Changes in the concentrations of hepatic metabolites on administration of dihydroxyacetone or glycerol to starved rats and their relationship to the control of ketogenesis

1. Glycerol and dihydroxyacetone, both antiketogenic and readily metabolized, but differing in their effects on the redox state of the hepatic NAD couples, were given to starved rats and the contents of metabolites were measured in freezeclamped liver and in the blood. The object was to study the effects of changes in the redox state and of the availability of oxidizable substrates on the rate of ketone-body formation. 2. Intramuscular administration of dihydroxyacetone, glycerol or glucose to starved rats decreased the concentrations of acetoacetate and 3-hydroxybutyrate in the blood by 70-80% within 60min., whereas there was no major change in the free fatty acid concentration. 3. Dihydroxyacetone, but not glucose or glycerol, caused an immediate and sustained twofold increase in the blood lactate concentration. 4. Dihydroxyacetone and glycerol caused a rapid fall in the hepatic concentrations of ketone bodies, dihydroxyacetone being more effective. 5. This decrease was not accompanied by significant changes in the concentrations of acetyl-CoA, long-chain acyl-CoA or free CoA. 6. The hepatic glycerophosphate concentration rose about 40-fold on administration of glycerol, whereas with dihydroxyacetone the increase was only about 50%. The large increase in glycerophosphate concentration after administration of glycerol was completely prevented by pretreatment of the rats with tri-iodothyronine. Triiodothyronine-treated rats showed the same decrease in ketone-body concentrations after administration of glycerol as the untreated rats. 7. Glycerol and dihydroxyacetone caused an increase in the hepatic lactate concentration; the pyruvate concentration rose only after injection of dihydroxyacetone. 8. Both compounds increased liver glycogen. 9. Calculation of the [free NAD(+)]/[free NADH] ratios indicated that dihydroxyacetone increased the ratio in cytoplasm and mitochondria, whereas glycerol caused a prompt fall in both compartments, followed at 10min. by a slight rise in the mitochondrial compartment. 10. Dihydroxyacetone did not alter the hepatic content of ATP. 11. The findings suggest that the main reason for the antiketogenic effect of glycerol and dihydroxyacetone was a consequence of their ready metabolism and the provision of an increased supply of C(3) intermediates for conversion into oxaloacetate. Under the test conditions, neither the hepatic content of alpha-glycerophosphate nor the redox state of the NAD couples appeared to play a major role in the regulation of ketogenesis.     

Activity and intracellular distribution of enzymes of ketone-body metabolism in rat liver

1. The activities of hydroxymethylglutaryl-CoA synthase and lyase in rat liver were found to be two- to 15-fold greater than those reported by other authors under similar conditions. 2. When expressed on the basis of body weight, no appreciable differences were found between the activities of hydroxymethylglutaryl-CoA synthase in whole homogenates of livers from normal and starved rats. The synthase activity increased by 70% and 140% in livers of alloxan-diabetic rats and rats fed on a high-fat diet respectively. 3. Hydroxymethylglutaryl-CoA lyase activity showed no significant increases in starvation or alloxan-diabetes, but a 40% increase was found in fat-fed rats. 4. Less than 12% of the activities of both enzymes were found in the cytoplasmic fraction of normal liver. The cytoplasmic activity doubled in alloxan-diabetes and starvation; on feeding with a high-fat diet the increase, though significant, was less marked. 6. The intracellular distribution of glutamate dehydrogenase indicated that the changes in the cytoplasmic activities observed were not due to leakage from the mitochondria. 7. Feeding with a normal or high-fat diet after 48hr. starvation caused within 24hr. a decrease in the cytoplasmic activity of hydroxymethylglutaryl-CoA synthase to values lower than those found in rats fed on a corresponding diet for a longer period of time. 8. Acetoacetyl-CoA deacylase activity in liver was about 20% of that of hydroxymethylglutaryl-CoA synthase and was primarily located in the cytoplasm. Starvation or alloxan-diabetes did not alter the acetoacetyl-CoA deacylase activity. 9. It is concluded that variations in the concentrations of enzymes involved in acetoacetate synthesis play no major role in the regulation of ketone-body formation in starvation and alloxan-diabetes. The changes in the cytoplasmic activities of hydroxymethylglutaryl-CoA synthase and lyase suggest that acetoacetate synthesis can occur in the cytoplasm. This may play a role in the disposal of surplus acetyl-CoA arising in the cytoplasm when lipogenesis is inhibited.     

ADIPOSE TISSUE : Morphological Changes Associated with Lipid Mobilization

Morphological changes associated with mobilization of lipid were studied in epididymal adipose tissue from fasted and from alloxan diabetic rats. In both groups of animals a decrease in lipid content was accompanied by the formation of complex frond-like cytoplasmic processes and of loops and folds of basement membrane which extended from cell surfaces. These changes, evident after 1 day of fasting, increased in magnitude with increasing weight loss. As the lipid content of the cell decreased further, lipid-cytoplasmic interfaces became irregular and convoluted. Cytoplasmic microvesicles were prominent and appeared to be greatly increased in number. Rosette-like structures composed of microvesicles were observed in both lipid-depleted fat cells and endothelium. The interpretation of these changes and their physiological significance are discussed in terms of the physical and chemical properties of lipids and lipid metabolism. It is postulated that microvesicles may represent the mechanism of transport of free fatty acids in fat cells and in endothelium. Hypotheses are proposed and illustrated schematically for the mode of formation of microvesicular rosettes, for the mobilization and uptake of lipids by fat cells, and for the transport of lipids through endothelium.     

The homogenous γG-immunoglobulin produced by mouse plasmacytoma 5563 and its subsequent heterogeneity in serum

The mouse plasma cell tumour 5563 has been shown to synthesize and secrete a single molecular species of gammaG-immunoglobulin, which was identified by labelling with (14)C-labelled amino acids. The heterogeneity of G-myeloma globulin as it is found in serum of tumour-bearing mice is due to subsequent changes in the charge properties of the newly secreted molecules. These changes have been reproduced in vitro. On incubation with sterile serum, the newly formed radioactive myeloma protein changed its chromatographic and electrophoretic properties to coincide with those of myeloma protein isolated from serum. Incubation of purified myeloma protein band a, under a variety of conditions, led to the characteristic pattern of serum myeloma protein showing multiple electrophoretic bands. The chemical nature of the molecular changes is not yet known. It is suggested that seruminduced changes could contribute to the electrophoretic heterogeneity of specific antibodies within the gammaG-class of immunoglobulins. This demonstration of the production of a single molecular species of immunoglobulin by a plasma cell tumour provides support for the concept of ;one-cell-one antibody'.     

Some extensions of the use of matrices in population theory

This paper extends Leslie's vector and matrix treatment of populations. A simple matrix is given for species in which adult mortality and fertility are independent of age, but in which the juvenile mortality rate differs from the adult. The population vector can be changed into a population matrix. This should allow equations using functions of the size of the population to be developed. Genetic variables such as sex or other polymorphisms can be introduced, and the notation allows different systems of selection or non-random mating to be specified.