The effects of the lectins, wheat germ agglutinin (WGA) and concanavalin A (Con A) on endothelium intact pre-contracted rabbit aorta were investigated. WGA (8.3pM) produced endothelium-dependent relaxations, while Con A (4.3 pM) produced a partially endothelium-dependent relaxation. The endothelium-dependent relaxations to WGA were completely reversed by N-acetylglucosamine, haemoglobin and methylene blue and were partially reversed by NG-monomethyl-L-arginine (L-NMMA). It is suggested that WGA works as an agonist in releasing endothelium-derived relaxing factor (EDRF) from the endothelium of rabbit aorta by interacting with a glycosylated receptor on endothelial cells.

The recovery of functional cell-surface bFGF receptors after trypsin treatment was studied in BHK cells and NIH 3T3 cells. Restoration of functional bFGF receptors occurred at an approximately linear rate with 50% of the high-affinity binding capacity restored after 4 hr. Restoration of functional receptors required protein synthesis but not RNA synthesis. Upon exposure of BHK cells to bFGF, cell-surface receptors were rapidly lost, with only 25% remaining after 1 hr. When the bFGF was removed, down-regulated BHK and NIH 3T3 cells recovered cell-surface receptors at about the same rate observed in trypsin-treated cells. The recovery of receptors after down-regulation was inhibited by protein synthesis inhibitors. Addition of the protein synthesis inhibitor cycloheximide to unperturbed cultures of BHK or NIH 3T3 cells resulted in a time-dependent loss of cell-surface bFGF receptors, demonstrating that the receptors turn over constantly in the absence of ligand. These results suggest that bFGF receptors do not recycle and must be continuously synthesized.

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1 The effect of wheat germ agglutinin (WGA), concanavalin A (Con A) and lentil lectin agglutinin (LCA) were investigated on pre-contracted canine coronary artery rings in vitro. 2 In endothelium-intact canine coronary artery, contracted with the thromboxane A2-analogue, U46619, WGA relaxed the tissue in a concentration-dependent manner, with an inhibitory concentration (ICm) of 112 ± 17 nM (n = 6). In the absence of an endothelium, WGA did not cause any relaxation of the tissue. 3 In endothelium-intact canine coronary artery, contracted with the thromboxane A2-analogue, U46619, LCA relaxed the tissue in a concentration-dependent manner, with an inhibitory concentration (ICso) of 423.1 ± 41 nM (n = 6). In the absence of an endothelium, LCA produced a 20.1 + 1.1% (n = 6) relaxation at the highest concentration tested (3 JAM).4 Concanavalin A (Con A) relaxed canine coronary artery in a partial endothelium-dependent manner with an IC50 of 104 ± 19 nM on endothelium-intact coronary artery and an ICs of 1.3 ± 0.3 JAM (n = 6) on endothelium-denuded tissues.5 The relaxation effects of WGA were attenuated by 1 mM N0-monomethyl L-arginine (L-NMMA) and completely inhibited by haemoglobin (3 JAM), methylene blue (10 JAM) and LY 83583 (30 JM). Ibuprofen had no effect on WGA-induced relaxation.6 The relaxant effects of WGA were reversed by addition of 20 mM N-acetyl-D-glucosamine (GlcNAc) and N-acetyl-D-galactosamine (GalNAc) but not by a-mannose, D-(+)-galactose, and P-lactose, whereas the endothelin-dependent relaxations to LCA and Con A were unaffected. 7 The endothelium-dependent relaxation induced by the lectins was unaffected by pretreatment of the tissue with 1 JAM atropine. 8 In the absence of extracellular calcium, WGA was also able to release EDRF suggesting that WGA acts through a second messenger system to release intracellular calcium. 9 We suggest that WGA acts as an agonist to release EDRF from endothelial cells possibly by binding to a sugar moiety, specific receptor or adhesion molecules on the endothelial cell surface.