title: Extent of alpha 2-receptor-mediated autoinhibition of vasoconstrictor nerve responses in mesenteric resistance vessels from normotensive and hypertensive rats.
abstract: The authors have previously shown that vasoconstrictor nerve responses of mesenteric small arteries from spontaneously hypertensive rats (SHR) are increased compared with normotensive rats. In this paper, whether this is due to differences in the degree of negative feedback of the transmitter on its own release is investigated. Small (i.d. 200 microns) arteries from the mesenteric arcades of SHR and normotensive control rats (NCR) were mounted in a Mulvany-Halpern myograph. In both SHR and NCR, nerve stimulation and applied noradrenaline elicited maximal contractions of similar magnitude, although SHR vessels were somewhat stronger and more responsive to nerve stimulation. Blocking alpha 2-receptors with 10 nM RX 781094 reduced the frequency for half-maximal activation to 84% and 80%, respectively, but did not eliminate the difference between the strains. Presynaptic alpha 2-receptors thus do not seem to cause the enhanced vasoconstrictor responses in SHR vessels.
mesh_terms: D000317:Adrenergic alpha-Antagonists / Q000494:pharmacology; D000818:Animals; D004146:Dioxanes / Q000494:pharmacology; D004558:Electric Stimulation; D006973:Hypertension / Q000503:physiopathology*; D019329:Idazoxan; D008297:Male; D008638:Mesenteric Arteries / Q000187:drug effects / Q000294:innervation / Q000502:physiology*; D009433:Neural Inhibition / Q000187:drug effects; D009638:Norepinephrine / Q000494:pharmacology; D051381:Rats; D011918:Rats, Inbred SHR; D011919:Rats, Inbred Strains; D011942:Receptors, Adrenergic, alpha / Q000187:drug effects / Q000502:physiology*; D014661:Vasoconstriction / Q000187:drug effects
chemical_list: D000317:Adrenergic alpha-Antagonists; D004146:Dioxanes; D011942:Receptors, Adrenergic, alpha; D009638:Norepinephrine; D019329:Idazoxan