Opposite to alpha(2)-adrenergic agonists, an imidazoline I-1 selective compound does not influence reflex bradycardia in rabbits
Autor(es): Sy, Guata Yoro; Bousquet, Pascal; Feldman, Josiane
Resumo: This work aimed to study the respective effects of central alpha(2)-adrenergic receptors (alpha(2)-ARS) and I-1 imidazoline receptors (I(1)Rs) in the facilitatory effects of imidazoline-like drugs on the reflex bradycardia (RB). Experiments were performed in anaesthetized rabbits. The reflex bradycardic response was induced by phenylephrine injected i.v. LNP 509, rilmenidine and dexmedetomidine were administered intracisternally (i.c.).LNP509 (I mg/kg, i.c.), a ligand highly selective for I(1)Rs, induced hypotension (54 +/- 3 vs. 93 +/- 2 mm Hg) and bradycardia (260 +/- 13 vs. 322 +/- 13 beats/min) (p < 0.05, n=5) but did not affect RB.Rilmenidine (I mu g/kg, i.c.), a hybrid ligand which binds to both I-1 and alpha(2)-ARs, also decreased arterial pressure (61 +/- 2 vs. 101 +/- 2 mm Hg) and heart rate (260 +/- 4 vs. 3 08 +/- 8) (p < 0.0 1, n = 5); it potentiated the RB (maximum R-R interval: 284 +/- 17 vs. 196 +/- 6 ms) (p < 0.05, n = 5). Dexmedetomidine (I mu g/kg, i.c.), a ligand selective for alpha(2)-ARs, reduced blood pressure (53 +/- 3 vs. 104 +/- 2 mm Hg) and heart rate (246 +/- 4 vs. 312 +/- 8 beats/min) (p < 0.05, n=5) and potentiated the RB (maximum R-R interval: 518 +/- 38 vs. 194 +/- 4 ms) (p < 0.05, n=5). The potentiation of RB was much greater than that observed with rilmenidine and was significantly prevented by L-NNA injected centrally.This study shows that: (i) an exclusive action on I(1)Rs which decreases arterial pressure, does not potentiate the RB ii) activation Of alpha(2)-ARs potentiates the RB (iii) the R-R prolongation caused by alpha(2)-ARs stimulation is prevented by central NOS inhibition. (c) 2006 Elsevier B.V All rights reserved.
Palavras-Chave: Imidazoline receptors; ?2-adrenergic receptors; Nucleus tractus solitarii; Rostroventrolateral medulla; nucleus reticularis lateralis; Nitric oxide; Phenylephrine induced bradycardia
Imprenta: Autonomic Neuroscience-Basic & Clinical, v. 128, n. 42401, p. 19-24, 2006
Descritores: Zika virus - Biochemistry
Data de publicação: 2006
