Diabetologia. Response of adipose tissue lipoprotein lipase activity and serum lipoproteins to acute hyperinsulinaemia in man.

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1 Diabetlgia (1984) Diabetlgia 9 Springer-Verlag 1984 Respnse f adipse tissue lipprtein lipase activity and serum lipprteins t acute hyperinsulinaemia in man H. Yki-J~irvinen, M.-R. Taskinen, V. A. Kivist and E.A. Nikkil~i Third Department f Medicine, University f Helsinki, Helsinki, Finland Summary. In rder t assess the shrt-term effects f hyperinsulinaemia and hyperglycaemia n adipse tissue lipprtein lipase activity and n serum lipprteins, we measured these variables in ten nrmal subjects during euglycaemic and hyperglycaemic hyperinsulinaemic clamps. The mean steadystate plasma glucse and insulin cncentratins, respectively, were 4.7 mml/1 and 11 mu/1 during euglycaemic mderateinsulin clamp, 4.9 mml/1 and 565 mu/1 during euglycaemic high-insulin clamp, and 8.8 mml/1 and 148 mu/l during hyperglycaemic clamp. Saline infusin was used as cntrl. The adipse tissue lipprtein lipase activity rse significantly ver 5 h during high-insulin clamp (p<.1) and during hyperglycaemic clamp (p<.5), but did nt change during the mderate-insulin clamp. The magnitude f change f lipprtein lipase activity frm baseline (either rise r fall) was inversely related t the preclamp activity during euglycaemic mderate-insulin clamp (r=-.67), during hyperglycaemic clamp (r= -.68) and during infusin f saline (r= -.75, p<.5). Ttal serum triglyceride cncentratin decreased significantly during all clamp studies cmpared with the cntrl experiment. This change was mainly accunted fr by a decrease f VLDL triglyceride. The LDL chlesterl level fell by an average f 5% (p<.5) during the high-insulin clamp and by 1% (p<.5) during the hyperglycaemic clamp. The HDL chlesterl level did nt change significantly. It is cncluded that adipse tissue lipprtein lipase activity in man is increased by physilgical insulin levels during hyperglycaemia and als by supraphysilgical insulin levels during euglycaemia, but is nt influenced by physilgical hyperinsulinaemia withut hyperglycaemia. Lw basal lipprtein lipase activity is mre sensitive t insulin-glucse stimulatin than primarily high lipprtein lipase activity. Acute hyperinsulinaemia decreases VLDL triglyceride and LDL chlesterl cncentratins. Key wrds: Adipse tissue lipprtein lipase, insulin, glucse, insulin sensitivity, lipprteins. Several studies have suggested that insulin participates in the regulatin f lipprtein lipase (LPL) activity in human adipse tissue. Insulin deficiency and insulin resistance in diabetic subjects are assciated with subnrmal levels f LPL which are restred with insulin treatment [1, 2]. In healthy subjects, adipse tissue LPL decreases during fasting [3, 4] and increases with carbhydrate feeding [5-7]. The LPL respnse is related t basal LPL activity [6]. In subjects with endgenus hypertriglyceridaemia [6] and in nrmtriglyceridaemic subjects n chrnic haemdialysis [8], the rise f LPL induced by high-carbhydrate feeding is inversely related t the basal level. Althugh these studies d nt separate the effects f insulin frm thse f glucse and gut hrmnes, they suggest that basal LPL activity influences its respnsiveness t varius regulatrs. This was als shwn by Sadur et al. [9] wh fund that nly lw LPL values in- creased during hyperinsulinaemia. It is nt knwn, hwever, whether a high basal enzyme activity r the dse f insulin is the mre imprtant regulatr f adipse tissue LPL activity. In the present study we measured the effects f insulin at tw plasma levels, during euglycaemia and during hyperglycaemia, n adipse tissue LPL activity. Since LPL participates in the regulatin f serum levels f bth VLDL and high-density lipprtein (HDL), the respnse f serum lipprteins was als examined. Subjects and methds Subjects Furteen healthy students (seven females and seven males), age range frm 19 t 31 years (22_ 1 years, mean SEM) were studied. Their weight (based n medium frame individuals frm the Metrplitan

