Endogenous digoxin-like immunoreactive factor (DLIF) serum concentrations are decreased in manic bipolar patients compared to normal controls

Background: A decrease in sodium pump activity in erythrocytes has been ass ociated with manic episodes of bipolar illness relative to euthymic moods. Since red blood cells are long-lived and lack a nucleus, it is likely that a plasma factor is responsible for the observed decrease in sodium pump act ivity. Methods: Utilizing a radioimmunoassay, we examined the serum concent rations of the digoxin-like immunoreactive factor (DLIF) in ill and well bi polar patients and compared the values to those of normal controls. Results : DLIF was significantly decreased in manic individuals as compared to norm al controls (143.6+/-S.E.M. 20.94 vs 296.6+/-12.76 pg digoxin equivalents/m l, respectively, F=4.77, P<0.05), but not compared to euthymic bipolar subj ects 213.8+/-86.92, P=0.77). There were no significant differences in DLIF concentrations between manic and euthymic bipolar individuals (P=0.8). Sinc e relapse in bipolar patients appears to display a seasonal pattern, we als o measured the plasma concentration of this factor over a 12-months period. Normal controls exhibited a seasonal pattern of change in serum DLIF conce ntrations with a nadir in the winter months. Plasma concentrations of DLIF in bipolar patients did not show a seasonal pattern and maintained low leve ls throughout the year. Limitations: Due to the nonspecificity of our antib ody, we could measure only total DLIF. Furthermore, it is unclear what the role of circulating DLIF, if any, may be on brain function. Conclusion. DLI F may be involved in the pathophysiology of mania. (C) 1999 Elsevier Scienc e B.V. All rights reserved.