تاثیر اپی تلیوم بر روی کاهش حساسیت گیرنده های آدرنرژیک بتای عضله صاف تراشه خوکچه هندی

Title

Influence of epithelium on beta-adrenoceptor sensitization of guinea pig tracheal smooth muscle

English Abstract

The effect of tissue incubation with a β2-agonist of denuded and intact epithelium trachea on the responsiveness to isoprenaline and β-receptor blocked by propranolol (CR-1) was examined in this study. We examined the effect of epithelium removal on the β-adrenoceptor desensitization resulting from incubation of guinea pig trachea in the β-adrenergic agonist isoprenaline (10 µM). Desensitization was measured as the change in EC50, the concentration of β-agonist that produced 50% relaxation of tracheal rings contracted with methacholine. As a second measure of desensitization, we measured the shift in EC50 resulting from incubation of tracheal rings with the β-adrenoceptor antagonist propranolol (20 nM), expressed as CR-1 ([post-propranolol EC50/baseline EC50]−1). Initially,we measured desensitization immediately after incubation in isoprenaline; subsequently, we repeated the protocol and allowed a 30 min rest between the end of incubation and the measurement. The sensitivity of denuded epithelium trachea to isoprenaline and (CR-1) was significantly higher than that of intact epithelium only in non-incubated preparations (p < 0.05 to p < 0.001). Incubation to isoprenaline caused a significant reduction in the tracheal response to isoprenaline in both the denuded groups (p < 0.005 for both cases) and intact epithelium groups (p < 0.05 for both cases). Incubation to isoprenaline also caused a significant reduction in (CR-1) value in both the denuded groups (p < 0.005 for group 2 and p < 0.001 for group 4) and intact epithelium only in group 1 (p < 0.05). However, the changes in EC50 due to tissue incubation with isoprenaline were significantly greater in denuded than intact epithelium trachea (p < 0.05 for all cases) and for CR-1 value only in groups 1 and 2 (p < 0.05). These results indicate decrease in both tracheal response to β-agonist (tolerance) and CR-1 (due to incubation of tissues with isoprenaline), which were greater in denuded epithelium groups.

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