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

Abstract

Background: A decrease in sodium pump activity in erythrocytes has been associated 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 activity. Methods: Utilizing a radioimmunoassay, we examined the serum concentrations of the digoxin-like immunoreactive factor (DLIF) in ill and well bipolar patients and compared the values to those of normal controls. Results: DLIF was significantly decreased in manic individuals as compared to normal controls (143.6±S.E.M. 20.94 vs 296.6±12.76 pg digoxin equivalents/ml, respectively, F=4.77, P<0.05), but not compared to euthymic bipolar subjects 213.8±86.92, P=0.77). There were no significant differences in DLIF concentrations between manic and euthymic bipolar individuals ( P=0.8). Since relapse in bipolar patients appears to display a seasonal pattern, we also measured the plasma concentration of this factor over a 12-months period. Normal controls exhibited a seasonal pattern of change in serum DLIF concentrations with a nadir in the winter months. Plasma concentrations of DLIF in bipolar patients did not show a seasonal pattern and maintained low levels throughout the year. Limitations: Due to the nonspecificity of our antibody, we could measure only total DLIF. Furthermore, it is unclear what the role of circulating DLIF, if any, may be on brain function. Conclusion: DLIF may be involved in the pathophysiology of mania.