• horse;
  • laminitis;
  • microvessels;
  • laminar;
  • black walnut


Reasons for performing study: Equine laminitis purportedly involves haemodynamic dysfunction at the level of the laminar vasculature. However, to date, no studies have been performed characterising the function of laminar arteries and veins during the prodromal stages of equine laminitis.

Hypothesis: That the prodromal stages of laminitis are associated with contractile dysfunction of the equine laminar vasculature.

Objective: To assess contractile function of laminar arteries and veins to phenylephrine (PE) and 5-hydroxytryptamine (5-HT).

Methods: Horses were administered black walnut heartwood extract (BWHE) or water (control horses) via nasogastric intubation. After euthanasia, laminar vessels (100–800 μm internal diameter) were isolated and mounted on small vessel myographs to assess contractile function.

Results: Contractile responses to PE or 5-HT were identical in laminar arteries isolated from either control horses or those administered BWHE. In contrast, responses to PE or 5-HT were significantly reduced in laminar veins isolated from BWHE-administered horses when compared with laminar veins isolated from control horses.

Conclusions and potential relevance: These results are consistent with the prodromal stages of laminitis being associated with selective dysfunction of laminar veins. Further studies are required to discern the precise nature of this dysfunction and its potential relevance to the pathogenesis of acute laminitis in the horse and possible therapeutic targets for treatment.