Central alpha-adrenoceptor subtypes involved in the emetic pathway in cats.
The intracerebroventricular (i.c.v.) injection of clonidine, xylazine, adrenaline and methoxamine elicited dose-dependent vomiting in cats in that order of potency. The vomiting induced by clonidine, xylazine and adrenaline was antagonized by i.c.v. yohimbine and phentolamine possessing alpha 2-adrenoceptor-blocking activity, but not by prazosin showing alpha 1-adrenoceptor-blocking activity. In contrast, methoxamine-induced vomiting was antagonized by prazosin, but not by yohimbine. The vomiting induced by xylazine and adrenaline was not prevented by i.c.v. 6-hydroxydopamine treatment, but was prevented by i.c.v. reserpine treatment. Ablation of the area postrema with some damage to extremely adjacent areas abolished the vomiting induced by each alpha-adrenoceptor agonist. These results indicate that both central alpha 1- and alpha 2-adrenoceptors are involved in the emetic pathway in cats, although alpha 2-adrenoceptors seem to have the main role. It is also suggested that monoamines, and in particular 5-hydroxytryptamine in the brain, are involved in the regulation of alpha-adrenoceptor-mediated vomiting.
Department of Veterinary Surgery, School of Veterinary Medicine and Animal Sciences, Kitasato University, Aomori, Japan.
Y
Y
Hikasa
T
T
Akiba
Y
Y
Iino
M
M
Matsukura
K
K
Takase
S
S
Ogasawara
D000316:Adrenergic alpha-Agonists / Q000494:pharmacology*; D000317:Adrenergic alpha-Antagonists / Q000494:pharmacology*; D000818:Animals; D002415:Cats; D003000:Clonidine / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D004837:Epinephrine / Q000494:pharmacology; D005260:Female; D008297:Male; D008729:Methoxamine / Q000494:pharmacology; D016627:Oxidopamine / Q000494:pharmacology; D011942:Receptors, Adrenergic, alpha / Q000502:physiology*; D012110:Reserpine / Q000494:pharmacology; D014839:Vomiting / Q000139:chemically induced / Q000503:physiopathology*; D014991:Xylazine / Q000494:pharmacology
D000316:Adrenergic alpha-Agonists; D000317:Adrenergic alpha-Antagonists; D011942:Receptors, Adrenergic, alpha; D014991:Xylazine; D012110:Reserpine; D016627:Oxidopamine; D008729:Methoxamine; D003000:Clonidine; D004837:Epinephrine