaffected by systemic changes.
• The study was divided into three experiments, which were each carried out in sequence on every horse.

Experiment Details

• In the first experiment, dopamine was infused intravenously at rates of 1.0, 2.5, and 5.0 micrograms per kg per minute.
• The second experiment involved the digital arterial infusion of dopamine at concentrations of 0.07, 0.7, and 1.2 ml/min.
• In the third experiment, an intra-arterial infusion of phentolamine was administered for five minutes before continuing with a dopamine infusion.
• For all experiments, measurements were taken of digital venous, arterial, and capillary pressures, total digital vascular resistance, and the precapillary to postcapillary resistance ratio.

Results

• Systemic infusion of dopamine did not elicit changes in the horse’s digital hemodynamics.
• Digital arterial infusion of dopamine led to a dose-dependent increase in arterial pressure and total digital vascular resistance.
• A rise in the precapillary to postcapillary resistance ratio was also observed when dopamine was infused into the digital artery.
• The vasoconstrictive response triggered by the intra-arterial infusion of dopamine was moderated by the phentolamine.

Conclusions

• The study indicated that while systemic infusion of dopamine did not impact the hemodynamics of the equine digit, direct infusion into the digital artery led to significant changes.
• Increased arterial pressure and vascular resistance were seen following digital arterial infusion of dopamine, suggesting a vasoconstrictive response in the digit.
• A specific ratio (pre- to post-capillary resistance) also increased with the infusion, further indicating a change in blood flow dynamics.
• The introduction of phentolamine seemed to counteract the effects of dopamine, suggesting it could be used to control these reactions.