Postsynaptic alpha 2-adrenergic receptor-mediated vasoconstriction in SHR tail arteries in vitro.
In isolated perfused tail arteries of spontaneously hypertensive rats (SHR), the selective alpha 2-adrenergic receptor antagonist idazoxan ( RX781094 ) at low concentrations antagonized vasoconstrictor responses induced by norepinephrine (NE) and low frequency periarterial field stimulation. The vasoconstrictor responses to the selective alpha 2-adrenergic receptor agonist TL99 or to phenylephrine were also antagonized by low concentrations of idazoxan . In contrast, idazoxan did not antagonize responses induced by the alpha 1-adrenergic receptor agonists amidephrine or methoxamine in perfused tail arteries of SHR. The alpha 1-adrenergic receptor antagonist prazosin was very potent against methoxamine or phenylephrine and responses to periarterial field stimulation in SHR and Wistar-Kyoto (WKY) rat tail arteries, but only showed a modest selectivity for TL99 -induced responses in SHR arteries. The results support the contention that postjunctional alpha 2-adrenergic receptors can be demonstrated in arterial smooth muscle in vitro and are particularly evident in arteries from hypertensive animals. In SHR tail arteries, postsynaptic alpha 2-adrenergic receptors contribute to the vasoconstrictor responses to exogenous NE and may be activated by endogenously released NE.
D000316:Adrenergic alpha-Agonists / Q000494:pharmacology*; D000317:Adrenergic alpha-Antagonists / Q000494:pharmacology*; D000818:Animals; D001158:Arteries / Q000294:innervation / Q000502:physiology*; D004146:Dioxanes / Q000494:pharmacology*; D004147:Dioxins / Q000494:pharmacology*; D006973:Hypertension / Q000503:physiopathology*; D019329:Idazoxan; D008297:Male; D051381:Rats; D011919:Rats, Inbred Strains; D011922:Rats, Mutant Strains; D011942:Receptors, Adrenergic, alpha / Q000502:physiology*; D013329:Structure-Activity Relationship; D013569:Synapses / Q000502:physiology*; D013623:Tail; D014661:Vasoconstriction / Q000187:drug effects*
D000316:Adrenergic alpha-Agonists; D000317:Adrenergic alpha-Antagonists; D004146:Dioxanes; D004147:Dioxins; D011942:Receptors, Adrenergic, alpha; D019329:Idazoxan