The effects of pentoxifylline on skeletal muscle contractility and neuromuscular transmission during hypoxia

OBJECTIVES: The objective of this study was to investigate the effects of pentoxifylline (PTX), a drug that is mainly used for indications related to tissue hypoxia, on hypoxia-induced inhibition of skeletal muscle contractility and neuromuscular transmission in mice. We hypothesized that chronic PTX treatment alters skeletal muscle contractility and hypoxia-induced dysfunction. MATERIALS AND METHODS: Mice were treated with 50 mg/kg PTX or saline intraperitoneally for a week. Following ether anesthesia, diaphragm muscles were removed; isometric muscle contractions and action potentials were recorded. Time to reach neuromuscular blockade and the rate of recovery of muscle contractility were assessed during hypoxia and re-oxygenation. RESULTS: The PTX group displayed 90% greater twitch amplitudes (P < 0.01). Hypoxia depressed twitch contractions and caused neuromuscular blockade in both groups. However, neuromuscular blockade occurred earlier in PTX-treated animals (P < 0.05). Muscle contractures developed during hypoxia were more pronounced in the PTX group (P < 0.05). Re-oxygenation reduced contracture and indirect muscle contractions resumed. The rate of recovery of contractions was faster (P < 0.05) and the amplitude of contractions was greater (P < 0.01) in the PTX group. PTX treatment increased amplitude (P < 0.05) and shortened action potential (P < 0.05) without altering resting membrane potential, excitation threshold, and neurotransmitter release. CONCLUSION: Chronic PTX treatment increases diaphragm contractility, but amplifies hypoxia-induced contractile dysfunction in mice. These results may implicate important clinical consequences for clinical usage of PTX in hypoxia-related conditions.