Obesity and Insulin Resistance: Effect of Race and Gender

Transcription

1 Relatin fthe White Bld Cell Cunt t Obesity and Insulin Resistance: Effect f Race and Gender Richard E. Pratley, Charltn Wilsn*, Cliftn Bgardus Abstract PRATLEY, RICHARD E, CHARLTON WILSON AND CLIFTON BOGARDUS. Relatin f the white bld cell cunt t besity and insulin resistance: effect f race and gender. Obes Res. 1995;3: Recent reprts suggest that the white bld cell (WBC) cunt is related t plasma insulin cncentratins and insulin resistance in healthy individuals. The present study examines whether these relatins are independent f besity and the pattern f bdy fat distributin and tests whether race and gender affect these relatins. WBC cunts, insulin respnses t a 75 gram ral glucse tlerance test (OGTT) and glucse dispsal during a tw-step hyperinsulinemic euglycemic clamp were measured in 300 men and wmen (149 Pima Indians, 100 whites, and 51 blacks) with a wide range f besity. WBC cunts were lwer in blacks than Pima Indians r whites and tended t be higher in wmen than men. The subgrups were cmparable in age and bdy weight, but percent bdy fat and plasma insulin cncentratins were higher and glucse dispsal during the glucse clamp was lwer in Pima Indians than in blacks r whites. In the grup as a whle, the WBC cunt crrelated with besity (bdy mass index and percent bdy fat), the waist t thigh rati (an index f the pattern f bdy fat distributin), and plasma insulin cncentratins and was negatively related t age and glucse dispsal during the clamp. In multiple regressin analyses, nly age, race and besity were significantly assciated with the WBC cunt. Submitted fr publicatin Nvember 18,1994. Accepted fr publicatinin final frm June 2, Frm the Clinical Diabetes and Nutritin Sectin, Phenix Epidemilgy and Clinical Research Branch, Natinal Institute f Diabetes and Digestive and Kidney Diseases, Natinal Institutes f Health, Phenix, AZ, and *Mescaler Indian Hspital, Mescaler, New Mexic. Reprint requests t Dr. Frailey, NlliINIDDK, 4212 N. 16th Street, Phenix, AZ Cpyright 1995 NAASO. When the analyses were restricted t Pima men, in whm crrelatins between the WBC cunt and the metablic variables appeared the strngest, the WBC cunt remained significantly assciated with plasma insulin cncentratins, but nt glucse dispsal, after cntrlling fr age and besity. The results f this study indicate that age, race, and besity are significantly assciated with the WBC cunt in healthy individuals. Plasma insulin cncentratins, but nt insulin resistance per se, may als be weakly assciated with the WBC cunt, but this may be ppulatin specific. Key wrds: leukcyte cunt, bdy cmpsitin, bdy fat distributin, glucse clamp technique Intrductin The white bld cell (WBC) cunt is related t a number f risk factrs fr cardivascular disease (6,9,12,15,16,22) and is itself an independent predictr f the develpment f crnary heart disease and strke (5,8,16). The magnitude f the risk f cardivascular disease cnferred by a high WBC cunt is cmparable t that f ther risk factrs (8,16). Fr example, WBC cunts in the upper range fnrmal are assciated with as much as a furfld increase in the risk f mycardial infarctincmparedt cuntsin the lw nrmal range (8). Recently, the WBC cunt was shwn t be directly related t insulin respnses t an ral glucse tlerance test (OGTT) and insulin resistance, indexed as the steady state plasma glucse during a mdified insulin suppressin test (6,15). Thus, it was prpsed that a high WBC cunt may be yet anther cmpnent f the grwing cluster f cardivascular risk factrs knwn as the insulin resistance syndrme r Syndrme X (6,15,24). In these studies, the WBC cunt was nt strngly related t the bdy mass index. In cntrast, ther studies have indicated that the WBC cunt is independently related t besity (9,21,22) and at least ne OBESITY RESEARCH Vl. 3 N.6 Nv

