Role of endothelium and nitric oxide in the in vitro response of equine colonic venous rings to vasoconstrictor agents.

The research article investigates how the veins from horse colons respond in-vitro to various substances that cause veins to narrow, with a focus on whether endothelium presence or treatment with a certain chemical (L-NAME) changes these responses.

Methodology

• The study was conducted on colonic veins collected from 8 adult horses.
• The veins were cut into small rings, placed in warm baths and tension force was applied to them. Rings were left to equilibrate for 45 minutes.
• The bath solution was replenished and tension reapplied at intervals of 15 minutes.
• Responses to cumulative concentrations (10(-8) to 10(-4) M) of each vasoconstrictor agent were determined for each vein ring.
• Three different groups of vein rings were evaluated: veins with the endothelium intact, veins with the endothelium stripped away (denuded), and veins treated with N omega-nitro-L-arginine methyl ester (L-NAME, a nitric oxide synthase inhibitor).

Results

• The study found that the sensitivity of colonic veins varied between the different vasoconstrictor agents used.
• The relative sensitivity was greatest for Angiotensin II and least for Vasopressin.
• Responses to Histamine, 5-Hydoxytryptamine and Norepinephrine were significantly greater than responses to Angiotensin II, Prostaglandin F2 alpha, Thromboxane B2 analogue and Vasopressin.
• Veins either with the endothelium stripped away or treated with L-NAME experienced higher maximal contractile responses than veins with the endothelium intact.

Conclusions

• The responses of colonic veins to vasoconstrictor agents were noticeably different; however, the sensitivity of these veins was not influenced by the presence of endothelium or by treatment with L-NAME.
• Veins with intact endothelium had higher responses than those where the endothelium had been removed or treated with L-NAME.
• Changes to the colonic veins that mimic conditions often seen in pathological enlargement of a horse’s colon, can influence blood flow, cause edema, and alter vascular responses to low blood volume and toxins in the blood.