Factors of increase in serum triglyceride-rich lipoproteins in uremic rats

Cyclosporine-induced insulin release in rats is related to an increase in plasma lipid levels

We studied the modifications of plasma lipid levels induced by cyclosporine (CsA), streptozocin (STZ) or both drugs in rats. Male Wistar rats (RT1y) were administered i.p. with CsA or STZ or both at the dosage of 15 mg/kg daily for 8 days and were sacrificed on day 9. Total lipid, triglyceride and total cholesterol plasma levels were measured. The plasma total lipid content was significantly increased in CsA-treated and in CsA + STZ-treated rats with respect to controls (662 +/- 29 and 632 +/- 32, respectively, vs 472 +/- 27 mg/dl). The triglyceride content was significantly higher in CsA-treated and in CsA + STZ-treated animals than in controls (137 +/- 8.7 and 188 +/- 14.1, respectively, vs 79 +/- 7.7 mg/dl). The total cholesterol level was not significantly different in CsA- and STZ-treated rats with respect to controls. CsA-treated and STZ-treated rats concomitantly revealed a significant impairment of glucose tolerance. In fact, 150 min after orogastric administration of 350 mg glucose, glycaemia was significantly more elevated in treated animals than in controls. We conclude that the increase in lipid levels induced by CsA treatment could be related to drug-induced damage to the pancreas islets, as shown by the early insulin release and fatty tissue degeneration.

Accelerated glycogenolysis in uremia and under sucrose feeding: role of phosphorylase alpha regulators

To understand the mechanism of hepatic glycogen depletion found in uremia and under sucrose feeding, we examined net hepatic glycogenolysis-associated active enzymes and metabolites during fasting. Liver was taken 2, 7, and 18 h after food removal in uremic and pair-fed control rats fed either a sucrose or cornstarch diet for 21 days. Other uremic and control rats fasted for 18 h were refed a sucrose meal to measure glycogen increment. Glycogen storage in uremia was normal, suggesting effective glycogen synthesis. During a short fast, sucrose feeding and uremia enhanced net glycogenolysis through different but additive mechanisms. Under sucrose feeding, there were high phosphorylase alpha levels associated with hepatic insulin resistance. In uremia, phosphorylase alpha levels were low, but the enzyme was probably activated in vivo by a fall of inhibitors (ATP, alpha-glycerophosphate, fructose-1,6-diphosphate, and glucose) and a rise of Pi, as verified in vitro. Enhanced gluconeogenesis was also suggested, but excessive hepatic glucose production was unlikely in uremia. During fasting, hypoglycemia occurred in uremia due to reduced glycogenolysis, inefficient hepatic gluconeogenesis, and impaired renal gluconeogenesis. This may be relevant to poor fasting tolerance in uremia, which could be aggravated under excessive sucrose intake.

Down-regulation of VLDL receptor expression in chronic experimental renal failure

VLDL receptor (VLDL-R) is a novel member of the LDL receptor gene family with distinct tissue distribution and function. It binds and internalizes VLDL particles and is primarily expressed in skeletal muscle, heart, brain and adipose tissue, which use fatty acids for energy production or storage. CRF is associated with elevated serum triglyceride and VLDL concentrations and depressed VLDL and chylomicron clearance. We have recently shown marked down-regulation of lipoprotein lipase expression in CRF. This study was conducted to test the hypothesis that VLDL-R expression may be similarly depressed in CRF. To this end, VLDL-R mRNA (Northern blot) and protein mass (Western blot) of skeletal muscle (soleus) and heart were measured in male Sprague-Dawley rats six weeks after 5/6 nephrectomy (CRF group) or sham operation (NL group). A group of erythropoietin (EPO)-treated (150 U/kg twice weekly) CRF animals was included to determine the possible effect of EPO-deficiency anemia (EPO-CRF group). Subgroups of animals were studied at weeks 1, 3 and 6. The CRF group showed a fivefold increase in plasma triglyceride concentration. This was associated with an impressive fourfold reduction in heart and skeletal muscle VLDL-R mRNA and protein mass. VLDL-R mRNA levels in the heart and skeletal muscle were directly related to creatinine clearance and inversely related to serum triglyceride and VLDL concentrations. EPO therapy led to a mild improvement in CRF hypertriglyceridemia but failed to improve VLDL-R expression. Thus, the rise in plasma triglyceride and VLDL concentrations in CRF animals was associated with marked down-regulation of VLDL-R expression. Down-regulation of VLDL-R expression, shown here for the first time, reveals another facet of disturbed lipid metabolism in CRF.

