VPT 421: Veterinary Toxicology (2+0)

MECHANISM OF ACTION

• Pyrethrins and type I pyrethroids act on sodium ion channels; decreasing peak sodium conductance, prolonging the sodium conductance and suppressing potassium conduction.
• These changes result in decreases in the amplitudes of action potentials and repetitive nerve discharges.
• Nerve conduction block can occur.
• Type II pyrethroids (contain a cyano group) also act on sodium ion channels which is thought to account for the sensory nerve stimulation associated with paresthesias in humans (and presumably other species).
• A depolarization of nerve membranes without repetitive discharges occurs with decreased action potential amplitudes.
• Type II pyrethroids are also believed to interfere with the binding of GABA and glutamic acid at their respective nervous system's receptor sites.
• Allethrin (and perhaps other pyrethroids) allosterically affects binding at the acetylcholine nicotinic receptor.
• Pyrethrins and pyrethroids also inhibit various adenosine triphosphatases including the calcium-ATPase and the calcium magnesium-ATPase in nervous tissues.