# Indomethacin Abolishes the Potentiation Effect of Testosterone on the Relaxation Induced by Salbutamol and Theophylline by Directly Blocking the K+ Channels in Airway Smooth Muscle

## TL;DR

Indomethacin blocks the muscle-relaxing effects of testosterone in airways by inhibiting potassium channels, which could worsen asthma symptoms in young males.

## Contribution

Indomethacin uniquely inhibits both K+ channels and prostaglandin synthesis, unlike other NSAIDs.

## Key findings

- Indomethacin fully abolishes testosterone-enhanced relaxation in airway smooth muscle.
- Indomethacin inhibits KV and BKCa K+ currents potentiated by testosterone.
- Indomethacin's dual mechanism may counteract testosterone's protective effects in asthma.

## Abstract

Indomethacin, ibuprofen, and acetylsalicylic acid (ASA) are non-steroidal anti-inflammatory drugs (NSAIDs) that inhibit prostaglandin (PG) synthesis. Previous studies in airway smooth muscle demonstrated that chronic exposure to testosterone (TES, 40 nM) enhances the relaxation induced by salbutamol and theophylline due to K+ channel increment, without modifying cyclooxygenase expression. This study examines how indomethacin, ibuprofen, and ASA affect K+ currents and the relaxation response to these bronchodilators. In organ baths, tracheas from young male guinea pigs chronically (48 h) treated with 40 nM TES showed increased relaxation to salbutamol and theophylline, which was completely abolished by indomethacin. Patch-clamp recordings revealed that TES increased salbutamol- and theophylline-induced K+ currents, and only indomethacin fully inhibited this potentiation; ibuprofen and ASA had partial effects. The involved currents included voltage-dependent K+ (KV) and high-conductance Ca2+-activated K+ (BKCa) channels. Our results demonstrate that indomethacin exerts a dual action, inhibiting K+ channel activity and PG synthesis, unlike ibuprofen and ASA. This dual mechanism explains its stronger inhibitory effect on TES-enhanced ASM relaxation. These findings suggest that indomethacin may counteract the protective effects of TES, which promotes anti-inflammatory and smooth muscle-relaxing states. Therefore, it is advisable to exercise caution when prescribing indomethacin to young males with asthma, as the protective role of TES may diminish, potentially resulting in an exacerbation of asthma symptoms.