2 wac Cunt, Obesity, and Insulin Resistance, Pratley et al. suggested that the WBC cunt als was related t the pattern fbdy fat distributin (22). This raises the pssibility that the relatin between the WBC cunt and insulin resistance is due t their mutual assciatin with a cmmn underlying factr such as abdminal besity. Thus, the present study was undertaken t clarify whether the WBC cunt is related t plasma insulin cncentratins r insulin resistance independently f besity and the pattern f bdy fat distributin, and further, t examine whether there are racial and gender differences in these assciatins. Methds Subjects Three hundred subjects (149 Pima Indians, 100 whites, and 51 blacks) admitted t the clinical research unit at the Phenix Indian Medical Center and studied between 1985 and 1994 are included in this reprt. Thirty six percent f the subjects were wmen. All subjects prvided written infrmed cnsent prir t participatin. Mst f the Pima Indians were participating in an nging lngitudinal study f risk factrs fr NIDDM (19) and were full blded Pima r an admixture f Pima and the clsely related Papag tribe. Blacks and whites had been recruited fr ther cmparative studies (25) and, by histry, had parents and grandparents wh were fthe same race as the vlunteer (25). T determine their health status, all vlunteers underwent a medical histry and physical examinatin and a fasting labratry prfile, including a cmplete bld cunt (CBC) upn admissin. Individuals with significant abnrmalities n screening, including diabetes (4), were excluded frm analysis. Nne f the subjects were taking medicatins which culd affect plasma insulin cncentratins, glucse metablism, r the WBC cunt and nne were allwed t smke during the study. This latter requirement effectively excluded regular smkers frm participatin. Frm 1985 t 1991 CBCs were perfrmed using an Orth ELT..8 (Orth, Braintree, MA) autmated analyzer. Subsequently, a Culter STKS (Culter Electrnics, Hialeah, FL) autmated analyzer was used. In 35 individuals CBCs were analyzed n bth machines. The WBC cunts determined using the tw systems were highly crrelated (r =0.996) and the slpe and intercept f the regressin (y =1.041x ) between the tw methds were nt significantly different than 1 and 0, respectively. Thus, it was nt necessary t crrect the WBC cunt fr this change in methdlgy. Bdy Cmpsitin Bdy mass index (BMI) was calculated as weightlheight 2 (kg/m 2). Bdy density was determined by hydrdensitmetry crrected fr residual lung vl- ume (11) which was simultaneusly measured using the helium dilutin technique (Warren E. Cllins, Inc. Braintree MA). Percent bdy fat was calculated frm bdy density measurements (17) and fat-free mass as the difference between ttal bdy mass and fat mass. The rati f the waist circumference at the umbilicus while supine t the thigh circumference at the gluteal fld while standing (WTR) was calculated as an index f the pattern f bdy fat distributin. The use f this rati largely avids the gender differences inherent t the mre cmmnly used waist-t-hip rati which arise frm differences in the anatmy f the pelvis. Furthermre, the WTR. has been shwn t crrelate as well r better with risk factrs fr cardivascular disease than the waist-t-hip rati (26) and in prspective studies it is an independent predictr f diabetes (19). Oral Glucse Tlerance Test While n the clinical research unit, subjects were prvided a weight-maintaining diet cntaining 45% t 50% carbhydrate, 30% t 40% fat and 15% t 20% prtein. After at least 3 days n this diet, a 75 gram OGTI was perfrmed. Bld samples were cllected at -15,0,30,60,90, 120, and 180 minutes fr determinatin f glucse and insulin cncentratins. Plasma glucse cncentratins were measured by the glucse xidase methd (Beckman Instruments, Fullertn, CA) and plasma insulin cncentratins were determined by radiimmunassay (13). The areas abve basal (mean f -15 and 0 samples) f the glucse and insulin respnses t the OGTI were calculated by trapezidal integratin frm 0 t 180 minutes. Hyperinsulinemic-Euglycemic Glucse Clamp A tw-step hyperinsulinemic-euglycemic