NIFEDIPINE ATTENUATES BOTH ALPHA-1 AND ALPHA-2 ADRENOCEPTOR-MEDIATED PRESSOR AND VASOCONSTRICTOR RESPONSES IN CONSCIOUS DOGS AND PRIMATES

  • 1 December 1986
    • journal article
    • research article
    • Vol. 239  (3) , 648-653
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 .mu.g/kg i.v.), PE (1 .mu.g/kg i.v.), M (20 .mu.g/kg i.v.) and B-HT 920 (1 .mu.g/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 .mu.g/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 vasconstriction.