Improved recovery from laryngeal-stimulation-induced apnea by alpha-adrenergic blockade in adult rabbits.

The apnea triggered by laryngeal stimulation (LS) is associated with a redistribution of blood flow towards the heart and the brain that depends upon peripheral vasoconstriction. The circulatory component of the response to LS has been shown to be reduced following injection of large dose of beta-adrenergic agonist that more intriguingly blunted the ventilatory response as well. To test whether the reduction of LS-induced apnea could be related to the decreased magnitude of the peripheral vasoconstruction, the effects of the alpha-adrenergic antagonist urapidil on the ventilatory and blood pressure responses to LS were studied in 6 adult rabbits. alpha-Adrenergic blockade reduced both the rise in blood pressure and the magnitude of hypopnea induced by LS. These results suggest that the circulatory component of the laryngeal chemoreflex, i.e. the peripheral vasoconstruction, contributes to the magnitude of the ventilatory depression.