Evidence for an accelerated adaptation to starvation in chronic uremia

During a 72-hr period of starvation plasma levels of glucose and immunoreactive insulin fell to a greater extent, and alanine, free fatty acid, and glycerol concentrations were higher in fasted chronically uremic rats than in nonuremic controls. These changes, in conjunction with a significant increase in the uremic group's activity of phosphoenolypyruvate-carboxykinase, the rate-limiting enzyme in hepatic gluconeogenesis, after only 12 hr of fasting suggest that alterations in glucose metabolism in uremia may contribute to an exaggeration and acceleration of the metabolic consequences of starvation.     

Quantitation of apolipoprotein A-I of human plasma high density lipoprotein.

High density lipoproteins (HDL) may be controlled via their major apolipoprotein, A-I. To study this apolipoprotein, a simple, precise, and accurate immunodiffusion assay for A-I was developed and applied in a sample of Bell Telephone Company employees. A-I showed a slight increase with age in men (r=0.11, n=263) and women (r=0.15, n=257). A-I correlated closely with HDL cholesterol (r=0.72). It was weakly related to total triglyceride in women (r=0.24) but was inversely related in men (r=-0.17). Women on estrogen had the highest A-I levels (149 mg/dl +/- 26, x +/- S.D., n=29, p is less than 0.05), followed by women on combination oral contraceptives (141 +/- 26, n=80) whereas women on no medication had lower levels (129 +/- 25, n=99, p is less than 0.01) but men had the lowest levels (120 +/- 20, p is less than 0.01) In a separate group of 14 women given estrogen for 2 wks (1 mug/kg/day), A-I increased by 24%. Thus A-I is increased by exogenous and, most likely, endogenous estrogen, Among hyperlipidemic referral subjects, those with hypercholesterolemia (n=43) and hypertriglyceridemic women (n=33) had normal A-I levels. Among hypertriglyceridemic men both A-I and HDL cholesterol values were decreased (115 +/- 20, p is less than 0.01 and 37 +/- 3, p is less than 0.01, respectively, n=68) but were significantly lower among a group of myocardial infarction survivors (107 +/- 16, p is less than 0.01, and 27 +/- 6, p is less than 0.01, respectively, n=24). High density lipoprotein levels and the content of cholesterol in HDL associated with A-I appear to be decreased in coronary heart disease.     

Lp(a) lipoprotein: relationship to sinking pre-beta lipoprotein hyperlipoproteinemia, and apolipoprotein B.

To assess the relationship between the Lp(a) and the "sinking pre-beta" (d smaller than 1.006) lipoprotein, the concentration of Lp(a) was quantified by radial immunodiffusion and the presence or absence of sinking pre-beta was assessed by agarose electrophoresis in overnight fasting plasma samples from 485 adults, comprised of 320 with normal lipid levels, 48 with type IIa, 40 with type IIb, and 77 with type IV lipoprotein phenotypes. The median Lp(a) level was 7.6 mg/100 ml, 89% (433 of 485) having detectable Lp(a) levels. Twenty-two per cent (107 of 485) had detectable pre-beta lipoprotein in the d greater than 1.006 plasma fraction (sinking pre-beta). Of the sinking pre-beta positive plasma samples, 96% (102 and 107) exceeded the median Lp(a) level, and sinking pre-beta was detected in all 44 samples with an Lp(a) concentration exceeding 40 mg/100 ml. The relationship of Lp(a) and sinking pre-beta to lipoprotein phenotype was assessed. Compared to the normolipidemic group, the type IIa group had higher Lp(a) percentile values (p smaller than 0.02), whereas the IIb and type IV groups had significantly lower Lp(a) values than the normolipidemic group. Ninety-two per cent (296 of 320) of the normolipidemic subjects had detectable levels of Lp(a) and 22% (70 of 320) had detectable sinking pre-beta lipoprotein. Ninety-four per cent (45 of 48) of the type IIa plasmas had detectable Lp(a) levels and 27% (13 of 48) had sinking pre-beta lipoproteins. Contrasted with the IIa group, only 80% (32 of 40) of the IIb plasmas had detectable Lp(a) levels and 18% (7 of 40) had sinking pre-beta lipoprotein. In the type IV plasmas 78% (60 of 77) had detectable Lp(a) and 22% (17 of 77) had sinking pre-beta lipoprotein. Lp(a) or log Lp(a) levels were not correlated with apolipoprotein B levels (n = 485, r = 0.002 or 0.037, respectively). Furthermore, Lp(a) levels remained essentially constant in three subjects whose aprptein B levels were altered in response to pharmacological and/or dietary manipulation. A fourth subject had a 50% increase in Lp(a) but this change did not correlate with apoprotein B changes. Thus, these findings suggest that Lp(a) is metabolically independnet of low density lipoprotein even though it shares the same structural protein, apoprotein B.     