glucse clamp was perfrmed as previusly described (18,19,25). Briefly, an intravenus catheter was placed in an antecubital vein fr infusin f insulin, glucse, and [3_3H].glucse. A secnd catheter was psitined in a retrgrade manner in a drsal hand vein fr bld sampling. This hand was kept in a warming bx thermstatically cntrlled at 70 C. A primed-cntinuus infusin f insulin (Velsulin, Nrdisk, Bethesda, MD) was administered at a dse f 40 mu/m 2 min bdy surface area fr ne hundred minutes. Immediately thereafter, a secnd primed-cntinuus insulin infusin was administered at a dse f 400 mu/m 2 min fr an additinall00 min. These rates f insulin infusin prduced mean steady state plasma insulin cncentratins f 744 ± 18 pmlll (mean ± SEM) during the lw dse and ± 246 pmiil during the high dse. Plasma glucse cncentratins were measured at 2.5- t 5-minute intervals during the clamp and maintained at apprximately basal level with a variable infusin f 20% glu- 564 OBESITY RESEARCH Vl. 3 N.6 Nv. 1995

3 WBC Cunt, Obesity, and Insulin Resistance, Pratley et al. -C :l 0 0 = Q)..J - 0- Ql "CO 0'" >< ld Q) :::.c: 3: Dl1Jr:P lb cfldo~ sured rate f appearance f glucse int plasma, endgenus glucse prductin was assumed t be zer. Glucse dispsal during the high-dse insulin infusin was calculated in a similar manner except that endgenus glucse prductin was assumed t be zer. Rates f glucse dispsal were adjusted fr differences in steady-state plasma glucse cncentratins (2). Since differences in glucse dispsal during the euglycemic glucse clamp are largely determined by differences in nn-xidative glucse dispsal (principally glycgen A 0.0 L..--_--L. -'--_----' -1-_----' Bdy Fat (%) -C :l Figure 1: Relatin between the white bld cell (WBC) cunt and percent bdy fat in Pima Indians (Li), whites (CI), and blacks ( 0 ). The WBC cunt crrelated with percent bdy fat (r = 0.33, P = ) in the grup as a whle cse. The rate f appearance f glucse int plasma was measured using a primed-cntinuus infusin f {3 3m glucse beginning 2 hurs befre the clamp and cntinuing thrugh the first (lw-dse) insulin infusin (27). Samples fr measurement f glucse specific activity were btained at during the last 20 minutes f B the basal perid and at 10-minute intervals begining at 60 min and cntinuing thrugh 100 minutes f the lw dse f the clamp. Glucse dispsal rates are typically quite stable during this perid and, under these cndi- 'E tins, measurements fendgenus glucse prductin 5 using this technique differ very little frm thse 0 btained using ther methds (7). Oxygen cnsumptin ~::I 0;; and carbn dixide prductin were measured fr an "C ~ hur befre the start f the insulin infusin and fr the 0 >< duratin f the clamp using a ventilated-hd indirect iiicalrimetry system (19,25). T determine ifhyperinsu- Q) linemia increased the WBC cunt acutely, CBCs were :E measured at baseline and at the end f the lw and high 3: dse insulin infusin in 16 individuals (9 men and 7 wmen, all Pima Indians). Calculatins Average glucse infusin rates were calculated fr the tw 20-minute perids between 60 t 100 minutes f the lw dse and 160 t 200 minutes f the high dse insulin infusin f the clamp. Glucse dispsal during the lw dse insulin infusin was taken as the mean glucse infusin rate plus endgenus glucse prductin. When the rate f glucse infusin exceeded the mea- 0.0 L L.- --L. --I Lg 1 0 [Fasting Insulin (pml/l)] 0.0 L...-_--'-.J.-_--L. -'-_----' Lg 1 0 [Insulin Area (pml-mln/l.j] Figure 2: Relatin between the white bld cell (WBe) cunt and (A) the lg10 f the fasting insulin cncentratin (r =0.35, P =0.0001) and (B) the lg10 f the insulin area abve basal (r =0.39, P =0.0001) in respnse t a 75 g ral glucse tlerance test in Pima Indians (Li), whites (0 ), and blacks (0 ). OBESITY RESEARCH Vl. 3 N.6 Nv

