Effects of fenoldopam on cecal blood flow and mechanical activity in horses.

This research investigates the impact of the drug fenoldopam on blood flow and mechanical activity in certain areas of the horses’ gastrointestinal tract. The study suggests that dopaminergic-1 receptors are present in the colonic vasculature of horses but not in certain areas of smooth muscle in their lower gut.

Overview of Research and Methodology

• The study was conducted on six healthy horses with observations made over three periods — during fenoldopam (or saline for control) infusion, 60 minutes into infusion, and 120 minutes after infusion.
• The subjects’ lateral cecal arterial blood flow, carotid arterial pressure, heart rate, and mechanical activity in the duodenum, right ventral colon, cecal body, and cecal apex were monitored throughout.
• Fenoldopam was introduced via intravenous infusion to the horses at dosages of 0.01, 0.05, and 0.1 micrograms/kg/min. A control group received a 0.9% NaCl (saline) solution.

Key Findings

• With the 0.9% saline solution, no significant changes in blood flow, pressure, heart rate, or mechanical activity were noted.
• Fenoldopam, a dopamine-1 receptor agonist, showed differentiated effects based on the dosage given.
• At a dosage of 0.01 micrograms/kg/min, fenoldopam significantly increased heart rate but had no significant effects on arterial pressures or blood flow.
• At dosages of 0.05 and 0.1 micrograms/kg/min, fenoldopam not only increased heart rate but also resulted in a significant decrease in carotid arterial pressure and an increase in lateral cecal arterial blood flow.
• Fenoldopam did not have any significant effect on mechanical activity measured in various parts of the horse’s gastrointestinal tract, regardless of the dosage.

Conclusions

• The research suggests that dopaminergic-1 receptors are present on colonic vasculature in horses, indicated by the altered blood flow and pressure responses to fenoldopam.
• However, the absence of any significant changes in mechanical activity in certain areas of the intestine even with fenoldopam administration suggests that there may not be dopaminergic-1 receptors on the visceral smooth muscle in those regions of the horses’ gastrointestinal tract.