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Atherothrombosis seems now to be the most appropriate term to describe the pathogenic events leading to the development of cardiovascular disease. An impaired fibrinolysis may not only contribute to and aggravate the tendency to thrombosis but fibrin deposit may also play a role in the development of the atherosclerotic plaque. Hypofibrinolysis is observed among obese subjects and it has been shown that an excess of plasminogen activator inhibitor 1 (PAI 1) the main regulator of the fibrinolytic system, is closely associated to other components of the insulin resistance syndrome, namely, excessive body weight, high waist to hip ratio, elevated blood pressure, hyperinsulinemia and hypertriglyceridemia. PAI 1 levels decrease with measures attempting at decreasing insulin resistance. However, the mechanisms leading to increased PAI 1 levels are still unknown. On the basis of epidemiological studies, and in vitro studies with PAI secreting cells such as hepatocytes or endothelial cells, insulin, insulin precursors, and lipoproteins, mainly VLDL, appear candidates for triggering this excessive secretion, but no definite answer has yet been found.

Among obese insulin resistant subjects plasminogen activator inhibitor 1 (PAI 1) levels are closely associated with fasting insulin levels in cross sectional as well as intervention studies. Insulin concentration by itself does not seem to modulate PAI 1 levels at least in acute conditions. PAI 1 levels could be more directly related to the insulin resistant state than to hyperinsulinaemia. To elucidate further this phenomenon we compared insulin, triglyceride and PAI 1 levels in twenty control subjects and in three groups of patients presenting insulin resistance 14 obese subjects, 6 patients with Cushing disease and 7 with acromegaly. None of the tested subjects was diabetic. Fasting insulin levels were elevated in obese (21.4 +/- 8.0) hypercortisolic (20.3 +/- 11.0) and acromegalic patients (16.1 +/- 5.0) compared to controls (9.2 +/- 3.0 microU/ml, m +/- SD). PAI activity and PAI 1 antigen levels were elevated in the obese group only (34.3 +/- 13.0 for PAI 1 activity) and not in the others: 10.2 +/- 10.0, 7.0 +/- 4.6 I U/l for hypercortisolic and acromegalic patients respectively (normal controls 9.7 +/- 5.4). Triglyceride levels were also elevated among obese subjects 2.2 +/- 1.3 vs 1.1 +/- 0.4 mM/l in the controls; they were slightly higher than normal but not significantly in the hypercortisolic (1.5 +/- 0.6) and acromegalic (1.43 +/- 0.6 mM/l) patients. The mechanism of insulin resistance is different in the three conditions studied here. This may explain why elevated PAI 1 concentration are restricted to the common form of insulin resistance as seen in obese subjects. Therefore insulin resistant state per se is not associated with elevated PAI 1 levels.