4 WBC Cunt, Obesity, and Insulin Resistance, Pratley et al. Table 1. Subject characteristics PimaMen PimaWmen WhiteMen WhiteWmen BlackMen BlackWmen N Race Gender Age(yr) 29.0± ± ± ± ± ±1.9 P=n.s. P=n.s. ( ) ( ) ( ) ( ) ( ) ( ) P<O.Ol Weight(kg) 100.1± ± ± ± ± 4.0 9O.6±6.0 P=n.s. (M>F) ( ) ( ) ( ) ( ) ( ) ( ) P=n.s. P=n.s. BMI(kglm2) 34.0± ± ± ± 1.5 3O.0± ±2.2 P=O.Ol P=0.03 ( ) ( ) ( ) ( ) ( ) ( )' (P>B) (F>M) BdyFat(%) 29.3±0.6 4O.5± ± ± ± ±2.0 P=O.OOOI P=O.OOOI ( ) ( ) ( ) ( ) ( ) ( ) (p>w>b) (F>M) Waist!Ihigh 1.68± ± ± ± ± ±0.03 P=O.OOOI P=n.s. ( ) ( ) ( ) ( ) ( ) ( ) (p>w>b) Fasting Insulin (pmiil) 154± ± ± ± ±13 155±23 P=O.OOOI P<O.Q1 (6-434) (35-524) (48-390) (48-462) (30-419) (54-359) (P>W,B) (F>M) Insulin Area (nmlminjl) 143± ± 14 86±7 1Q6±10 70±8 109± 18 P=O.OOOI P=n.s. ( ) (12-430) (20-342) (22-318) (13-181) (26-256) (P>W,B) Ml w {J.unl/ kgembs -min) 15.5± ± ± ± ± ±3.3 P=O.OOOI P=n.s. ( ) ( ) ( ) ( ) ( ) ( ) (p<w<b) Mhigh{J.unl/ kgembs -rnin) 47.7± ± ± ± ± ±3.9 P=O.OOOI P=n.s. ( ) ( ) ( ) ( ) ( ) ( ) (P<W,B) Nn-xidative Dispsall w {J.unl/ kgembs <min) 3.9± ± ± ± ± ± 1.7 P=O.OOOI P=n.s. ( ) ( ) ( ) (-2.3-2) ( ) ( ) (P<W,B) Nn-xidative Dispsalhigh (J.unl/ kgembs -rnin) 28.3± ± ± ± ± ±2.8 P<O.Q1 Pen.s, ( ) ( ) ( ) ( ) ( ) ( ) (P<W,B) WBCCunt (x 1091L) 8.4± ± ±02 8.4± ± ±0.5 P=O.OOOI P=n.s. ( ) ( ) ( ) ( ) ( ) (32-9.8) (P,W>B) Values are means± SEM with the rangein parentheses belw. In the final tw clumns the P values fr the effects f race and genderare given. Grupdifferences which weresignificant (P < 0.05)usinga Bnferrni crrected t-testcmparisn are presented in parentheses belwthese values (P = PimaIndians, W = whites, B = blacks, M = males, andf = females). M = meanglucse dispsal during the40 mu/m 2e :min (lw) and 400 mu/m2e min (high) insulin infusin f the glucse clamp. EMBS= estimated metablic bdysize(fat-free mass+ 17.7). 566 OBESITY RESEARCH Vl. 3 N.6 Nv. 1995

5 WBC Cunt, Obesity, and Insulin Resistance, Pratley et al. synthesis) (20) this was calculated by subtracting glucse xidatin rates, determined by indirect calrimetry, frm ttal glucse dispsal during bth the lw and high insulin dses (20). In rder t cmpare glucse dispsal rates in subjects with a wide range f besity, it is necessary t nrmalize glucse dispsal t the amunt f metablically active tissue. Accrdingly, ttal and nnxidative glucse dispsal were expressed per kg f estimated metablic bdy size (EMBS) which equals fat-free mass plus This crrectin, which has previusly been detailed (18), is based upn the fact that the regressin between metablic rate (a measure f metablic bdy size) and fat-free mass has a significant nn-zer intercept. insulin cncentratins (Figure 2a) and insulin respnses t the OGTT (Figure 2b) and was negatively related t ttal glucse dispsal during the lw and high dse insulin infusins (Figures 3a and 3b) and nn-xidative glucse dispsal during the lw dse f the clamp. T determine whether the WBC cunt was independently related t plasma insulin cncentratins and glucse dispsal, multiple regressin mdels were tested which A c j Statistical Analysis All data were analyzed using SAS (Cary, N.C.). Plasma insulin cncentratins were lg transfrmed t achieve a nrmal distributin prir t parametric analyses. Grups were cmpared by analysis f variance and when significant grup effects were present, differences were specified with Bnferrni crrected r-tests. Simple and multiple linear regressin mdels with calculatin f partial crrelatin cefficients were used t analyze the relatinships amng selected variables. Data are presented as means ± SEM and P values < 0.05 were cnsidered significant. Results Subjects (Table 1) The grups were cmparable in age and bdy weight. BMI and percent bdy fat were higher in wmen than in men. Despite this, the WTR was similar in men and wmen. BMI, percent bdy fat, and the WTR were highest in the Pima Indians and lwest in the blacks. Fasting plasma insulin cncentratins and insulin respnses t the OGTT were higher in Pima Indians than in whites r blacks and tended t be higher in wmen than in men. Pima Indians als were the mst insulin resistant, reflected by their lw levels f ttal and nn-xidative glucse