Atropine is more efficient than ZM241385 to reduce a drastic level of fade caused by cisatracurium at 50 Hz/Atropina e mais eficiente que ZM241385 para reduzir o intenso nivel de fadiga causada por cisatracurium a 50 Hz

The effects of atropine (non selective muscarinic antagonist) and ZM241385 ([A.sub.2A] receptors antagonist) in the cisatracurium-induced drastic (100%) level of fade at 50 Hz (10 s) (100% Fade) were compared in the phrenic nerve-diaphragm muscle preparations of rats indirectly stimulated at a physiological tetanic frequency (50 Hz). The lowest dose and the instant cisatracurium caused 100% Fade were investigated. Cisatracurium induced 100% Fade 15 min after being administered. Atropine reduced the cisatracurium-induced 100% Fade, but the administration of ZM241385 separately, or combined with atropine, did not cause any effect in the cisatracurium-induced 100% Fade. Data indicate that the simultaneous blockage of [M.sub.1] and [M.sub.2] muscarinic receptors on motor nerve terminal by atropine is more efficient than the blockage of presynaptic [A.sub.2A] receptors for a safer recovery of patients from neuromuscular blockade caused by cisatracurium. Keywords: tetanic fade, adenosine, muscarinic receptors, train-of-four, neuromuscular blocker. Os efeitos de atropina e ZM241385 (antagonistas de receptores [A.sub.2A]) no drastico (100%) nivel de fadiga (100% Fadiga) produzido pelo cisatracurio a 50 Hz (10 s) foram comparativamente investigados em preparacoes nervo frenico musculo diafragma isolado de ratos indiretamente estimuladas com a frequencia fisiologica tetanizante de 50 Hz. A menor dose e o instante no qual cisatracurio causou 100% Fadiga foram pesquisados. O cisatracurio induziu 100% Fadiga 15 min depois de ser administrado. A atropina reduziu a fadiga de 100% causada pelo cisatracurio, mas ZM241385, ou a administracao combinada de atropina com ZM241385, nao causou qualquer efeito na 100% Fadiga produzida pelo cisatracurio. Os dados indicam que o bloqueio simultaneo dos receptores muscarinicos [M.sub.1] e [M.sub.2] no terminal nervoso motor pela atropina e mais eficiente do que o bloqueio dos receptores pre-sinapticos [A.sub.2A] no auxilio da recuperacao mais segura do bloqueio da transmissao neuromuscular causada por cisatracurio. Palavras-chave: fadiga, adenosina, receptores muscarinicos, trem de quatro, bloqueadores neuromusculares.