2 H. Yki-J~irvinen et al.: Adipse tissue lipprtein lipase and insulin 365 Life Insurance Cmpany standards, 1959) ranged frm 93 t 114% (13 +2%) ideal bdy weight. All subjects were cnsuming a weightmaintaining diet that cntained at least 2 g f carbhydrate/day fr 3 days befre each study. N subject had a family histry f diabetes mellitus r lipid disrders, and nne was taking any medicatin. Exercise histries were variable. The purpse, nature, and ptential risks f the study were explained t all subjects and infrmed cnsent was btained befre their participatin. The experimental prtcl was apprved by the Ethical Cmmittee f the Helsinki University Hspital. Experimental prtcl All studies were begun at 8. h after a 1 t 12-h vernight fast. An indwelling retrgrade catheter was inserted int a hand vein fr bld sampling. The hand was then inserted int a heated chamber (7 ~ t arterialize venus bld [1]. Adipse tissue bipsies fr determinatin f LPL activity and bld samples fr lipid analyses were taken 3-45 rain befre starting glucse and insulin r saline (.15 tl/l) infusins, and these were repeated after 5-h clamp. Fur prtcls (A-D) were used t study the effects f insulin and/r glucse r saline n LPL activity and bld lipids. A ttal f 4 studies were perfrmed in the 14 subjects. Ten subjects (five males and five females) participated in 32 studies (1euglycaemic lw-insulin (A) and six high-insulin (B) clamps, 1 hyperglycaemic damps (C), and six saline cntrl studies (D)). The remaining fur subjects participated in a euglycaemic high-dse insulin clamp and a saline cntrl study (eight studies). There was at least a 1-day interval between the studies. Prtcls A and B: euglyeaemic hyperinsulinaemic clamps at tw levels fhyperinsulinaemia. The effect f tw levels f hyperinsulinaemia at basal plasma glucse cncentratin was determined by the insulin clamp technique [11]. Priming plus cntinuus infusin f crystalline prcine insulin (Actrapid, Nv, Cpenhagen, Denmark) were administered. The priming dses were given in a lgarithmically-decreasing manner fr 1 min t raise the plasma insulin cncentratin t the desired levels [1 and 6 mu/1 in the lw-insulin (prtcl A, five males, five females) and high-insulin (prtcl B, five males, five females) euglycaemic clamps, respectively]. Thereafter insulin was infused fr 29 rain at a cnstant rate f 4 mu. m -2- min -1 (prtcl A) r 18 mu. m-2. rain-1 (prtcl B) t maintain the desired insulin level. Bld samples fr determining plasma insulin cncentratin were taken at 3-min intervals. Basal plasma glucse values were measured in the mrning befre each study. The plasma glucse was maintained at the basal level by the determinatin f the plasma glucse cncentratin frm arterialized venus bld every 5 rain and cncmitant adjustment by infusin f 2% glucse slutin. Under these steady-state cnditins f cnstant hyperinsulinaernia and euglycaemia, hepatic glucse prductin is suppressed [11] and the amunt f glucse infused (M) serves as a measure f the ttal amunt f glucse metablised by the bdy. Prtcl C: hyperglycaemic clamp with hyperinsulinaemia. In 1 subjects (five males, five females) the plasma glucse cncentratin was acutely raised and maintained at 4. mml/1 abve basal level by a priming (5.5 rag-kg-1, min-1) and variable infusin f a 2% glucse slutin. The variable infusin was started at min, when the 1-min plasma glucse cncentratin became available. The priming (-1rain) and cntinuus (1-29min) infusins f insulin (4 mu. m 2. rain-l) were given as described abve in the lw-dse euglycaemic clamp prtcl. Prtcl D: saline cntrl infusin. Ten subjects (five males and five females) received infusin f saline (.15 tl/l) fr 5 h. Plasma glucse and