Fifteen common polymorphic variants at six loci (apolipoproteins AI, B, CIII and E, hepatic lipase and lipoprotein lipase) involved in plasma lipid transport have been studied in 210 northern Spanish men, of whom 98 had proven coronary artery disease. The other 112 men were clinically free from coronary artery disease and acted as controls. The genotypes were investigated for relationships with plasma lipid and lipoprotein levels, as well as for the presence of coronary artery disease. As expected, the mean levels of plasma triacylglycerols (triglycerides) and lipoprotein (a) and the number of smokers were significantly higher in the disease group, and high-density lipoprotein (HDL)-cholesterol was significantly lower. Surprisingly, plasma cholesterol and low-density lipoprotein cholesterol were not different between the two groups. With regard to the common mutations, plasma triacylglycerol levels were related to the Hin dIII variants of lipoprotein lipase ( P < 0.05), to the apolipoprotein CIII variant (C3175G in exon 4) and to the apolipoprotein AI Xmn I polymorphisms ( P < 0.05 and P < 0.02 respectively). The apolipoprotein E variants were related to plasma cholesterol ( P < 0.05), HDL-cholesterol ( P < 0.02), plasma triacylglycerols ( P < 0.05) and the triacylglycerol/HDL ratio ( P < 0.01). Only the three-codon insertion/deletion variants of the apolipoprotein B signal peptide region discriminated between the two groups with or without arterial disease ( P = 0.02). The possible functional effects of these common mutations are discussed.

1. A genetic polymorphism of apolipoprotein (apo) C-III was studied in 49 Caucasian patients with extra-coronary atherosclerosis demonstrated by angiography. 2. Twelve patients (24%) possessed an uncommon allelic variant of the apo A-I/C-III gene cluster compared with two (4%) in 50 healthy controls ( P < 0.01). 3. Of 27 patients with carotid atherosclerosis, 22% had the uncommon genotype ( P < 0.02), and in aortofemoral atherosclerosis ( n = 22) 27% possessed the uncommon variant ( P < 0.01). 4. When normotriglyceridaemic subgroups ( n = 32) with arterial disease were studied the difference in genotype frequencies persisted, 22% having the uncommon allele ( P < 0.01), suggesting that such genetic variants have effects independent of circulating levels of plasma lipids.

1. DNA insertions in the 5′-flanking region of the insulin gene have been studied by Southern-blot-hybridization techniques using a cloned gene probe in 159 unrelated Caucasians. 2. Subjects homozygous for a large DNA insertion at this locus were found to have a higher risk of concurrence of non-insulin-dependent diabetes (NIDD) than controls ( P < 0.01). 3. Analysis of a single large NIDD pedigree ( n = 67 in four generations; 11 diabetic subjects) showed no linkage between the size of DNA inserts and diabetes (Lod score = −5.7), suggesting a separate diabetogenic locus (or loci) in this family.

1. A variant very-low-density lipoprotein was associated with severe hypertriglyceridaemia. Urea—polyacrylamide gel electrophoresis of the tetramethylurea-soluble apolipoproteins of these very-low-density lipoproteins (VLDL) showed that the apolipoprotein C-II content was less than 10% of that in VLDL from hypertriglyceridaemic (3–120 mmol/l) controls. 2. VLDL were incubated with bovine milk lipoprotein lipase (LPL) and a 9,10- 3 H-labelled triglyceride emulsion. The VLDL deficient in apolipoprotein C-II were a poor activator of LPL, compared with the effect of VLDL with normal content of apolipoprotein C-II obtained from either normal or hypertriglyceridaemic sera. 3. The efficacies of various VLDL as substrates for activated LPL were examined. Apolipoprotein C-II-deficient VLDL were a poor substrate for the activated enzyme compared with normal or hypertriglyceridaemic VLDL, and compared with an artificial triglyceride emulsion. 4. The abnormal VLDL were obtained from a subject with an IgG3 lambda myeloma protein. Intravenous infusion of normal plasma containing apolipoprotein C-II was followed by rapid, complete, but short-lived (5–10 days) clearance of serum triglyceride. The effect was observed on three occasions until treatment of the myeloma was effective. 5. The monoclonal protein behaved as a cryoglobulin, and formed large particle complexes with triglyceride-rich lipoproteins, especially at temperatures below 37°C. The apolipoprotein C-II deficiency, and consequent hypertriglyceridaemia, may be secondary to an autoantibody directed against apolipoprotein C-II. VLDL from relatives with hypertriglyceridaemia, but without myeloma, had normal apolipoprotein content, activated LPL, and were efficient substrates for the enzyme.