Pathogenesis of dyslipoproteinemia in renal insufficiency: the role of lipoprotein lipase and hepatic lipase

The lipoprotein pattern, observed in patients with renal failure, suggests impaired catabolism of triglyceride-rich lipoproteins. This is supported by the findings of numerous studies addressing the pathogenesis of the dyslipoproteinemia of uremia. Aberrant lipoprotein composition, resulting in disturbed substrate characteristics for lipoprotein lipase and unfavourable receptor ligand function, probably constitutes the primary pathology. The structural details of the lipoproteins that are responsible for this dysfunction are not yet established. In this regard, abnormal apolipoprotein pattern and, possibly more important, biological modifications must be taken into consideration. Low activity of lipoprotein lipase does not seem to be a primary pathogenetic factor. However, there is little doubt that it plays a contributory part. The role of hepatic lipase is controversial.

The role of abdominal adiposity and insulin resistance in dyslipidemia of chronic renal failure

The atherogenic profile of high triglyceride, reduced high-density lipoprotein (HDL) cholesterol, and small low-density lipoprotein particle size found in patients on chronic hemodialysis is known to be associated with insulin resistance and abdominal obesity in the general population. To assess the influence of insulin resistance and abdominal adiposity on the lipid profile in subjects on hemodialysis, intravenous glucose tolerance test and dual-energy x-ray absorptiometry were performed in 26 nondiabetic subjects on hemodialysis and compared with 22 nondiabetic control subjects matched for age, sex, and body mass index. Subjects on hemodialysis were found to have higher triglyceride (133 mg/dL [95% confidence interval, 115 to 159 mg/dL] v 97 mg/dL [95% confidence interval, 80 to 124 mg/dL]; P < 0.05), lower HDL cholesterol (36 +/- 3 mg/dL v 51 +/- 4 mg/dL [mean +/- SEM]; P < 0.01), enhanced insulin response to glucose (2.72 +/- 0.28 mUL(-1) min per mg dL(-1) v 1.67 +/- 0.22 mUL(-1) min per mg dL(-1); P < 0.01), and reduced sensitivity to the action of insulin (2.24 min(-1) per mUL(-1) min [95% confidence interval, 1.86 to 2.75 min(-1) per mUL(-1) min] v 4.17 min(-1) mUL(-1) min [95% confidence interval, 2.95 to 5.9 min(-1) per mUL(-1) min]; P < 0.01) than the control subjects. Abdominal adiposity measured by dual-energy x-ray absorptiometry (2,004 +/- 210 g v 2,163 +/- 198 g [mean +/- SEM]; P = NS) and percentage of body fat distributed to the abdomen (10.5% +/- 0.3% v 9.7% +/- 0.5% [mean +/- SEM]; P = NS) did not differ between the two groups. Subjects on hemodialysis were insulin resistant, but unlike control subjects, their lipid profile was not predicted by their insulin sensitivity. Abdominal adiposity was associated with a deteriorating lipid profile and insulin resistance in subjects on hemodialysis, as it was in control subjects. The presence of renal failure resulted in additional insulin resistance and a higher triglyceride level in the leaner subjects on hemodialysis compared with control subjects with similar levels of abdominal fat. In the more obese subjects, insulin sensitivity and triglyceride level did not differ between the two groups of subjects, although HDL cholesterol level remained low in subjects on hemodialysis. In conclusion, insulin resistance in subjects on hemodialysis did not directly account for their abnormal lipid profile. The negative impact of abdominal adiposity on the metabolic profile was preserved in subjects on hemodialysis, but the presence of renal failure itself resulted in insulin resistance in the leaner subjects and dyslipidemia in all subjects on hemodialysis compared with control subjects of comparable abdominal adiposity.