dispsal during bth the lw and high insulin dses f the clamp, while whites and blacks had similar, higher respnses. There were n significant differences in glucse dispsal during the clamp between men and wmen. The WBC cunt was significantly lwer in blacks than in either whites r Pimas, and tended t be higher in wmen than men. B -c j ~:::J 0';-- "C~ >< -- ED Q) :::.c 3= L-_-'-_-'--_--L.._---L_---l_---l Glucse Dispsal - Lw Dse (mml/k9embs min) Glucse Dispsal - High Dse (mml/k9embs min) Relatin fthe WBC Cunt t BdyCmpsitin and Metablic Variables (Table 2) : In the grup as a whle, the WBC cunt was negatively crrelated with age and psitively crrelated with weight, BMI, percent bdy fat (Figure 1) and the WTR. The WBC cunt als crrelated with fasting plasma Figure 3: Relatin between the white bld cell (WBC) cunt and glucse dispsal during (A) the lw dse (40 mu/m 2 min) (r = -0.25, P = ) and (B) high dse (400mU/m 2 min) (r = 0.13, P < 0.05) insulin infusin f the clamp in Pima Indians (A), whites (0), and blacks (0). OBESITY RESEARCH Vl. 3 N.6 Nv

6 WBC Cunt, Obesity, and Insulin Resistance, Pratley et al. Table 2. Crrelatins (pearsn Prduct Mment) fthe WBC t anthrpmetric and metablic variables Entire Pima Pima White White Black Black Grup Men Wmen Men Wmen Men Wmen Age C B Weight _ B D BMI D D Bdy Fat D D A A WaistfThigh D Lg Fasting Insulin D D Lg Insulin Area D C M (lw dse) D B M (high dse) A A Nn-xidative Dispsal (lw dse) C Nn-xidative Dispsal (high dse) : A A A =P<0.05, B = P<O.Ol, C= P<O.OOl, D=P= M = mean glucse dispsal during the 40 mu/m 2-min (lw) and 400 mu/m2emin (high) insulin infusin f the glucseclamp. cnsidered separately fasting plasma insulin cncentratins, the insulin area in respnse t the OGTT, and ttal and nn-xidative glucse dispsal during the lw and high dses f the clamp as predictrs f the WBC cunt. All mdels included age, race, gender, and percent bdy fat as cvariates. Only age, race, and percent bdy fat were independently assciated with the WBC cunt in these mdels, whereas nne f the metablic variables were independently related t the WBC cunt. Tgether age, race, and percent bdy fat accunted fr apprximately 20% f the variance in the WBC cunt, with race cntributing abut 10% t the variance, and age and percent fat cntributing 4% t 6% apiece. Since the WBC cunt was significantly lwer in blacks and tended t be higher in wmen, crrelatins between the WBC cunt, plasma insulin cncentratins, and glucse dispsal were als examined in subgrups by race and gender (Table 2). In Pima men, the WBC cunt was crrelated t BMI, percent bdy fat, fasting plasma insulin cncentratins, insulin respnses t OGTT, ttal glucse dispsal during the lw and high dse f the clamp, and nnxidative glucse dispsal during the high dse. In Pima wmen, the WBC cunt was related nly t percent bdy fat, and was nt related t any f the metablic variables. Similarly, in black men the WBC cunt was related t percent fat, but nt t any metablic parameter, whereas in black wmen the WBC was psitively crrelated with glucse dispsal during the high dse f the clamp. In whites, the WBC was neither related t besity nr t any f the metablic variables. T determine if the WBC cunt was independently related t insulin cncentratins and glucse dispsal in the Pima men and black wmen, partial crrelatin cefficients between the WBC cunt and the metablic variables were calculated which cntrlled fr the effects f age and percent bdy fat. In Pima men fasting plasma insulin cncentratins and insulin respnses t 568 OBESITY RESEARCH Vl. 3 N.6 Nv. 1995