insulin cncentratins were measured at h and 5 h. Assay f heparin-releasable LPL activity in the adipse tissue Heparin-releasable LPL activity was measured frm needle-bipsy specimens. Subcutaneus adipse tissue bipsy was taken by aspira- tin frm the gluteal regin. The skin at bipsy sites was anaesthetized with 1% ligncaine. The tissue was taken int saline (.15 tl/l) at rm temperature, washed, bltted, weighed and used fr assay f LPL activity either immediately r after strage at - 7 ~ The activity was measured frm heparin eluates f tissue pieces using labelled trilein emulsin as substrate [12]. The interassay cefficient f variatin fr the measurement f LPL activity f the internal milk standard averages 86% with a range f 8%-116% arund the mean [12]. The results are expressed as ~ml nn-esterified fatty acids (NEFA) release t it] 1 h by 1 g f tissue. Separatin f lipprteins The lipprtein fractins were islated by sequential fltatin [13] in a Beckman Mdel L 7 ultracentrifuge (Beckman Instruments, Pal Alt, Califrnia, USA) using a Type 5.3 Ti Beckman rtr. VLDL was separated by spinning serum at a density f 1.6 g/ml fr 18 h at 38, rev/min. The tp layer (= VLDL) was remved by tube slicing and the density f the infranatant was adjusted t 1.63 g/ml with a slutin f KBr (354 g/l) + NaC1 (153 g/l) and the LDL was flated t the surface by spinning fr 24 h at 38, rev/min. The density f the LDL infranatant was raised t g/ml with the same KBr- NaCI mixture and the high density lipprtein 2 (HDL2) was separated by centrifugatin at 38, rev/min fr 65 h. After tube slicing the density f the bttm fractin was adjusted t 1.21 g/ml with the KBr-NaC1 mixture and the HDL3 was flated t the surface by spinning fr 65 h at 35, rev/min. After islatin the fur lipprtein fractins were dialysed vernight against NaC1 (.15 tl/l) at +4~ and their chlesterl and triglyceride cntents were analysed. Analytical methds Plasma glucse was determined during the studies by the glucse xidase methd using the Beckman glucse analyser (Beckman Instruments, Clinical Instruments Divisin, Fullertn, Califrnia). Plasma insulin cncentratins were determined by radiimmunassay [14]. The cncentratin f chlesterl was determined by an enzymatic methd using a cmmercial reagent kit ( f Behringer Diagnstica, Mannheim, FRG). Triglycerides were measured by autanalyzer using kit f Behringer Diagnstica [15]. Serum NEFA cncentratin was determined accrding t Msinger [16]. Data analysis Statistical cmparisns between clamp studies and saline infusin were perfrmed using Student's t-test fr unpaired bservatins and Pearsn's linear regressin analysis using Bimedical Data Prcessing (BMDP) cmputer prgrams 3D and 8D, and prgram 2D fr data descriptin including analysis f distributin f variables [17]. Wilcxn's rank-sum test fr unpaired bservatins was used when distributin was nt nrmal [18]. Statistical cmparisns f baseline values between different studies were calculated with analysis f variance using BMDP cmputer prgram 7D [17]. All results are expressed as mean + SEM. Results Plasma glucse and insulin cncentratins, and ttal glucse metablism during clamp studies Euglycaemic clamps. The fasting plasma glucse cncentratins (4.8 _+.1 and mml/1) were maintained at and 4.9 _+.1 retl/1 with cefficients f variatin f % and % during lwand high-dse insulin clamps. The fasting plasma insu-

