In vitro responses of equine colonic arterial and venous rings to adenosine triphosphate.

This study investigates the influence of Adenosine Triphosphate (ATP) on the vasomotor tone of equine colonic vasculature. The findings suggest ATP induces a biphasic response in equine colonic arterial and venous rings, and may be a useful treatment for modulating colonic vasomotor tone in horses with specific conditions.

Research Methodology

• Arteries and veins were taken from the left ventral colon of 14 mixed-breed horses, with none having prior cardiovascular or gastrointestinal tract disease.
• These arterial and venous rings were then precontracted with specific measures of ‘endothelin-1’.
• The vascular rings went through 2 different conditions – remaining endothelium-intact, and becoming endothelium-denuded.
• One group of endothelium-intact rings were also treated with a compound ‘N omega-nitro-L-arginine methyl ester’, known as L-NAME, which inhibits nitric oxide production.
• Adenosine triphosphate was added at various concentrations and their effects were observed, generating relaxation percentage versus time curves.
• The “areas under the curves” were calculated, signifying the percentage of relaxation time.

Key Findings

• Both arterial and venous rings’ relaxation response to ATP was dose-dependent, meaning that higher ATP concentrations resulted in a stronger response.
• Relaxation time in response to certain concentrations of ATP was significantly greater than for rings not treated with ATP.
• When the endothelium (a thin membrane that lines the inside of the heart and blood vessels) was removed, the relaxation response declined slightly but was not entirely eliminated.
• L-NAME did not attenuate the relaxation response in arteries, indicating that nitric oxide production is not responsible for the observed relaxation response.
• Interestingly, ATP seemed to induce a ‘biphasic’ vascular response at higher concentrations. This convoys an initial contraction, followed by a slow and long-term relaxation.
• This research coincidentally supports the possibility of a novel medication to modulate the colonic vasomotor tone in horses with conditions like strangulating volvulus of the ascending colon by using ATP.

Conclusion

• This research reveals that ATP has a significant vasorelaxation effect on equine colonic arterial and venous rings, presenting a potential treatment for horses affected by certain colonic disorders.
• The observed response is unique, characterized by an initial contraction followed by a slow and persistent relaxation which is possibly mediated by a mechanism different from the production of nitric oxide.