Acute psychological stress reduces plasma triglyceride clearance

Psychophysiology, 39 ~2002!, 80–85. Cambridge University Press. Printed in the USA. Copyright © 2002 Society for Psychophysiological Research DOI: 10.1017.S0048577201020133

Acute psychological stress reduces plasma triglyceride clearance

CATHERINE M. STONEY,a SHEILA G. WEST,a JOEL W. HUGHES,a LISA M. LENTINO,a MONTENIQUE L. FINNEY,a JAMES FALKO,b and LINDA BAUSSERMAN c a

Department of Psychology, Ohio State University, Columbus, Ohio, USA Department of Endocrinology, Ohio State University, Columbus, Ohio, USA c The Miriam Hospital, Brown University, Providence, Rhode Island, USA b

Abstract Acute stress elevates blood lipids, with the largest increases among men and postmenopausal women. The mechanisms for the effect are unknown, but may be due to altered lipid metabolism. This study investigated if acute stress induces transient reductions in triglyceride clearance in middle-aged men and women, and determined if gender and menopause affect triglyceride metabolism. Of the 35 women, half were premenopausal, and half were naturally postmenopausal; men ~n 5 35! were age matched. Clearance of an intravenously administered fat emulsion was assessed twice: once during a nonstress session, and again during a stress-testing session. During the stress session, a battery of behavioral stressors ~serial subtraction, speech, mirror tracing, and Stroop! were performed for 40 min. The clearance rate of exogenous fat was significantly diminished during the stress, relative to the nonstress session. Women had more efficient clearance, relative to men, but there were no effects of menopausal status. The diminished ability to clear an intravenous fat emulsion during stress suggests one mechanism for stress-induced elevations in lipids. Descriptors: Lipid reactivity, Lipid metabolism, Gender differences, Stress reactivity, Triglyceride clearance rate supported the conclusions of the descriptive review ~Niaura, Stoney, & Herbert, 1992; Niaura, Stoney, Matacin, Ma, & McParlin, 1996!. Overall, despite some important null findings ~Muldoon et al., 1992!, the bulk of the literature indicates that acute psychological stressors are associated with transient, but consistent, elevations in the atherogenic lipids. Although it is well understood that persistent elevations in total cholesterol, LDL-c, and triglycerides elevate risk for atherosclerotic heart disease ~Castelli et al., 1986; Jeppesen et al., 1998; McGill et al., 1997!, the etiological importance of short-term elevations in these parameters remains unknown. However, there is some indirect evidence that acute rises in the atherogenic lipids may be clinically relevant. For example, postprandial lipemia ~transient elevations in triglyceride-rich lipoproteins! is related to intimamedia thickening of the extracranial carotid arteries, independent of other cardiovascular risk factors ~Ryu et al., 1992!, in middleaged individuals. Specifically, individuals who were subsequently found to have greater carotid artery wall thickness ~an atherosclerotic index! have more persistent postprandial lipemia, relative to healthy individuals. Other investigations have noted greater postprandial triglyceride elevations among those with established coronary artery disease ~Groot et al., 1991; Simpson et al., 1990!, relative to those with no documented atherosclerotic disease. Most relevant to the current study are those investigations demonstrating that individuals at increased risk of atherosclerotic disease have larger magnitude elevations in total cholesterol, triglycerides, and LDL-c when stressed, relative to individuals at lower risk of disease. For example, men relative to age-matched women ~Stoney,

Because total cholesterol, low density lipoprotein-cholesterol ~LDL-c!, and triglycerides are risk factors for the development of cardiovascular diseases ~Castelli, Garrison, & Wilson, 1986; Jeppesen, Hein, Suadicani, & Gyntelberg, 1998; McGill, McMahan, Malcom, Oalmann, & Strong, 1997!, considerable interest has focused on factors that contribute to variations in lipid concentrations. Many investigations have demonstrated that during shortterm psychological stressors in humans, triglycerides, total cholesterol, and LDL-c rise ~Brindley, McCann, Niaura, Stoney, & Suarez, 1993; McCann, Warnick, & Knopp, 1990; Stoney & West, 1997!. A review of the early literature in this area has indicated consistent evidence for significant elevations in the atherogenic lipids during acute and0or episodic stressors ~Dimsdale & Herd, 1982!. A meta-analytic review of the more contemporary literature This work was supported in part by National Institutes of Health grants HL-48411 and HL-48363 ~CMS!, by MO1-RR0034 to Ohio State University General Clinical Research Center, and by the Ohio State University Predoctoral ~JWH! and Postdoctoral ~SGW! Fellowships. We are indebted to Mr. Tom Michalski of Baxter Healthcare, Deerfield, IL., for supplying the Travamulsion used in this study. We wish to gratefully acknowledge the expert technical contributions of Karen Cook, the outstanding staff of the Ohio State University General Clinical Research Center, and the participation of the study volunteers. Dr. West is now at Pennsylvania State University, University Park, PA. Dr. Lentino is now at the Veteran’s Administration Hospital, Bedford, MA. Dr. Hughes is now at Duke University, NC. Address reprint requests to: Catherine M. Stoney, Ph.D., Ohio State University, 210 Townshend Hall, 1885 Neil Avenue, Columbus, OH 432101222, USA. E-mail: [email protected].