Down-regulation of tissue lipoprotein lipase expression in experimental chronic renal failure

Chronic renal failure (CRF) is associated with hypertriglyceridemia, impaired clearance of very low density lipoproteins (VLDL) and chylomicrons and their remnants as well as triglyceride-enrichment of various lipoproteins. These abnormalities are indicative of depressed lipoprotein lipase (LPL)-mediated hydrolysis of triglycerides in VLD and chylomicrons. In fact, impaired post-heparin lipolytic activity and decreased adipose tissue LPL activity has been previously demonstrated in CRF. The reduction in LPL activity in CRF has been attributed to PTH-induced insulin resistance and the presence of excess lipase inhibitors in uremic plasma. However, the effect of CRF on gene expression of LPL has not been elucidated and was studied here. Heparin-releasable, detergent-extractable and total LPL activities, as well as LPL mRNA of the heart, soleus muscle and fat body were determined in male Sprague-Dawley rats at baseline and on weeks 1, 3 and 6 following 5/6 nephrectomy (CRF group) or sham operation (control group). The CRF group exhibited a marked and steady rise in plasma triglycerides along with a steady decline in LPL activities and mRNA levels of all tissues studied. In contrast, the study parameters remained virtually unchanged throughout the study period in the control group. A strong inverse correlation was found between plasma triglycerides and LPL activity in the study animals. LPL activity was directly related to LPL mRNA. We conclude that CRF results in marked down-regulation of LPL expression that can contribute to dyslipidemia and altered energy metabolism in uremia. The effect of depressed LPL expression is compounded by the previously demonstrated elevations in uremic plasma of Apo C-III and pre-beta-HDL, which are potent inhibitors of LPL.

Benefits of calcitriol therapy and serum phosphorus control in dogs and cats with chronic renal failure. Both are essential to prevent of suppress toxic hyperparathyroidism

Daily oral calcitriol at low doses is safe and effective in the control of renal secondary hyperparathyroidism in dogs and cats. Low doses of calcitriol are most effective when started early in uremia before the advanced stages of renal secondary hyperparathyroidism. At early stages calcitriol both diminishes PTH synthesis in the parathyroid cells present and prevents the hyperplasia that, if unchecked, results in the most extensive an difficult-to-control hyperparathyroidism. The salutary effects on the dog's or cat's sense of well being, appetite, activity, strength, and lifespan as reported by the veterinarians of our survey are attributed primarily to keeping PTH levels below a toxic threshold. Additionally, some of the benefits achieved by calcitriol are likely a direct consequence of calcitriol interacting with the vitamin D receptor in a wide variety of tissues throughout the body. Phosphorus restriction through a combination of diet and intestinal phosphate binders is important to allow calcitriol therapy to successfully lower PTH levels, but it likely has no direct effects that are independent of interactions involving calcitriol. Phosphorus restriction is also important to minimize chances for adverse tissue mineralization. Calcitriol therapy can be considered for treatment of chronic renal failure after serum phosphorus has been decreased to less than 6.0 mg/dL in patients in whom it was initially elevated. Calcitriol supplementation to dogs and cats with chronic renal failure makes good endocrinologic sense. Calcitriol deficits cause increased PTH and, as these two hormones are designed to maintain calcium and phosphorus homeostasis, the PTH increase is initially adaptive. One of the important effects of PTH is to stimulate additional calcitriol formation as a powerful means to raise blood calcium through increased calcium absorption from the diet. With too great an increase in PTH, however, its effects become harmful to many tissues due to the widespread distribution of the PTH receptor in many cell types that are likely normally responsive only to the paracrine PTH-related peptide that shares the PTH receptor. Exogenous supplemental calcitriol administration allows concentrations of calcitriol in the bloodstream to remain normal without the toxic consequences of excessive PTH secretion that would otherwise be provoked. Studies involving young dogs with subtotal nephrectomy may not parallel those on older dogs and cats with spontaneous chronic renal failure. In particular, higher doses are needed to effect PTH change in these young dogs than we have found necessary for older dogs and cats. Because survey participants agreed most strongly with the idea that their calcitriol-treated dogs and cats were living longer than comparably uremic animals they had treated previously, further studies to evaluate the ability of calcitriol to retard the progression of renal lesions and loss of excretory renal function seem warranted. Additional studies to document the beneficial effects of calcitriol on the many organs adversely affected by excess PTH during uremia are also needed because findings thoroughly documented and proven in humans and rats may not always extrapolate to dogs and cats.

