534th MEETING, NOTTINGHAM
433
were removed and perfused as described by Hearse & Chain (1972). In each experiment
the heart, either a diabetic or a normal control, was perfused initially as a working aerobic
preparation. During this 15min control period the heart was perfused with bicarbonate
buffer, pH7.4 (Krebs & Henseleit, 1932), containing glucose ( 1 l . l m ) and was made
to work against a hydrostatic pressure of 9800Pa (100cmH20). The perfusion fluid was
equilibrated with 0 2 + C 0 2(95: 5). At the end of the control period, during which time
the aortic flow was measured and the stability of the preparation was ascertained, the
heart was converted into an anoxic K+-arrested non-recirculating Langendorff (1895)
preparation. During this 30min anoxic period the heart was perfused with bicarbonate
buffer, pH7.4, containing glucose (11.1mM) in which the K+ concentration was increased
to 1 6 m ~The
. perfusion fluid was equilibrated with N2+C02(95: 5). At the end of the
anoxic period the heart was simultaneously reoxygenated and converted into a working
system perfused with bicarbonate buffer, pH7.4, containing glucose (11.1 m ~ ) The
.
recovery of the aortic flow was monitored and was expressed as a percentage of the control value for the pre-anoxic working heart.
The hearts from normal rats showed a rapid and progressive post-anoxic recovery,
after approx. 2min reaching 80-90 % and after 30min reaching 90-97 % of the pre-anoxic
control value. In contrast, the hearts from over half of the diabetic rats exhibited a characteristic and unusual recovery profile. Initially the diabetic hearts recovered well, but after
approx. 2min they developed symptoms of failure that lasted for periods of up to 4min.
during which time, although beating, the hearts failed to develop sufficient pressure and
the aortic flow fell to very low values or even zero. After this period the hearts entered a
second phase of recovery with the aortic flow reaching 80-85 % of its control value after
a further 25 min.
If insulin (0.01 unitlml) was included in the anoxic perfusion fluid a marked change in
the post-anoxic recovery profiles was observed. The period of failure observed in the
diabetic heart was completely eradicated and the heart recovered very rapidly. Under
these conditions both normal and diabetic hearts recover to 75-95 % in 2min, reaching
87-97 % in 30min.
Clearly, under the conditions of this study, the diabetic hearts appear to be far more
vulnerable to an anoxic crisis than are normal hearts. The presence of exogenous supplies of insulin during anoxia, however, permits a considerably improved recovery in the
diabetic heart.
This work was carried out with the aid of a grant from the British Heart Foundation.
Chain, E. B., Mansford, K. R. L. & Opie, L. H. (1969) Biochem. J. 54,537-546
Hearse, D. J. & Chain, E. B. (1972) Biochem. J. 128, 1125-1133
Krebs, H. A. & Henseleit, K. (1932) Hoppe-Seyler's Z . Physiol. Chem. 210, 33-66
Langendorff, 0. (1895) Pfugers Arch. Gesamte Physiol. 61, 291-332
The Comparative Effects of Glucose and ]Fructose on the Hepatic
Secretion of Very-Low-Density Lipoproteins
D. L. TOPPING and P. A. MAYES
Division of Biochemistry, Royal Veterinary College, London NW1 OTU, U.K.
Many studies indicate that the feeding of animals on diets high in fructose or sucrose
elevates plasma triglyceride concentrations. The digestion of sucrose, which is considerably more rapid than that of starch, causes the flooding of the hepatic circulation
with both fructose and glucose. However, there is little information on whether fructose,
when compared with glucose on a molar basis, has a greater potential for stimulating
the hepatic secretion of very-low-density lipoproteins ( d < 1.006). In a previous paper
(Topping & Mayes, 1972) we described the immediate stimulation by a fructose infusion
of the secretion of very-low-density lipoproteins by the perfused liver. The effects of a
Vol. 1
434
BIOCHEMICAL SOCIETY TRANSACTIONS
similar infusion of glucose were not studied. It therefore remained of considerable importance to ascertain whether there are differences in the metabolic effects of each
hexose when they are utilized by the liver under comparable conditions.
Livers from fed male rats (340-3608) were perfused with defibrinated whole rat blood
essentially as described by Mayes & Felts (1966). The rate of perfusion was approx.
lml/min per g of liver. The concentration of blood glucose was stabilized at 160200mg/100ml. [l-14C]Oleatewas infused as a complex with albumin to maintain a free
(non-esterified) fatty acid concentration of approx. 0.9pmol/ml of serum. A solution of
fructose (in 0.9% NaCI) was infused to maintain a concentration of 25mg/100ml of
blood. In other experiments glucose was infused at an identical rate.
At similar rates of infusion the liver removed fructose and glucose from the circulation
at approximately the same rate. However, the rate of secretion of very-low-density
lipoprotein was significantly higher (P<0.05) in the presence of fructose. Production was
linear for the duration of the experiment (9Omin), being 100 and 140pmol of triglyceride
fatty acid/h per liver for the glucose and fructose groups respectively. Fructose increased
the esterification of labelled oleate and decreased its oxidation to 14C02and 14C-labelled
ketone bodies. However, the export by the liver of serum free fatty acids, as 14C-labelled
very-low-density-lipoprotein triglycerides, was unchanged.
The results indicate that important metabolic differences exist between fructose and
glucose when they are compared on a mole-for-mole basis. The data support previous
observations (Topping & Mayes, 1972) that fructose enhances the secretion of very-lowdensity-lipoprotein triglycerides by increasing the contribution of a source of liver
glycerides other than those derived from serum free fatty acids. The observations also
help to account for the differing abilities of various dietary carbohydrates to induce
hypertriglyceridaemia (McDonald, 1965).
The support of the Medical Research Council is gratefully acknowledged.
Mayes, P. A. & Felts, J. M. (1966) Proc. Eur. SOC.Study Drug Toxicity 7 , 16-29
McDonald, I. (1965) Clin. Sci. 29, 193-197
Topping, D. L. & Mayes, P. A. (1972) Biochem. J. 126, 295-311
The Peptide Composition of Cod Serum High-Density Lipoprotein
E. R. SKINNER
Department of Biochemistry, University of Aberdeen, Marischal College,
Aberdeen AB9 lAS, U.K.
High-density lipoprotein of mammalian serum contains several distinct protein components (apolipoproteins) whose functions and whose relationship to other serum lipoprotein classes are under investigation in many laboratories. Detailed studies have been
made on the apolipoproteins of human (Scanu et al., 1969; Shore & Shore, 1969) and rat
serum (Koga et al., 1971), but little is known about the nature of the serum apolipoproteins of lower vertebrates. The present communication describes the isolation and
characterization of the apolipoproteins of the serum high-density lipoprotein of the cod
(Gadus morhua L.), an organism that depends highly on lipid for its source of energy and
possesses special features such as hepatic lipid storage that may make it a useful model
system.
. Individual lipoprotein classes were prepared by sequential flotation and the density of
each class was established empirically. For the preparation of cod high-density lipoprotein the following procedure was used: serum was adjusted to a density at 20°C of
1.095g/ml by the addition of an equal volume of 1.95~-NaBr
containing 0.27rn~-EDTA,
and centrifuged at lOOOOOg for 18h at 10°C in the no. 40 rotor of the Spinco model L 2
preparative ultracentrifuge. Under these conditions, the very-low-density and lowdensity lipoproteins were concentrated in the upper 1 ml volume of the centrifuge tube.
I973