Abnormal lipoprotein-lipase-mediated plasma triglyceride removal in untreated diabetes mellitus associated with hypertriglyceridemia.

Hypertriglyceridemia is common in untreated diabetes mellitus. An abnormality in the interaction of lipoprotein lipase with endogenous circulating plasma lipoprotein triglyceride has been demonstrated in untreated diabetes. These diabetics have a decreased maximal removal capacity for plasma triglyceride (27.0 mg TG/kh/hr) and increased Km (390 mg/dl) for endogenous plasma triglyceride-lipoprotein lipase interaction compared to that found in nondiabetic hypertriglyceridemic subjects (Vmax, 32.0; km, 157). Diabetics treated for at least two months have a maximal removal capacity and Km similar to that of nondiabetic subjects (Vmax, 32.7; Km, 192). No evidence for an increase in triglyceride production due to diabetes per se was found. When diabetic subjects with triglyceride levels over 400 mg/dl were selected for study, most were found to have an independent familial form of hypertriglyceridemia.     

Broad-beta disease versus endogenous hypertriglyceridemia: levels and lipid composition of chylomicrons and very low density lipoproteins during fat-free feeding and alimentary lipemia.

To assess the roles of endogenous and exogenous lipid in the production of the abnormal lipoprotein patterns characteristic of broad-beta desease (with a type IVIII lipoprotein pattern) and endogenous hypertriglyceridemia (with a type IV pattern), oral fat loads (50 g/M-2) were administered to six subjects with broad-beta disease and to eight with endogenous hypertriglyceridemia following at leat 72 hr of 0% fat, 85% carbohydrate isocaloric formula feeding. Total plasma and Sf greater than 400, 100-400, 60-100, 30-60, and 20-30 lipoprotein cholesterol, triglyceride, and phospholipid levels were measured at 0 hr, 6 hr (at or before the peak of alimentary lipemia), and 24 hr following the fat load. Following fat-free feeding the levels and composition of the endogenous Sf greater than 400 lipoproteins were similar in both disorders; whereas total Sf20-400, and most notably, Sf 30-60 and 20-30 levels were increased and enriched in cholesterol in the subjects with broad-beta disease.     

High-density lipoproteins in myocardial infarction survivors.

Subjects with existing coronary heart disease and those with many of the conditions associated with increased risk of coronary disease have reduced levels of high-density lipoprotein (HDL) cholesterol. Since HDL cholesterol is only one index of HDL composition, a reduction of HDL cholesterol could reflect a change in HDL composition and/or a decrease in all HDL constituents. Therefore the present studies assessed the major apolipoproteins of HDL, A-I and A-II, in addition to HDL cholesterol in 90 male myocardial infarction (MI) survivors and their lipid-matched male controls. The MI survivors had significantly lower (p < 0.01) A-I (112 ± 2 mg/dl, mean ± SEM), A-II (29 ± 1 mg/dl), and HDL cholesterol (39 ± 1 mg/dl) than the lipid-matched control group (A-I, 121 ± 2; A-II, 33 ± 1; HDL cholesterol, 43 ± 1) and than a population-based male control group (n = 172; A-I, 121 ± 2; A-II, 33 ± 1; HDL cholesterol, 45 ± 1). The HDL cholesterol/A-I ratio in the MI survivors was slightly lower than the ratio in the lipidmatched control group but significantly lower (P < 0.02) than that in the population-based control group. The HDL cholesterol of both control groups was significantly negatively related to log triglyceride (r = ?0.43). Similarly the HDL cholesterol of the MI survivors was inversely correlated with log triglyceride (r = ?0.51), but the slope of this relationship was significantly steeper in the MI survivors. These results are consistent with a relative decrease of HDL in MI survivors over and above that attibutable to their increased triglyceride levels.     