Plasma lipids and the progression of nephropathy in diabetes mellitus type II: effect of ACE inhibitors

Ninety-four normotensive type II diabetics with normal renal function and microalbuminuria were randomized to receive enalapril 10 mg/day or placebo and were followed for five years. In the patients treated by enalapril plasma creatinine values and albuminuria remained stable throughout the observation period. Their plasma total cholesterol decreased from an initial value of 245 +/- 27 mg/dl to mean study value of 236 +/- 29 mg/dl, and to a fifth year value of 232 +/- 27 mg/dl (P < 0.001). The changes in HDL cholesterol and triglyceride values were nonsignificant. In the placebo group there was a significant increase in albuminuria and a mean decline of 13% in reciprocal creatinine values during the five years. Plasma total cholesterol increased from an initial mean value of 246 +/- 24 to a mean study value of 252 +/- 25 mg/dl, and to a fifth year mean value of 259 +/- 32 mg/dl (P < 0.001). There was a significant correlation between both initial and mean plasma total cholesterol values, and the decline in renal function and the rise in albuminuria in the placebo treated patients. This correlation persisted after stratification for blood pressure. Treatment with enalapril did not eliminate these correlations. Cholesterol may be an additional risk factor for diabetic nephropathy. ACE inhibitors may have a modest cholesterol lowering effect in diabetic patients mediated, in part, through the decline in albuminuria.

Post-transcriptional regulation of 3-hydroxy-3-methylglutaryl coenzyme A reductase and cholesterol 7 alpha-hydroxylase in rats with subtotal nephrectomy

Chronic renal failure is associated with hyperlipidemia and atherosclerosis. The mechanism responsible for the observed increase of serum cholesterol in chronic renal disease is not certain. The objective of the present study was to characterize the effect of induced renal failure on 3-hydroxy-3-methylglutaryl coenzyme A reductase (HMG-CoA reductase) and cholesterol 7 alpha-hydroxylase, the two rate determining enzymes of the cholesterol and bile acid biosynthetic pathways, respectively. Studies were carried out in rats with subtotal (75%) nephrectomy, which resulted in a marked elevation of blood urea nitrogen (371 +/- 44% of control, P < 0.001), and was accompanied by significant increases in the levels of serum cholesterol (133 +/- 7%, P < 0.005) and triglycerides (185 +/- 25, P < 0.01). In nephrectomized rats, an increase in the specific activity of HMG-CoA reductase (219 +/- 30% above control levels, P < 0.02) was observed. This increase occurred in the presence of elevated hepatic microsomal cholesterol concentrations (150 +/- 13% of controls, P < 0.01). Surprisingly, the increase in HMG-CoA reductase specific activity was not associated with parallel increases in HMG-CoA reductase steady-state mRNA levels and gene transcriptional activity. These uremic rats also exhibited a marked increase in the specific activity of cholesterol 7 alpha-hydroxylase (240 +/- 559% of controls, P < 0.05). There was no concomitant increase in cholesterol 7 alpha-hydroxylase steady-state mRNA levels or gene transcriptional activity. The factors responsible for the observed increases in HMG-CoA reductase and cholesterol 7 alpha-hydroxylase specific activity in renal failure remain to be determined.(ABSTRACT TRUNCATED AT 250 WORDS)