3 366 lin cncentratins (7._+.6 and 9.1_+l.mU/l) increased t steady-state levels (3-3 min) f 11 _+ 3 and 565 _+ 22 mu/1 during lw- and high-insulin euglycaemic clamps, respectively. The stability f the plasma insulin cncentratin is indicated by the cefficients f variatin which were 11.6 _+ 1.9% and 12.9 _+ 1.% in the lw- and high-dse studies, respectively. The amunts 'T 5" c~ 1.6 LL I.U Z 1.2 E v.j Q. ".8 ffl r.4 t~ l "~.4..8 Saline A C Clamps Fig. 1. Abslute change in adipse tissue LPL during infusin f saline (n= 1), euglycaemic lw-dse (n= 1, A) and high-dse (n = 1, B) insulin clamps and during hyperglycaemic hyperinsulinaemia (n=1, C). ~ p<.5, * p<.1 B H. Yki-J~irvinen et al.: Adipse tissue lipprtein lipase and insulin f glucse infused during lw- and high-dse euglycaemic clamp studies (2-3 min) were and _ 1.2 mg. kg -1. min -1, respectively. A direct relatinship was bserved between the individual values in the tw euglycaemic clamps (r=.94, p<.1). Hyperglycaemic hyperinsulinaemic clamp. The fasting plasma glucse cncentratin f mml/1 was elevated and maintained at mml/1 with a cefficient f variatin f % (2-3 min). The fasting insulin cncentratin rse t mU/1 (3-3 rain). The amunt f glucse infused t maintain hyperglycaemia was _+ 1.3 mg. kg -1. min -1. The rate f glucse utilizatin was significantly higher during hyperglycaemic clamp than during the euglycaemic high-insulin clamp (p <.5, paired t-test). The individual rates f glucse metablism during the hyperglycaemic clamp were related t the rates f glucse metablism during the lw-dse (r=.86, p<.1) and high-dse (r=.94, p<.1) insulin euglycaemic clamps. Adipse tissue LPL activity Basal LPL activities were , , 2.26_+.59, and 1.78 _+.37 ~tml NEFA.g-I.h -1 in lw- (A) and high-dse (B) euglycaemic clamps, hyperglycaemic clamp (C) and saline cntrl study (D), respectively (NS). When cmpared with saline cntrls, a significant stimulatry respnse f LPL was bserved during the high-dse insulin clamp (p<.1, Fig. 1) and the hyperglycaemic clamp (p <.5) but nt during the lw-dse insulin clamp. During saline infusin LPL activity fell by 3% t 1.29_+.29 ~tml NEFA.g-I-h -~ A T T r~ B LL U.I Z -.I - ; Q -'.,! 1J ~ 3 ffl.~- 2 C D.~_ 1 ~ 2-2 ffl.{3 - ~ ~ - [ I I I Basal adipse tissue LPL (,l~ml NEFA.g-I.h -1) Fig. 2. Relatinship between the abslute change f adipse tissue LPL and the basal enzyme activity during the 5-h euglycaemic lw-dse (r= -.67, p<.5, A), and high-dse (r= -.48, NS, B) insulin clamps, during hyperglycaemic hyperinsulinaemia (r = -.68, p <.5, C) and during infusin f saline (r= -.75, p <.5, D)

4 H. Yki-J~irvinen et al.: Adipse tissue lipprtein lipase and insulin 367 Table 1. Change f lipprtein triglyceride and chlesterl cncentratins during 5-h euglycaemic hyperinsulinaemia, hyperglycaemic hyperinsulinaemia, and infusin f saline Euglycaemic hyperinsulinaemia 1 mu. kg-1. rain -~ 4.5 mu.kg -~.rain -1 insulin infusin insulin infusin (n = 1) (n = 1) Hyperglycaemic Infusin hyperinsulinaemia f saline (n = 1) (n = l) Mean plasma glucse (3-3min, mml/1) Mean plasma insulin (3-3min, mu/1) _ _ _+1.7 Serum NEFA (mml/1) h _+.7 5 h d' e d' e d" e a Triglyeeride (mml/1) Ttal h _ h c, e d' e d' e ~ VLDL Oh h.18.68, e c, e d.41 _+.1 a LDL h h c, e HDL Oh _ h.28 _ b Chlesterl (mml/1) Ttal h 3.57 _ _ _ _+.24 5h 3.46_+.1U 3.69_+.2 d'e 3.14_+.18 ~,e 4.8_+.17 VLDL h.19 _ _ _+.5 5 h d.15_+.5 d c.16_+.4 a LDL Oh _ h , e 2.4 _+.16, e 2.75 _+.11 a HDL Oh _ _.11 5 h _ _.7 a 1.3 +_ Results are expressed as mean + SEM. a p <.5 ; b p <.1, c ]7 <.5, d p <.1 fr differences between and 5 h (paired t-test); e p <.5 fr changes during clamps versus changes during saline infusin (unpaired t-test) (p <.2). The abslute change f LPL activity was inversely related t basal LPL level during the euglycaemic lw-dse insulin clamp (r=-.67, p<.5, Fig. 2 A), the hyperglycaemic clamp (r = -.68, p <.5, Fig. 2 C), and during saline infusin (r= -.75, p <.5, Fig. 2 D), but nt during the high-insulin euglycaemic clamp (r=.48, NS, Fig. 2 B). Serum lipids and lipprteins Inhibitin f liplysis as judged frm the decline in NEFA levels ccurred during all clamps (Table 1). During saline infusins, NEFA levels rse by 55% (p<.5). During all three clamp experiments, serum ttal triglyceride cncentratins fell significantly. The mst prminent change was seen in VLDL triglycerides, which decreased significantly during all clamps. LDL