5-HT Receptor Antagonism Attenuates the Ischemia-Reperfusion Injury After Rabbit Lung Preservation

Mediators of neutrophil lymphocyte ratio in the relationship between ondansetron pre-treatment and the mortality of ICU patients on mechanical ventilation: causal mediation analysis from the MIMIC-IV database

AIMS

The mortality of critically ill patients undergoing mechanical ventilation (MV) is high and few strategies are available. We explored the relationship between ondansetron pre-treatment, the neutrophil:lymphocyte ratio (NLR), and platelet:lymphocyte ratio (PLR), and mortality of ventilated patients in the intensive care unit.

METHODS

We developed a retrospective cohort study that involved patients undergoing MV in the Multiparameter Intelligent Monitoring in Intensive Care IV (MIMIC-IV) database. Causal mediation analysis was conducted to assess the relationship of ondansetron use and mortality and explore the potential causal pathway mediated by the NLR or PLR. The primary outcome was 28-day mortality.

RESULTS

A total of 17,927 eligible patients was obtained (5665 had taken ondansetron before MV initiation and 12,262 patients had not). The OR for 28-day mortality for ondansetron use uncorrelated with the mediator (NLR, PLR) was 0.72 (95%CI=0.64-0.81, P <0.001). Ondansetron was also associated with a reduction in 28-day mortality after controlling for the mediator of NLR (OR = 0.98, 95%CI = 0.97-0.99, P < 0.01). For the indirect effect, the NLR could explain 13.47% (95%CI = 8.59-20.54%, P < 0.01) of the impact of ondansetron use on 28-day mortality. The proportion mediated increased to 21.50% (95%CI = 12.36-47.44%, P < 0.01) for 90-day mortality. Adjusted mediation analysis revealed no suggestion of a causal mediation pathway for this effect by the PLR (P = 0.12).

CONCLUSIONS

NLR may play substantial roles in the relationship between ondansetron pre-treatment before initiation of mechanical ventilation and the reduction of death risk in ventilated patients.

Stimulatory Effect of 5-Hydroxytryptamine (5-HT) on Rat Capsaicin-Sensitive Lung Vagal Sensory Neurons via Activation of 5-HT3 Receptors

5-hydroxytryptamine (5-HT) is an inflammatory mediator known to be released in lung. Capsaicin-sensitive lung vagal (CSLV) afferents function as a primary sensor for detecting chemical stimuli and produce consequent reflexes during lung inflammation. To characterize the effect of 5-HT on CSLV afferents, responses of cardiorespiratory reflexes and single-unit C-fiber afferents to right-atrial injections of 5-HT were investigated in anesthetized Sprague-Dawley rats. Bolus injection of 5-HT (8 μg/kg) caused an immediate augmented breath and apnea, accompanied by hypotension and bradycardia. These initial responses were then followed by a brief pressor response and a more sustained depressor response. After a perineural treatment of both cervical vagi with capsaicin to block the conduction of C fibers, 5-HT still triggered the augmented breath, but no longer evoked the apnea, bradycardia and hypotension, indicating an involvement of C-fiber activation. The remaining augmented breath induced by 5-HT after perineural capsaicin treatment was totally eliminated by vagotomy. To further study the effect of 5-HT on CSLV afferents, activities arising from these afferents were determined using the single-fiber recording technique. Right-atrial injection of 5-HT evoked an intense discharge in CSLV afferents in a dose-dependent manner. The highest dose of 5-HT (16 μg/kg) activated 79% (19/24) of CSLV afferents which were also sensitive to capsaicin (0.8 μg/kg). The pretreatment of tropisetron, a selective antagonist of the 5-HT₃ receptor, completely blocked CSLV-afferents stimulation induced by 5-HT but did not affect that by capsaicin. Furthermore, a similar afferent response of CSLV afferents was mimicked by phenylbiguanide, a selective agonist of the 5-HT₃ receptor. In isolated rat lung vagal C neurons, 5-HT induced intense calcium transients in a dose-dependent manner. The highest concentration (3 μM) of 5-HT activated 67% (18/27) of the CSLV neurons. The 5-HT-induced response was totally abolished by pretreatment of tropisetron. In conclusion, 5-HT exerts an intense stimulatory effect on lung C-fiber terminals mediated through an activation of the 5-HT₃ receptor, which may contribute to the airway hypersensitivity under lung inflammation.