Uremia-induced disturbances in hepatic carbohydrate metabolism: enhancement by sucrose feeding

A high-sucrose (S) diet accentuates anorexia and stunts growth in uremic (U) rats, and an oral S load induces a greater hyperfructosemia in U rats than in control (C) rats. Four studies were performed to determine the roles of S feeding and an acute S load on liver carbohydrate (CHO) metabolism in U and C rats (eight to 10 rats per group). We also examined the plasma responses to either water or a S load. Levels of the main metabolites of glycolysis, gluconeogenesis, and glycogenesis were measured under basal conditions (7 hours' postmeal) in U and C rats fed either a cornstarch diet (study I) or S diet (study II) and at 30 and 60 minutes after an intragastric S load (studies III and IV) in s-fed U and C rats. The weight gain, food intake, and plasma creatinine and urea levels of the rats in the four studies were comparable. Weight gain and liver weight (g/100 g body weight) were lower in U than in C rats. In the plasma, baseline levels of lactate were decreased by uremia and S feeding and those of glucose (G) were increased by S feeding. The increases in plasma G and fructose (F) levels after a S load were greater in U rats than in C rats, whereas those of plasma lactate were comparable. In the liver under basal conditions, uremia markedly decreased levels of glycogen, F-1,6-diphosphate (F-1,6-diP), F-2,6-diP, 3-glycero-phosphate (3-glycero-P), dihydroxyacetone phosphate (DHAP), pyruvate, lactate, and adenosine triphosphate (ATP), and the phosphorylation state (ATP/adenosine diphosphate [ADP] x inorganic phosphorus [PI]), increased phosphoenolpyruvate (PEP), ADP, and Pi levels, but did not affect the cytosolic redox state (pyruvate/lactate). In addition to uremia, S feeding further decreased levels of glycogen, F-2,6-diP, 3-glycero-P, and ATP. After S loading, liver F levels increased more in U than in C rats, but glycogen and 3-glycero-P levels increased less in U than in C rats. Liver lactate and pyruvate levels increased more in U than in C rats, and the pyruvate/lactate and DHAP/3-glycero-P ratios were higher in U than in C rats after a S load. The ATP level and the phosphorylation state in U rats increased 30 minutes later in U than in C rats. Our findings indicate that uremia causes a depletion in liver glycogen, which is enhanced by S feeding and could be partially attributed to decreased glycogen synthesis.(ABSTRACT TRUNCATED AT 400 WORDS)

Lipoprotein metabolism and renal failure

Lipoprotein metabolism is altered in the majority of patients with renal insufficiency and renal-failure, but may not necessarily lead to hyperlipidemia. The dyslipoproteinemia of renal disease has characteristic abnormalities of the apolipoprotein (apo) profile and lipoprotein composition. It develops during the asymptomatic stages of renal insufficiency and becomes more pronounced as renal failure advances. The qualitative characteristics of renal dyslipoproteinemia are not modified substantially by dialysis treatment. Patients with chronic renal disease may therefore be exposed to dyslipoproteinemia for long periods of time. The characteristic plasma lipid abnormality is a moderate hypertriglyceridemia. The alterations of lipoprotein metabolism affect both the apoB-containing very low-density and intermediate-density, and low-density lipoproteins and the apoA-containing high-density lipoproteins. The main underlying abnormality of lipoprotein transport is a decreased catabolism of the apoB-containing lipoproteins caused by decreased activity of lipolytic enzymes and altered lipoprotein composition. There is an increase of intact or partially metabolized, triglyceride-rich, apoB-containing lipoproteins with a disproportionate elevation of apoC-III and, to a lesser extent, apoE, resulting in a marked increase of the intermediate-density lipoproteins and an enrichment of triglycerides, apoC-III, and apoE in the low-density lipoproteins. In high-density lipoproteins there are decreases in the concentrations of cholesterol, apolipoproteins A-I and A-II, and the high-density lipoprotein-2 to high-density lipoprotein-3 ratio. These abnormalities result in a characteristic decrease of the apoA-I to apoC-III ratio and anti-atherogenic index apoA-I/apoB. The pathophysiologic links between the renal insufficiency and the abnormalities of lipoprotein transport are still poorly defined. Changes in the action of insulin on lipolytic enzymes, possibly mediated via increased levels of parathyroid hormone, have been suggested to play a contributory role. The clinical consequences of a defective lipoprotein transport may be related to the atherogenic character of lipoprotein abnormalities. Renal dyslipoproteinemia may contribute to the development of atherosclerotic vascular disease and progression of glomerular and tubular lesions with subsequent deterioration of renal function. Dietary and/or pharmacologic intervention may ameliorate the uremic dyslipoproteinemia, but the long-term clinical effects of such treatment have yet to be established.

