Effects of intravenously administered fructose and glucose on splanchnic secretion of plasma triglycerides in hypertriglyceridemic men

Metabolism Clinical and Eqxrimental VOL. XXVI,

SEPTEMBER

NO. 9

1977

Effects of Intravenously Administered Fructose and Glucose on Splanchnic Secretion of Plasma Triglycerides in Hypertriglyceridemic Men Bernard

M. Wolfe

Studies were undertaken in man to test the hypothesis that fructose produces higher mtes of triglyceride secretion from the liver than equimolar amounts of glutricose. Splanchnic metabolism of glycerides and other substmtes was studied during prolonged intravenous administmtion of 9,10-‘H-palmitate and either fructose or glucose (30 g/hr) to hypertriglyceridemic men maintained on a highcarbohydmte diet for 2 wk. The secretion of plasma triglycerides from the splanchnic from splanchnic region was quantified flow and chemical (and radio-chemical) measurements of the transsplanchnic gradients of 3H-labeled free fatty acids and triglycerides. Very high rates of release of triglycerides from the splanchnic region (average 84 g triglyceride/day) were observed during the infusion of hypercaloric amounts of either hexose. Mean values for splanchnic secretion of plasma triglyceride fatty acids were not significantly different during administration of fructose versus glucose [values for chemical production: 108 f 28 (SE) and 96 f 20 ~mole/min/sq m, respectively]

and Surai

P. Ahuja

and were more than one-half the mte of tmnsport of plasma free fatty acids. In contrast to the postabsorptive state, labeled plasma free fatty acids did not comprise a major source of the secreted plasma triglyceride fatty acids. During intravenous infusion of fructose versus glucose, the mean fmction of triglyceride fatty acids of plasma very low-density lipoproteins derived from plasma free fatty acids was 14.8% versus 8.9%, respectively; after a 12-hr infusion of either labeled hexose, that derived from fructose or glucose, though it increased with time, it reached only 5.1% and 3.6%, respectively. Elevated mtes of secretion of plasma triglycerides, evidently derived from stored liver fat or glycogen, contribute to the accentuation of lipemia by either fructose or glucose. Considering the high capacity for triglyceride release of the human liver during hypercaloric carbohydmte administration, the results imply that impaired peripheml removal mcchanisms may underlie the elevation of serum triglyceride levels in many patients with endogenous hyperlipemia.

From the Westminster, Victoria and University Hospitals and Department of‘ Medicine, of Western Ontario, London, Ontario, Canada. Received for publication July 28, 1976. Supported by Grant MA 4248from the Medical Research Council of Canada. Reprint requests should be addressed to Dr. Bernard M. Wolfe, Department of Medicine, Hospital, London, Ont., Canada N6A 5A5. 0 1977 by Grune & Stratton, Inc. ISSN 0026-0495.

Metddism,

Vol. 26, No. 9 (September), 1977

University

University

963

964

WOLFE

AND

AHUJA

E

NDOGENOUS HYPERTRIGLYCERIDEMIA is frequently associated with’,’ and may predispose to premature onset of coronary atherosclerosis.394 Leveis of plasma triglycerides tend to rise in postabsorptive man during ingestion of diets that contain a high proportion of calories in the form of carbohydrate,5-7 especially if the diet is rich in sucrose8+9 or fructose.‘O The preponderant lipemic effect of fructose may relate to inefficient disposal of plasma very low-density lipoprotein triglyceride fatty acids (VLDL-TGFA) in peripheral tissues. ” However, it has also been postulated that fructose may produce higher rates of hepatic secretion of VLDL-TGFA than glucose. A differential effect could be accounted for by preferential incorporation of fructose into hepatic and plasma VLDL-TGFA” or enhanced esterification of free fatty acids (FFA). There have been no previous measurements of plasma TGFA secretion in man during consumption of glucose or fructose, except for one study in which the rate of esterification of FFA to TGFA during glucose ingestion was taken as an index of TGFA secretion.13 The latter did not take into account the major contribution of precursors other than FFA to the synthesis of plasma TGFA. To test the hypothesis that fructose produces a higher rate of splanchnic (hepatic) secretion of TGFA than glucose, we have undertaken studies of TGFA secretion in two similar groups of asymptomatic hypertriglyceridemic men. The high rates of hepatic secretion of plasma TGFA in these studies facilitated measurement of transsplanchnic chemical gradients of triglycerides. Thus, chemical secretion of TGFA was calculated simply by multiplying concentration gradient by plasma flow. Splanchnic uptake of FFA and their conversion to plasma TGFA and VLDL-TGFA were also investigated. The studies were performed under steady-state conditions during the fed state induced by constant intravenous infusion of hypercaloric amounts of fructose or glucose. The same conditions allowed the study of splanchnic exchange of amino acids and carbohydrates, the subject of a separate report.14 MATERIALS

Subjects and Experimental

AND METHODS

Procedures

The groups of subjects are described in Table 1. Subjects receiving fructose are designated group F and those receiving glucose group G. All subjects were asymptomatic and had no clinical evidence of disordered circulation. Each subject had hyperlipemia (range of fasting serum triglycerides during isocaloric diet, 155-287 mg/dl; cholesterol, 163-305 mg/dl). The lipoprotein electrophoretic pattern (on cellulose acetate) showed an increase in prebetalipoproteins in all subjects, but was otherwise normal. All subjects had normal levels of serum glucose while fasting Table 1. Characterization of Groups of Subjects

No. of

Age

Height

Weight

Group*

Subjects

(vr)

(cm)

(kg)

F

3

36 f

4

169&2

G

4

35

5

175zt8

Values *F, eridemic

represent

mean

hypcrtriglyceridemic men given

f

f

7% f 101

f

Ponderal

Pocked

Surface

Index

Volume of

ArEX8

[ht (in)/ v/t (lb)‘/3]

Eryihrocytes

(sq 4

(%)

7

1.87

f

0.09

12.1

f

0.2

43 f

10

2.15

f

0.12

11.5

f

0.5

45 zk 1

0.3

(30

g/hr);

SE. men

an intravenous

given

cm

infusion

intravenous of glucose

(30

infusion g/hr).