chlesterl fell significantly during bth the hyperglycaemic and the high-dse euglycaemic clamps. N significant change in HDL chlesterl r HDL triglyceride r their subfractins ccurred as cmpared t saline infusin. Relatinships between glucse and lipid metablism in the basal state and during clamps Neither basal LPL activity nr the change in LPL during any f the clamps crrelated with the amunt f glucse metablised (M). Neither was any crrelatin fund between the M-value and decreases in ttal serum triglyceride and VLDL triglyceride. Discussin In previus studies where adipse tissue LPL has been measured after ral glucse r a meal, n crrelatin between the change f LPL and the relative insulin respnse has been fund [5-7]. In cntrast, the present study shws by the use f euglycaemic insulin clamps at tw insulin levels that insulin des increase activity f adipse tissue LPL in a dse-dependent manner. The cncentratin f insulin required fr stimulatin f adipse tissue LPL activity was far beynd thse seen after ral feeding [5-7]. This raises the pssibility that ther stimulatrs f adipse tissue LPL, either unrelated t

5 368 H. Yki-Jgrvinen et al.: Adipse tissue lipprtein lipase and insulin insulin r secndary t endgenus insulin release, may be present after ral feeding. During the cntrl saline infusin, the subjects cntinued fasting fr 5 h; adipse tissue LPL decreased in nine f the ten subjects studied, and the decrease was directly related t the initial enzyme activity. These changes are in keeping with ur previus data demnstrating a decrease in adipse tissue LPL during calric restrictin, when the decrease in LPL was als related t the basal enzyme activity [4]. During the euglycaemic lw-insulin, hyperglycaemic, and high-insulin clamps, the increases in adipse tissue LPL in 6/1, 8/1 and 9/1 subjects, respectively, ccurred almst exclusively when basal LPL activity was lw (Fig. 2), whereas high basal LPL activities decreased during all clamps. This tendency f high LPL activities t decrease (r t remain unchanged cmpared with saline infusin) decreased with increasing insulin levels. This was shwn during the high-insulin euglycaemic clamp, when nly the highest basal LPL value decreased (Fig.2B). It culd be argued that it is unphysilgical t study changes in LPL during hyperinsulinaemia maintained by intravenus infusin. Hwever, the intravenus rute ffers the pssibility t study changes in LPL withut interference by gut hrmnes, althugh even after ral stimuli the basal LPL activity seems t determine its respnse. An inverse relatinship between fasting levels f adipse tissue LPL and its increase after high-carbhydrate feeding has previusly been demnstrated in bth nrmal and hypertriglyceridaemic subjects [6, 19, 2]. Patients with high fasting LPL actually had lwer pst-prandial levels [6]. The mechanism by which basal LPL regulates its respnse t insulin remains a mystery. Its physilgical r61e culd be t prevent excessive strage f fat in adipse tissue and, n the ther hand, t prmte strage f fat after a perid f liplysis such as may fllw insulin deficiency in diabetics [1] r a reductin f insulin secretin during fasting [3]. Respnse f LPL t insulin may be related t insulin sensitivity since in bese insulin-resistant subjects, fr example, LPL respnses t glucse are reduced [21]. In this study, we did nt bserve any crrelatin between basal LPL activity and glucse metablism, nr any between change f LPL and glucse metablism. T knw whether the respnse f LPL t insulin is related t the amunt f insulin-mediated glucse metablised, ne shuld cmpare subjects with similar basal LPL levels but different degrees f insulin resistance. Here we fund n significant relatinships between basal LPL activities and the rates f glucse metablism during the clamps. Thus, it appears that basal LPL activity is largely independent f insulin-mediated glucse metablism