Platelet and plasma serotonin in glomerulonephritis. III: The nephritis of systemic lupus erythematosus.

Intraplatelet and plasma serotonin levels were measured in 269 samples from 44 patients with systemic lupus erythematosus (SLE) and clinical nephritis. The intraplatelet serotonin levels were depressed and the plasma serotonin levels were raised in lupus nephritis. There was a strong correlation between both lowered intraplatelet serotonin concentration and raised plasma "serotonin", and the overall clinical activity of the disease. This correlation was also observed in the majority of individual patients studied serially; the platelet serotonin levels correlated with both clinical and immunological tests. Serotonin uptake by platelets was significantly diminished, but there was no correlation between serotonin uptake and platelet serotonin levels. There was, however, a correlation between the amount of platelet-aggregating material in the serum and depression of intraplatelet serotonin. This study provides further evidence of in vivo platelet activation in SLE nephritis, and provides a measure of the activation in relation to the clinical and immunological activity of the disease.