title: The pressor effect of angiotensin-(1-7) in the rat rostral ventrolateral medulla involves multiple peripheral mechanisms.
abstract: OBJECTIVE
  In the present study, the peripheral mechanism that mediates the pressor effect of angiotensin-(1-7) in the rostral ventrolateral medulla was investigated.
  
  
  METHODS
  Angiotensin-(1-7) (25 pmol) was bilaterally microinjected in the rostral ventrolateral medulla near the ventral surface in urethane-anesthetized male Wistar rats that were untreated or treated (intravenously) with effective doses of selective autonomic receptor antagonists (atenolol, prazosin, methyl-atropine, and hexamethonium) or a vasopressin V1 receptor antagonist [d(CH2)5 -Tyr(Me)-AVP] given alone or in combination.
  
  
  RESULTS
  Unexpectedly, the pressor response produced by angiotensin-(1-7) (16 ± 2 mmHg, n = 12), which was not associated with significant changes in heart rate, was not significantly altered by peripheral treatment with prazosin, the vasopressin V1 receptor antagonist, hexamethonium or methyl-atropine. Similar results were obtained in experiments that tested the association of prazosin and atenolol; methyl-atropine and the vasopressin V1 antagonist or methyl-atropine and prazosin. Peripheral treatment with the combination of prazosin, atenolol and the vasopressin V1 antagonist abolished the pressor effect of glutamate; however, this treatment produced only a small decrease in the pressor effect of angiotensin-(1-7) at the rostral ventrolateral medulla. The combination of hexamethonium with the vasopressin V1 receptor antagonist or the combination of prazosin, atenolol, the vasopressin V1 receptor antagonist and methyl-atropine was effective in blocking the effect of angiotensin-(1-7) at the rostral ventrolateral medulla.
  
  
  CONCLUSIONS
  These results indicate that angiotensin-(1-7) triggers a complex pressor response at the rostral ventrolateral medulla that involves an increase in sympathetic tonus, release of vasopressin and possibly the inhibition of a vasodilatory mechanism.
authors.affiliation: Instituto Nacional de Ciência e Tecnologia em Nanobiofarmacêutica, Instituto de Ciências Biológicas, Universidade Federal de Minas Gerais, Belo Horizonte, MG, Brazil.
authors.forename: Rita C
authors.initials: RC
authors.lastname: Oliveira
authors.forename: Maria J
authors.initials: MJ
authors.lastname: Campagnole-Santos
authors.forename: Robson A S
authors.initials: RA
authors.lastname: Santos
mesh_terms: D000803:Angiotensin I / Q000008:administration & dosage / Q000494:pharmacology*; D000818:Animals; D065092:Antidiuretic Hormone Receptor Antagonists; D062186:Arterial Pressure / Q000187:drug effects; D006339:Heart Rate / Q000187:drug effects; D018738:Hexamethonium / Q000008:administration & dosage; D008297:Male; D008526:Medulla Oblongata / Q000187:drug effects* / Q000503:physiopathology; D008845:Microinjections; D010446:Peptide Fragments / Q000008:administration & dosage / Q000494:pharmacology*; D051381:Rats; D017208:Rats, Wistar; D013997:Time Factors; D014665:Vasodilator Agents / Q000008:administration & dosage / Q000494:pharmacology*
chemical_list: D065092:Antidiuretic Hormone Receptor Antagonists; D010446:Peptide Fragments; D014665:Vasodilator Agents; D018738:Hexamethonium; D000803:Angiotensin I; C118790:angiotensin I (1-7)