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Stress reduces triglyceride clearance

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Matthews, McDonald, & Johnson, 1988!, postmenopausal women relative to age-matched premenopausal women ~Stoney, Owens, Guzick, & Matthews, 1997!, and those with a positive parental history of myocardial infarction relative to those with no parental history ~Stoney & Hughes, 1999! have all been shown to have larger total cholesterol, LDL-c, and0or triglyceride elevations during acute psychological stressors. The mechanisms for the increase in lipids during short-term stress are currently unknown. Although some data indicate that a portion of stress-induced increases in lipids are a result of hemoconcentration resulting from the well-documented passive plasma volume shifts during psychological stress ~Muldoon et al., 1992; Patterson, Gottdiener, Hecht, Vargot, & Krantz, 1993!, other studies have demonstrated persistent stress-related elevations in lipids even after controlling for plasma volume shifts ~Stoney & Hughes, 1999; Stoney, Niaura, & Bausserman, 1997!. Additionally, the extent of stress-related change in lipids is not consistent across all measured parameters ~McCann et al., 1995!. Thus, it is likely that multiple mechanisms are responsible for stress-induced alterations in the lipoproteins. Because most studies of lipid reactivity have specifically examined triglyceride responsivity to stress, a potentially fruitful first step in understanding the mechanisms for stressassociated changes in lipids is to examine possible mechanisms for triglyceride elevations during stress. One hypothesis regarding the mechanism for short-term elevations in triglycerides is that acute psychological stress might induce transient reductions in triglyceride clearance ~Le Fur et al., 1999!. No study has tested this notion directly. This is, in part, because the removal rate of triglycerides from the circulation is difficult to evaluate during acute stressors, because it requires ingestion of a high-fat meal and subsequent evaluation of triglyceride concentrations over a period of 8–12 h. The use of the triglyceride tolerance test, in which a triglyceride-rich emulsion is administered intravenously in order to subsequently calculate the triglyceride clearance rate, is a practical alternative. The triglyceride tolerance test is well described, requires only 40 min, and is associated with only minimal risk to subjects ~Rossner, 1974; Taskinen, Nikkila, Kuusi, & Tilikoura, 1983; Thompson et al., 1991!. Most importantly, the resulting clearance rate, K 2 , has been demonstrated to be a valid index of processes by which triglyceride-rich lipids are

removed from the circulation ~Rossner & Kirstein, 1984!, and is highly reproducible over time ~Rossner, 1974; Taskinen et al., 1983!. The purpose of the current study was to directly test the hypothesis that stress induces a metabolic change in plasma triglyceride, by comparing the clearance of an exogenously administered fat emulsion in healthy individuals during a psychological stress session and again during a separate, nonstress session. Because both gender and menopausal status have been shown in some studies to be important determinants of physiological response to stress ~Burker, Fredrikson, Rifai, Siegel, & Blumenthal, 1994; Kirschbaum, Wust, & Hellhammer, 1992; Stoney et al., 1988!, we examined both premenopausal and naturally postmenopausal women, along with age-matched men. In this regard, examination of gender differences is particularly important, because triglyceride levels are a more important risk factor for atherosclerotic disease in women than in men ~Castelli, 1992!. Method Participants Participants for this study were 70 healthy, nonsmoking, normolipidemic, middle-aged men ~n 5 35! and women ~n 5 35!. They were recruited from the local community by way of newspaper advertisements, and all were paid for their time. Of the participants who responded to the advertisements and were eligible, 89% ultimately participated in the study. Reasons for not participating were primarily time constraints and difficulties with scheduling. By design, approximately one-half of the participants ~n 5 36! were between the ages of 40 and 48 years ~mean age 5 42.9 years!, and the other half ~n 5 34! were between the ages of 54 and 61 years ~mean age 5 55.9 years!. Both age groups consisted of the same number of men and women. All of the younger women were premenopausal and had normal menstrual cycles. All of the older women were naturally postmenopausal for at least the previous 12 months. Age and other relevant demographic characteristics are presented in Table 1. The study was approved by the Ohio State University Institutional Review Board, and all participants gave written informed consent on each testing day. Inclusionary and exclusionary criteria were as follows. All participants were healthy and nonobese. No participant was or had