1. The concentrations of adenosine 3′:5′-cyclic monophosphate (cyclic AMP) in human adipose tissue were studied after intravenous insulin administration (0·3 unit/kg body weight) in obese diabetic and obese non-diabetic subjects. 2. The declines in plasma glucose, glycerol and free fatty acids in the two groups after insulin were similar if allowances were made for the fasting hyperglycaemia in the diabetic subjects. 3. Insulin in vivo lowered the concentrations of cyclic AMP in adipose tissue from non-diabetic subjects. 4. Insulin administration in vivo did not alter the tissue concentrations of cyclic AMP in adipose tissue of obese diabetic subjects. This lack of effect of insulin provides evidence for tissue resistance in vivo to the action of insulin in diabetes mellitus.

1. The metabolism in vivo and in vitro of an abnormal low-density lipoprotein (LDL) obtained from a patient with an inherited form of hypercholesterolaemia was compared with that of LDL obtained from a normal subject. 2. The rates of turnover of the apoprotein of the two types of LDL in a normal subject, and their uptake and catabolism by normal lymphocytes in vitro , were similar. 3. It is concluded that the abnormal behaviour of the patient's LDL may not be due to an abnormality in the apoprotein component.

1. The esterification of exogenous palmitate to diglyceride and triglyceride in adipocytes was studied in obese and diabetic patients with and without hypertriglyceridaemia. The rate of esterification correlated significantly with the triglyceride content of adipocytes. 2. In diabetic patients with hypertriglyceridaemia, the rate of esterification to triglyceride was significantly greater than in diabetic patients with normotriglyceridaemia. This difference could not be attributed to differences in glucose tolerance or to the degree of obesity. 3. Fasting plasma insulin levels were greater in the hypertriglyceridaemic group than in the normotriglyceridaemic group. The difference in esterification rates could have been due to differences in adipocyte size. 4. The esterification of fatty acid in adipose tissue of diabetic patients was lower than in non-diabetic subjects and this difference could not be accounted for by differences in adipocyte size or differences in the intracellular pools of fatty acid in adipose tissue. 5. The role of esterification of exogenous fatty acids in adipose tissue as a possible determinant of the uptake of glyceride fatty acids from plasma is discussed.

1. Glucose 6-phosphate, fructose 6-phosphate, fructose diphosphate, glycerol phosphate and uridine diphosphate glucose have been measured in human adipose tissue and blood from obese subjects under fed and fasting conditions and in obese diabetic and non-diabetic subjects before and after an oral glucose load (100 g). 2. Adipose tissue metabolites expressed as nmol/g wet weight correlated inversely with adipocyte diameter. 3. After fasting, fructose diphosphate and glycerol phosphate in adipose tissue decreased significantly. 4. The basal concentrations of metabolites in blood and adipose tissue were maintained at similar concentrations in diabetic and non-diabetic subjects despite very different blood glucose concentrations. 5. The significant increase in adipose tissue glucose 6-phosphate after the glucose load seen in the non-diabetic but not in the diabetic subjects suggests that glucose uptake is decreased in the diabetic adipocyte.

1. Homogenates of subcutaneous adipose tissue from obese subjects contained sufficient citrate cleavage enzyme (EC 4.1.3.8: ATP—citrate oxaloacetate lyase), acetyl-CoA carboxylase (EC 6.4.1.2: acetyl-CoA—carbon dioxide ligase) and fatty acid synthetase to account for the rates of fatty acid synthesis reported in the literature for intact tissues in vitro. 2. The distribution of label in fatty acids after incubations of adipose tissue with [1- 14 C]acetate was consistent with fatty acid synthesis de novo , not chain elongation. 3. The activities of citrate cleavage enzyme and fatty acid synthetase in subcutaneous adipose tissue were reduced by short periods of starvation. 4. These findings indicate that human adipose tissue is capable of fatty acid synthesis de novo and that two of the enzymes concerned adapt to starvation.

