title: Seasonal variation in maintenance of phenylephrine-induced tone in isolated equine digital arteries under hypoxic or hyperoxic conditions in vitro.
abstract: Digital vasoconstriction, ischaemia and hypoxia may predispose to acute laminitis. Laminitis incidence varies seasonally, peaking in spring and summer. Direct seasonal influences on equine digital artery (EDA) contractility have not been investigated. This study assessed seasonal variation in maintenance of phenylephrine (PHE)-induced tone in isolated EDAs under hypoxic (95% nitrogen) and hyperoxic (95% oxygen) conditions. The objective was to measure change in arterial tone over time after constriction to a plateau with PHE. Tone was measured at plateau and over time and percentage change calculated. Hyperoxic EDAs maintained PHE-induced tone over 1 h with no seasonal variation. Hypoxic EDAs relaxed in fall (median [inter-quartile range] 59% [44-77%] decrease from plateau; P=0.008), contracted in spring (65% [20-192%] increase from plateau; P=0.03) and did not significantly change tone in winter (18% [0-28%] decrease; P=0.13). Continued contraction under hypoxic conditions in spring may contribute to digital vasoconstriction.
authors: Royal Veterinary College, Hawkshead Lane, North Mymms, Hatfield, Hertfordshire AL9 7TA, United Kingdom. kborer@rvc.ac.uk
authors: K E
authors: KE
authors: Borer-Weir
authors: S R
authors: SR
authors: Bailey
authors: P A
authors: PA
authors: Harris
authors: N J
authors: NJ
authors: Menzies-Gow
authors: J
authors: J
authors: Elliott
mesh_terms: D000818:Animals; D001158:Arteries / Q000187:drug effects / Q000503:physiopathology*; D006724:Hoof and Claw / Q000098:blood supply* / Q000187:drug effects / Q000502:physiology; D006736:Horses; D018496:Hyperoxia / Q000503:physiopathology / Q000662:veterinary; D000860:Hypoxia / Q000503:physiopathology / Q000662:veterinary; D066298:In Vitro Techniques; D010656:Phenylephrine / Q000494:pharmacology*; D012621:Seasons; D014661:Vasoconstriction / Q000187:drug effects / Q000502:physiology; D014662:Vasoconstrictor Agents / Q000494:pharmacology*
chemical_list: D014662:Vasoconstrictor Agents; D010656:Phenylephrine