Dyslipoproteinemia in diabetic renal failure

Plasma concentrations of lipids and apolipoproteins (Apo) were determined in 34 patients with long-standing type I (insulin-dependent) diabetes mellitus. Twenty-four patients had renal insufficiency (GFR 4 to 55 ml/min) due to diabetic nephropathy, while 10 patients had no clinical signs of nephropathy. Results were compared with those in 42 non-diabetic patients with comparable degree of renal insufficiency and with asymptomatic control subjects. Diabetic patients without nephropathy had plasma lipid and apolipoprotein concentrations similar to those of the control subjects. Diabetic patients with renal insufficiency had a significant increase in triglycerides (TG) and, to a lesser extent, in total cholesterol (TC). The patients also had reduced levels of ApoA-I and ApoA-II, increased levels of ApoC-II and ApoC-III, while increases in levels of ApoB and ApoE were statistically significant in patients with GFR < 20 ml/min. These lipids and apolipoprotein abnormalities were accentuated with decreasing renal function. The reduction in the ApoA-I/ApoC-III ratio characteristic of renal insufficiency was found in normo- and hyper-TG diabetic patients with nephropathy; this ratio was correlated with the GFR levels. Patients with higher HbA1C values had higher levels of ApoC-II and ApoC-III. The findings in the diabetic patients corresponded with those in non-diabetic patients with renal insufficiency. However, diabetic patients had higher ApoC-III and ApoE levels. The abnormalities of lipid metabolism in diabetic renal insufficiency seem to reflect primarily metabolic impairments characteristic of renal insufficiency, but may be further accentuated by the diabetic state and the metabolic control.

Decreased low-density lipoprotein receptor function and mRNA levels in lymphocytes from uremic patients

The mechanisms by which renal failure causes hyperlipoproteinemia remain unclear. To investigate the potential role of the low-density lipoprotein (LDL) receptor in lipoprotein metabolism in uremia we measured LDL receptor function in peripheral blood mononuclear cells (PBMC) from uremic patients and control subjects using a functional assay in which proliferation of lectin-stimulated PBMC in the presence of lovastatin was dependent upon internalization of exogenous cholesterol via a functional LDL receptor. The amount of LDL required to reverse 50% of lovastatin-induced inhibition of proliferation in PBMC from uremic patients was significantly greater (3.6 +/- 1.8 micrograms/ml, N = 33, P < 0.05) than controls, (1.99 +/- 0.6 micrograms/ml, N = 37). Abnormal LDL receptor function in four uremic patients normalized following renal transplantation. To investigate the molecular basis for LDL receptor dysfunction, we directly quantitated LDL receptor messenger RNA (mRNA) in PBMC from uremic patients and control subjects using a ribonuclease protection assay. LDL receptor mRNA expression in uremic patients was 0.42 +/- 0.08 (N = 10), significantly lower (P < 0.015) than in normal subjects, 0.71 +/- 0.08 (N = 14). These data suggest that an acquired defect in LDL receptor function in PBMC from uremic patients exists which may be due to decreased LDL receptor expression. These abnormalities, if present in other tissues, could contribute to the aberrant lipoprotein metabolism which is a consistent feature of uremia.

