Some implications of the high intrasynaptic norepinephrine concentrations in resistance arteries.
Norepinephrine concentrations in excess of 10(-4) M are achieved at the post-junctional membrane of the adrenergic synaptic cleft in resistance arteries at least for short periods of time. These concentrations are greater than the threshold of low affinity non-alpha-adrenoceptors-'extraceptors', that respond to norepinephrine and would be sufficient to overcome the blockade by alpha-adrenoceptor antagonists. The relationship of such activity to the excitatory junction potential and the relevance of this to contraction in vivo remains a matter of conjecture.
D000317:Adrenergic alpha-Antagonists / Q000494:pharmacology; D000818:Animals; D001158:Arteries / Q000294:innervation*; D008433:Mathematics; D018377:Neurotransmitter Agents / Q000378:metabolism; D009638:Norepinephrine / Q000378:metabolism*; D009994:Osmolar Concentration; D011817:Rabbits; D051381:Rats; D011942:Receptors, Adrenergic, alpha / Q000502:physiology; D013569:Synapses / Q000378:metabolism*; D014655:Vascular Resistance; D014661:Vasoconstriction
D000317:Adrenergic alpha-Antagonists; D018377:Neurotransmitter Agents; D011942:Receptors, Adrenergic, alpha; D009638:Norepinephrine