Evaluation of opioid receptors in synovial membranes of horses.
OBJECTIVE
To evaluate mu-opioid receptors in synovial membranes of horses and determine whether these receptors are up-regulated in nerve endings during inflammation.


METHODS
Synovial tissue obtained from 39 client-owned horses during arthroscopy and 14 research horses during necropsy; brain and synovial tissues were obtained during necropsy from 1 horse, and control tissues were obtained from a mouse.


METHODS
Horses were classified into 7 groups on the basis of histologically determined degree of inflammation. Binding of primary rabbit antibody developed against mu-opioid receptors in equine synovial tissue was studied, using western blot analysis. Synovial membranes were tested for mu-opioid receptors by immunohistochemical staining, using a diaminobenzidine-cobalt chloride chromogen. Homogenates of synovial membranes were evaluated by use of radioligand binding.


RESULTS
Examination of western blots of equine thalamus revealed that rabbit antibody developed against mu-opioid receptors yielded a band (molecular weight, 55 kd) that corresponded with that of other opioid receptors. Use of immunohistochemical staining of synovial tissue revealed considerable staining in the proliferative lining layer and in regions surrounding vascular structures. Specific radioligand binding of tissue homogenates was found in all groups. We did not detect significant differences in binding between horses with inflammation and horses without inflammation.


CONCLUSIONS
Results of immunohistochemical analysis and radioligand binding of tissue homogenates suggest that there are opioid receptors in synovial membranes of horses. Our results support the practice of intra-articular administration of opioids to relieve pain after arthroscopic surgery in horses.
Sheehy
J G
JG
Professional Veterinary Medicine Program, College of Veterinary Medicine and Biomedical Sciences, Colorado State University, Fort Collins 80524, USA.
Hellyer
P W
PW
Sammonds
G E
GE
Mama
K R
KR
Powers
B E
BE
Hendrickson
D A
DA
Magnusson
K R
KR
D000818:Animals; D001182:Arthroscopy / Q000662:veterinary; D006734:Horse Diseases / Q000378:metabolism / Q000473:pathology; D006736:Horses; D007150:Immunohistochemistry / Q000662:veterinary; D007249:Inflammation / Q000378:metabolism / Q000662:veterinary; D009270:Naloxone / Q000494:pharmacology; D009292:Narcotic Antagonists / Q000494:pharmacology; D017450:Receptors, Opioid, mu / Q000378:metabolism*; D013264:Stifle / Q000378:metabolism / Q000473:pathology / Q000601:surgery; D013583:Synovial Membrane / Q000378:metabolism* / Q000473:pathology
D009292:Narcotic Antagonists; D017450:Receptors, Opioid, mu; D009270:Naloxone