Are so many adrenergic receptor subtypes really present in domestic animal tissues? A pharmacological perspective.
Authors: Badino P, Odore R, Re G
Journal: Veterinary journal (London, England : 1997)
Summary
# Editorial Summary Adrenergic receptors mediate the effects of catecholamines and sympathomimetic drugs throughout the body, yet their tissue distribution and functional properties remain poorly characterised in domestic animals despite extensive research in laboratory species and humans. Badino and colleagues reviewed the structural classification of adrenergic receptor subtypes and synthesised available evidence on their distribution and function across equine, canine and bovine tissues, revealing substantial species-specific variation that cannot be predicted from human or rodent data. In horses, cardiac beta(1)-receptors predominate under normal conditions, whilst gastrointestinal smooth muscle relaxation depends primarily on beta(3)-receptor activation, and respiratory tissues show region-dependent beta(2)-receptor functionality; equine digital vasculature also displays distinct receptor populations. Cattle demonstrate alpha(1)- and alpha(2)-receptor heterogeneity in reproductive tissues, with beta(2)-receptors more abundant than beta(1) in ovarian and myometrial membranes, and sympathetic activation may contribute to ovarian cyst pathogenesis through altered receptor expression. The practical implication is clear: therapeutic decisions regarding sympathomimetic drugs, beta-blockers and other adrenergic agents must account for species-specific receptor distribution and function rather than relying on extrapolated pharmacology, particularly when treating cardiovascular, respiratory or gastrointestinal conditions in horses and cattle.
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Practical Takeaways
- •Adrenergic receptor distribution and function differ significantly between domestic animal species, so therapeutic approaches using sympathomimetic drugs cannot be directly transferred from laboratory animal or human research to equine, canine, or bovine patients.
- •In horses with cardiac disease, beta(2)-AR upregulation rather than downregulation may occur, suggesting different pharmacological responses to beta-blockers than in other species.
- •Regional differences in beta-AR subtypes throughout the equine respiratory and gastrointestinal tracts mean drug responses will vary by anatomical location and tissue type.
Key Findings
- •Dogs with dilated cardiomyopathy show significant down-regulation of beta-adrenergic receptors in both heart and circulating lymphocytes, confirming adrenergic system involvement in pathogenesis.
- •In healthy horses, cardiac beta-ARs are predominantly beta(1) subtype, while heart failure increases beta(2) expression rather than causing down-regulation.
- •Equine ileal smooth muscle sympathetic relaxation depends mainly on beta(3)-AR activation with minor beta(2) involvement, and respiratory tract beta(2)-AR response is tissue-dependent with higher activity in trachea.
- •Bovine ovarian and myometrial tissues express higher beta(2)-AR concentrations than beta(1), and sympathetic activation may play a role in ovarian cyst pathogenesis through altered beta-AR levels.