of

fructose

G,

hypertriglyc-

IV-ADMINISTERED

FRUCTOSE

AND GLUCOSE

and 2 hr after a 100-g carbohydrate

breakfast,

965

except

for one subject

(G.C.),

who had evidence

of

mild glucose intolerance (2-hr postprandial serum glucose, 167 mg/dl). Each subject had normal serum concentrations of albumin, globulins, total and direct bilirubin, alkaline phosphatase, thyroxine, creatinine, calcium, sodium, potassium, chloride, and bicarbonate. Each had normal hematologic and urine analyses in addition to a normal chest roentgenogram. One subject (MS.) had an elevated level of serum uric acid (8.4 mg/dl). The dietary preparation of the subjects, the experimental schedule, and the details of the adAll subjects maintained their body weight ministration of radioisotopes have been described.14 within 2 kg and consumed no ethanol during the 3-4 wk before the study of splanchnic metabolism. One previously described subject (R.Y.) was omitted from group F for purposes of comparing rates of triglyceride secretion because his fasting triglycerides fell to normal (74 mg/dl) when he received the isocaloric diet. All subjects were maintained on isocaloric balanced diets for l-2 wk before receiving hypercaloric high-carbohydrate diets for 2 wk prior to the study. During the study of splanchnic metabolism each of these subjects received a l6-hr continuous infusion of IO% fructose in water (group F) or IO% glucose in water (group G) into an arm vein, starting IO hr after the previous evening snack. Then, I4 hr after the evening snack, an intravenous pulse injection of tracer amounts of U-‘4C-fructose* or U-t4C-glucose, respectively, was given. followed by a constant intravenous infusion of the radioisotope for 5-12 hr. Simultaneously, constant infusions of indocyanine green and albumin-bound 9,10-3H-palmitate (0.4 &i/min) were started and maintained for 5 and I2 hr, respectively. Two hours after starting the isotopic infusion, a right hepatic vein and an artery were catheterized, as previously described.‘4-‘6 Simultaneous samples of arterial and hepatic venous blood were obtained for measurement of transsplanchnic chemical and radiochemical gradients at 20-min intervals between 3 and 5 hr, and venous samples were obtamed (from an arm vein)5. 8, IO, I I, and I2 hr after the onset of the isotopic infusion.14

Analyses The content and radioactivity of FFA, TGFA, and VLDL-TGFA in heparinized blood plasma and concentration of @-hydroxybutyrate in blood were determined as previously described.“-‘* Radioactivity in VLDL-14C-TGFA was determined after alkaline hydrolysis of VLDL-14Ctriglycerides;” that present in “C-glyceride-glycerol of VLDL-‘4C-triglycerides was obtained from the difference between that present in VLDL-‘4C-triglyceride and that in VLDL14C-TGFA. Plasma cholesterol was analyzed by the method of Abel et al.” Coefficients of variation calculated from triplicate analyses in this study were 3.6% for FFA, 3.9% for labeled FFA in whole plasma, 1.9% for TGFA, 2.4% for labeled TGFA in whole plasma, 3.5% for plasma VLDL-TGFA. 3.7% for labeled VLDL-TGFA, 4.8?/, for cholesterol, and 3.99; for P-hydroxybutyrate.

Materials 9,10-3H-Palmitic acid (320 mCi/mmole) was obtained from New England Nuclear, Mass. More than 97% of applied counts were recovered in the FFA fraction on thin-layer matography (Silica Gel H, chloroform:methanol:water:glacial acetic acid = 75:25:3: I). pyrogen-free U-‘4C-glucose (3.9 mCi/mmole) was obtained from New England Nuclear. pyrogen-free U-‘4C-fructose (275 mCi/mmole) was obtained from Mallinkrodt Chemical St. Louis, MO. U-‘4C-glucose and U-‘4C-fructose were certified over 98’4 pure.

Boston, chroSterile, Sterile, Works,

Calculations I. The equations used have been previously described.‘5-‘7.2’ See the Appendix. 2. Transsplanchnic chemical concentration gradients of TGFA in whole blood plasma were based on 5-7 sets of determinations in each subject (each determination calculated from I2 analyses). Transsplanchnic chemical concentration gradients of VLDL-TGFA were based on at least 4 determinations (each calculated from 4 analyses).

*The pulse injection of U-‘4C-fructose constant infusion was given.

was omitted

in two subjects

in group

F, although

the

966

WOLFE

AND AHUJA

3. Values for splanchnic conversion of 3H-FFA to plasma TGFA and VLDL-TGFA were based on at least 4 determinations (each calculated from triplicate analyses for ‘H-FFA and 3H-TGFA during the interval 3-5 hr after starting the isotopic infusion. 4. As in a previous study of glucose-fed miniature swine,” the specific activity of plasma FFA entering the liver was estimated by averaging the specific activity of arterial and hepatic venous FFA. Only peripheral venous blood was obtained during the interval 5-12 hr after starting the constant intravenous infusion of 9,10-3H-palmitate, and the following relationship was assumed:

Specific activity of FFA of peripheral venous plasma x mean specific activity of FFA Specific activity of of arterial and hepatic venous plasma at 5 hr specific activity of FFA of ’ FFA entering the liver = peripheral venous plasma at 5 hr Since the subjects remained under steady conditions throughout values for this ratio would probably also remain constant. 5. The following relationship was assumed:

the entire study, it was felt that

Fraction of plasma specific activity of ‘H-TGFA of arterial VLDL VLDL-TGFA derived from FFA = estimated specific activity of ‘H-FFA entering liver during the time interval when the value for this ratio was constant.‘5-‘7*22 6. Splanchnic plasma flow was measured as previously described.‘4q’5 7. Linear regressions and the correlation coefficient r were calculated as previously described.‘4,‘5 Differences between groups were evaluated according to Snedecor and Cochran for unpaired samples.23 Variance was expressed as the standard error of the mean. 8. The terminology used in this report was generally as recommended;” however, splanchnic secretionof TGFA17 was used instead of “splanchnic net inflow transport of TGFA” and clearance was expressed16 in rmole/min rather than in volume cleared per unit time. RESULTS

Characteristics of Groups of Subjects

There were no significant differences between groups F and G in age, height, weight, body surface area, ponderal index, or packed volume of erythrocytes (Table 1). Likewise, there were no significant differences between groups F and G in the values for the mean concentration of plasma triglycerides (173 f 9 versus 234 f 19 mg/dl, respectively) or plasma FFA (0.71 versus 0.87 mM, respectively) after a 12-15 hr fast during the period of administration of the isocaloric balanced diet. As expected, the concentration of fasting plasma triglycerides rose variably in both groups (from 8% to 130%) during ingestion of the high-carbohydrate diet;25 however, mean plasma FFA fell 12% f 3% in group F and 15% f 9% in group G (p > 0.05). Fasting serum levels of cholesterol were below the approximate 95th percentile for age-adjusted values26 in each subject (mean value during isocaloric diet in group F, 250 f 19 mg/dl; in group G, 243 f 31 mg/dl). Comparison of Values Obtained During Studies of Splanchnic Metabolism

