SINGLE-PASS REMOVAL OF [C-14]-5-HYDROXYTRYPTAMINE AND [H-3]NOREPINEPHRINE BY RABBIT LUNG, INVIVO - KINETICS AND SITES OF REMOVAL

  • 1 January 1983
    • journal article
    • research article
    • Vol. 224  (1) , 28-33
Abstract
Multiple indicator dilution techniques were employed to study the kinetics and sites of removal of [14C]-5-hydroxytrypamine (5-HT) and [3H]norepinephrine (NE) by rabbit lung in vivo. Percentage of single-pass transpulmonary removal of 5-HT decreased from 87 .+-. 2 to 73 .+-. 3, 49 .+-. 7 and 34 .+-. 2% when the total dose of administered 5-HT was increased from 8 .times. 10-9 to 30, 75 and 150 .times. 10-9 mol, respectively. Similarly, percentage of removal of NE decreased from 23 .+-. 2 to 18 .+-. 2, 11 .+-. 2 and 5 .+-. 2% when the amount of NE administered was increased from 0.3 .+-. 10-9 to 10, 50 and 100 .times. 10-9 mol, respectively. Kinetic constants of removal were calculated assuming either homogeneous or heterogenous pulmonary perfusion; values for the apparent Km averaged 1.1 .+-. 0.4 .times. 10-6 M (5-HT) and 0.9 .+-. 0.3 .times. 10-6 M (NE), whereas values for the apparent Vmax of removal were 17.4 .+-. 2.6 .times. 10-9 mol/min per g of lung wet wt (5-HT) and 4.0 .+-. 0.9 .times. 10-9 mol/min per g of lung wet wt (NE). Increasing the dose of administered 5-HT had little effect on NE removal and increasing the dose of NE caused only small reductions in 5-HT extraction, indicating distinct sites of removal of these 2 amines by rabbit pulmonary endothelium.