in healthy subjects. The mst prminent change in serum lipprteins during the induced hyperinsulinaemia was the decrease in VLDL triglyceride accmpanied by a decrease in VLDL chlesterl. A significantly smaller decrease in VLDL triglyceride als ccurred during infusin f saline, prbably due t cntinued fasting, when VLDL triglyceride is hydrlyzed by LPL in muscle [5]. The fall in VLDL triglyceride was f similar magnitude during all clamps despite marked differences in glucse and insulin levels. This indicates that a maximal decrease in circulating basal VLDL triglyceride is reached at insulin levels which are in the high physilgical range. The mechanism respnsible fr the fall in VLDL triglyceride cannt be directly deduced frm the present study. A change in VLDL merely reflects the net effects f alteratins in secretin and catablism. Under similar lwdse insulin euglycaemic clamp cnditins Sadur et al. [9] bserved a fall in ttal serum triglyceride after 8 min despite unchanged adipse tissue LPL. In ur study, significant increase in LPL ccurred nly during the high-dse insulin clamp but the decrease in VLDL triglyceride was similar during all clamps. This indirectly suggests that the fall in serum triglyceride was due mre t decreased secretin f VLDL than t enhanced triglyceride liplysis by LPL. Bazelmans et al. [22] recently shwed that the magnitude f fall in plasma triglyceride cncentratin during euglycaemic hyperinsulinaemia is nt crrelated with the decrease in NEFA but is psitively related t the insulin sensitivity. This indicates that in additin t decreasing plasma NEFA, insulin has mre direct effects n hepatic triglyceride secretin. In ur present subjects n crrelatin was fund between fall f triglyceride and insulin sensitivity, but this may be simply related t the fact that they were lean, yung individuals withut insulin resistance. Anther remarkable change in lipprtein cncentratins during hyperinsulinaemia was the reductin f LDL chlesterl. Even thugh the percentage change was nt great it was quite cnstant and did nt ccur during saline infusin. Mrever, any change which ccurs during 5 h in a lipprtein with a plasma half-life f several days must mean a prfund change in transprt kinetics. Several previus findings suggest that insulin enhances the catablism f LDL thrugh the highaffinity receptr pathway. Thus, insulin stimulates LDL receptr activity in vitr in human fibrblasts by increasing the receptr number [23]. A similar change ccurs in viv in mnnuclear cells after 4 h hyperinsulinaemia [24]. The catablism f LDL in viv is als stimulated by hyperinsulinemia induced by ttal parenteral nutritin [25] r high sucrse feeding [26]. Ultimately, there is a high psitive crrelatin between the fractinal catablic rate f LDL aplipprtein B and plasma insulin respnse [27]. Hwever, a reductin f VLDL prductin during acute hyperinsulinaemia may cntribute t the fall f LDL since the latter riginates partly as a degradatin prduct f VLDL [28]. Acknwledgements. This study was supprted by grants frm the Finnish Culture and the Sigrid Juselius Fundatin, the Finnish State Medical Research Cuncil (Academy f Finland), the Fundatin fr

6 H. Yki-J~rvinen et al.: Adipse tissue lipprtein lipase and insulin 369 Diabetes Research f the Finnish Diabetes Assciatin, and Nrdisk Insulinfnd (Gentfte, Denmark). The help f S.-L. Karnen, Ph.D. fr insulin determinatins, and skillful technical assistance f Miss A. Sal, Mrs. H. Hilden, Miss P. Ter~vfiinen, Mrs. L. Lehikinen and Mrs. S.