title: Inhibitory effect of GABA on sympathetic neurotransmission in rabbit ear artery.
abstract: GABA 100 microM inhibited neurogenic vasoconstrictor responses elicited in rabbit ear artery by field stimulation at various frequencies. GABA was ineffective both on resting tone and on noradrenaline (0.05-5 microM)- and high-K+ (24-54 mM)-induced tonic contraction. GABA effectiveness against field stimulation-induced vasoconstriction was inversely related to the frequency of stimulation. This action of GABA was mimicked by a selective GABAB agonist, such as baclofen (100 microM), but not by selective GABAA agonists as muscimol (100 microM) and homotaurine (100 microM). The selective GABAB antagonists 5-aminovaleric acid (1 mM) and homotaurine (100 microM) completely suppressed the inhibitory effect of GABA on field stimulation-induced vasoconstrictions. GABA action was partially reversed also by the selective GABAA antagonist picrotoxin (100 microM); however, this drug "per se" determined an increase in amplitude of field stimulation-induced contractions which in turn could have determined the minor effect of GABA. As a whole these data suggest that GABA can inhibit sympathetic neurotransmission in rabbit ear artery through the stimulation of a prejunctional receptor of the GABAB subtype.
authors.forename: S
authors.initials: S
authors.lastname: Manzini
authors.forename: C A
authors.initials: CA
authors.lastname: Maggi
authors.forename: A
authors.initials: A
authors.lastname: Meli
mesh_terms: D000596:Amino Acids / Q000494:pharmacology; D021542:Amino Acids, Neutral; D000818:Animals; D001158:Arteries / Q000187:drug effects / Q000294:innervation; D001418:Baclofen / Q000494:pharmacology; D004431:Ear, External / Q000098:blood supply; D004558:Electric Stimulation; D018756:GABA Antagonists; D066298:In Vitro Techniques; D008297:Male; D009118:Muscimol / Q000494:pharmacology; D009638:Norepinephrine / Q000494:pharmacology; D010852:Picrotoxin / Q000494:pharmacology; D011188:Potassium / Q000494:pharmacology; D011817:Rabbits; D013564:Sympathetic Nervous System / Q000187:drug effects*; D009435:Synaptic Transmission / Q000187:drug effects*; D013654:Taurine / Q000031:analogs & derivatives / Q000494:pharmacology; D014661:Vasoconstriction / Q000187:drug effects; D005680:gamma-Aminobutyric Acid / Q000494:pharmacology*
chemical_list: D000596:Amino Acids; D021542:Amino Acids, Neutral; D001418:Baclofen; D018756:GABA Antagonists; D009118:Muscimol; D009638:Norepinephrine; D010852:Picrotoxin; D011188:Potassium; D013654:Taurine; D005680:gamma-Aminobutyric Acid; C001355:tramiprosate; C013809:5-aminovaleric acid