Values for serial arterial and peripheral venous conMetabolism of FFA. centrations of plasma FFA during intravenous administration of fructose or glucose (average infusion rate was 133% f 8% of basal caloric requirement) did not vary systematically during the first 5 hr of radioisotopic infusion. However, there was a slight decrease in FFA level during the later part of the studies

IV-ADMINISTERED

FRUCTOSE

967

AND GLUCOSE

pmol/ml

PLASMA

VLDL-TGFA

PLASMA

FFA

10 r 81 at

Mean plasma concentmtions of Fig. I. major lipid metobolites during hypercaloric intmvenous infusion of fructose in group F(e) and glucose in group G (0). Values for three rubiects in growp F and four in group G ora for arterial blood plasma during 3-5 hr and for peripheral venous blood plasma during 8-12 hr after the onset of the isotopic infusion. Variance between rubieck, expressed as SE, was less than 25% for each metabolite.

pmol/ml

0

-4 0

3

5

_tiol;rr I- - - -

8

of Infusion of Fructose

Infusion

10

12

of Rodiopolmitate-

or Glucose

(30 g/hr)

--

-

- i

which was rather more marked in group F (Fig. 1). The mean arterial plasma concentration of FFA during the main period of blood sampling (7-9 hr after starting the hexose infusions) was significantly higher in group F than in G (0.41 + 0.04 versus 0.20 f 0.02 mM, Table 2). Mean total net inflow transport of FFA was also appreciably higher (48%) in group F than in G (0.1 < p < 0.2). Splanchnic extraction fraction and uptake of FFA and the fraction of the total net inflow transport of FFA taken up in the splanchnic vascular bed were not significantly different between groups F and G. Mean values for the specific activity of ‘H-FFA of arterial and hepatic venous plasma relative to that of peripheral venous plasma after a 5-hr infusion of 9,10-3H-palmitate were 132% f 16% and 104% f 5% in groups F and G, respectively. Values for the fraction of FFA taken up in the splanchnic region that was secreted as TGFA into hepatic venous plasma did not vary systematically over the interval of 3-5 hr after starting the isotopic infusion. The mean value for the fraction of FFA converted to plasma TGFA in group F was significantly higher than in group G (27% f 2% versus 167; f 2%, p < 0.05). The fraction of FFA converted to plasma VLDL-TGFA in the splanchnic region was also significantly higher than that converted to plasma TGFA in group G (28% + 1% versus 16% f 2%,p < 0.05), but not in group F (40% f 3% versus 27% f 2%, 0.05 < p < 0.1). The specific activity of plasma 14C-FFA after the infusion of U-‘4C-fructose or U-14C-glucose for 12 hr was less than 2% of that of either labeled hexose given. Values for mean arterial blood concentration of &hydroxybutyrate were similarly low in groups F and G (16 f 7 and 7 =t 1 PM, reTable 2. Arterial Concentration and Metabolism of FFA Splanchnic

Arterial PlWWl

Net

Concentration Group

T,0”%pWt $4)

Extraction

Uptake

Fraction

(Arterial)

F

0.41

*

0.04

178

*

23

0.32

*

0.04

54

G

0.20

l

0.02*

110

*

19

0.47

l

0.04

33 *

Valuer

represent

‘Significantly

meon different

value from

*

SE for three

group

m) Uptake

Inflow

(flmole,min,m

(rmols/ml)

(tmale/min/rq

subjects

F, p < 0.05.

in group

Net

z+ 16

F and

(From

6 four

27 +

4

24

S

*

Portal

I”R0W)

Release

subjects

Pi2

G.

Uptake

Totot

Splanchnic Uptake/

(Arterial

Net

+ Portal)

Tranrport

64*

18

187

l

24

0.34

*

1,

126

+ 24

0.39

+ 0.02

49

lb t6 in group

Total Total

+

Inflow

Total Inflow

Net

Tronrport 0.07

968

WOLFE

Table 3.

AND

AHUJA

Arterial Concentmtion, SpecificActivity, and Splanchnic Secretion of Plasma TGFA

Arterial

Splanchnic Secretion of TGFA (pmole/min/sq

Plasma Concentration

m)

(pmole/ml) Group

TGFA

VLDL-TGFA

F

8.0 *

1.5

6.3 zt 1.3

G

10.0 *

2.2

7.9 f

Values represent mean f *Specific

x

Chemical 14.8 zt 2.9

1.8

TG~tdiochemical

108 h-28

8.9 + I .O

96 f

130 f

20

Chemir~iLDL~~~~hemicol

38

120 & 42

169 f

100 l 40

138 + 27

157 + 44

42

SE for three subjects in group F and four subiectr in group G.

activity of arte&l

VLDL-TGFA

expressed as per cent of estimated

specific activity

of FFA entering

the liver

during the interval of time when the value for this ratio was constant. tValues

derived from measurement

of transsplanchnic

gradients

of five to seven sets pf crieriol

and

hepatic

venovs

and

hepatic

venous

blood samples. %Values derived

from

measurement

blood sampler. VLDL were separated

of

transrplanchnic

gradients

of at least four sets of artericll

from whole plasma by ultracentrifugation.

