Reactivity of equine palmar digital arteries and veins to vasodilating agents.

The study investigates how different vasodilating agents react with palmar digital arteries and veins from healthy horses. The results highlight that effectiveness of these agents varies based on the origin of the initial arterial or venous constriction.

Methods and Procedure

• The researchers obtained palmar digital arteries and veins from healthy horses. These horses were under general anesthesia and the arteries and veins were removed surgically.
• The obtained vessels were sectioned into 4 mm vascular rings.
• These vascular rings were suspended in tissue baths and linked to force displacement transducers to enable continuous recording of vascular tension.
• In vitro vascular responses to several vasodilators were studied, including acetylcholine, acepromazine, isoxsuprine hydrochloride (isoxsuprine), prostaglandin E2 (PGE2), and prostaglandin I2 (prostacyclin).

Experiment Process

• The arteries and veins were first preconstricted with norepinephrine hydrochloride (norepinephrine), or prostaglandin F2 alpha (PGF2 alpha).
• Following this, these vessels were exposed to each vasodilator under study.
• For each drug, the concentrations producing 50% maximum relaxation (EC50) and the maximum percentage of relaxation were ascertained.

Results of the Study

• Acetylcholine emerged as the most potent arterial vasodilator as it required the smallest EC50 value to achieve efficacy.
• PGE2 was the least potent arterial vasodilator.
• Among all the studied vasodilators, prostacyclin was found to be the least potent venodilator.
• While acepromazine, isoxsuprine, and PGE2 presented no significant differences in their effects, isoxsuprine was able to produce greater arterial relaxation than any other agent.
• Both isoxsuprine and acepromazine caused significantly greater venous relaxation than acetylcholine and PGE2.
• Prostacyclin resulted in minimal vasodilation of arteries or veins.
• It was observed that acepromazine and isoxsuprine relaxed the veins more than the arteries.
• The use of PGF2 alpha for preconstriction instead of norepinephrine led to a significant decrease in the potency and effectiveness of acepromazine and isoxsuprine in producing vasodilation.

The conclusion drawn from these results is that acepromazine and isoxsuprine are able to relax the equine digital vasculature, but their effectiveness is contingent on the source of the constriction.