Effect of phenformin on lipid transport in hypertriglyceridemia

The effect of phenformin on lipid metabolism was studied in nine hypertriglyceridemic subjects consuming isocaloric liquid formula diets. On a fat-free, 85% carbohydrate hydrate diet, phenformin reduced plasma triglyceride, cholesterol, and free fatty acid levels, the mean decreases being 14%, 13%, and 16%, respectively. The predominant effect of the drug was on very low density lipoprotein levels, with no change in low density lipoproteins. Plasma triglyceride and cholesterol levels were also reduced in the majority of subjects on a diet containing 40% of calories as fat and 45% as carbohydrate, but phenformin did not have any effect on the carbohydrate induction of triglyceride elevation. Basal insulin levels were reduced by the drug in all subjects (mean change, ?23%) and fasting glucose levels were lowered in the majority. The plasma lipolytic rate measured on endogenous substrate during a prolonged heparin infusion on the fat-free diet was reduced by phenformin (mean change, ?15%), although postheparin lipolytic activity on an artificial substrate was unchanged. Free fatty acid turnover, measured during the same procedure, fell in parallel with the fatty acid levels (mean change, ?27%). It is proposed that phenformin lowers plasma triglyceride levels in most subjects by reducing endogenous triglyceride production, and that the effects of the drug on glucose, insulin, and free fatty acid homeostasis contribute to this action. It is suggested that in some subjects the drug may also impair triglyceride clearance from plasma, and that this may account for the variable therapeutic response, since in three subjects phenformin did not decrease triglyceride levels on both diets.     

Myocardial infarction in the familial forms of hypertriglyceridemia.

Among 74 hypertriglyceridemic patients who were referred for study because of hypertriglyceridemia, family investigations detected 19 with familial hypertriglyceridemia and 24 with familial combined hyperlipidemia. The frequency of myocardial infarction among adult living hyperlipidemic relatives of patients with familial combined hyperlipidemia was 17.5% (10/57). Five of these relatives had their infarct between the ages of 40 and 50 yr of age, and five before the age of 40 yr. The frequency of myocardial infarction in living hyperlipedemic relatives with familial hypertriglyceridemia was 4.7% (2/43) and was similar to the frequency of myocardial infarction among normolipidemic relatives (4.5%) or among spouse controls (5.2%). Mortality data due to myocardial infarction among relatives of index patients failed to contribute meaningful information.     

Requirement of low density lipoproteins for the lysolecithin acyl transferase activity in human plasma: Assay of enzyme activity in abetalipoproteinemic patients

Previous studies from this laboratory have shown that the lecithin:cholesterol acyl transferase (LCAT) of normal human plasma can convert lysolecithin to lecithin in the presence of low density lipoproteins (LDL). In order to study the importance of LDL for the lysolecithin acyl transferase (LAT) activity, the LCAT and LAT activities were assayed in two patients with abetalipoproteinemia. The plasma from both patients had only 5%–6% of the LAT activity present in normal plasma. This activity was stimulated up to 22-fold by the addition of normal LDL but not very low density lipoproteins (VLDL) or high density lipoproteins. The LAT activity of normal plasma was only stimulated by two-threefold by LDL. The LCAT activity in both patients was reduced to 42%–46% of the control values. This activity was stimulated up to fourfold by the addition of LDL as well as VLDL which is comparable to the activation obtained with control plasma. These results therefore suggest that LDL is physiological activator of LAT reaction in normal human plasma.     