spectively), as were those for mean splanchnic production of /3-hydroxybutyrate (4 f 1 and 3 f 1 pmole/min/sq m, respectively). Transport of plasma TGFA . Values for serial arterial and peripheral venous concentration of plasma VLDL-TGFA were steady during the study of splanchnic metabolism and were not significantly different between groups F and G (Fig. 1, Table 3). Mean values for splanchnic secretion of plasma TGFA and VLDL-TGFA determined chemically or radiochemically were not significantly different between groups F and G (Table 3; p > 0.5). Secretion of plasma TGFA was attributable to secretion of plasma VLDL-TGFA. Mean chemical values for the splanchnic secretion of plasma VLDL-TGFA were not significantly different from those for TGFA in either group F or G (p > 0.5 and 0.05 < p < 0.1, respectively). Mean values for splanchnic secretion of plasma VLDL-TGFA determined radiochemically were significantly higher than those determined chemically in group G (p < 0.005) but not in group F (0.05 < p < 0.1). Mean chemical values for splanchnic secretion of VLDL-TGFA or TGFA were not significantly different from those determined radiochemically in either group F or G (p > 0.1). Likewise, values for clearance of VLDL-TGFA from plasma in the extrasplanchnic tissues in groups F and G (109 f 27 and 119 f 24 pmole/min/sq m, respectively) were not significantly different from the corresponding values for chemical rates of secretion of plasma TGFA (p > 0.4 and p > 0.5, respectively). All measures of transport of plasma TGFA within each group were closely correlated (Table 4). Splanchnic secretion of TGFA has been found to slightly underestimate hepatic secretion in glucose-fed miniature swine.” There was no detectable secretion of unlabeled TGFA from the intestine inasmuch as values for clearance of VLDL-TGFA from blood plasma were similar to those for splanchnic secretion of TGFA. Values for arterial concentration of plasma VLDL-TGFA correlated highly with (1) chemical values for splanchnic secretion of VLDL-TGFA (r = 0.82, p < 0.025) and (2) values for clearance of VLDL-TGFA from plasma in extrasplanchnic tissues (r = 0.94, p < 0.001; Fig. 2). In all subjects, values for the ratio: Precursors ofplasma VLDL-TGFA. specific activity of ‘H-TGFA

of arterial VLDL x 100

estimated specific activity of ‘H-FFA entering liver reached a plateau within 8 hr of starting the infusion of 9,10-3H-palmitate

IV-ADMINISTERED

FRUCTOSE

Table 4.

AND

GLUCOSE

969

Correlations Between Different Techniques for Measuring Turnover of Plasma TGFA and VLDGTGFA Codlicient

of Correlation

r

Groups F and G Combined*

Comparison Chemical

rates

of secretion

of secretion Chemical

of plasma

rates

region

of plasma VLDL-TGFA

of secretion

rates

splanchnic

clearance

of secretion

region

from

of plasma

vs. extrasplanchnic

Chemical

TGFA

vs. chemical splonchnic

TGFA

from

VLDL-TGFA

vs. extrasplanchnic

clearance

region

VLDL-TGFA

from

vs. rodiochemical splanchnic

Chemical

rates

chemical

rates

of plasma

of secretion

of plasma

VLDL-TGFA

of plasma

TGFA

splanchnic

rates region

of secretion

of plasma

vs. extrasplonchnic

glycerides

0.68

0.89

0.47

0.91g

0.998

0.83

0.69

0.93

0.53

from

0.734

0.79

0.86

splonchnic

TGFA

from

clearance

of plasma 0.66

based

on

eight

fell to normal

subjects,

(74

mg/dl)

tValues

based

on four

subjects,

fVolues

based

on four

subjects.

$Significont

0.83

vs. rodio-

VLDL-TGFA *Values

0.93

TGFA

region Radiochemical

0.874

of plasma

region

of secretion

rates

of secretion

correlation,

including

during

a

subject

the control

including

Group G$

from

VLDL-TGFA Chemical

Ft

splanchnic

of plasma

of plasma

Group

rates

(R.Y.)

(isocaloric)

given

0.70

fructose,

whose

0.72 fasting

serum

tri-

diet.

R.Y.

p < 0.05.

(Fig. 3). The values for this ratio during the plateau period provide an estimate of the fraction of plasma VLDL-TGFA derived from plasma FFA,‘5m18which averaged 14.8% and 8.9% in groups F and G, respectively (Table 3). Conversely, most of the plasma VLDL-TGFA (mean values: 85% and 91% in groups F and G, respectively) appeared to be derived from precursors other than circulating FFA. These values should be regarded as estimates, because the plasma concentration of FFA fell slightly and the corresponding specific activity rose during the later part of this study (Fig. 1). In addition, by contrast PLASMA

VLDL-TGFA

(rmol/ml) 12 -

10 -

8-

6-

Fig. 2. Relation between concentration of plasma VLDL-TGFA and extrasplanchnic cleamnce of plasma VLDL-TGFA in individual subiects receiving hypercaloric intravenous infusions of fructose (e) or glucose (0).

I

0 50

100

EXTRASPLANCHNIC PLASMA

150 CLEARANCE

VLDL-TGFA

(pmol/min

m2)

200 OF

WOLFE

970

Fig. 3. 20

0

0 tS +-4I -4

0

b

3

5 Hours of Infusion

I- - - - - - - - -Infusion

I

I

8

10

of Rodiopolmitate

of Hexore

(30 g/k)

Mean values for ratio of specific

activity of 3H-TGFA of arterial plasma VLDL x 100 to estimated specific activity of 3H-FFA entering the liver for three subjects receiving hypercaloric intravenous infusions of fructose (e) in group F or four

.

10

AND AHUJA

J 12

receiving glucose (0) in group G. Variance between subjects, expressed as SE, was less than 25% in each group.

I_(

- - - - - - - -I

with studies in glucose-fed miniature swine, ” it has not been feasible to ascertain whether averaging of the specific activity of FFA of hepatic venous and arterial blood provides a precise measure of tte specific activity of FFA entering human liver during fructose or glucose feeding. Values for serial arterial and peripheral venous blood concentration of fructose and glucose were essentially constant over the interval 3-12 hr after starting the isotopic infusions in groups F and G’* (mean coefficients of variation, 6.0% f 0.3% and 5.6% f 6%, respectively). The mean specific activity of the carbons of arterial blood glucose in groups F and G after intravenous infusion of the corresponding labeled hexose for 3 hr or more was also constant and was not significantly different from that of the labeled hexose administered.‘* Under these steady-state conditions, only a small fraction of plasma VLDLTGFA was derived immediately from fructose or glucose. Mean values for the ratio specific activity of ‘*C-TGFA carbon of arterial VLDL x 100 specific activity of administered ‘*C-hexose carbon rose progressively (Fig. 4) and did not plateau. Values attained after 5 hr of infusion of labeled fructose were consistently higher than those attained with corresponding infusions of labeled glucose (mean values, 2.1% i 0.6% versus 0.6% f O.l%, respectively, 0.1 < p < 0.2); the mean value in group F after infusion of labeled fructose for 12 hr was 5.1% f 1.0%. Values for this ratio after infusion of U-**C-glucose for 12 hr in two subjects of group G were 3.2% and 4.0x, respectively, overlapping with group F. During infusion of U-‘*Cglucose for 5 hr,% with subsequent maintenance of the infusion of unlabeled glucose for 7 hr, values in two subjects of group G for the ratio specific activity of ‘*C-TGFA carbon of arterial VLDL x 100 specific activity of ‘*C-glucose carbon in arterial blood during administration

of ‘*C

rose for another 5 hr following termination Mean values for the ratio

of the infusion of the ‘*C (Fig. 5).

specific activity of ‘*C-glyceride-glycerol

carbon of arterial VLDL x 100

specific activity of administered *The specific activity of arterial blood glucose carbon the isotopic infusion did not vary by more than 10%.

