Factors influencing the magnitude and duration of responses to endogenous and exogenous noradrenaline in rabbit pulmonary artery and portal vein.
1 In the rabbit portal veins, cocaine potentiated responses to (-)-noradrenaline, and prolonged relaxation following transmural stimulation. Neither process was altered by hydrocortisone and U-0521, oxytetracycline or 4-aminopyridine alone or in combination with cocaine. These findings indicated that neuronal uptake was principally responsible for the inactivation of noradrenaline in this tissue. 2 In the rabbit pulmonary artery, the rate of relaxation following transmural stimulation was prolonged by cocaine and by hydrocortisone and U-0521, and further prolonged by the combination of all three drugs. These findings suggest that both neuronal and extra-neuronal uptake are responsible for the inactivation of noradrenaline in this tissue. 3 4-Aminopyridine potentiated responses to (-)-noradrenaline and prolonged relaxation after transmural stimulation in pulmonary artery possibly as a consequence of a postjunctional action in this tissue. 4 The rabbit portal vein was less sensitive to (-)-noradrenaline and relaxed more after transmural stimulation than the pulmonary artery. It is suggested that this reflects the denser noradrenergic innervation and smaller neuromuscular distance present in the portal vein.
D000818:Animals; D004558:Electric Stimulation; D066298:In Vitro Techniques; D009126:Muscle Relaxation / Q000187:drug effects; D009131:Muscle, Smooth, Vascular / Q000187:drug effects*; D009638:Norepinephrine / Q000494:pharmacology* / Q000502:physiology; D011169:Portal Vein / Q000187:drug effects; D011651:Pulmonary Artery / Q000187:drug effects; D011817:Rabbits; D013997:Time Factors
D009638:Norepinephrine