EFFECTS OF ACUTE MENTAL STRESS ON SERUM-LIPIDS - MEDIATING EFFECTS OFPLASMA-VOLUME

The present study assessed the acute effects of mental stress (mental arithmetic) on serum cholesterol, triglycerides, high-density lipoprot ein-cholesterol (HDL-C), and low-density lipoprotein-cholesterol (LDL- C), and the extent to which stress-induced changes are attributable to decreases in plasma volume. Total cholesterol, triglycerides, HDL-C, and LDL-C were assessed in 18 healthy men (35 +/- 7 years) during a re sting baseline (30 minutes), challenging mental arithmetic (math; 10 m inutes), and recovery (30 minutes). Five additional subjects served as controls receiving no stress intervention. An indirect estimation of the change in plasma volume was computed from hematocrit and hemoglobi n at each time point. Results indicated significant (p < .001) increas es in cholesterol, triglycerides, LDL-C, and HDL-C levels during menta l arithmetic. Changes in lipid levels during stress were not related t o plasma epinephrine levels or changes. Significant (p < .002) increas es in hematocrit and hemoglobin levels reflected a 9.23% decrease in p lasma volume during mental arithmetic. Correcting for this decreased p lasma volume, changes in cholesterol, triglycerides, HDL-C, and LDL-C levels during math were no longer significant (p > .16, p > .23, p > . 27, and p > .42, respectively). These results indicate that acute psyc hological stress can cause a rapid and substantial decrease in plasma volume, producing hemoconcentration. Thus, stress-mediated increases i n circulating lipid concentrations are a secondary result of decreased plasma volume, perhaps due to vascular fluid shifts. Methodologically , stress-induced hemoconcentration during mental stress suggests that acute plasma volume decreases may need to be evaluated in studies of t he biochemical effects of stress on high molecular weight substances.