Insulin acutely increases agonist-induced airway smooth muscle contraction in human and rat

Obesity increases incidence and severity of asthma but the molecular mechanisms are not completely understood. Hyperinsulinemia potentiates vagally induced bronchoconstriction in obese rats. Since bronchoconstriction results from airway smooth muscle contraction, we tested whether insulin changed agonist-induced airway smooth muscle contraction. Obesity prone and resistant rats were fed a low-fat diet for 5 weeks and treated with insulin (Lantus, 3 units/rat s.c.) 16 h before vagally induced bronchoconstriction was measured. Ex vivo, contractile responses to methacholine were measured in isolated rat tracheal rings and human airway smooth muscle strips before and after incubation (0.5 - 2 h) with 100 nM insulin or 13.1 nM insulin like growth factor-1 (IGF-1). M2 and M3 muscarinic receptor mRNA expression was quantified by qRT-PCR and changes in intracellular calcium were measured in response to methacholine or serotonin in isolated rat tracheal smooth muscle cells treated with 1 µM insulin. Insulin, administered to animals 16 h prior, potentiated vagally induced bronchoconstriction in both obese prone and resistant rats. Insulin, not IGF-1, significantly increased methacholine-induced contraction of rat and human isolated airway smooth muscle. In cultured rat tracheal smooth muscle cells, insulin significantly increased M2, not M3, mRNA expression and enhanced methacholine- and serotonin-induced increase in intracellular calcium. Insulin alone did not cause an immediate increase in intracellular calcium. Thus, insulin, acutely potentiated agonist-induced increase in intracellular calcium and airway smooth muscle contraction. These findings may explain why obese individuals with hyperinsulinemia are prone to airway hyperreactivity and give insights into future targets for asthma treatment.

Histamine (H1) Receptors, Cyclooxygenase Pathway and Nitric Oxide Formation Involved in Rat Tracheal Smooth Muscle Relaxant Effect of Berberine

In this study we aimed to examine the relaxant effect of berberine, a compound extracted from a variety of herbs, on rat tracheal smooth muscle (TSM) and its possible mechanism(s). Cumulative concentrations of berberine (20, 65, 200 and 600 μg/mL) were added on pre-contracted TSM by methacholine or KCl in non-incubated or incubated tissues with atropine, chlorpheniramine, propranolol, diltiazem, glibenclamide, indomethacin, L-NG-nitro arginine methyl ester (L-NAME) and papaverine. The relaxant effects of theophylline (0.2, 0.4, 0.6 and 0.8 mM) as positive control and saline (1 mL) as negative control were also examined in non-incubated tissues. Berberine showed significant and concentration-dependent relaxant effects in non-incubated tissues contracted by KCl and methacholine (p<0.01 to p<0.001). There was no significant difference in the relaxant effects of berberine between non-incubated and incubated tissues with atropine, propranolol, diltiazem, glibenclamide, and papaverine. The relaxant effects of second concentrations of berberine in incubated tissues with L-NAME, its three lower concentration in incubated tissues with chlorpheniramine and its all concentrations in incubated tissues with indomethacin were significantly lower than non-incubated tissues (p<0.05 to p<0.001). The EC50 values of berberine in incubated tissues with chlorpheniramine was significantly higher than the non-incubated condition (p<0.05). Our findings reveal a relatively potent relaxant effect of berberine that is lower than the effect of theophylline. Proposed mechanisms for the relaxant effect of berberine are histamine (H1) receptor blockade, inhibition of cyclooxygenase pathways and/or nitric oxide formation.