The effect of an admixture of sodium hydrogen phosphate or heparin-coating to poly(D,L)lactide--results of an animal study

The study was aimed at investigating the effect of an admixture of sodium hydrogen phosphate (NaP) on the pH value around degrading poly(D,L)lactide (PDLLA) and the possible improvement of PDLLA biocompatibility by coating its surface with heparin. PDLLA +/- NaP was injection-molded to form rods (20 x 3 x 2 (mm)) and cubes (3 x 2 x 2 (mm)). Half of the pure PDLLA samples were surface-coated using heparin. One rod and cube each of PDLLA, PDLLA + NaP and PDLLA/Hep were implanted into the dorsal muscles of 42 rats. From the 2nd to 52nd week after operation, pH measurements were performed in the environment around the implants. The samples were then harvested for histological and mechanical analyses. No significant decrease in pH-values was observed in the tissue around the implants. Pure PDLLA and PDLLA/Hep samples were macroscopically resorbed after 52 weeks, while the degradation of PDLLA + NaP was still in progress. Approximately 80% of the initial bending strength of PDLLA or PDLLA/Hep rods was present after six weeks, while the bending strength of PDLLA + Nap was reduced to 50% after 4 weeks. Heparin-coating of PDLLA did not improve its biocompatibility but did increase its resorption. While no significant effect of NaP on pH value was found, its admixture did reduce the mechanical characteristics of the implants.

Endothelial function after prolonged coronary artery oxygen persufflation in a rabbit model of heart preservation

Coronary oxygen persufflation may serve as a means to improve storage conditions and organ preservation time for cardiac transplantation. We examined whether coronary oxygen persufflation and prolonged preservation time alter the endothelium-dependent relaxation of isolated coronary arteries. Isolated rabbit hearts were subjected to four different protocols: control (no preservation), 3 h cold storage in Bretschneider's solution, 18 h cold storage in Bretschneider's or University of Wisconsin solution, combined with coronary oxygen persufflation. After 2 h parabiotic reperfusion, intramural segments of coronary arteries were isolated and isometric tension was recorded using a small-vessel myograph. Endothelial function was examined using carbachol and substance P, applied after vessel constriction using high (30 mmol/l) K(+) or U 46.619, a thromboxane receptor agonist. In another series, coronary flow was measured after Bretschneider's +/-18 h coronary oxygen persufflation, or in freshly isolated, retrogradely perfused Langendorff hearts. Flow responses to substance P, acetylcholine or bradykinin were recorded. In saline-reperfused intact hearts no change in the normal effects of endothelium-dependent relaxants was detected after 18 h, irrespective of coronary oxygen persufflation. However, after isolation of the resistance vessels endothelium-dependent relaxation was abolished after long-term preservation and persufflation. Similar results were obtained after mechanical removal of the endothelium using control hearts. Short-term preservation without persufflation resulted in relaxations similar to those in non-preserved control hearts. Long-term preservation of rabbit heart including coronary oxygen persufflation results in unchanged endothelium-dependent relaxation in intact heart, but abolishes the endothelium-dependent relaxation after isolation of the vessels.