Effects of isoproterenol on adrenergic constriction in vascular smooth muscle

A series of isolated segments of carotid arteries from Dutch-belted, adult, male rabbits were studied with respect to their response to a beta receptor agonist. Segments of 3-cm length were mounted in a chamber with constant surrounding temperature and pressure and perfused at constant pressure. Inflow pressure, outflow pressure, and flow rate were measured, and values of resistance (R) were calculated. Subsequent to control R, each vessel was exposed to a vasoconstricting concentration of either norepinephrine (NE: 10(-8), 10(-9), 10(-10) M) or potassium (K+: 100mM, 50 mM) followed by three doses of the beta-adrenergic agonist, isoproterenol (IP: 10(-7), 10(-6), 10(-5)M) administered simultaneously with each constrictor. R was not altered by IP during NE infusion but was significantly increased at all levels of IP during both K+ infusions. When the K+ series was repeated with alpha blockade, IP did not alter R. Thus, beta receptors do not appear to be functionally present in the adult rabbit carotid artery.