Prostaglandin E1 uptake by isolated cat lungs perfused with physiological salt solution

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Abstract
The instantaneous extraction of prostaglandin E1 (PGE1) was measured after a bolus injection of PGE1 and [14C]dextran into the pulmonary artery of isolated cat lungs perfused with a physiological salt solution [Krebs-Ringer-bicarbonate buffer (KRB)]. The extraction ratio vs. time curves exhibited characteristic shapes. For low injected doses of PGE1, the extraction ratios were constant early in time; for high doses, they were concave upward. A model assuming homogeneous perfusion and a saturable uptake mechanism (Michaelis-Menten kinetics) for the PGE was used in a linear regression analysis to estimate Vmax and Km. The kinetic parameters were compared with previous results for blood-perfused lungs; the Km values were significantly smaller than in blood-perfused lungs but the Vmax values were not significantly different. PGE1 uptake evidently was greater in KRB than in blood-perfused lungs when the dose of PGE1 was low but the difference disappeared at high doses. The absence of plasma protein binding in KRB-perfused lungs may be responsible for the lower Km.