Table 1. Demographic and Cardiovascular Characteristics of Study Participants (Mean 6 SD) Women

Age ~years! Body weight ~kg! a Height ~cm! a % Body fat a Body mass index ~BMI! Race ~% distribution! b Caucasian African-American Other Marital status ~%! Married Divorced Other Baseline triglyceride ~mg0dL! c a

Men

Younger

Older

Younger

Older

42.4 6 1.27 70.6 6 13.7 164.1 6 5.3 32.5 6 7.6% 26.2 6 4.7

57.2 6 2.27 68.2 6 12.3 164.6 6 5.3 32.9 6 7.3% 25.2 6 4.8

43.4 6 2.12 83.7 6 11.4 175.0 6 5.8 23.0 6 3.9% 27.1 6 3.8

57.8 6 2.48 87.4 6 14.8 180.1 6 7.1 22.5 6 6.3% 26.8 6 3.3

80.0% 10.0% 10.0%

61.1% 33.3% 5.6%

94.7% 0% 5.3%

90.5% 4.8% 4.8%

60.0% 30.0% 10.0% 78.2 6 33.7

52.9% 17.6% 29.4% 97.5 6 58.6

78.9% 21.1% 0% 151.3 6 116.4

75.0% 10.0% 15.0% 133.4 6 69.2

Gender effects, ps 5 .0001. b p 5 .032. c Gender effect, p 5 .007.

82 been in the previous 6 months taking hormones in any form; for example, no woman was taking oral contraceptives or postmenopausal hormone replacement therapy. No participant regularly took aspirin or any other prescription medication, and all were completely alcohol-free for at least the previous week. All participants followed their usual diet for 1 week prior to participation. All had fasting triglyceride values in normal ~between the 20th and 80th percentiles for age and sex! ranges. At the time of each testing session, all were fasting for 12 h. Physiological Measures Triglycerides, corrected for free glycerol ~Howdieshell, Bhalla, DiPiro, Kuske, & Baisen, 1995! and changes in plasma volume ~Dill & Costill, 1974; van Beaumont, 1972!, were determined using Beckman reagent ~Buccolo & David, 1973!. The laboratory participates in the national survey for clinical laboratories sponsored by the College of American Pathologists. In addition, it has participated in the CDC Lipid Standardization program since 1977, and is currently in the monitoring phase III. The coefficient of variation for triglycerides is 1.5. Hematocrit was measured in a microhematocrit centrifuge. Hemoglobin was determined with Drabkin Reagent using a hemoglobin kit and calibrators from Sigma Chemical ~St. Louis, MO!. Hematocrit and hemoglobin were measured to estimate the changes in plasma volume ~Dill & Costill, 1974; van Beaumont, 1972!. Body weight and height were assessed on a calibrated balance scale. An estimate of percent body fat was obtained by a bioelectric impedance system ~BIA; RJL Systems Inc., Clinton Twp., Michigan!, and based on population-based algorithms ~Lukaski, Johnson, Bolonchuk, & Lykken, 1985!. The Quetelet index ~kg0m 2 ! was subsequently calculated to provide a measure of relative weight ~BMI!.