7 WBC Cunt, Obesity, and Insulin Resistance, Pratley et al, the OGTT remained significantly assciated with the WBC cunt (partial r = 0.25 and 0.26, P < 0.05, respectively), whereas neither lw nr high dse glucse dispsal was assciated (partial r = 0.13, P = n.s. fr bth) after cntrlling fr age and besity. In black wmen glucse dispsal during the high dse remained significantly assciated with the WBC (partial r = 0.64, P < 0.05, N=14) after cvarying fr age and percent bdy fat Acute EffectfInsulin n the WBC Cunt The mean WBC cunt measured befre the start f the clamp was 7.5 ± 0.6 x There were n significant changes in the WBC cunt during either the lw dse (7.4 ± 0.5 x ) r the high dse (6.9 ± 0.5 x ) insulin infusin. Discussin The results fthis study indicate that age, race, and besity are the majr determinants f the WBC cunt in healthy individuals amng thse variables we cnsidered. Tgether, these factrs accunt fr apprximately 20% f the variance in the WBC cunt. In cntrast t previus reprts (6,15), ur results d nt suggest that insulin cncentratins r insulin resistance are imprtant determinants f the WBC cunt. Althugh WBC cunts were crrelated t plasma insulin cncentratins in bivariate analyses in the grup as a whle, they were nt significantly related when the effects f age, besity, race, and gender were accunted fr in multiple regressin mdels. Analysis f the data in the individual subgrups supprts this cnclusin as the WBC was crrelated t plasma insulin cncentratins in nly ne f the six grups (Pima men). Similarly, these data d nt suggest a strng relatin between the WBC cunt and insulin resistance determined using the euglycemic glucse clamp technique. In the grup as a whle, glucse dispsal was nt related t the WBC cunt after cntrlling fr the effects f age, race and percent bdy fat. Amng the subgrups, glucse dispsal during the high dse f the clamp was nly related t the WBC in black wmen and in this grup the crrelatin was psitive, suggesting that insulin resistance was assciated with lwer WBC cunts, rather than higher WBC cunts as previusly reprted (6,15). T ur knwledge, this is the first study which has examined the effects f acute hyperinsulinemia n the WBC cunt. While the results f ur studies in a limited number f subjects d nt suggest that insulin has an acute effect t increase the WBC cunt, this des nt preclude the pssibility f a chrnic effect f insulin. Our bservatins that age, race and besity are independently related t the WBC cunt are in accrd with previus reprts (8,9,12,21,22). Facchini (6) and Jeppesen (15) reprted that the assciatins between the WBC cunt and plasma insulin cncentratins r insulin resistance were independent f besity. In these studies, the WBC was nly weakly related t the bdy mass index, perhaps reflecting the selectin f a relatively lean ppulatin. In the present study percent bdy fat determined by hydrdensitmetry was mre clsely related t the WBC cunt than was the BMI. In additin, subjects in the present study were, n average, mre bese and mre imprtantly, there was a greater range f besity (4% t 50% bdy fat) than in prir studies. These differences may explain why a larger prprtin f the variance in the WBC cunt was accunted fr by besity than by insulin in the present study. Since the relatin between the WBC cunt and insulin cncentratins is relatively weak, it is pssible that there were insufficient numbers f subjects in all subgrups but the Pima men t detect a significant relatin in this study. In this regard, a large multi-center epidemilgical investigatin f risk factrs fr athersclersis fund that bth fasting plasma insulin cncentratins and besity were independently related t the WBC cunt (22). Similarly, the lack f an independent relatinship between the WBC cunt and insulin resistance culd reflect the small sample size f certain subgrups. This is less likely t be the case in the Pima men, where the sample size was cmparable t that f previus reprts (15), and in this grup, the lack f a relatin between the WBC cunt and insulin resistance may, in fact, reflect racial differences. We have previusly demnstrated that bld pressure and insulin resistance are nt related in the Pima Indians as they are in whites (25). Thus, ifthe WBC cunt is anther cmpnent f an "insulin resistance" syndrme, it is pssible that this relatin is nt expressed in the Pimas, despite their significant insulin resistance. Since abdminal