The effect of L-glutamic acid on airway function and reactivity in the rabbit

The ingestion of monosodium glutamate in sensitive individuals has been reported to cause severe asthma. We therefore studied the effects of L-glu on airway function and histamine (H) responsiveness in the rabbit. Histamine dose response curves (HDR's) were performed by measuring total lung resistance (R_L) after inhalation of saline and increasing concentrations of H (1-30 mg/ml). The concentration of H producing a 20% increase in R_L (PC₂₀H) was obtained by interpolation. To assess the effects of L-glu, 8 rabbits were infused with L-glu (0.2 g/kg/hr) or saline in random order (14 days apart) for 4 hours followed by an HDRC. To look at possible late effects, a repeat HDRC was also performed in 6 rabbits 12 hours after completion of the L-glu infusion. In order to see whether rabbits rendered hyperresponsive responded to L-glu, the above protocol was performed in 7 rabbits following the inhalation of 3 μg of the activated complement fragment C₅a des Arg. The L-glu infusions increased the plasma levels approx. ten-fold (mean±SEM 0.119±0.012 base-line, 1.272±0.061 mmol/l post infusion). L-glu did not increase the PC₂₀H or baseline R_L in either the normal rabbits at 4 or 12 hours or in the C₅a des Arg treated rabbits at 4 hours. It is concluded that L-glu does not cause bronchoconstriction or an increase in airway responsiveness to H in the rabbit.