‘*C-hexose carbon during

the interval

3-5 hr after

starting

IV-ADMINISTERED

FRUCTOSE

971

AND GLUCOSE

Fig. 4. Ratios of specific activity of carbons of “C-glyceride-glycerol (0) and “C-TGFA (0) of arterial plasma VLDL x 100 relative to that of the administered U-“C-glucose in a representative subject of group G.

-4

0

3

-Hr,urr

5

10

8

of lnfwion of [ 9,10-3H

12

1polmibte+

I------ ,nf,,rion of Glucore (30&r)

- - - - - - I

also rose progressively, attaining higher values after infusion of labeled fructose for 5 hr, as compared with glucose (13.0% f 2.5% versus 6.0% f 1.8x, respectively, 0.1 < p < 0.2). The mean value in group F after infusion of labeled fructose for 12 hr was 18% f 2% (n = 3). Values for this ratio after infusion of U-L4C-glucose for 12 hr in two subjects of group G were 9.7% and 24x, respectively (Fig. 4). A plateau was reached for values of this ratio within 10 hr of infusion of U-‘4C-glucose in group G, whereas the respective values in group F continued to rise very slightly in two subjects and plateaued in another at this time (data not shown). As a result, the percentage of the total “C-triglyceride label that was in the fatty acid moiety rose significantly over the period 3-12 hr after starting the radioisotopic infusions (mean values, from 46% f 7% to 59% + 4% in group F and from 32% f 6% to 62% f 6% in group G, p < 0.05). The mean value in group G for this percentage at 5 hr (41% f 6%) was significantly different from those at 3 or 12 hr (p < 0.001); the differences in group F between the value at 5 hr and those at 3 or 12 hr were not significant. DtSCUSSlON

Metabolism of FFA The fed state induced by a hypercaloric high-carbohydrate diet and subsequent hypercaloric intravenous infusion of either fructose or glucose in hypertriglyceridemic men is characterized by decreased lipolysis’5 (Table 2) and a reduction in the contribution of FFA to plasma TGFAIS (Table 3) as when glucose is given orally. “J* An elevation of arterial serum insulin levelsI could explain the low rate of transport of FFA in group G (Table 2); however, in group F the mean arterial serum insulin concentration (17 f 3 PI-J/ml) was in the range reported for postabsorptive subjects.29 Inhibition of lipolysis in group F could have been mediated by fructose-induced elevation of blood lactate or pyruvate30 or increased effectiveness of insulin due to reduced glucagon secretion during the high-carbohydrate diet.3’ The lower splanchnic uptake of

;[rL%l&_J~~ -4

0

3

C-Hours

k------

5 of InLrion

8 af r 9,10-3H

lnfuriDnofGluco~eOg/hr)------,

IO

1&mi,ok+

12

Fit. 5. Ratios of the specific activity of carbons of CTGFA of arterial plasma VIOL x 100 relative to that of arterial blood glucose (during administmtion of U-“C-glvcose) for a representative sub ject of group G who received a constant infusion of U-“C-glucose for 5 hr followed by unlabeled glucose given at a similar mte for 7 hr.

972

WOLFE

AND AHUJA

FFA in group F as compared with postabsorptive hypertriglyceridemic menI may be attributable to lower net inflow transport of FFA and/or less efficient extraction of FFA entering the splanchnic region (Table 2). The fraction of the total net inflow transport of FFA which was taken up in the splanchnic region in groups F and G was similar to that of healthy young men, but lower than that of hypertriglyceridemic men studied in the postabsorptive state (p < 0.05).‘5 The significantly (52%) higher fraction of FFA taken up in the splanchnic region that was secreted as TGFA into hepatic ‘venous plasma in group F, as compared with group G (27% f 2% versus 16% f 2%) suggests that esterification of FFA into plasma TGFA in human liver is enhanced by fructose treatment. The fraction of FFA entering the splanchnic region which was converted to plasma TGFA in group G was similar to that of fasted subjects.15*16Although l,3-‘4C-glycerol has been reported to be more rapidly incorporated into hepatic triglycerides in fructose-fed versus glucose-fed rats, there was no difference in the rates of incorporation of these substrates into rat plasma triglycerides after Triton administration.32 Glucose feeding may promote plasma VLDL secretion by enhancing lipoprotein protein synthesis.33 Uptake of 3H-TGFA of lipoproteins of density > 1.006 from whole plasma in the liver or extrahepatic splanchnic region could explain the higher values for splanchnic conversion of FFA to plasma VLDL-TGFA versus plasma total TGFA (see Results), and the higher values for splanchnic secretion of VLDLTGFA (contained in density < 1.006) as compared to plasma total TGFA.17 Values for mean arterial blood concentration and splanchnic production of P-hydroxybutyrate were significantly lower in groups F and G than those previously reported for hypertriglyceridemic men studied in the postabsorptive state (p < 0.05).15 Transport of Plasma TGFA

Secretion of plasma TGFA into hepatic venous blood plasma was much higher in groups F and G (Table 3) than previously reported for postabsorptive hypertriglyceridemic or normotriglyceridemic men that had been studied with similar techniques and that had been maintained on strict isocaloric diets prior to study (p < 0.05).‘5*‘6There have been no comparable studies of TGFA transport in the fed state in either healthy or hypertriglyceridemic subjects maintained on isocaloric high-carbohydrate or balanced diets. The only reported study of the transport of plasma triglycerides during carbohydrate feeding did not quantify the full contribution of precursors other than FFA to plasma TGFA, nor did it allow for the disappearance of labeled VLDL-TGFA from plasma during the period of study. I3The present study of the fed state takes into account the major contribution to plasma VLDL-TGFA of fatty acids derived from precursors other than FFA.” For this and other reasons,15 our values for transport of TGFA are an order of magnitude higher than those previously reported for subjects receiving glucose.13 The finding of similar rates of splanchnic secretion of plasma TGFA in fructose-fed and glucose-fed hypertriglyceridemic men in the present study sug-

