Platelets isolated by albumin gradient retain normal activation pathways.

Isolated platelets from samples with low counts produce technical problems. Albumin gradient (AG) has been shown to be useful for this purpose, preserving the aggregating response of these cells. The influence of this method in the enzymatic pathways that regulate the platelet activation is studied. Platelets were isolated by either AG or conventional centrifugation methods and labelled with C-14-arachidonic acid (C-14-AA). Isolated platelets were activated with thrombin (5 U/ml) and lipids were extracted according to Bligh and Dyer. Platelet phospholipids and prostanoids were resolved by TLC. The incorporation of C-14-AA by platelets was similar by both methods (31.7 +/- 18% versus 47.2 +/- 6.9%), as well as the distribution of C-14-AA in the five major platelet phospholipids. Formation of radioactive thromboxane B2, hydroxyheptadecatrienoic acid and hydroxyeicosatetraenoic acid by activated platelets was also similar by both methods. These findings suggest that platelet isolation by albumin gradient preserves the enzymatic pathways responsible for the activation of these cells.

Metformin induces an agonist-specific increase in albumin production by primary cultured rat hepatocytes.

Metformin (MET) is known to increase several biological effects of insulin (INS), but there is no information concerning its direct effects on protein synthesis. We studied the action of MET on albumin production by primary cultures of freshly isolated rat hepatocytes, alone or in combination with various agonists: INS, IGF-1, EGF, thyroxin, and dexamethasone. While having no effect alone, MET in vitro potentiates the effects of INS, IGF-1, and EGF. When this increasing effect toward INS was studied over a broad concentration range, MET appeared to improve low-acting INS levels and to intensify the maximal INS effects. In contrast, MET did not change the production of albumin stimulated by thyroxin or dexamethasone. Animals chronically pretreated with MET in vivo showed a higher yield of isolated hepatocytes, better attachment, and especially higher viability after liver perfusion and during cell culture. This may largely explain why basal albumin rates were higher than in in vitro-treated cells. The effect of MET in the presence of the agonists exhibited the same agonist-specificity as in vitro. Our data provide new insights into the pharmacology of MET by showing that hepatic protein synthesis is increased by MET and INS. From the specificity of action of MET towards INS, IGF-1, and EGF (but not thyroxin or dexamethasone), we hypothesize that this biguanide may act on intracellular pathways located between membrane receptors and sites of branching in the signaling cascades shared by these agonists.