The effect of growth hormone on the growth failure of chronic renal failure

To investigate the effects of growth hormone (GH) on the reversal of growth failure in uremia, recombinant human GH (rhGH) was administered to rats with chronic renal failure (CRF). The dosage of rhGH was 3 IU/day (i.p.) for 13 days after the induction of CRF by 5/6 nephrectomy. Animals were classified into four groups: untreated nephrectomized rats (NX, n = 40), GH-treated nephrectomized rats (NX+GH, n = 18), sham-operated rats fed ad libitum (SHAMAL, n = 27), and sham-operated rats pair-fed with 10 NX rats (SHAMPF, n = 10). NX and NX+GH rats developed a similar and moderate degree of CRF, serum urea nitrogen being (mean +/- SEM) 49 +/- 3 and 54 +/- 4 mg/dl, respectively, compared with 16 +/- 4 and 19 +/- 0 mg/dl in SHAMAL and SHAMPF groups. Weight (56.0 +/- 3.3 g) and length (3.5 +/- 0.1 cm) gains of NX rats were lower than those of SHAMAL rats (94.2 +/- 4.0 g, P less than or equal to 0.0001 and 4.1 +/- 0.2 cm, P less than or equal to 0.01). Growth of the SHAMPF group and the matched NX rats was not significantly different. Weight (56.2 +/- 5.0 g) and length (3.4 +/- 0.2 cm) gains of NX+GH and NX rats were similar, the beneficial effect of GH therapy on growth being observed in only those animals with more severe degrees of uremia. This growth-promoting action resulted from greater food efficiency and not from stimulated food intake. The hypercholesterolemia seen in NX rats, 81 +/- 2 mg/dl versus 55 +/- 3 mg/dl in SHAMAL (P less than or equal to 0.0001), was not increased in the NX+GH group, 87 +/- 3 mg/dl. There was a positive and significant correlation between serum cholesterol and serum urea nitrogen values in NX and NX+GH animals. This study suggests that growth impairment of mild CRF is mainly due to malnutrition and is refractory to GH administration. GH therapy improves the growth rate of animals with advanced CRF without aggravating their lipid abnormalities.

Correction by insulin of disturbed TG-rich LP metabolism in rats with chronic renal failure

To define the role of insulin in lipid disturbances of chronic renal failure, chronically uremic rats (U+) were supplemented by continuous insulin infusion over a 35-day experimental period and compared with control ad libitum-fed rats (C) and uremic rats without insulin (U). Uremic rats were characterized by hypoinsulinemia, an increase in both circulating very low-density lipoprotein (VLDL) and their cholesterol concentration, a normal hepatic triglyceride secretion rate (TGSR) determined with Triton WR 1339, and a low adipose tissue lipoprotein lipase (LPL) activity. Chronic insulin infusion at low rate (0.5 IU/24 h) to U+ rats normalized serum insulin (from 17.0 +/- 0.6 mU/l in U rats to 23.4 +/- 1.7 mU/l in U+ rats), serum VLDL triglycerides (from 804 +/- 65 to 410 +/- 36 mg/l), and serum VLDL cholesterol (from 43 +/- 8 to 16 +/- 3 mg/l). Hepatic TGSR decreased significantly after insulin treatment (from 0.58 +/- 0.03 to 0.44 +/- 0.03 mumol/min). Moreover, adipose tissue LPL was restored to normal by insulin supplementation (from 460 +/- 60 to 860 +/- 150 mU per total epididymal fat in U and U+ rats, respectively). Correction of the disturbed VLDL metabolism was associated with multiple actions of insulin including 1) a decrease of peripheral lipolysis, 2) a decrease of hepatic TGSR, and 3) an increase of adipose tissue LPL activity. Because cholesterol-rich VLDL are potentially atherogenic, their normalization with insulin treatment in this animal model suggests a viable area of investigation for the prevention of accelerated atherogenesis in chronic renal failure.