IV-ADMINISTERED

FRUCTOSE

AND

973

GLUCOSE

gests that the preponderant effect of sucrose or fructose on serum VLDLtriglyceride levels in man,*s9 as in the rat,” may relate to less efficient disposal of plasma VLDL-TGFA in peripheral tissues (due to failure to increase lipoprotein lipase activity) during fructose feeding. The implication of this appraisal of the capacity for triglyceride release by human liver with carbohydrate administration in hypertriglyceridemia is apparent. In normal individuals peripheral removal mechanisms must accommodate sufficiently such that large differences in triglyceride secretion result in only limited increases in circulating triglyceride levels. This suggests that impaired removal must underlie many cases of endogenous hyperlipemia. High rates of splanchnic secretion of TGFA have also been reported in human subjects that were on unrestricted diets prior to study after an overnight fast. 34Deposition in adipose tissue of three-fourths of TGFA derived from the secreted plasma VLDL in groups F and G, as found in previous studies of carbohydrate-fed rabbits,35 could amount to 63 g/day and could account for 570 kcal/day administered in excess of expected basal requirements. This storage function of adipose tissue is consistent with the observed low rate of fatty acid synthesis de novo in adipose tissue from obese human subjects maintained on hypercaloric high-carbohydrate diets.36 Precursors of Plasma VLDL-TGFA

Only a small fraction of arterial VLDL-TGFA in fed subjects was derived. from FFA; the remainder of the secreted VLDL-TGFA could have been derived from fatty acids synthesized de novo or stored in the liver. By contrast, the similarity of values for splanchnic secretion of TGFA derived from FFA and those for clearance of TGFA from plasma in extrasplanchnic tissues suggests that most plasma VLDL-TGFA of subjects fasted 15 hr are derived from FFA;16 furthermore, full radioisotopic equilibration of plasma FFA with VLDL-TGFA has been reported in fasting lean normotriglyceridemic men.15*22 Hypertriglyceridemic men store excessive amounts of FFA in the liver in the postabsorptive state.” The rate of storage after a 15-hr fast (about 40 /rmole/ min/sq m) is about 40% of the rate of splanchnic secretion of plasma TGFA in the present studies of the fed state (Table 3). Measurements of splanchnic uptake of hexoses, glycerol, and amino acids in these subjects indicate that fructose and glucose were the preponderant potential sources of substrate for hepatic synthesis of VLDL-TGFA.14 The hexose-derived carbon available for de novo synthesis of VLDL-TGFA was not significantly different from the carbon requirement for synthesis of the secreted VLDL-TGFA derived from precursors other than FFA in groups F (87 f 28 versus 91 f 28 pmole FFA equivalents,* respectively) or G (130 f 9 versus 88 f 28 pmole FFA equivalents, respectively, p > 0.05; Table 3).14 The delay of equilibration of fructose- and glucose-carbon with carbon of VLDL-TGFA (Figs. 4 and 5) suggests that these hexoses may mix in vivo with a large hepatic pool of unlabeled substrate, such as glycogen, before incorporation into VLDL-TGFA.“” By contrast with previous studies in fasted sub*Each molecule

of FFA was assumed

to contain

17 carbon

atoms.

974

WOLFE

AND AHUJA

‘3*22de novo synthesis of plasma VLDL-14C-TGFA from U-14C-glucose was readily demonstrable in the present studies of the fed state (Figs. 4 and 5, and Results). Most of the 14Ctaken up by porcine liver in vivo during a 24-hr hypercaloric intravenous infusion of U-r4C-glucose is found in glycogen; however, an appreciable amount of radioactivity is also found in protein with lesser amounts in phospholipid and TGFA (Wolfe and O’Hea, unpublished observations). During subsequent infusion of similar amounts of unlabeled glucose, the labeled carbons of hepatic TGFA (secreted in plasma VLDL-TGFA) appear to be replenished from labeled liver glycogen, protein, and/or phospholipid fatty acids. Hepatic glycogen levels increase during administration of either fructose or glucose38 and correlate positively with the ability of liver to synthesize fatty acids from acetate.39 Values obtained for the fraction of plasma VLDL-TGFA derived from the respective labeled hexose after 5 hr of intravenous infusion were consistently higher for fructose versus glucose. This is in accord with the finding by Zakim12 that, at a concentration of 5 mM, fructose is more rapidly converted to TGFA in human liver slices than glucose. The failure of the present study to detect a significant difference in the rate of hepatic release of triglycerides between subjects receiving fructose and those receiving glucose (see Results) may be explained by the differences in the blood concentration of the respective hexoses in groups F and G (mean values, 2.0 + 0.1 mM fructose versus 9.3 f 0.2 mM glucose). The concentration of substrate utilized is known to have an important effect on hepatic TGFA synthesis. 4o Assuming an average human liver weight of 1.6 kg:’ it can be calculated that hepatic synthesis of TGFA from glucose in human liver slices in vitro42,43is less than 1% of hepatic secretion of plasma TGFA in vivo (Table 3). The present studies demonstrate the value of the in vivo approach to physiologic studies of the regulation of serum triglyceride levelsCOand delineate the role of the liver in carbohydrate accentuation of lipemia.

jects

ACKNOWLEDGMENT We are grateful to Dr. C. Tao for technical assistance and to E. Wolfe for helping with aspects of this investigation. We thank Nancy Crown and Marline Wyatt for supervising dietary management of these patients, Dr. R. Fowlis and Dr. C. Sang for assisting with sampling of blood, and Dr. R. J. Have1 and DT. R. N. Redinger for valuable criticism of manuscript.

all the the the

APPENDIX

Metabolism of FFA”v2’ I. Arterial net inflow transport of FFA (wmole/min) rate of infusion of radiopalmitate (cpm/min) = specific activity of arterial plasma FFA (cpm/pmoie)’ 2. Splanchnic extraction fraction of radiopalmitate =

concentration

of arterial plasma FFA (cpm/ml) - concentration concentration

in hepatic venous plasma

of arterial plasma FFA (cpm/ml)

3. Splanchnic uptake (arterial) of FFA (&mole/ml plasma) = concentration of arterial plasma FFA (pmole/ml) x splanchnic extraction fraction of radiopalmitate.

