Palmar digital vessel relaxation in healthy horses and in horses given carbohydrate.
OBJECTIVE
To compare in vitro smooth muscle relaxation of palmar digital vessels from healthy horses with those from horses in the prodromal stage of experimentally (carbohydrate) induced laminitis.


METHODS
16 adult horses.


METHODS
Segments of palmar digital vessels were obtained from 5 healthy horses and 6 horses given carbohydrate. Vascular rings from the palmar digital artery and vein were suspended in individual organ baths containing buffer solution and indomethacin; isometric tension was recorded, and contraction and relaxation were compared. Smooth muscle contraction in response to cumulative addition of phenylephrine was recorded in the absence and presence of 1 microM NG-nitro-L-arginine methyl ester (L -NAME). After wash out, vascular rings were preconstricted with phenylephrine (0.3 microM), and cumulative endothelium-dependent (acetylcholine-induced) and independent (nitroprusside-induced) smooth muscle relaxations were recorded in the absence or presence of L -NAME.


RESULTS
Phenylephrine increased vascular smooth muscle tone in ring preparations of palmar digital arteries and veins. Addition of acetylcholine or nitroprusside induced relaxation of palmar digital artery and vein ring preparations. Use of L-NAME (1 microM) significantly reduced maximal relaxation induced by acetylcholine, but not by nitroprusside. Maximal relaxation induced by acetylcholine, but not by nitroprusside, was reduced in vascular rings prepared from carbohydrate-overloaded horses.


CONCLUSIONS
Reduced endothelium-dependent relaxation of palmar digital vessels may have a role in the pathophysiology of acute laminitis after carbohydrate overload in horses.
Department of Large Animal Medicine, University of Georgia, Athens 30602, USA.
D A
DA
Schneider
A H
AH
Parks
S C
SC
Eades
R L
RL
Tackett
D000109:Acetylcholine / Q000494:pharmacology; D000818:Animals; D002241:Carbohydrates / Q000009:adverse effects; D004727:Endothelium / Q000502:physiology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005260:Female; D005534:Foot Diseases / Q000139:chemically induced / Q000503:physiopathology / Q000662:veterinary; D005552:Forelimb / Q000503:physiopathology; D006724:Hoof and Claw / Q000098:blood supply*; D006734:Horse Diseases / Q000139:chemically induced / Q000503:physiopathology*; D006736:Horses; D066298:In Vitro Techniques; D007249:Inflammation / Q000139:chemically induced / Q000662:veterinary; D008297:Male; D009119:Muscle Contraction / Q000187:drug effects; D009126:Muscle Relaxation / Q000187:drug effects; D009131:Muscle, Smooth, Vascular / Q000503:physiopathology*; D019331:NG-Nitroarginine Methyl Ester / Q000494:pharmacology; D009599:Nitroprusside / Q000494:pharmacology; D010656:Phenylephrine / Q000494:pharmacology; D011897:Random Allocation; D017695:Soft Tissue Injuries / Q000503:physiopathology / Q000662:veterinary*; D014662:Vasoconstrictor Agents / Q000494:pharmacology; D014665:Vasodilator Agents / Q000494:pharmacology
D002241:Carbohydrates; D004791:Enzyme Inhibitors; D014662:Vasoconstrictor Agents; D014665:Vasodilator Agents; D009599:Nitroprusside; D010656:Phenylephrine; D000109:Acetylcholine; D019331:NG-Nitroarginine Methyl Ester