Postprandial adipose tissue lipoprotein lipase activity in primary hypertriglyceridemia

The fasting activity of adipose tissue lipoprotein lipase has been previously reported to be either normal or reduced in subjects with a primary form of hypertriglyceridemia. The postprandial activity of adipose tissue lipoprotein lipase has not been previously reported in these subjects. In subjects with primary hypertriglyceridemia the fasting lipoprotein lipase activity eluted from pieces of adipose tissue by heparin and the enzyme activity present in extracts of acetone-ether tissue powders were similar to the level of enzyme activity found in normal subjects. There also was no difference in the postprandial adipose tissue heparin-elutable lipoprotein lipase activity between these two groups when measured after high carbohydrate feeding. When the subjects with primary hypertriglyceridemia were further subdivided by genetic diagnosis, there was no difference in the level of adipose tissue lipoprotein lipase of subjects with familial hypertriglyceridemia, familial combined hyperlipidemia, or in those in whom no specific genetic diagnosis could be made. The change in lipoprotein lipase activity after feeding was inversely related to the fasting enzyme level in both the normal subjects (r = ?0.58, p < 0.05, n = 12) and the hypertriglyceridemic subjects (r = ?0.92, p < 0.01, n = 11). In the normal subjects, the plasma triglyceride response to feeding correlated inversely with the postprandial change in lipoprotein lipase activity (r = ?0.76, p < 0.02, n = 12). Adipose tissue lipoprotein lipase activity in patients with primary lipoprotein lipase deficiency was markedly reduced in the fasting state and remained essentially zero after feeding. This suggests that a functional role exists for the enzyme activity as measured.     

Postheparin plasma triglyceride lipases in chronic hemodialysis: evidence for a role for hepatic lipase in lipoprotein metabolism.

Elevated plasma triglyceride levels frequently occur in patients with chronic renal failure receiving longterm hemodialysis. Postheparin plasma lipolytic activity, an indirect measure of triglyceride removal, is low in hemodialysis patients, but this activity measures both hepatic triglyceride lipase (HTGL) and lipoprotein lipase (LPL). To determine if HTGL and/or LPL are low in hemodialysis patients and related to lipoprotein lipid levels, both activities were measured by a selective antibody-inhibition technique in postheparin plasma from 20 hemodialysis patients with a wide range of plasma triglyceride levels ($\text{104–676}\text{mg}\text{100}\text{ml}$), and the relationships between the enzyme activities and lipoprotein lipid levels were examined. To more accurately compare subjects, the heparin doses were adjusted for the differences in plasma volumes between the hemodialysis patients and the nonuremic control subjects. Hemodialysis patients with elevated plasma triglyceride levels (↑TG) had HTGL levels (148 ± 67 nmole/min/ml, n=10) which were similar to the dialysis patients with normal triglyceride levels (nlTG) (134 ± 64 nmole/min/ml, n=10) and both groups were significantly lower (p<0.05, p<0.02, respectively) than the levels of the control subjects (208 ± 61 nmole/min/ml, n=11). The HTGL levels of the hemodialysis patients with ↑TG correlated inversely with plasma total cholesterol (r_s=−0.833, p<0.01) and the d>1.006 fraction cholesterol (low + high density lipoproteins, r_s=−0.863,p<0.01), but not triglyceride. The activity of HTGL of the entire group of hemodialysis patients correlated with the plasma total cholesterol (r_s=−0.615, p<0.01), d>1.006 fraction cholesterol (r_s=−0.731, p<0.01) and low density lipoprotein cholesterol (r_s=−0.659, p<0.01). The LPL levels of the hemodialysis patients with the ↑TG (52 ± 24 nmole/min/ml) were lower than those with nlTG (70 ± 25 nmole/min/ml) and the levels of both hemodialysis groups were significantly lower (p<0.01, p<0.02, respectively) than the LPL levels in the control subjects (110 ± 43 nmole/min/ml). The ratio of LPL to total postheparin plasma lipolytic activity was lower in the hemodialysis patients with ↑TG (0.32 ± 0.15), than in the hemodialysis patients with nlTG (0.47 ± 0.18, p<0.06) or the control subjects (0.45 ± 0.09, p<0.05). Unlike HTGL, the levels of LPL did not correlate with lipid levels in the hemodialysis patients. Thus, both postheparin plasma HTGL and LPL are low in hemodialysis patients. The relationship between HTGL and low density lipoprotein cholesterol levels suggests a possible role for HTGL in low density lipoprotein catabolism.     