IV-ADMINISTERED

FRUCTOSE

4. Net splanchnic

AND GLUCOSE

975

release of FFA (~mole/ml

plasma)

= [concentration of arterial plasma FFA (~mole/ml) x extraction fraction of radiopalmitate] - [concentration - concentration in hepatic venous plasma].

in arterial

plasma

miniature swine I7 the mean hepatic extraction fraction In fasted dogs’s and glucose-fed of FFA averaged 80%-84x of that of the entire splanchnic region. Assuming that these values also apply to man, total splanchnic release of FFA can be calculated and hepatic uptake of FFA released from the extrahepatic region can be estimated. 5. Total

splanchnic

release of FFA (amole/ml

net splanchnic = 1 - (splanchnic 6. Hepatic

plasma)

release (pmolelml

extraction

fraction

uptake of FFA derived from splanchnic region (pmole/ml plasma) = equation 5 - equation 4.

plasma)

of radiopalmitate FFA

7. Total

splanchnic uptake of FFA (rmole/ml = equation 3 + equation 6.

entering

x 0.8)

portal

venous

blood

from extrahepatic

plasma)

8. Splanchnic

uptake of FFA (cpm/ml plasma) - concentration in arterial plasma FFA (cpm/ml) x splanchnic extraction fraction of radiopalmitate.

9. Splanchnic

uptake (arterial) of FFA (pmole/min) = sptanchnic uptake (arterial) of FFA (rmole/ml x splanchnic plasma flow (ml/min).

plasma)

10. Net splanchnic

release of FFA (pmole/min) = net splanchnic release of FFA (rmole/ml x splanchnic plasma flow (ml/min).

plasma)

11. Hepatic uptake of FFA derived from FFA entering portal venous blood from extrahepatic splanchnic region (pmole/min) = hepatic uptake of FFA derived from FFA entering portal venous blood from extrahepatic splanchnic region (~mole/ml plasma) x splanchnic plasma flow (ml/min). 12. Total splanchnic uptake of FFA (amole/min) = total splanchnic uptake of FFA (pmole/ml x splanchnic plasma flow (ml/min). 13. Total net inflow transport of FFA (rmole/min) = arterial net inflow transport (pmole/min)

Splanchnic Secretion

plasma)

+ equation

I1

of Plasma TGFA or VLDL-TGFA

Chemical method.

1. Splanchnic

secretion of plasma TGFA or VLDL-TGFA = concentration in hepatic venous plasma (wmole/ml - concentration in arterial plasma.

(pmole/ml plasma)

plasma)

2. Splanchnic secretion of plasma TGFA or VLDL-TGFA (rmole/min) = splanchnic secretion of TGFA or VLDL-TGFA (pmole/ml plasma) x splanchnic plasma flow (ml/min). Radiochemical method.”

1. Splanchnic

secretion of plasma TGFA (cpm/ml plasma) = concentration in hepatic venous plasma (cpm/ml plasma) - concentration in arterial plasma.

976

WOLFE

2. Splanchnic

secretion

splanchnic = splanchnic

of TGFA

secretion uptake

AND AHUJA

(pmole/min)

of TGFA

of labeled

(cpm/ml

plasma)

FFA (cpm/ml

plasma)

x [(SAFFA~+~/~)~/(~~VLDL-TGFA~I x total splanchnic uptake of FFA (rmole/min) where (SAVLDL_rGFA)r is the mean specific activity of TGFA of arterial VLDL and (SAFFAa+h,Zkis the mean value for the specific activity of FFA in arterial and hepatic venous blood plasma during the terminal period when values for this ratio reached a plateau. 3. Clearance

of VLDL-TGFA

(t2 - t,) x [(RH - RA),

from plasma x EHPF,]

in the extrasplanchnic - (RA,z

- RA,,)

region (pmolelmin)

PV

= 02 - 4) X ~WVLDL-TGFA~,

+ SA~~~~-~~~~t2)

where RH is the radioactivity in VLDL-TGFA of hepatic venous blood plasma, RA the radioactivity in VLDL-TGFA of arterial blood plasma, (RH - RA), the mean difference in radioactivity in VLDL-TGFA between hepatic venous and arterial plasma during the interval of time (t2 - tt). PV the plasma volume, SAvt~L_ronA the specific activity of TGFA of arterial VLDL, and EHPF, the mean splanchnic plasma flow (ml/min). The time interval (t2 - tt) for individual calculations was restricted to periods when radioactivity in arterial VLDL-TGFA was increasing at an approximately linear rate (or was constant).16

REFERENCES 1. Brunzell JD, Schrott HG, Motulsky AG, et al: Myocardial infarction in the familial forms of hypertriglyceridemia. Metabolism 25: 313-320, 1976 2. Goldstein JL, Hazzard WR, Schrott HG, et al: Hyperlipidemia in coronary heart disease. I. Lipid levels in 500 survivors of myocardial infarction. J Clin Invest 52:1533-1577, 1973 3. Sale1 AF, Riggs K, Mason DT, et al: The importance of type IV hyperlipoproteinemia as a predisposing factor in coronary artery disease. Am J Med 57:897-903, 1974 4. Carlson LA, Bottiger LE: Ischaemic heart disease in relation to fasting values of plasma triglycerides and cholesterol. Lancet I:8655868, 1972 5. Hatch FT, Abell LL, Kendall FE: Effects of restriction of dietary fat and cholesterol upon serum lipids and lipoproteins in patients with hypertension. Am J Med 19:48-60, 1955 6. Ahrens EA, Hirsch J, Oette K, et al: Carbohydrate-induced and fat-induced lipemia. Trans Assoc Am Physicians 74: 134- 146, 1961 7. Farquhar JW, Frank A, Gross RC, et al: Glucose, insulin and triglyceride responses to high and low carbohydrate diets in man. J Clin Invest 45:1648-1656, 1966 8. Kaufmann NA, Poznanski R, Blondheim SH, et al: Changes in serum lipid levels of hyperlipemic patients following the feeding of

starch, sucrose 261-269, I966

and glucose.

