Identification and characterisation of beta-adrenoceptors on intact equine peripheral blood lymphocytes with the radioligand (-)-[125I]-iodocyanopindolol.
Authors: Abraham G, Broddet O E, Ungemach F R
Journal: Equine veterinary journal
Summary
# Editorial Summary Beta-adrenoreceptors on equine lymphocytes have been definitively characterised for the first time using radioligand binding techniques, revealing a predominantly beta2-adrenoreceptor phenotype (>90%) with minimal beta1 component. Abraham and colleagues identified approximately 320 binding sites per lymphocyte with high affinity, demonstrating that these receptors are functionally coupled to intracellular signalling through cyclic AMP generation in a dose-dependent manner consistent with classical beta-adrenergic physiology. The selectivity of beta2-adrenoreceptors on these immune cells suggests that sympathetic nervous system activity—and drugs targeting adrenergic pathways—will preferentially modulate lymphocyte function through this receptor subtype, with implications for stress-related immunosuppression and the use of beta-agonists in equine practice. This work establishes a robust *in vitro* model for investigating how neuroendocrine factors influence immune competence in horses, potentially explaining variable vaccine responses, infection susceptibility during high-stress periods, and individual variation in response to medication. For practitioners, these findings underpin the biological basis for observing immune dysfunction in stressed horses and provide mechanistic justification for managing stress as a component of preventive health protocols.
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Practical Takeaways
- •This in vitro model establishes that equine lymphocytes express functional beta2-adrenoceptors, providing a foundation for understanding neuroimmune regulation in horses
- •The predominantly beta2-adrenoceptor phenotype on equine lymphocytes may inform therapeutic strategies using beta-adrenergic agents in equine medicine
- •ICYP binding assay offers a suitable research tool to study beta-adrenoceptor system function and regulation in equine models relevant to clinical conditions
Key Findings
- •ICYP binding to equine lymphocytes was rapid, saturable with 320±20 binding sites per cell, and high affinity (KD 14.4±1.7 pmol/l)
- •Beta-adrenoceptors on equine lymphocytes are predominantly beta2-subtype (>90%) with possible minor beta1 component (<10%)
- •Selective beta2-antagonist ICI 118,551 was approximately 1000 times more potent than beta1-selective antagonist CGP 20712A in inhibiting ICYP binding
- •Agonist potency order for both ICYP binding inhibition and cAMP stimulation was: (-)-isoprenaline > (-)-adrenaline > (-)-noradrenaline