INHIBITION OF RESPIRATORY NEURAL DISCHARGES BY CLONIDINE AND 5-HYDROXYTRYPTOPHAN

  • 1 January 1982
    • journal article
    • research article
    • Vol. 222  (3) , 771-777
Abstract
Activation of receptors for norepinephrine or serotonin in the CNS by i.v. injection of clonidine (10-50 .mu.g/kg) or 5-hydroxytryptophan (20-40 mg/kg) inhibits phrenic neural discharges in anesthetized, artificially ventilated cats. Clonidine induces a rapid and complete inhibition of phrenic nerve activity which lasts for 1-3.2 h. The inhibition is prevented by prior administration of phenoxybenzamine (10 mg/kg) or tolazoline (3 mg/kg). 5-Hydroxytryptophan, injected after inhibition of peripheral amino acid decarboxylase (carbidopa, 30-50 mg/kg), elicits a gradual but complete inhibition of phrenic nerve discharges which persists for 1-10 h and is unaltered by .alpha.- or .beta.-adrenoceptor blocking agents. The inhibitions produced by clonidine and 5-hydroxytryptophan are overcome transiently during hypercapnia. Stimulation of carotid body chemoreceptors by i.a. [intraarterial] injections of lobeline, doxapram or 0.015 N HCl in saline also briefly, reinstates phrenic nerve discharges after inhibition by clonidine. Inhibition is also overcome during electrical stimulation of the carotid sinus nerve.