Inhibition of respiratory neural discharges by clonidine and 5-hydroxytryptophan.
Activation of receptors for norepinephrine or serotonin in the central nervous system by i.v. injection of clonidine (10-50 micrograms/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 to 3.2 hr. 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 to 10 hr 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. 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.
D006916:5-Hydroxytryptophan / Q000494:pharmacology*; D000818:Animals; D002230:Carbidopa / Q000494:pharmacology; D002415:Cats; D002628:Chemoreceptor Cells / Q000187:drug effects; D003000:Clonidine / Q000494:pharmacology*; D005260:Female; D008297:Male; D010643:Phenoxybenzamine / Q000494:pharmacology; D010791:Phrenic Nerve / Q000187:drug effects*; D011941:Receptors, Adrenergic / Q000187:drug effects; D011942:Receptors, Adrenergic, alpha / Q000187:drug effects; D011985:Receptors, Serotonin / Q000187:drug effects; D012125:Respiratory Center / Q000187:drug effects; D009435:Synaptic Transmission / Q000187:drug effects; D014043:Tolazoline / Q000494:pharmacology
D011941:Receptors, Adrenergic; D011942:Receptors, Adrenergic, alpha; D011985:Receptors, Serotonin; D010643:Phenoxybenzamine; D006916:5-Hydroxytryptophan; D014043:Tolazoline; D003000:Clonidine; D002230:Carbidopa