-L Runeberg is greatly appreciated. References 1. Taskinen M-R, Nikkilfi EA (1979) Lipprtein lipase activity f adipse tissue and skeletal muscle in insulin-deficient human diabetes. Relatin t high density and very lw density lipprteins and respnse t treatment. Diabetlgia 17: Taylr KG, Galtn D J, Hlswrth G (1979) Insulin-independent diabetes: defect in the activity f lipprtein lipase in adipse tissue. Diabetlgia 16: Perssn B, Hd B, Angervall G (197) Effects f prlnged fast n lipprtein lipase eluted frm human adipse tissue. Acta Med Scand 188: Taskinen M-R, Nikkil~i EA (1979) Effects f calric restrictin n lipid metablism in man. Athersclersis 32: Lithell H, Bberg J, Hellsing K, Lundqvist G, Vessby B (1978) Lipprtein-lipase activity in human skeletal muscle and adipse tissue in the fasting and fed states. Athersclersis 3: Gldberg AP, Chait A, Brunzell JD (198) Pstprandial adipse tissue lipprtein lipase activity in primary hypertriglyceridemia. Metablism 29: Pykfilist6 J, Smith PH, Brunzell JD (1975) Determinants f human adipse tissue lipprtein lipase. Effects f diabetes and besity n basal- and diet-induced activity. J Clin Invest 56: Gldberg A, Sherrard DJ, Brunzell JD (1978) Adipse tissue lipprtein lipase in chrnic hemdialysis: rle in plasma triglyceride metablism. J Clin Endcrinl Metab 47: Sadur CN, Eckel RH (1982) Insulin stimulatin f adipse tissue lipprtein lipase. Use f the euglycemic clamp technique. J Clin Invest 69: McGuire EAM, Helderman JH, Tbin JD, Andres R, Berman R (1976) Effects f arterial versus venus samples: an analysis f glucse kinetics in man. J Appl Physil 41 : DeFrnz RA, Tbin JD, Andres R (1979) Glucse clamp technique: a methd f quantifying insulin secretin and resistance. Am J Physi1237:E214-E Taskinen M-R, Nikkilfi EA, Huttunen JK, Hilden H (198) A micrmethd fr assay f lipprtein lipase activity in needle bipsy samples f human adipse tissue and skeletal muscle. Clin Chim Acta 14: Havel RJ, Eder HA, Brabdn JH (1955) The distributin and chemical cmpsitin f ultracentrifugally separated lipprteins in human serum. J Clin Invest 34: Desbuquis B, Aurbach GD (1971) Use f plyethylene glycl t separate antibdy-bund peptide hrmnes in radiimmunassay. J Clin Endcrinl Metab 33: Wahlefeld AW (1974) Triglycerides: determinatin after enzymatic hydrlysis. In: HV Bergmeyer (ed) Methds f enzymatic analysis, 2 edn. Academic Press, New Yrk, pp Msinger F (1965) Phtmetric adaptatin f Dle's micrdeterruinatin f free fatty acids. J Lipid Res 6: Dixn WJ (ed) (1981) BMDP statistical sftware University f Califrnia Press, Berkeley 18. Swinscw TDW (1981) Statistics at square ne. British Medical Assciatin, Lndn 19. Nilssn-Ehle P, Carlstrrm S, Belfrage P (1975) Rapid effects n lipprtein lipase activity in adipse tissue f humans after carbhydrate and lipid intake. Scand J Clin Lab Invest 35: Brunzell JD, Schwarz RS, Eckel RH, Gldberg AP (1981) Insulin and adipse tissue lipprtein lipase activity in humans. Int J Obesity 5 : Taskinen M-R, Nikkil~i EA (1981) Lipprtein lipase in adipse tissue and skeletal muscle in human besity: respnse t glucse and t semistarvatin. Metablism 3: Bazelmans J, Nestel PJ, Nlan C (1983) Insulin-induced glucse utilizatin influences triglyceride metablism. Clin Sci 64: Chait A, Bierman EL, Albers JJ (1979) Lw-density lipprtein receptr activity in cultured human skin fibrblasts. J Clin Invest 64: 14A 24. Mazzne T, Fster D, Albers JJ, Chait A (1982) Lw density lipprtein catablism is enchanced by insulin. Diabetes 31 (Suppl 2): 14A 25. Chait A, Fster D, Miller DG, Bierman EL (1981) Acceleratin f lw-density lipprtein catablism in man by ttal parenteral nutritin. Prc Sc Exp Bil Med 168: Nestel PJ, Reardn M, Fidge NH (1979) Sucrse-induced changes in VLDL- and LDL-B apprtein remval rate. Metab Clin Exp 28: Kissebah AH, Alfarsi S, Evans DJ, Adams PW (1983) Plasma lw density lipprtein transprt kinetics in nninsulin-dependent diabetes mellitus. J Clin Invest 71: Eisenberg S (198) Origin f plasma lw and high density lipprtein. In: Gtt VAM, Smith LC, Allen B (eds) Athersclersis. Springer, New Yrk, pp Received: 25 August 1983 and in revised frm: 18 June 1984 Dr. Hannele Yki-Jfirvinen Third Department f Medicine University f Helsinki SF-29 Helsinki 29 Finland