1 Pulmonary prostacyclin (PGI2) biosynthesis was evaluated in relation to endothelial integrity before and after complement activation in isolated plasma-perfused lung lobes of the dog. 2 The plasma was activated with zymosan (ZAP, n = 4), yeast cells (YAP, n = 4) or yeast with 3 yM indomethacin (Indo + YAP, n = 3). Immunoreactive 6-oxo-prostaglandin F a (i-6-oxo-PGF J and thromboxane B2 (iTXB2) were measured to monitor PGI2 and TXA2 biosynthesis.3 The kinetic parameters Km and V,,. of 5-hydroxytryptamine (5-HT) uptake were calculated on the basis of multiple indicator diffusion data to evaluate endothelial integrity. 4 YAP and ZAP induced a biphasic increase of the arterial perfusion pressure. The immediate pressure peak was partly mediated by TXA2 and the TXB2 was subsequently cleared by the lung.5 The apparent V.,x of 5-HT uptake remained constant throughout the experiment. Thus, complement activation did not affect the number of endothelial 5-HT carrier sites available to the perfusate. 6 The apparent Km of 5-HT uptake was enhanced in 9 lungs exposed to activated plasma complement for 20 min. This decreased affinity for 5-HT probably reflects endothelial injury. It was transient as the apparent Km had returned to the baseline value after 60 min. 7 PGI2 clearance and biosynthesis were virtually absent in the control period. PGI2 formation increased drastically after infusion of ZAP or YAP and was proportional to the endothelial injury expressed as elevated Km or pulmonary oedema. Thus, PGI2 biosynthesis might be a marker of severe endothelial distress.

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Prostacyclin (PGI2) formation and the saturable uptake of 5-hydroxytryptamine (5HT) were studied as indices of endothelial integrity in isolated lungs. 5HT uptake was characterized by its kinetic parameters Km and Vmax. These were calculated from multiple indicator dilution data on the basis of an organ model of 5HT uptake. Perfused dog lung lobes were exposed to plasma activated with yeast (YAP) or zymosan (ZAP). YAP induced a transient elevation of Km. This increase probably reflects endothelial injury. Vmax remained unchanged, suggesting that the perfused endothelial surface remained stable. PGI2 biosynthesis was negligible in the control period, but started immediately after exposure to ZAP or YAP. It was proportional to the transient elevation of Km and to the pulmonary oedema. The data suggest that PGI2 might be a marker of severe endothelial distress.

Blood platelets are the principal source of serotonin (5-hydroxytryptamine, 5HT) in the circulation. As it is assumed that 5HT release by activated platelets can influence vascular tone, we investigated whether platelet derived 5HT can penetrate from the lumen into the vessel wall. Venous blood was collected from pentobarbitone anaesthetized dogs on 5.8 mM EDTA, platelet rich plasma was prepared and incubated with 3H-5HT and 14c-adenine. After washing, a platelet suspension (PS, 108/ml) was made in Ca2+ free Krebs'. A segment of each saphenous vein was removed and de-endothelialized for about half (2-3 cm) of its length. The PS was perfused (37°C, 3 ml/min) for 15 min (4 dogs) or 30 min (4 dogs) through the lumen in the absence (one V. saphena) or presence (contralateral vein) of 0.1 unit thrombin/ml. Thereafter, 1 cm of the area with and the area without endothelium was excised, and these segments were washed 24 times with 5 ml Krebs. The 3H and 14c content of wash fluid and solubilized tissue was measured. The 12th wash contained 1.0 unit thrombin in order to verify that the 3H was not derived from adhering platelets. The 14c data indicated that - at low shear stress -similar platelet numbers adhere to the intima with or without endothelium, but in the absence of endothelium thrombin-induced aggregates remain loosely attached to the intima. The wash procedure removed the majority of these adhering platelets, as well as their 3H. In all tissues 3H accumulated, eg 708 dpm after 15 min and 1673 dpm after 30 min perfusion followed by washout. Both values were 7 to 10 fold enhanced when the platelet release reaction was induced with thrombin. In addition, endothelial denudation doubled the 3h accumulation under both circumstances. Previous experiments with soluble 5HT indicated that 70 % of the 3h is present in the adrenergic nerve terminals of the vessel. Application of the PS to the outside of the vessel led to a larger 3h accumulation, but then there was no indication of a difference between area's with or without endothelium.In conclusion, removal of the endothelial metabolic barrier enhanced vascular accumulation of 5HT, but the occurrence of a release reaction appeared to be more important in determining the access of platelet derived 5HT to vascular smooth muscle cells and adrenergic nerve endings.