besity is assciated with many f the cmpnents f the insulin resistance syndrme including hyperinsulinemia and insulin resistance (24), we hypthesized that the WBCcunt wuld be related t the pattern f bdy fat distributin. Althugh the WBC cunt was, in fact, crrelated t the WTR in bivariate analyses in the grup as a whle, this relatin was nt independent when age, race, gender and besity als were cnsidered. A crrelatin between the WBC cunt and the pattern f bdy fat distributin als was fund in the ppulatin study cited abve (22); hwever, it was nt reprted whether this relatin was independent f besity. Althugh ur analyses indicate that the WBC cunt is independently related t besity this study is crsssectinal in nature. Thus, it is nt pssible t infer frm these results that a causal relatin exists between besity and higher WBC cunts. Nevertheless, several plausible mechanisms which culd link the WBC cunt t OBESITY RESEARCH Vl. 3 N.6 Nv

8 WBC Cunt, Obesity, and Insulin Resistance, Pratley et al. besity have been prpsed (21,22). Mst white bld cell types have insulin receptrs (10,23) which may be imprtant in their prductin and maturatin, thus, it is tempting t speculate that the hyperinsulinemia assciated with besity is respnsible fr the relatin between the WBC and besity. This is Unlikely t be the nly explanatin, hwever. In the subgrup f Pima men, percent bdy fat was significantly related t the WBC cunt, even after cntrlling fr the effects f plasma insulin (partial r =0.36, P < and r =0.47, P = fr fasting insulin and insulin area, respectively) suggesting that ther mechanisms are imprtant as well. It als has been pstulated that the relatin between the WBC cunt and besity is due t excess adrencrtical hrmnes (21), estrgens (21) r catechlarnines (22) in bese individuals, but the evidence fr these mechanisms is largely circumstantial. Leukcytes express receptrs fr a large number f hrmnes including receptrs fr crtisl, estrgens, and catechlamines (1,3). In additin, certain physilgic and pathphysilgic cnditins such as Cushings disease, pregnancy, and exercise are assciated with increases in the WBC cunt (1). Whether r nt these hrmnal mechanisms playa rle in healthy individuals remains t be tested. Based n evidence that the WBC cunt predicts cardivascular events, it has been suggested that athersclersis itself may lead t increased WBC cunts (5,16). This pssibility seems unlikely t accunt fr ur bservatins since the Pima Indians have a lw prevalence f cardivascular disease, despite their besity and insulin resistance (14). Finally, at least tw studies have fund that a high WBC cunt is related t lw levels f habitual physical activity (9,22). Thus, it is pssible that the relatin f the WBC t besity is secndary t the effects f physical activity. In cnclusin, the results f the present study indicate that age, race, and besity are independently related t the WBC cunt. Plasma insulin cncentratins and insulin resistance are als related t the WBC cunt but these relatins are relatively weak and appear t be due largely t their mutual assciatin with besity. In certain specific grups, hwever, insulin and glucse dispsal may be independently related t the WBC cunt. While the interrelatins between the WBC cunt, insulin and besity remain uncertain, in mst studies the variance in the WBC explained by insulin is rather small. Thus, further studies will be necessary t understand the relevance f these relatins t the insulin resistance syndrme and the ptential rle f leukcytes in the pathgenesis f athersclersis. Acknwledgments The authrs thank the many research vlunteers whse participatin ver the years has made these stud- ies pssible. The hard wrk and dedicatin f the technical and nursing staffs f the Clinical Research Unit, especially that f Ms. Carl Massengill.and Ms. Marjrie Gldsmith, are gratefully acknwledged. References 1. Athens JW. Granulcytes-neutrphils. In: Lee GR, Bithell TC, Ferster I, Athens JW, Lukens IN, eds. Win/rbe's Clinical Hematlgy. Philadelphia: Lea and Ferbinger; 1993: Best JD, Tabrsky GJ Jr, Halter JB, Prte D Jr. Glucse dispsal is nt prprtinal t plasma glucse level in man. Diabetes. 