Alpha 1- and alpha 2-adrenoceptors at different levels of the canine saphenous vein.
Presynaptic alpha2- and postsynaptic alpha1-adrenoceptors were compared at the distal and proximal parts of the dog saphenous vein. The results obtained show that: (1) yohimbine is more effective against postsynaptic responses to phenylephrine distally than proximally. On the contrary, WB-4101 is more effective proximally; (2) phenylephrine increases inositol monophosphate production at both levels, but the increase is more pronounced distally; (3) UK-14, 304 and adrenaline reduce and yohimbine and phentolamine increase the release of 3H-noradrenaline caused by electrical stimulation at both levels. However, while adrenaline as well as the antagonists are equipotent at the two levels, UK-14,304 is more potent distally than proximally. In conclusion, we suggest that: more alpha 1A-adrenoceptors exist distally than proximally; imidazoline sites can exist at the distal level which contribute to the higher potency of UK-14,304 distally.
Guimarães
S
S
Department of Pharmacology, Faculty of Medicine, Porto, Portugal.
Moura
D
D
Nunes
J P
JP
Vaz-da-Silva
M J
MJ
Guimarães
J T
JT
D000818:Animals; D000068438:Brimonidine Tartrate; D004146:Dioxanes / Q000494:pharmacology*; D004285:Dogs; D004558:Electric Stimulation; D004837:Epinephrine / Q000494:pharmacology; D066298:In Vitro Techniques; D007294:Inositol / Q000378:metabolism; D007295:Inositol Phosphates / Q000378:metabolism; D009131:Muscle, Smooth, Vascular / Q000187:drug effects / Q000378:metabolism / Q000502:physiology; D009638:Norepinephrine / Q000378:metabolism*; D010656:Phenylephrine / Q000494:pharmacology; D011810:Quinoxalines / Q000494:pharmacology; D011942:Receptors, Adrenergic, alpha / Q000378:metabolism*; D012501:Saphenous Vein / Q000187:drug effects / Q000378:metabolism / Q000502:physiology*; D013569:Synapses / Q000502:physiology; D015016:Yohimbine / Q000494:pharmacology*
D004146:Dioxanes; D007295:Inositol Phosphates; D011810:Quinoxalines; D011942:Receptors, Adrenergic, alpha; D010656:Phenylephrine; D015016:Yohimbine; D007294:Inositol; D000068438:Brimonidine Tartrate; C010654:(2-(2',6'-dimethoxy)phenoxyethylamino)methylbenzo-1,4-dioxane; D009638:Norepinephrine; D004837:Epinephrine