C.M. Stoney et al. tion of several standard laboratory-based tasks, presented in fixed order. This methodology was based on previous studies demonstrating that these and similar stressors, when combined and presented for extended time periods, result in sustained increases in blood pressure, heart rate, and neuroendocrine parameters ~McCann et al., 1993!. Each task lasted for 4 min, 40 s, and each was presented twice over the 40-min testing session. Tasks were varied slightly during the stress-testing session to decrease the opportunity for habituation to the tasks. Because the triglyceride tolerance test requires exactly 40 min to complete, the tasks were performed continuously during this 40-min period; the only time interval between the tasks was a brief ~20-s! videotaped set of instructions. The serial subtraction task is a frustrating, achievementoriented task that requires participants to subtract a two-digit number from a four-digit number, both quickly and accurately. Both the two-digit and four-digit numbers were changed from session to session, to alleviate practice effects. The speech task requires participants to develop and recite a speech regarding a hypothetical situation. Participants were instructed that their speeches would be videotaped and rated. The mirror tracing task is a frustrating, psychomotor task that requires participants to trace the outline of a figure while viewing only the mirror image of the figure. The Stroop Color-Word Interference task requires participants to view slides with a stimulus color word, printed in a color different from the named color, on one side of the slide. On the other side of the slide are several color words. Subjects are instructed to attend only to the actual color of the letters of the stimulus word, and match that with the identical color word. Each of these tasks has been used extensively ~Allen, Stoney, Owens, & Matthews, 1993; Gliner, Bunnell, & Horvath, 1982; Hjemdahl, Freyschuss, Juhlin-Dannfelt, & Linde, 1984; Kamarck, Jennings, Pogue-Geile, & Manuck, 1994; Stoney, Niaura, Bausserman, & Matacin, 1999!.

Triglyceride Tolerance Test The triglyceride tolerance test was performed once during the stress session, and once during the nonstress session. After collecting a blood sample for the assessment of baseline triglyceride concentrations, the test commenced with the intravenous administration of a bolus dose of a fat emulsion ~Travamulsion 10% 1 ml0kg body weight, Baxter-Travenol Laboratories, Deerfield, IL! in the forearm catheter over 1 min, as previously described ~Sady et al., 1986!. Blood samples, for the determination of triglyceride concentrations, were taken during the last minute of every 5-min period, for 40 min. The timing of the triglyceride measures is based on requirements for the calculation of triglyceride clearance. The indwelling catheter was maintained with small amounts of saline injected after every sample; the initial 4 ml of blood from the catheter was discarded prior to each sample collection. Preinfusion triglyceride concentrations were subtracted from the triglyceride values at subsequent time points. The resultant triglyceride concentration data were plotted semilogarithmically against time, and the disappearance rate constant ~a single K2 value! was calculated, based on the entire 40 min of triglyceride data ~Rossner, 1974!. K 2 reflects differences in peripheral clearance when endogenous production of triglycerides is constant ~Sady et al., 1986; Thompson et al., 1991!, and this K2 value is the primary variable of interest in the current study.

Procedure Participants were recruited to participate in two separate testing sessions, spaced at least 1 day, but not more than 3 days, apart. In one session ~Session T!, the triglyceride tolerance test was administered while participants rested quietly. In the other ~Session TS!, the triglyceride tolerance test was administered while participants actively engaged in a continuous series of psychological stressors. Order of the testing sessions was counterbalanced. For each of the two sessions, participants arrived at the Ohio State University General Clinical Research Center after an overnight fast, and were asked to rest in a sitting position for 30 min. Following the rest period and after obtaining written, informed consent, body composition measures were taken. A 19-gauge, indwelling venous catheter was placed in the antecubital space of the dominant arm, and a blood sample was taken for the subsequent analysis of triglycerides. After another 30-min rest period, the triglyceride tolerance test began, as described above. Each test lasted for 40 min. During each session, a single K 2 value was calculated, based on the rate of change of triglyceride concentrations over the entire 40-min period, as described above. At the completion of each session, participants were given a light meal and reminded of the next scheduled visit. At the completion of both sessions, participants were debriefed and paid.

Behavioral Stressors During one of the two testing sessions, participants were asked to perform a continuous series of stressors, consisting of a combina-

Data Reduction and Analysis Triglyceride values were log transformed because of nonnormal distributions; nontransformed data are displayed in all tables and

