Regulation of noradrenaline release in human cerebral arteries via presynaptic alpha 2-adrenoceptors.
1. Electrical stimulation induced tritium release from branches of human middle cerebral arteries preincubated with [3H]noradrenaline (NA), which was reduced by the alpha 2-adrenoceptor agonists, clonidine and B-HT 920, and not affected by the alpha 1-agonist, methoxamine. 2. The stimulated tritium release was inhibited by yohimbine (alpha 2-antagonist), and increased by phentolamine (alpha-antagonist) and prazosin (alpha 1-antagonist). 3. The inhibitory effect of clonidine was antagonized by yohimbine. 4. NA uptake was markedly reduced when the interval between the death and the autopsy was greater than 5 hr. 5. These data indicates the existence of presynaptic inhibitory alpha 2-adrenoceptors, but not alpha 1, in human cerebral arteries, and that the adrenergic nerve endings start to degenerate from 5 hr after death.
Sanchez-Merino
J A
JA
Departamento de Fisiología, Facultad de Medicina, Universidad Autónoma, Madrid, Spain.
Arribas
S
S
Arranz
A
A
Marín
J
J
Balfagón
G
G
D000316:Adrenergic alpha-Agonists / Q000494:pharmacology*; D001381:Azepines / Q000494:pharmacology; D002536:Cerebral Arteries / Q000187:drug effects / Q000378:metabolism*; D003000:Clonidine / Q000037:antagonists & inhibitors / Q000494:pharmacology; D004558:Electric Stimulation; D006801:Humans; D008729:Methoxamine / Q000494:pharmacology; D009638:Norepinephrine / Q000493:pharmacokinetics*; D011942:Receptors, Adrenergic, alpha / Q000187:drug effects / Q000378:metabolism*; D013997:Time Factors; D014316:Tritium / Q000378:metabolism; D015016:Yohimbine / Q000494:pharmacology
D000316:Adrenergic alpha-Agonists; D001381:Azepines; D011942:Receptors, Adrenergic, alpha; D014316:Tritium; D015016:Yohimbine; C024763:talipexole; D008729:Methoxamine; D003000:Clonidine; D009638:Norepinephrine