In vitro response of large colon arterial and venous rings to vasodilating drugs in horses.
OBJECTIVE
To determine in vitro vasomotor response of equine large colon arterial and venous rings with and without endothelium to vasodilator drugs, including dopamine (DOP), dopexamine (DPX), acepromazine (ACE), isoxsuprine (ISX), and nifedipine (NFP).


METHODS
7 adult horses.


METHODS
Relaxation of large colon arteries and veins in response to vasodilating drugs was determined by measuring the change in tension of vessel rings when exposed to a cumulative concentration range (10(-8) to 10(-4)M) of each drug. Vessel rings, with and without endothelium, were mounted in organ baths, attached to a transducer, and contracted with norepinephrine (NE). Cumulative concentration-response relationships, percentage maximal relaxation, and EC50 (concentration of drug required to relax the NE-induced contracted tissue to 50% of its contracted state) values were calculated.


RESULTS
There were significant differences among drugs for EC50 (ACE = ISX < NFP) and percentage maximal relaxation (ACE = ISX > NFP = DPX > DOP) values in veins. Endothelium removal from veins had no significant effect. There were no differences in EC50 values for arteries; however, percentage maximal relaxation was significantly different among drugs (ACE = ISX = NFP > DPX = DOP). Endothelial removal resulted in higher EC50 and lower percentage maximal relaxation values, compared with endothelium-intact arteries.


CONCLUSIONS
ACE and ISX were the most potent and efficacious drugs evaluated and could potentially be used to improve blood flow after correction of large-colon volvulus. Dopamine cannot be recommended because of its biphasic response and potential to further decrease blood flow. Endothelium removal altered the vasodilatory responses of colonic arterial rings, but did not affect venous rings.
Department of Veterinary Clinical Sciences, School of Veterinary Medicine, Louisiana State University, Baton Rouge 70803, USA.
S A
SA
Sedrish
C S
CS
Venugopalan
E P
EP
Holmes
C E
CE
Koch
R M
RM
Moore
D000075:Acepromazine / Q000494:pharmacology / Q000627:therapeutic use; D000818:Animals; D001158:Arteries / Q000187:drug effects; D002316:Cardiotonic Agents / Q000494:pharmacology / Q000627:therapeutic use; D003106:Colon / Q000098:blood supply* / Q000187:drug effects / Q000503:physiopathology; D003108:Colonic Diseases / Q000503:physiopathology / Q000628:therapy / Q000662:veterinary; D004298:Dopamine / Q000031:analogs & derivatives / Q000494:pharmacology / Q000627:therapeutic use; D018492:Dopamine Antagonists / Q000494:pharmacology / Q000627:therapeutic use; D004305:Dose-Response Relationship, Drug; D004730:Endothelium, Vascular / Q000166:cytology / Q000187:drug effects / Q000502:physiology; D006734:Horse Diseases / Q000628:therapy; D006736:Horses; D066298:In Vitro Techniques; D007415:Intestinal Obstruction / Q000503:physiopathology / Q000628:therapy / Q000662:veterinary; D007556:Isoxsuprine / Q000494:pharmacology / Q000627:therapeutic use; D009119:Muscle Contraction / Q000187:drug effects; D009131:Muscle, Smooth, Vascular / Q000166:cytology / Q000187:drug effects*; D009543:Nifedipine / Q000494:pharmacology / Q000627:therapeutic use; D009638:Norepinephrine / Q000494:pharmacology; D014665:Vasodilator Agents / Q000494:pharmacology* / Q000627:therapeutic use; D014680:Veins / Q000187:drug effects
D002316:Cardiotonic Agents; D018492:Dopamine Antagonists; D014665:Vasodilator Agents; C046318:dopexamine; D000075:Acepromazine; D009543:Nifedipine; D007556:Isoxsuprine; D004298:Dopamine; D009638:Norepinephrine