Stress reduces triglyceride clearance figures for easier interpretation. Triglyceride values were corrected for changes in plasma volume ~Dill & Costill, 1974!. Body weight, height, percent body fat, and BMI among the four groups of participants were compared with a set of 2 ~Gender: men vs. women! 3 2 ~Age: younger vs. older! analyses of variance ~ANOVAs!. Differences in marital status and ethnic composition of the groups were tested with chi-square analyses. The primary question of interest was to determine whether intravenous triglyceride clearance ~K2 ! was altered during the stress testing session, relative to the nonstress testing session, and to test potential group differences in K 2 . The analysis was a 2 ~Gender: men vs. women! 3 2 ~Age: younger vs. older! 3 2 ~Session: T vs. TS! ANOVA for repeated measures, performed on the K 2 values. A secondary question regarding the extent of the influence of exogenous reproductive hormones on triglyceride clearance rates was examined in a preliminary fashion, by enrolling an additional sample of 19 naturally postmenopausal women who were being treated with hormone replacement therapy. These women were age matched ~mean age 5 57.4 years! to the postmenopausal women not taking hormone replacement, and they participated in the protocol as described above. All women had been taking 0.625 mg conjugated equine estrogens and 2.5 mg medroxyprogesterone acetate ~Prempro! per day for at least the previous 6 months. The triglyceride clearance values of these women were compared to those of the postmenopausal women not taking hormones only in a 2 ~Group: postmenopausal women with vs. without hormone replacement! 3 2 ~Session: T vs. TS! repeated measures ANOVA. Results Group Differences in Descriptive Characteristics The chi-square analysis indicated that there were no significant group differences in marital status, p 5 .221. The ethnic composition of the groups was significantly different, chi-square 5 22.5, p 5 .032, reflecting the larger number of African-American participants among the group of older women. Height, weight, baseline triglyceride concentrations, and BIA differed, as expected, by gender, all Fs . 7.6, all ps , .007. There were no age effects for any of these descriptive characteristics, including height, p 5 .1; weight, p 5 .9; BIA, p 5 .9; and baseline triglyceride concentrations, p 5 .5.

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Figure 1. Disappearance curves of intravenous fat emulsion during a stress ~TS; solid squares! and a nonstress ~T; cross-hatch! session. The top panel illustrates data from one representative participant showing small differences between a nonstress ~T! and stress ~TS! session in clearance rates ~K2 !. The bottom panel is taken from one representative participant showing large differences between a nonstress ~T! and stress ~TS! session in clearance rates ~K2 !. Across all participants, K 2 values were significantly diminished during stress ~TS!.

were being treated with hormone replacement therapy were recruited. The triglyceride clearance values of these women were compared to those of the postmenopausal women not taking hormones, indicating no significant main effects or interaction terms for group, all Fs , 1, all ps . .3. These results suggest that there was no significant influence of hormone replacement therapy on triglyceride clearance during psychological stress. Discussion

Effects of Stress on Intravenous Fat Clearance Rate (K2 ) The analysis performed on the K2 values revealed several important main effects. The significant effect for session, F~1,66! 5 8.34, p , 0.005, reflects the significantly reduced K2 value during stress ~Session TS M 5 2.8%0min, SD 5 1.3!, relative to rest ~Session T M 5 3.2%0min, SD 5 1.5; see Figure 1 and Table 2!. The significant effect for gender, F~1,66! 5 29.0, p , 0.0001, reflects the expected overall higher K2 value in women relative to men. There were no other significant main effects or interaction terms. The lack of significant interaction terms indicates that the effect of psychological stress on the clearance of the fat emulsion is similar in men and women, and is not significantly affected by age in men and women, or by menopausal status in women. Effects of Exogenous Reproductive Hormones To test, in a preliminary fashion, the putative influence of exogenous reproductive hormones on triglyceride clearance rates, an additional sample of 19 naturally postmenopausal women who

This study demonstrates that acute psychological stress induces transiently delayed clearance of triglyceride-rich lipoproteins in

Table 2. Triglyceride Clearance (K2 ) Values (Mean 6 SD) by Group and Session a

Men Younger Older Women Younger Older a

Session T ~no stress!

Session TS ~stress!

2.15 ~60.79! 2.79 ~60.89!

1.86 ~60.92! 2.45 ~60.75!

4.22 ~62.09! 3.76 ~61.26!

3.67 ~61.52! 3.32 ~61.15!

Session effect, p 5 .005. Gender effect, p 5 .0001.

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C.M. Stoney et al.

