Cardiovascular effects of L-glutamate microinjection in the supraoptic nucleus of unanaesthetized rats.
We report on the cardiovascular effects of L-glutamate (L-glu) microinjection in the hypothalamic supraoptic nucleus (SON) as well as possible receptor and mechanisms involved. Microinjection of L-glu in 100 nL in the SON caused dose-related pressor and bradycardic responses in unanesthetized rats. Responses were markedly reduced in urethane-anesthetized rats. The response to L-glu 10 nmol was blocked by local pretreatment with 2 nmol of the non-NMDA-receptors antagonist NBQX and not affected by 2 nmol of the selective NMDA-receptor antagonist LY 235959, suggesting that non-NMDA receptors mediate these responses. The pressor and bradycardic response to L-glu was potentiated by intravenous pretreatment with the ganglion blocker pentolinium and was blocked by intravenous pretreatment with the V1-vasopressin receptor antagonist dTyr(CH2)5(Me)AVP, suggesting involvement of circulating vasopressin in this response. Additionally L-glu microinjection into the SON increased plasma vasopressin levels (control: 1.3 +/- 0.2 pg/mL, n = 6; L-glu: 14.7+/-2.3 pg/mL, n=6). In conclusion the results suggest that pressor responses to SON microinjection of L-glu are caused by activation of non-NMDA glutamate receptors and mediated by vasopressin release into systemic circulation.
Busnardo
C
C
Department of Pharmacology, School of Medicine of Ribeirão Preto, University of São Paulo, Av. Bandeirantes 3900, 14049 900 Ribeirão Preto, SP, Brazil.
Tavares
R F
RF
Antunes-Rodrigues
J
J
Corrêa
F M A
FM
D000818:Animals; D001127:Arginine Vasopressin / Q000031:analogs & derivatives / Q000097:blood / Q000494:pharmacology; D001794:Blood Pressure / Q000187:drug effects; D018691:Excitatory Amino Acid Antagonists / Q000494:pharmacology; D005730:Ganglionic Blockers / Q000494:pharmacology; D018698:Glutamic Acid / Q000008:administration & dosage / Q000494:pharmacology*; D006339:Heart Rate / Q000187:drug effects; D007546:Isoquinolines / Q000494:pharmacology; D008297:Male; D008845:Microinjections; D010425:Pentolinium Tartrate / Q000494:pharmacology; D011810:Quinoxalines / Q000494:pharmacology; D051381:Rats; D017208:Rats, Wistar; D013495:Supraoptic Nucleus / Q000502:physiology*; D014667:Vasopressins / Q000378:metabolism*
D018691:Excitatory Amino Acid Antagonists; D005730:Ganglionic Blockers; D007546:Isoquinolines; D011810:Quinoxalines; D014667:Vasopressins; D001127:Arginine Vasopressin; C062865:2,3-dioxo-6-nitro-7-sulfamoylbenzo(f)quinoxaline; D018698:Glutamic Acid; D010425:Pentolinium Tartrate; C068622:argipressin,(1-mercaptocyclohexaneacetic acid)(1)-O-ethyl-Tyr(2)-; C088643:LY 235959