1981;30: Cicca DR, Vargas Rig LM. Estrgen receptrs in human nntarget tissues: bilgical and clinical implicatins. EndcrRev. 1995;16: Diabetes Mellitus: reprt f a WHO study grup. WHO Tech Rep Ser. 1985;727: ErnsfE, Hammerschmidt DE, Bagge U, Matrai A, Drmandy JA. Leukcytes and the risk f ischemic diseases. lama. 1987;257: Facchini F, Hllenbeck CB, Chen YN, Chen Y-D I, Reaven GM. Demnstratin f a relatinship between white bld cell cunt, insulin resistance, and several risk factrs fr crnary heart disease in wmen. I Intern Med. 1992;232: Finegd DT, Bergman RN, Vranic M. Mdelingerrr and apparent istpe discriminatin cnfund estimatin f endgenus glucse prductin during euglycemic glucse clamps. Diabetes. 1988;37: Friedman GD, Klatsky AL, Siegelaub AB. The leukcyte cunt as a predictr f mycardial infarctin. N Engl I Med. 1974;290: Friedman GD, Tekawa I, Grimm RH, Manli T, Shannn SG, Sidney S. The leukcyte cunt Crrelates and relatinship t crnary risk factrs: The CARDIA study. IntI Epidemil. 1990;19: Fussganger RD, Kahn CR, Rth J, De Meyts P. Binding and degradatin f insulin by human peripheral granulcytes. Demnstratin f specific receptrs with high affmity. I Bii Chem. 1976;251: Gldman RF, Buskirk ER. Bdy vlume measurement by underwater weighing: descriptin f a methd. In: Brzek I, Henschel A, eds. Techniques fr Measuring Bdy Cmpsitin: Prceedings f a Cnference. Washingtn D.C.: Natinal Academy f Sciences, Natinal Research Cuncil; 1961: Hansen LK, Grimm RH, Nealn JD. The relatinship f white bld cell cunt t ther cardivascular risk factrs. Int J Epidemil. 1990;19: Herbert V, Lau K, Gttlieb CW, Bleicher SJ. Charcal cated immunassay f insulin. I Clin Endcrinl Metab. 1965;25: Ingelfinger, JA, Bennett PH, Liebw 1M, Miller M. Crnary heart disease in the Pima Indians. Electrcardigraphic findings and pstmrtem evidence f mycardial infarctin in a ppulatin with a high 570 OBESITY RESEARCH Vl. 3 N.6 Nv. 1995

9 wac Cunt, Obesity, and Insulin Resistance, Pratley et al. prevalence f diabetes mellitus. Diabetes. 1976;25: Jeppesen JL, Maheux P, Facchini FS. White bld cell cunt and insulin resistance in healthy nnsmking men. Am Heart J. 1994;127: Kannell WB, Andersn K, Wilsn PWF. White bld cell cunt and cardivascular disease. Insights frm the Framingham Study. JAMA. 1992;267: Keys A, Brzek J. Bdy fat in man. Physil Rev. 1953;33: Lilllja S, Bgardus C. Obesity and insulin resistance: Lessns learned frm the Pima Indians. Diabetes Metab Rev. 1988;4: Lilllja S, Mtt DM, Spraul M, et al. Insulin resistance and insulin secretry dysfunctin as precursrs f nninsulin dependent diabetes mellitus. N Engl J Med. 1993;329: Lilllja S, Mtt DM, Zawadzki JK, Yung AA, Abbtt WG, Bgardus C. Glucse strage is a majr determinant f in viv "insulin resistance" in subjects with nrmal glucse tlerance. J Clin Endcrinl Metab. 1986;62: Nanji AA, Freeman JB. Relatinship between bdy weight and ttal leukcyte cunt in mrbid besity. Am J Clin Pathl. 1985;84: Niet FJ, Szki M, Flsm AR, Rck R, Mercuri M, fr the ARIC investigatrs. Leukcyte cunt crrelates in middle-aged adults: The athersclersis risk in cmmunities(aric)study. Am J Epidemil: 1992;136: Pedersen 0, Beck-Nielsen H. A study f insulin receptrs in human mnnuclear leukcytes. Acta Endcrinl (Cpenh). 1976;83: Reaven GM. Rle f insulin resistance iri human disease. Diabetes. 1988;37: Saad MF, LiUija S, Nymba BL, et al. Racial differences in the relatin between insulin and bld pressure. N Engl J Med. 1991;324: Seidell JC, Ciglini M, Charzewska J, Eilsinger B-M, Deslypere J-P, Cruz A. Fat distributin in Eurpean men: a cmparisn f anthrpmetric measures in relatin t cardivascular risk factrs. Int JObes. 1991;16: Steele R. Influence f glucse lading and f injected insulin n hepatic glucse utput. Ann N Y Acad Sci. 1959;82: OBESITY RESEARCH Vl. 3 N.6 Nv