plasma in healthy, middle-aged men and women. Several previous investigations have demonstrated that pharmacological ~Rossner, 1974!, exercise ~Sady et al., 1986!, and dietary ~Huttunen, Ehnholm, Nikkila, & Ohta, 1975! manipulations of fasting triglyceride concentrations can result in alterations in the fat tolerance test. Other investigations have shown reduced postprandial lipemia with a single bout of exercise in normolipidemic individuals ~Aldred, Perry, & Hardman, 1994! and among endurance athletes ~Merrill et al., 1989!, and one study has reported enhanced postprandial lipemia during stress ~Le Fur et al., 1999!. However, the present study is the first demonstration that psychological stress, which transiently increases triglyceride concentrations, also significantly alters triglyceride clearance. Specifically, these results demonstrate that acute psychological stress in healthy men and women leads to a reduced clearance rate of exogenous fat. We also report significant sex differences for triglyceride clearance rates at rest, a finding which is in keeping with the previous literature, which has reported that women generally have a higher fractional removal rate of intravenously administered fat emulsion ~Rossner & Kirstein, 1984!. However, the results of the present investigation did not indicate a significant influence of gender on the reduced K 2 value during stress, relative to the nonstress period. Although some studies have reported gender differences in total cholesterol and LDL-c response to stress, with men showing enhanced responses relative to women ~Stoney et al., 1988!, gender differences in triglyceride stress responses have generally not been reported. Thus, the finding that the effects of psychological stress on the clearance of the fat emulsion is not significantly affected by gender is consistent with the lack of gender differences in triglyceride stress responses. In the current study, we also wished to test the extent to which menopausal status impacts on triglyceride clearance during stress. Premenopausal and naturally postmenopausal women did not significantly differ in either resting or stress-related K 2 values. To test more directly the influence of ovarian hormones on triglyceride clearance rate, we conducted an additional analysis with a group of postmenopausal women who had been regularly taking hormone replacement therapy for at least the previous 6 months. Comparisons between this group of women with the naturally postmenopausal women not taking hormone replacement therapy also indicated no significant difference in the stress-associated triglyceride clearance rate. Further, although we did not control for menstrual cycle phase, it is highly unlikely this impacted our findings because lipids change very little or not at all during cycling ~Reed, Kris-Etherton, Stewart, & Pearson, 2000!. Thus, these findings suggest that both endogenous and exogenous ovarian hormones are not potent influences on the rate of stressinduced clearance of triglyceride. The groups in the current study were reasonably similar with regard to most demographic characteristics, with the exception of

ethnicity. Both groups of men and the premenopausal women consisted of predominately Caucasian participants, whereas the postmenopausal women consisted of about 60% Caucasian and 33% African-American participants. Although we did not find evidence for an effect of ethnicity on triglyceride clearance, given the ethnic differences in patterns of cardiovascular disease, future studies in this area should specifically examine the impact of ethnicity. The use of the intravenous fat emulsion to study the elimination of plasma triglyceride from circulating blood has several advantages. Large variability in response to oral preparations have been noted, likely due to the variations in absorption processes and chylomicron formation in the gastrointestinal tract. The use of an intravenous tolerance test entirely eliminates this confound, and the test is highly reproducible even after intervals of up to 6 months ~Rossner, 1974!. Additionally, the stress-induced elevations in triglyceride can be rapid. The intravenous fat tolerance test is also rapid, and allows a better test of the mechanisms of acute changes in triglyceride during stress. The mechanism for stress-associated reduction of triglyceride clearance is not known, but may be due to reduced activity of lipoprotein lipase ~LPL!, which is the rate-limiting enzyme for catabolism of the triglyceride-rich lipoproteins. Although no published studies have tested the notion that stress changes LPL activity, preliminary data from our laboratory suggest that lipase activity, particularly LPL, is diminished during acute psychological stress ~Stoney, 1997!. The overall results of the current study, in combination with previous data, suggest that psychological stress may acutely alter lipoprotein metabolism by reducing clearance of the triglyceride-rich lipoproteins. Significant data has accumulated to show that both chronic and acute psychological stress are associated with elevations in the triglyceride-rich lipoproteins. At least two lines of research suggest that such stress-induced alterations may be clinically important. First, short-term elevations in triglycerides in the form of postprandial triglyceridemia are greater among cardiac patients, relative to nonpatient controls ~Ryu et al., 1992; Simpson et al., 1990; Steiner, 1993!. In fact, it has been postulated that atherogenesis is enhanced during postprandial lipemia ~Zilversmit, 1979!. Second, some individuals at elevated risk for cardiovascular diseases demonstrate exaggerated triglyceride response to stress ~Stoney & Hughes, 1999; Stoney et al., 1997!. Although the mechanism~s! for stress-induced lipid reactivity have not been articulated, one hypothesis is that acute stress reduces the clearance of triglycerides. The current study provides the first evidence that short-term stress can reduce plasma triglyceride clearance in healthy men and women. Future studies must determine the extent to which such diminished clearance rates are related to and may explain the transient elevations in triglycerides during stress, and the clinical relevance of diminished stress-induced triglyceride clearance rates.

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~Received February 22, 2001; Accepted July 24, 2001!