Antagonism of a specific dopaminergic receptor agonist with metoclopramide in horses.

The study aims to investigate the effects of fenoldopam, a dopaminergic receptor agonist, and metoclopramide, a dopaminergic receptor antagonist, on cecal arterial blood flow and carotid arterial pressure in horses, concluding that dopaminergic receptors mediate alterations in local blood flow and systemic pressure.

Research Methods

• The research was conducted on 7 healthy horses. Horses were selected as the subject of research due to their significant physiological differences compared to small animals.
• Fenoldopam was administered nasogastrically at dosages of 3, 6, and 9 mg/kg. These dosages were chosen to analyse changes in lateral cecal arterial blood flow, mean internal carotid arterial pressure, and heart rate with different amounts of the drug.
• To study the antagonistic effects, metoclopramide was infused intravenously at a rate of 0.125 mg/kg/h. This established the ability of metoclopramide to block fenoldopam’s effects on arterial blood flow and pressure.

Results

• Fenoldopam caused a significant increase in cecal arterial blood flow within 30 minutes of administration at all dosages. The peak increases ranged from 120 to 153 ml/min, compared to a baseline flow of approximately 68 ml/min.
• Carotid arterial pressure saw no significant changes after administering fenoldopam at a dosage of 3 mg/kg. However, higher dosages (6 and 9 mg/kg) significantly reduced the pressure. The constant administration of fenoldopam decreased carotid arterial pressure from 113 to between 81 and 88 mm of Hg.
• The intravenous infusion of metoclopramide successfully blocked the impact of fenoldopam on cecal arterial blood flow and carotid arterial pressure. Thus, showing its antagonistic properties towards the receptor.

Conclusions

• The results of the study lead to the conclusion that dopaminergic receptors play a role in mediating alterations in local blood flow and systemic pressure in horses.
• This information might have implications in understanding the basis of various treatments involving dopaminergic receptors and could potentially influence the development of new therapeutic strategies in veterinary medicine.