Insulin and glucagon relationships during aging in man

To determine if the glucoregulatory hormones, insulin and glucagon, are altered with aging in man, 44 healthy volunteers, 22–81 yr of age, were evaluated by measurement of basal levels of glucose, insulin, and glucagon in relationship to their fat mass. In addition, the secretory capacities of the alpha and beta cells were assessed by measurement of the amounts of glucagon and insulin released after intravenous administration of glucose and arginine, respectively. Although no significant differences in weight could be distinguished longitudinally, the percentage adiposity was found to increase with age. Basal concentrations of glucose, glucagon, and insulin were not appreciably altered as a function of advancing years. After intravenous glucose, the glucose disappearance rate (K_g) was significantly slower in the elderly in comparison with the young, yet no differences in glucose-induced release were found. Similarly, insulin responses after arginine infusion between young and old were indistinguishable. The release of glucagon in response to arginine infusion was not perceptibly altered during aging. Thus, despite a decline in K_g with advancing age in this healthy population, gross changes in insulin and glucagon release were not apparent. We infer from these data that decreased carbohydrate tolerance accompanying aging in some populations may be due to factors other than abnormalities in secretion of insulin and glucagon.     

Stress-induced inhibition of triglyceride secretion in vivo in sand rats (Psammomys obesus)

The effects of acute stress upon circulating triglyceride, glucose, insulin, free fatty acids, and glycerol were investigated in obese desert sand rats. Three groups of animals, designated “nonstress,” “nonexertional stress,” and “exertional stress,” were studied. Acute stress, with or without accompanying exercise, was associated with significant decreases in circulating triglyceride; significant increases in circulating glucose, free fatty acids, and glycerol; and variable changes in circulating insulin. Since these data indicated that substrate availability and hepatic insulization were adequate and therefore could not explain the observed fall in circulating triglyceride, endogenous triglyceride secretion rates were examined by the Triton method. Compared to predicted rates based upon earlier studies, both nonexertional and exertional stress were associated with significantly decreased endogenous triglyceride secretion. Thus, acute stress in the sand rat, with or without accompanying exercise, appears to induce an immediate decrease in endogenous triglyceride secretion and circulating triglyceride.     

Pathophysiology of lipoprotein transport.

A system for classification of genetic and acquired forms of hyperlipidemia in humans based on lipoprotein physiology is described. Most hyperlipidemia can be accounted for by defects in one of four sites of physiologic regulation: (1) triglyceride-rich lipoprotein production, (2) lipoprotein lipase-mediated triglyceride catabolism, (3) remnant lipoprotein catabolism, and (4) extrahepatic cholesterol-rich lipoprotein catabolism.     

Effect of clofibrate on postheparin plasma triglyceride lipase activities in patients with hypertriglyceridemia

The lipoprotein lipase (LPL) and hepatic triglyceride lipase (HL) activities of post-heparin plasma were determined by a specific immunochemical method in 17 patients with primary hyperlipoproteinemia before and during treatment with clofibrate. The drug caused a significant reduction of serum cholesterol (11%) and triglyceride (45%) levels. Postheparin plasma LPL activity rose in all subjects, the average change being 46% (P < 0.001). The increase of LPL was positively correlated to the pretreatment LPL activity. There was no correlation between the serum triglyceride concentration and post-heparin LPL activity either before or during clofibrate administration. On the other hand, in the clofibrate responders there was a weak correlation between the relative changes of triglyceride concentration and LPL activity (r = 0.43, p < 0.05). During clofibrate treatment the LPL activity of the hypertriglyceridemic patients was significantly higher than the corresponding value of untreated healthy normoglyceridemic subjects of similar age. The post-heparin plasma HL activity was not influenced by clofibrate.     

Prevalence of serum lipid abnormalities in chronic hemodialysis.

Fasting levels of serum triglyceride, cholesterol, high-density lipoprotein (HDL), apoprotein A-I, HDL cholesterol, and HDL triglyceride were measured in 94 uremic males receiving maintenance hemodialysis and 6 uremic males receiving chronic peritoneal dialysis. These patients had higher serum triglyceride levels (p less than 0.001) and lower cholesterol levels (p less than 0.001) than normal controls. The dialysis patients treated with androgen or propranolol and those who were hypothyroid or diabetic had significantly higher triglyceride levels than the other dialysis subjects. The dialysis patients who had no additional secondary causes of hypertriglyceridemia had abnormalities in HDL; in comparison to normals and triglyceride-matched controls, these patients had elevated HDL triglyceride levels and low HDL cholesterol levels, despite similar HDL apoprotein A-I levels. The HDL cholesterol levels appeared to be lower in those patients than could be accounted for by their degree of hypertriglyceridemia.     