Am J Clin Nutr

18:

9. Antar MA, Little JA, Lucas C, et al: Interrelationship between the kinds of dietary carbohydrate and fat in hyperlipoproteinemic patients. Atherosclerosis I I: 191-201, 1970 10. MacDonald I: Influence of fructose and glucose on serum lipid levels in men and preand postmenopausal women. Am J Clin Nutri 18:369-372, 1966 11. Bar-on H, Stein Y: Effect of glucose and fructose administration on lipid metabolism in the rat. J Nutr 94:95-105, 1968 12. Zakim D: The effect of fructose on hepatic synthesis of fatty acids. Acta Med Stand (Suppl542):205-214, 1972 13. Sandhoffer F, Bolzano K, Sailer S, et al: Quantitative Untersuchungen liber den Einbau von Plasmaglucose-Kohlenstolf in Plasmatriglyceride und die Veresterungsrate von freien Fettsluren des Plasma zu Plasmatriglyceriden wiihrend oraler Zufuhr von Glucose bei primlrer kohlenhydrotinduzierter Hypertriglyceridamie. Klin Wochenschr 47:1086-1094, 1969 14. Wolfe BM, Ahuja SP, Marliss EB: Effects of intravenously administered fructose and glucose on splanchnic amino acid and carbohydrate metabolism in hypertriglyceridemic men. J Clin Invest 56:970-977, 1975 15. Have1 RJ, Kane JP, Balasse EO, et al:

IV-ADMINISTERED

FRUCTOSE

Splanchnic metabolism of free fatty acids and production of triglycerides of very low density lipoproteins in normotriglyceridemic and hypertriglyceridemic humans. J Clin Invest 49: 2017-2035, 1970 16. Wolfe BM, Kane JP, Have1 RJ, et al: Mechanism of the hypolipemic effect of clofibrate in postabsorptive man. J Clin Invest 52: 2146-2159, 1973 17. Wolfe BM, Belbeck LW: Splanchnic and hepatic triglyceride secretion during hypercaloric intravenous glucose infusion in conscious swine. J Lipid Res 1619-27, 1975 18. Basso LV, Have1 RJ: Hepatic metabolism of free fatty acids in normal and diabetic dogs. J Clin Invest 49:537-547, 1970 19. Rodbell M: Metabolism of isolated fat cells. Effects of hormones on glucose metabolism and lipolysis. J Biol Chem 239:375-380, 1964 20. Henry RJ: Determination of total cholesterol, in Clinical Chemistry, Principles and Techniques. New York, Hoeber Medical Division, Harper & Row, 1965, p 852 21. Balasse EO, Bier DM, Have1 RJ: Early effects of anti-insulin serum on hepatic metabolism of plasma free fatty acids in dogs. Diabetes 21:280-288, 1972 22. Barter PJ, Nestel PJ: Precursors of plasma triglyceride fatty acids in obesity. Metabolism 22:779-785, 1973 23. Snedecor GW, Cochran WG: Statistical Methods (ed 6). Ames, Iowa State University Press, 1967, p 114 24. Brownell CL, Berman M, Robertson JS: Nomenclature for tracer kinetics. Int J Appl Radiat Isot 19:249-262, 1968 25. Glueck CJ, Levy RI, Fredrickson DS: Immunoreactive insulin, glucose tolerance, and carbohydrate inducibility in types II, III, IV, and V hyperlipoproteinemia. Diabetes 18:739747, 1969 26. Fredrickson DS, Lees RS: Familial hyperlipoproteinemia, in Stanbury JB, Wyngaarden JB, Fredrickson DS (eds): The Metabolic Basis of Inherited Disease (ed 3). Toronto, McGraw-Hill, 1972, p 545 27. Barter PJ, Nestel PJ: Plasma free fatty acid transport during prolonged glucose consumption and its relationship to plasma triglyceride fatty acids in man. J Lipid Res 13: 483-490. 1972 28. Sailer S, Sandhofer F, Bolzano K, et al: den Einflua der Glucose auf den Umsatz der freien Fettsauren des Plasmas, die Einbau-

eber

977

AND GLUCOSE

rate der freien Fettsauren

in Plasmatriglyceride

und die Wirkung von Noradrenalin auf StoffwechselgrS@en beim Menschen. Wochenschr 45:918-924, 1967

diese Klin

29. Muller WA, Faloona CR, Unger RH: The influence of the antecedent diet upon glucagon and insulin secretion. N Engl J Med 285: 1450-1454.1971 30. Boyd AE, Giamber SR, Mager M, et al: Lactate inhibition of lipolysis in exercising man. Metabolism 23:531-542, 1974 31. Eaton P, Kipnis DM, Karl I, et al: Effects of glucose feeding on insulin and glucagon secretion and hepatic gluconeogenesis in the rat. Am J Physiol227:lOll104, 1974 32. Waddell M, Fallon HJ: The effect of high-carbohydrate diets on liver triglyceride formation in the rat. J Clin Invest 52:27252731. 1973 33. Eaton RP, Kipnis DM: Effect of glucose feeding on lipoprotein synthesis in the rat. Am J PhysioL2 17: I 153-l 159, 1969 34. Boberg J, Carlson LA, Freyschuss U, et al: Splanchnic secretion rates of plasma triglycerides and total and splanchnic turnover of plasma free fatty acids in men with normo- and hypertriglyceridaemia. Eur J Clin Invest 2:454466, 1972 35. Have1 RJ, Felts JM, Van Duyne CM: Formation and fate of endogenous triglycerides in blood plasma of rabbits. J Lipid Res 3:297308, 1962 36. Sjostrom L: Fatty acid synthesis de novo in adipose tissue from obese subjects on a hypercaloric high-carbohydrate diet. Stand J Clin Lab Invest 32:339-349,1973 37. Wolfe BM, O’Hea EK: Relation between liver glycogen and synthesis of plasma triglycerides. Clin Res 21:1064a, 1973 38. H:son Nilsson L, Hultman E: Liver and muscle glycogen in man after glucose and fructose infusion. Stand J Clin Lab Invest 33:5-IO, 1974 39. Haugaard ES, Stadie WC: Relation between glycogen content and synthesis of fatty acids by rat liver. J Biol Chem 199:741-744. 1952 40. Romsos DR, Leveille GA: Effect of dietary fructose on in vitro and in vivo fatty acid synthesis in the rat. Biochim Biophys Acta 360: I-II, 1974 41. Clearfield HR: Anatomy and physiology of the liver, in Bockus HL (ed): Gastroenterology (ed 2) vol 3. Philadelphia, W B Saunders, 1966, p 88

978

42. Zakim D, Herman RH, Gordon WC: The conversion of glucose and fructose to fatty acids in the human liver. Biochem Med 2:427437, 1969 43. Kuo PT, Feng L, Cohen NN, et al: Lipogenesis in the hepatic tissue: Lipogenesis and

WOLFE

AND AHUJA

lipolysis in the adipose tissue of hyperglyceridemic and atherosclerotic patients. Trans Assoc Am Physicians 78:187-204, 1965 44. Have1 RJ, Kane JP: Quantification of triglyceride transport in blood plasma: A critical analysis. Fed Proc 34:2250-2257, 1975