title: Presynaptic effects of l-alanine on peripheral sympathetic neurotransmission.
abstract: Concentrations ranging from 0.1 nM to 30 microM of the aminoacids l-alanine (l-ALA), taurine, hypotaurine and beta-ALA were assayed on the chronotropic responses of rat isolated atria stimulated through their cardioaccelerans nerves. The increases in atrial rate obtained in frequency-response curves to nerve stimulation (0.1-12.8 Hz) were not modified by taurine, hypotaurine and beta-ALA but were reduced by l-ALA (0.01 and 0.1 microM). L-ALA did not modify the chronotropic responses to exogenous norepinephrine (NE). In the atria labeled in vitro with [3H]NE, the release of radioactivity evoked by postganglionic nerve stimulation at 2 Hz (6 V, 0.5 msec duration for 2 min) was reduced to 70% of control values by 0.1 microM l-ALA. The release of [3H]NE evoked by 60 and 100 mM KCl was also reduced by 0.1 microM l-ALA to 40 and to 70% of control values, respectively. L-ALA (0.1 microM) did not affect the outflow of tritium provoked by a 1-min incubation with 1 microM tyramine. The chronotropic responses to nerve stimulation were not modified by the l-ALA metabolites pyruvate and glutamate but were reduced by an analog of l-ALA, alpha-(methylamino)-isobutyric acid, which also diminished the release of [3H]NE elicited by nerve stimulation at 2 Hz.(ABSTRACT TRUNCATED AT 250 WORDS)
mesh_terms: D000409:Alanine / Q000494:pharmacology*; D000818:Animals; D001640:Bicuculline / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D005260:Female; D006325:Heart Atria / Q000187:drug effects; D006339:Heart Rate / Q000187:drug effects; D008297:Male; D009638:Norepinephrine / Q000494:pharmacology; D011189:Potassium Chloride / Q000494:pharmacology; D051381:Rats; D013331:Strychnine / Q000494:pharmacology; D013564:Sympathetic Nervous System / Q000187:drug effects*; D009435:Synaptic Transmission / Q000187:drug effects*; D013654:Taurine / Q000031:analogs & derivatives / Q000494:pharmacology; D015091:beta-Alanine / Q000494:pharmacology
chemical_list: D015091:beta-Alanine; D013654:Taurine; C003949:hypotaurine; D011189:Potassium Chloride; D013331:Strychnine; D000409:Alanine; D009638:Norepinephrine; D001640:Bicuculline