Force adaptation through the intravenous route in naïve mice

Area of Science:

• Respiratory Physiology
• Smooth Muscle Biology
• Pharmacology

Background:

• Airway smooth muscle (ASM) force adaptation, or tone, increases ASM contractile capacity during sustained contraction.
• Tone is known to enhance responses to inhaled methacholine, but this may be confounded by airway heterogeneity and closure.
• This study investigates whether force adaptation, independent of airway heterogeneity, underlies tone's potentiation of methacholine response.

Purpose of the Study:

• To determine if airway smooth muscle tone potentiates the response to methacholine delivered intravenously, bypassing airway heterogeneity.
• To assess the role of force adaptation in tone-induced potentiation of methacholine response.
• To investigate potential sex differences in the potentiation of methacholine response by tone.

Main Methods:

• Female and male BALB/c mice were challenged with intravenous methacholine.
• Two conditions were tested: with and without a 20-minute period of induced airway smooth muscle tone.
• Respiratory mechanics (elastance and resistance) were measured using oscillometry.

Main Results:

• Airway smooth muscle tone significantly potentiated the methacholine response in both female and male mice.
• Potentiation of respiratory system elastance (Ers) was 64% in females and 405% in males.
• Potentiation of respiratory system resistance (Rrs) was 129% in females and 225% in males, indicating sex-specific differences in response.

Conclusions:

• Airway smooth muscle tone potentiates the response to intravenous methacholine in both sexes.
• Significant sexual dimorphisms exist in the resistive versus elastic components of this potentiation.
• These findings support the hypothesis that force adaptation is the mechanism by which tone enhances lung response to methacholine.