1. Isoprenaline (1 μmol/l) and glucagon (1 μmol/l) raised the levels of cyclic AMP in isolated adipose cells of the rat to a maximum after incubation for approximately 15 min. 2. The effect of glucagon was impaired by pretreatment of adipose cells with trypsin (0.2 mg/ml and 2.0 mg/ml) and N -ethylmaleimide (5 mmol/l). The β-adrenergic receptor was insensitive to such forms of treatment. 3. Insulin (430 μunits/ml) lowered the intracellular levels of cyclic AMP in adipose cells stimulated with isoprenaline (1 μmol/l) and glucagon (1 μmol/l). This effect was observed after incubation for 5 min. 4. Pretreatment of cells with trypsin (0.2 mg/ml and 2.0 mg/ml) and N -ethylmaleimide (0.5 and 5 mmol/l) abolished the effect of insulin in decreasing the intracellular levels of cyclic AMP. At the higher concentration of trypsin a rise in intracellular levels of cyclic AMP was observed in the presence of insulin. 5. Similar concentrations of trypsin and N -ethylmaleimide decreased the disappearance of unlabelled insulin from the incubation medium and also decreased the binding of 125 I-labelled insulin to isolated fat cells. 6. The effect of insulin on decreasing the intracellular levels of cyclic AMP in modified adipose cells significantly correlated with the disappearance of unlabelled insulin from the medium and with the percentage of total 125 I-labelled insulin bound to cells. 7. The possibility is discussed of using the disappearance of insulin or binding of 125 I-labelled insulin to adipose cells as a measure of insulin-receptor availability on the plasma membrane of fat-cells.

1. The activities of hexokinase (EC 2.7.1.1) and phosphofructokinase (EC 2.7.1.11) have been studied in homogenates of adipose tissue taken from human diabetics, fasting and control patients. 2. Three isoenzymes of hexokinase were observed with apparent K m values for glucose of 1.04 × 10- 5 m, 2.6 × 10- 4 m and 2.9 × 10- 4 m, respectively. 3. No change in activity of hexokinase was found in adipose tissue of untreated diabetics ( n = 22), treated diabetics ( n = 13) or non-diabetic controls. However, fasting was associated with a decrease of approx. 40% in the activity of hexokinase in adipose tissue. 4. In contrast, there was a marked decrease in the activity of phosphofructokinase in adipose tissue from untreated diabetics ( n = 24) which was restored to normal by either insulin therapy or treatment by hypoglycaemic drugs. 5. There was a negative correlation between the phosphofructokinase/hexokinase ratio in adipose tissue and the fasting blood glucose ( P = 0.01) and the 2 h blood glucose ( P = 0.03) after an oral glucose load (50 g). 6. The functional significance of the changes in enzyme activities is discussed in relation to the glucose intolerance of diabetes.

1. The effects of glucose, glucose 6-phosphate, and l-glycerol 3-phosphate on the incorporation of [1- 14 C]palmitate into neutral lipid have been studied in homogenates of adipose tissue obtained from adult diabetics and control patients. In the diabetic, glucose, glucose 6-phosphate and l-glycerol 3-phosphate supported incorporation of 19, 27 and 62% of total counts respectively; whereas in paired non-diabetic controls the respective values were 78, 80 and 84%. 2. Confirmation of these results were provided by finding slower rates of conversion of [U- 14 C]glucose into phosphate esters in diabetic adipose tissue compared to paired non-diabetic controls. Rates were improved but not restored to normal by treatment of diabetic patients with insulin. 3. These results could not be explained on the basis of differences in isotope dilution in precursor pools or to the presence of raised levels of free fatty acids in diabetic tissue. 4. A group of latent diabetics showed a pattern of substrate utilization more like fully developed diabetes than non-diabetic controls. Rates of glucose phosphorylation were slower in latent diabetics than in paired controls. 5. Studies were also performed with homogenates of adipose tissue prepared from patients with Cushing's disease, obesity and pregnancy, these groups being predisposed to develop adult diabetes. 6. In Cushing's disease (eight patients) glucose, glucose 6-phosphate and l-glycerol 3-phosphate supported incorporation of 9 ± 1 (13), 19·2 ± 3·9 (10) and 23·2 ± 3·3 (9)% of total counts at 2 hr respectively; whereas in paired controls respective values were 19·7 ± 3·4 (10), 25·7 ± 2·8 (10) and 26·4 ± 2·9 (10)%. Support for these results was provided by finding slower rates (by about 50%) of conversion of [U- 14 C]glucose into phosphate esters in tissue from Cushing's disease compared to paired controls. 7. Ten obese patients with no clinical evidence of diabetes showed a pattern of substrate utilization more like diabetic adipose tissue; whereas another eight obese patients resembled their non-obese controls. 8. Adipose tissue from six pregnant patients (over 10 weeks) showed a diabetic pattern of substrate utilization; and confirmation was provided by rates of [U- 14 C]glucose conversion into phosphate esters (as counts × 10 min −1 mg protein −1 hr −1 ) of 929 ± 75 (5) in pregnancy versus 1386 ± 198 (5) in paired controls.