Acute effect of insulin on guinea pig airways and its amelioration by pre-treatment with salbutamol.

Objective: To study the magnitude of insulin-mediated airway hyper-reactivity and to explore the protective effects of salbutamol in inhibiting the insulin-induced airway hyper-responsiveness on tracheal smooth muscle of guinea pigs in vitro.

Methods: The quasi-experimental study was conducted at the Pharmacology Department of Army Medical College, Rawalpindi, in collaboration with the Centre for Research in Experimental and Applied Medicine from December 2011 to July 2012. It used 18 healthy Dunkin Hartely guinea pigs of either gender. Effects of increasing concentrations of histamine (10-8-10-3M), insulin (10-8-10-3 M) and insulin pre-treated with salbutamol (10-6 M) were observed on isolated tracheal strip of guinea pig in vitro by constructing cumulative concentration response curves. The tracheal smooth muscle contractions were recorded with Transducer on Four Channel Oscillograph. Mean and standard error of mean were calculated. SPSS 16 was used for statistical analysis.

Results: Histamine and insulin produced a concentration-dependent reversible contraction of isolated tracheal muscle of guinea pig. The mean of maximum amplitudes of contraction with histamine, insulin and insulin pretreated with salbutamol were 92.5 +/- 1.20 mm, 35 +/- 1.13 mm and 14.55 +/- 0.62 mm respectively. Salbutamol shifted the concentration response curve of insulin to the right and downwards.

Conclusions: Salbutamol significantly reduced the insulin mediated airway hyper-reactivity in guinea pigs, suggesting that pre-treatment of inhaled insulin with salbutamol may have clinical implication in the amelioration of its potential respiratory adverse effects such as bronchoconstriction.