title: Nifedipine attenuates both alpha-1 and alpha-2 adrenoceptor-mediated pressor and vasoconstrictor responses in conscious dogs and primates.
abstract: Effects of the calcium channel blocker, nifedipine, were examined on the pressor and vasoconstrictor responses to stimulation of alpha-1 and alpha-2-adrenoceptors in chronically instrumented conscious dogs and Rhesus monkeys. Norepinephrine (NE), a mixed alpha-1 and alpha-2 adrenoceptor agonist, phenylephrine (PE) and methoxamine (M), selective alpha-1 adrenoceptor agonists, and B-HT 920, a selective alpha-2 adrenoceptor agonist, were injected i.v. after ganglionic (hexamethonium), beta adrenoceptor (propranolol) and muscarinic receptor (atropine methyl bromide) blockade. In the dog, NE (0.1 microgram/kg i.v.), PE (1 microgram/kg i.v.), M (20 micrograms/kg i.v.) and B-HT 920 (1 microgram/kg i.v.) produced similar increases in mean arterial pressure (NE, 52 +/- 4 mmHg; PE, 42 +/- 4 mm Hg; M, 43 +/- 7 mm Hg; B-HT 920, 45 +/- 6 mm Hg) and total peripheral resistance (NE, 20.8 +/- 5.8 mm Hg/l/min; PE, 23.1 +/- 4.2 mm Hg/l/min; M, 18.2 +/- 2.1 mm Hg/l/min; B-HT 920, 24.8 +/- 7.1 mm Hg/l/min). Nifedipine (0.5 microgram/kg/min i.v.) caused a similar attenuation of the pressor (NE, -54 +/- 8%; PE, -43 +/- 8%; M, -49 +/- 6%; B-HT 920, -56 +/- 8%) and vasoconstrictor (NE, -66 +/- 11%; PE, -52 +/- 9%; M, -60 +/- 13%; B-HT 920, -57 +/- 10%) responses to each of the alpha-adrenoceptor agonists. Nifedipine also attenuated pressor responses to alpha-1 and alpha-2 adrenoceptor agonists similarly in conscious monkeys. Thus, in conscious dogs and monkeys, calcium channel blockade attenuates similarly both alpha-1 and alpha-2 adrenoceptor-mediated vasoconstriction.
mesh_terms: D000818:Animals; D001381:Azepines / Q000494:pharmacology; D001794:Blood Pressure / Q000187:drug effects*; D002302:Cardiac Output / Q000187:drug effects; D004285:Dogs; D005260:Female; D006339:Heart Rate / Q000187:drug effects; D008253:Macaca mulatta; D008297:Male; D008729:Methoxamine / Q000494:pharmacology; D009543:Nifedipine / Q000494:pharmacology*; D009638:Norepinephrine / Q000494:pharmacology; D010656:Phenylephrine / Q000494:pharmacology; D011942:Receptors, Adrenergic, alpha / Q000187:drug effects / Q000502:physiology*; D014655:Vascular Resistance / Q000187:drug effects; D014661:Vasoconstriction / Q000187:drug effects*
chemical_list: D001381:Azepines; D011942:Receptors, Adrenergic, alpha; D010656:Phenylephrine; C024763:talipexole; D008729:Methoxamine; D009543:Nifedipine; D009638:Norepinephrine