Effect of serum albumin on vascular smooth muscle metabolism

In studies on metabolism of vascular smooth muscle, it was observed that incubation of intact porcine carotid artery strips with 3% bovine or porcine serum albumin had profound effects on the oxidation of substrates and O2 consumption. Arteries incubated over 180 min with charcoal-treated and dialyzed albumin demonstrated time-dependent stimulation of glucose oxidation (145%; P < 0.0001, n=6) and O2 consumption (116%; P< 0.001, n=6). These results were not mimicked by incubation with 3% solutions of ovalbumin or porcine skin gelatin. However, the oxidation of the medium chain fatty acid octanoate was inhibited in the presence of albumin over a broad range of octanoate concentrations (0.5-5.0 mM). Short chain fatty acid oxidation (acetate, 5 mM), in contrast, was not inhibited by albumin. Wash-out of albumin only partially reversed the stimulation of O2 consumption and incubation of arteries with a polyanionic compound, polyethylene sulfonate (5 mg/ml), blunted the stimulatory effect of albumin on O2 consumption. Albumin also produced anaplerosis of the Krebs cycle, and an increase in the content of glutamate and alanine (P < 0.005, n=8). The metabolic effects of albumin were associated with time-dependent uptake of albumin (30.9 +/- 1.5 nmol/g per 210 min; P<0.01, n=15). ATP-dependent proteolysis of the albumin taken up was also observed. These results demonstrate novel and important intracellular effects of serum albumin on energy metabolism of vascular smooth muscle.