Efeito da interrupção abrupta do tratamento crônico com brometo de ipratrópio na resposta contrátil de traquéias isoladas de ratos

Abstract

In order to evaluate ipratropium bromide (IB) abrupt withdrawal effects after chronic treatment in isolated rat tracheas, male rats weighing 200-250g were placed in plastic chambers and submitted to inhalation of IB (600µM) during seven minutes. This protocol was repeated each four hours during 14 days. Two inhalation chambers were used, one with experimental group (IB inhalation) and the other with control group (CONT, saline). Another group was ovalbumin (OVA) actively sensitized (SZ) and submitted to the same protocol of inhalation. These animals were challenged 24hours before the beginning of the experiments by antigen inhalation (OVA: 1mg/ml; 5mg/ml; 15/15 minutes) (group DESF). At the end of IB treatment period the animals were killed and 0, 4, 8, 12 hours after the last inhalation the tracheas were quickly removed. After dissection the tracheal rings were transferred to a 8 ml organ bath containing Krebs-Henseleit solution mMol/l: NaCl 113.0; KCl 4.7; CaCl2.2H2O 1.2; KH2PO4 1.2; MgSO4.7H2O 1.2; NaHCO3 25.0; Glucose 11.0; 37º C; 95%O2/5%CO2). Concentration-effect curves (CEC) were constructed to carbachol (Cch), serotonin (5-HT), potassium (KCl), calcium (CaCl2) and electric stimulus. CEC to Cch obtained with tracheas isolated from rats submitted to only one IB inhalation showed shift to the right with an increase in the EC50 values [EC50x10-7M: CONT=1.78(1.32-2.32); IB=14.6(2.05-58.1) p<0.05]. Immediately after chronic treatment CEC to Cch also showed significant increase at EC50 level [EC50x10-7M: CONT=2.33(1.25-4.32); IB=42.5(21.1-85.8); p<0,01]. Experiments realized with isolated rats tracheas 4, 8, 12 hours after ended the IB chronic treatment showed a Cch maximum response (MR) progressive increase, reaching the greater value 12 hours after IB chronic treatment interruption [MR-12h: CONT=1.69±0.04; IB=2.64±0.23 gF, p<0.01). This kind of supersensitivity characterized by a vertical increase, was also obtained to other agonists and contractile stimulus. In this way the results showed supersensitivity to serotonin (MR-12h: CONT=0.59±0.04; IB=1.06±0.10; gF; p<0.01), potassium (MR-12h: CONT=0.70±0.05; IB=1.27±0.17; gF; p<0.01) and electric stimulus (MR-12h: CONT=1.25±0.07; IB=1.64±0.06; gF; p<0.01). Calcium CCE were obtained 12hours after the end of IB chronic treatment, after the addition of KCl or Cch in calcium free buffer. This kind of experiment measured, respsctively and indirectly the influx of calcium by voltage operated channelsVOC) and by receptor operated channels(ROC). The results demonstrated that influx of calcium was facilitated in both calcium channels studied in this work (MR-12h: CaCl2/KCl: CONT=1.00±0.09; IB=1.54±0.19; gF; p<0.01) (MR-12h: CaCl2/Cch; CONT= 1.27±0.10; IB=1.66±0.05; gF; p<0.01). The experiments with OVA challenged animals, realized immediately after the end of chronic treatment, showed a decreased in the sensibility. The CEC to Cch were shift to the right [EC50X10-7M: CONT=2.10(1.28-3.44); IB=17.13(4.37-67.05), P<0,01]. However, trachea isolated from rat challenged 12 hours after the end of the treatment, showed an increase in the contractility and in the MR obtained to carbachol (MR-12h: CONT=2.48±0.19; IB=3.48±0.13; gF; p<0,01). These data suggest that IB chronic inhalation process follow suppression induced an evident Cch contractile response increase in isolated rat trachea, reaching a maximum value 12 hours after interrupted IB chronic treatment abrupt suppression, was here demonstrated to several agonists and electric stimulus. Supersensitivity was also detected to carbachol contractile response through the same withdrawal experimental protocol in isolated tracheas from rats challenged with OVA. This increased contractile response obtained in rats tracheal smooth muscle, 12 hours after the end of ipratropium bromide chronic treatment, could be related with a component linked with the facilitation influx of calcium by voltage operated channels (VOC) and/or receptor operated channels (ROC).