title: Mesenteric vasoconstriction and hindquarters vasodilatation accompany the pressor actions of exendin-4 in conscious rats.
abstract: The hemodynamic effects of the glucagon-like peptide-1 (GLP-1) receptor agonist, exendin-4, and putative underlying mechanisms were assessed in conscious male Sprague-Dawley rats. At a dose of 25 ng kg(-1) i.v., exendin-4 had little effect, but doses of 250 and 2500 ng kg(-1) had significant tachycardic effects (+66 +/- 9 and +95 +/- 16 beats min(-1) at 5 min, respectively) and pressor actions (+10 +/- 2 and +12 +/- 1 mm Hg), accompanied by substantial falls in mesenteric vascular conductance (-38 +/- 3% and -47 +/- 3%) and increases in hindquarters vascular conductance (+82 +/- 14% and +126 +/- 15%). The latter were likely due to adrenaline-mediated activation of beta(2) adrenoceptors since they were abolished by the beta(2) adrenoceptor antagonist, ICI 118551 [(+/-)-1-[2,3-(dihydro-7-methyl-1H-inden-4-yl)oxy]-3-[(1-methylethyl)amino]-2-butanol) hydrochloride], or propranolol [(RS)-1-[(1-methylethyl)amino]-3-(1-naphthalenyloxy)-2-propanol], and absent in adrenal-demedullated rats. In the presence of beta-adrenoceptor antagonism, the tachycardic effects of exendin-4 were suppressed, but the pressor action was enhanced. Enhancement of the pressor action of exendin-4 was not seen in adrenal-demedullated rats or in animals given phentolamine in addition to propranolol, consistent with a component of the pressor action of exendin-4 being due to an adrenaline-mediated positive inotropic effect mediated by alpha-adrenoceptors. The mesenteric vasoconstrictor effect of exendin-4 was unaffected by antagonism of alpha-adrenoceptors, vasopressin receptors, angiotensin receptors, or GLP-1 receptors, although antagonism of the latter substantially inhibited the hindquarter vasodilator effects of exendin-4. These results are consistent with exendin-4 having cardiovascular effects through GLP-1 receptor-dependent and -independent mechanisms, some of which involve sympathoadrenal activation.
authors.affiliation: School of Biomedical Sciences, University of Nottingham, UK. sheila.gardiner@nottingham.ac.uk
authors.forename: Sheila M
authors.initials: SM
authors.lastname: Gardiner
authors.forename: Julie E
authors.initials: JE
authors.lastname: March
authors.forename: Philip A
authors.initials: PA
authors.lastname: Kemp
authors.forename: Terence
authors.initials: T
authors.lastname: Bennett
mesh_terms: D000818:Animals; D001012:Aorta, Abdominal / Q000187:drug effects*; D001794:Blood Pressure / Q000187:drug effects; D004305:Dose-Response Relationship, Drug; D000077270:Exenatide; D000067757:Glucagon-Like Peptide-1 Receptor; D006339:Heart Rate / Q000187:drug effects; D006439:Hemodynamics / Q000187:drug effects*; D006614:Hindlimb / Q000098:blood supply; D008297:Male; D017538:Mesenteric Artery, Superior / Q000187:drug effects*; D010455:Peptides / Q000494:pharmacology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D018027:Receptors, Glucagon / Q000819:agonists*; D014661:Vasoconstriction / Q000187:drug effects; D014664:Vasodilation / Q000187:drug effects; D014688:Venoms / Q000494:pharmacology*
chemical_list: C000593835:Glp1r protein, rat; D000067757:Glucagon-Like Peptide-1 Receptor; D010455:Peptides; D018027:Receptors, Glucagon; D014688:Venoms; D000077270:Exenatide