Effects of acute intravenous administration of parathion or paraoxon on bronchoconstriction in guinea pigs.

Abstract

<p>Bronchoconstriction was measured in anesthetized guinea pigs in response to electrical stimulation of both vagus nerves or to intravenous ACh before and after intravenous administration of parathion (1 mg/kg) or paraoxon (100 ng/kg or 100 µg/kg). Baseline bronchoconstrictions were within normal physiological parameters (8–17 mmH2O at 5 Hz, 17–59 mmH2O at 10 Hz, and 51–127 mmH2O at 15 Hz). Parathion (hatched bars) inhibited vagally-induced bronchoconstriction by approximately 50% at all three frequencies (A). In contrast, paraoxon at 100 ng/kg (gray bars) and 100 µg/kg (black bars) acutely increased vagally-induced bronchoconstriction in a frequency-dependent manner (A). Paraoxon at 100 ng/kg did not potentiate ACh-induced bronchoconstriction (B) or significantly inhibit AChE activity (C). However, at 100 µg/kg, paraoxon potentiated ACh-induced bronchoconstriction (B) and inhibited AChE (C). Data are presented as mean ± SE; n = 3–4 guinea pigs (* <i>p</i><0.05).</p