Heterogeneity of primary lipoprotein lipase deficiency

Lipoprotein lipase activity appeared in plasma within 10 min of beginning a heparin infusion in control subjects in whom adipose tissue lipoprotein lipase activity was normal. Plasma lipoprotein lipase activity was maintained throughout a heparin infusion lasting 4–6 hr. Three subjects with primary diminished adipose tissue lipoprotein lipase activity had markedly decreased lipoprotein lipase activity for the duration of the heparin infusion. However, the findings in two additional subjects suggest that the activity released during the early phase and during the late phase of the heparin infusion might come from different tissues. One subject had no adipose tissue lipoprotein lipase activity, but had levels of lipoprotein lipase in postheparin plasma similar to controls during the early phase of the heparin infusion. The other subject had normal adipose tissue lipoprotein lipase activity in the fasted and fed state, yet had little lipoprotein lipase activity in postheparin plasma during the early phase of the heparin infusion. This patient developed levels similar to that seen in plasma in the control subjects at the end of the heparin infusion. These findings suggest that (1) the activity that appears soon after initiating the heparin infusion is released from tissues other than adipose tissue, while that appearing later is of adipose tissue origin and (2) subjects with primary abnormalities of lipoprotein lipase form a heterogenous group of individuals.     

Glucagon responses to hypoglycemia in adrenalectomized man

In order to examine the possibility that epinephrine is involved in either the mediation or modulation of the enhanced glucagon release during glucopenia, glucagon responses to insulin-induced hypoglycemia were evaluated in four men with bilateral adrenalectomy in comparison with ten normal men. In the adrenalectomized patients, the mean nadir of plasma glucose and the rate of ascent to baseline levels were indistinguishable from those observed in normal subjects. Similarly, glucagon responses in the adrenalectomized group were not different from those encountered in the normal volunteers. We conclude that epinephrine does not contribute significantly to the augmented glucagon release during abrupt glucopenia in normal man and is not necessary for normal recovery from hypoglycemia.     

Effect of intravenous glucagon on urinary catecholamine excretion in normal man.

We have evaluated intravenous glucagon as pharmacologic stimulus to adrenal catecholamine secretion in normal human subjects. Urinary epinephrine and norepinephrine were measured at two hourly intervals before and after the intravenous injection of saline, 4 mg glucagon, or 0.1 mu/kg crystalline insulin. Urinary epinephrine was increased 2.3-fold over baseline after both saline and glucagon. By contrast, insulin hypoglycemia produced a 24-fold rise in urinary epinephrine. No rise in urinary norepinephrine was detected in any test. Under the conditions of this study, we conclude that epinephrine excreted after glucagon injection is due to the stress of the test itself. In normal man, glucagon either does not stimulate adrenal catecholamine secretion, or the effect is too small to measure. By contrast, in pheochromocytoma, glucagon may be specific for catecholamine secretion, based on data from the literature. In normal subjects, insulin hypoglycemia remains the only proved method for assessing adrenal catecholamine reserve.     

Thyrotropin levels in hyperlipidemic survivors of myocardial infarction.

In an earlier investigations, the prevalence of hyperlipidemia in a group of patients who survived myocardial infarction was determined, and family studies were performed to allow genetic classification of patients with hyperlipidemia. Radioimmunoassay for thyrotropin (TSH) has now been performed on plasmas from most of these hyperlipidemic survivors. Elevated TSH values were found in five of the 18 hyperlipidemic women over age 60, and in seven of the remaining 104 hyperlipidemic subjects. Among the various genetically defined types of hyperlipidemia, the highest prevalence of TSH elevations was seen in women with sporadic (nonfamilial) hypertriglyceridemia; four of the ten had an abnormal TSH level, and two of the remainder were receiving thyroid medication. Hypercholesterolemia was not strongly correlated with TSH abnormalities. These data support the hypothesis that clinically inapparent thyroid damage may be associated with coronary artery disease.