Effects of one month treatment with propranolol and metoprolol on the relaxant and contractile function of isolated trachea from rats exposed to cigarette smoke for four months

Abstract

Background and objective: The effects of one-month treatment of β-adrenergic receptor (AR) blockers on the relaxant function of airway in chronic obstructive pulmonary disease (COPD) are unknown. A passive cigarette smoking rat model was used to investigate the effect of β-AR blockers.

Methods: Thirty-six rats were randomly divided into six groups: control (C); propranolol (P); metoprolol (M); smoking (S); smoking + propranolol (SP); and smoking + metoprolol (SM). Histological analysis of the lungs was done and isolated tracheal segments were studied in vitro to assess the contractile and relaxant function of the smooth muscle. The level of norepinephrine (NE) was measured.

Results: Airway inflammation was more severe in group S than group C (p < 0.001), and it was alleviated in group SP (p < 0.001) while had no change in group SM. After propranolol or metoprolol administration, the level of NE was significantly lower in both SP and SM groups (p < 0.01). The maximal contractile response to acetylcholine (Ach) in groups S and SM was increased compared to group C (p < 0.01). Propranolol significantly inhibited contractile response in group SP (p < 0.05), while metoprolol did not show the same effect. The curve of maximum relaxant rate to isoprenaline (Iso) shifted to the left in group SP (p < 0.01), while group SM showed no changes.

Conclusion: One-month treatment with propranolol increased the relaxant effect mediated by the β₂-AR and decreased the contractile response to Ach by reducing the level of NE.

• β-adrenergic receptor blocker
• cigarette smoke exposure
• contractile and relaxant function
• tracheal smooth muscle