Contribution of alpha- and beta- adrenoceptors and neuropeptide-Y to autonomic dysreflexia

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Abstract
Modest increases in urinary bladder pressure result in acute hypertensive episodes in humans with spinal cord lesions above T5. The underlying mechanisms of this condition, referred to as autonomic dysreflexia, are not well understood. The aim of this study was to characterize the contribution of alpha- and beta-adrenoceptors as well as circulating neuropeptide-Y (NPY) to the pressor response to bladder distension in conscious cervical spinal rats. Rats were chronically instrumented with arterial and venous catheters. After 2–3 days, a complete spinal transection (C7) was performed, and the urinary bladder was catheterized: 24 h later, mean arterial pressure (MAP) responses to 5 min bladder distensions (+40) were measured under control conditions and after administration of specific autonomic antagonists. To assess the contribution of alpha and beta adrenergic mechanisms the α antagonist prazosin (0.45mg/kg i.v.) and β antagonist propranolol (4 mg/kg i.v.), were administered individually or together. Blood samples were taken before, during and after bladder distension for determination of plasma NPY by radioimmunoassay. The pressor response to bladder distension was approximately 30 mmHg under control conditions. The response was attenuated (−38%), but not abolished, by prazosin. A similar attenuation (−41%) was observed with propranolol. There were no changes in plasma NPY in response to bladder distension. Finally, the pressor response was completely abolished by combined alpha- and beta-adrenergic blockade. These results suggest that autonomic dysreflexia is mediated exclusively by adrenergic receptors in the spinal rat. Moreover, both α and β adrenergic receptors contribute to the pressor response induced by bladder distension in the conscious cervical spinal rat.