Cardiovascular mechanisms activated by microinjection of baclofen into NTS of conscious rats.
The peripheral mechanisms responsible for pressor response produced by microinjections of baclofen (GABA(B) agonist) into the nucleus tractus solitarii (NTS) of conscious rats were studied. Bilateral microinjections of baclofen (10-1,000 pmol/100 nl) produced a dose-related increase in mean arterial pressure (MAP) and heart rate. The maximal response was observed after 15 min. Intravenous injection of prazosin decreased MAP to control levels. Subsequent treatment with Manning compound (vasopressin receptor antagonist; iv) produced an additional decrease in MAP. In a different group of rats, vasopressin antagonist was injected first and MAP was significantly decreased; however, it remained elevated compared with prebaclofen injection levels. Subsequent treatment with prazosin abolished the baclofen-induced pressor response. Reductions in baclofen-induced pressor response with prazosin treatment were followed by a reflex tachycardia in animals that received a 100 pmol/100 nl dose of baclofen. The tachycardia was not observed with a dose of 1,000 pmol/100 nl. The pressor response induced by microinjection of baclofen into the NTS of conscious rats may be produced by both increases in sympathetic tonus and vasopressin release.
Landulpho
Carlos Daniel Almeida Pitanga
CD
Department of Physiology, Universidade Federal de São Paulo-Escola Paulista de Medicina, São Paulo, SP 04023-060, Brazil.
Dias
Ana Carolina Rodrigues
AC
Colombari
Eduardo
E
D000317:Adrenergic alpha-Antagonists / Q000494:pharmacology; D000818:Animals; D001127:Arginine Vasopressin / Q000031:analogs & derivatives* / Q000494:pharmacology; D001418:Baclofen / Q000494:pharmacology*; D001794:Blood Pressure / Q000187:drug effects; D002320:Cardiovascular Physiological Phenomena / Q000187:drug effects*; D002319:Cardiovascular System / Q000294:innervation*; D004305:Dose-Response Relationship, Drug; D018755:GABA Agonists / Q000494:pharmacology; D058786:GABA-B Receptor Agonists; D006339:Heart Rate / Q000187:drug effects; D006727:Hormone Antagonists / Q000494:pharmacology; D008297:Male; D008845:Microinjections; D011224:Prazosin / Q000494:pharmacology; D051381:Rats; D017208:Rats, Wistar; D017552:Solitary Nucleus / Q000187:drug effects* / Q000502:physiology
D000317:Adrenergic alpha-Antagonists; D018755:GABA Agonists; D058786:GABA-B Receptor Agonists; D006727:Hormone Antagonists; D001127:Arginine Vasopressin; C025043:vasopressin, 1-(1-mercaptocyclohexaneacetic acid)-2-(O- methyl-L-tyrosine)-8-L-arginine-; D001418:Baclofen; D011224:Prazosin