Propofol protects against opioid-induced hyperresponsiveness of airway smooth muscle in a horse model of target-controlled infusion anaesthesia.

This study investigates how propofol, a sedative-hypnotic drug, and remifentanil, an opioid, affect airway contraction in horses. Results suggest that remifentanil can cause hypersensitivity in the airways, which can potentially be mitigated by propofol.

Objective of the Research

• The research was aimed to study the effect of two drugs, propofol and remifentanil, on the contractile response of horse airway smooth muscle.
• While propofol and remifentanil are commonly used in total intravenous anaesthesia (TIVA) procedures, there was no existing data about their impact in causing bronchial hyperresponsiveness (BHR) in horses.

Methodology and Experimental Design

• The experiment involved assessing the influence of propofol and remifentanil on equine isolated bronchi response to electrical field stimulation (EFS).
• Factors such as the role of capsaicin-sensitive sensory nerves, inducible nitric oxide synthase (iNOS) and the neurokinin 2 (NK2) receptor were examined.
• The interactions were analyzed using Bliss Independence theory and experiments were repeated on desensitized and passively sensitized airways.

Findings

• The results showed that remifentanil induced BHR in both non-sensitized and passively sensitized bronchi.
• However, the administration of propofol significantly prevented this effect, suggesting a protective role of this medication.
• Furthermore, the inactivation of capsaicin-sensitive sensory nerves and blocking of the NK2 receptor inhibited the BHR induced by remifentanil.
• In contrast, inhibiting iNOS, a molecule that can suppress inflammation, reverted the protective effect of propofol on BHR induced by remifentanil.
• Overall, propofol was found to interact synergistically in preventing remifentanil-induced BHR.

Implications

• This study suggests that remifentanil stimulates capsaicin-sensitive sensory nerves that facilitate the cholinergic neurotransmission through the activation of NK2 receptor — a pathway which leads to BHR.
• The findings of this study indicate that the combination of propofol and remifentanil can be safely administered during TIVA procedures, even in horses affected by heaves, a chronic lung condition.