Contractile responses of isolated equine digital arteries under hypoxic or hyperoxic conditions in vitro: role of reactive oxygen species and Rho kinase.

The research study investigates the triggers for equine acute laminitis, a disease in horses affecting their hooves. Using equine digital arteries (EDAs) taken from horses post-mortem, the researchers tested the effects of different oxygen levels on these arteries in organ baths, and determined that low-oxygen conditions significantly increased contraction in the arteries. They also found that the hypoxia-enhanced contraction is mediated by reactive oxygen species, produced by NAPDH oxidase, and heightened by certain inhibitors.

Study Overview

• This study was primarily focused on identifying the causes of acute laminitis in horses. The researchers particularly considered vasoconstriction, ischaemia, hypoxia and reperfusion injury as potential triggers of the disease.
• The primary approach was testing the contractile responses of isolated equine digital arteries (EDAs) — arteries found in horses’ hooves. These EDAs were sourced from horses post-mortem.
• The EDAs were tested under both high and low-oxygen conditions in organ baths for up to three hours.

Synthetic substances tested

• The EDAs were tested with several synthetic substances — Phenylephrine (PHE), 5-hydroxytryptamine (5-HT), high potassium (K+), and 9,11-dideoxy-9α,11α-epoxymethanoprostaglandin F2α (U44069).
• It was found that contraction of EDAs was notably increased when placed in low-oxygen environments, with every tested substance leading to such a result, except for U44069.
• The biggest contrast was noted in vessels with a functional endothelium, compared to those where the endothelium was removed.

Role of NADPH oxidase and Rho kinase

• Fasudil, a Rho kinase inhibitor, and apocynin, an NADPH oxidase inhibitor, were tested on EDAs. Both notably lowered low-oxygen-enhanced contracting in response to PHE and 5-HT.
• The findings suggest that the increased contraction of EDAs during hypoxia is partially facilitated by reactive oxygen species (ROS), produced by NAPDH oxidase.
• Also noted is the role of Rho kinase. When activated by the ROS, it causes an increase in calcium sensitisation which results in the enhanced contraction of smooth muscles.