Lipid metabolism in primary cultured hepatocytes from daunomycin-nephrotic rats

We investigated the lipid metabolism in primary cultured hepatocytes to elucidate the causes of hyperlipidemia, increased cholesteryl esters, and decreased triglyceride levels in the livers of daunomycin-nephrotic rats. The incorporation of 14C-palmitate into phospholipids and triglycerides in primary cultured hepatocytes and medium was similar in daunomycin-nephrotic and control rats. The incorporation of 14C-acetate into phospholipids, triglycerides, cholesterol, cholesteryl esters, and total fatty acids in primary cultured hepatocytes was increased in daunomycin-nephrotic rats. The radioactivity of phospholipids, triglycerides, cholesterol, cholesteryl esters, and very-low-density lipoprotein lipids in medium was increased in the hepatocytes of daunomycin-nephrotic rats using 14C-acetate as a precursor. The increased cholesterogenesis and the increased secretion of triglycerides synthesized from acetate by hepatocytes may be due to an increased cholesteryl ester content and a decreased triglyceride content in the livers of daunomycin-nephrotic rats. The increased secretion of lipids synthesized from acetate by hepatocytes may be due to increased accumulation of lipids in serum and very-low-density lipoprotein in daunomycin-nephrotic rats.

High density lipoprotein catabolism in primary cultured hepatocytes from daunomycin-induced nephrotic rats

We investigated into HDL (high density lipoprotein) catabolism with primary cultured hepatocytes to elucidate the causes of increased HDL apolipoproteins in the plasma of daunomycin-induced nephrotic rats (D rats). The phospholipid, triglyceride, cholesterol, cholesteryl ester and apolipoprotein contents in HDL increased in D rats compared with control rats (C rats). The uptake (binding plus internalization) of (125)I-HDL from D rats to two groups of hepatocytes was significantly greater than that of (125)I-HDL from C rats. Uptake of (125)I-HDL from D rats to D rats' hepatocytes was significantly greater than that of (125)I-HDL from C rats to C rats' hepatocytes. The degradation of (125)I-HDL from D rats was greater than that of (125)I-HDL from C rats using two groups of hepatocytes. These results demonstrated that the uptake and degradation of HDL to D rats' hepatocytes were greater than those of HDL to C rats' hepatocytes. The increased HDL apolipoprotein content in the plasma of D rats may not be due to decreased uptake and degradation of HDL in hepatocytes compared with C rats.

[Chylomicron and VLDL metabolism in daunomycin-induced nephrotic rats]

Lipid metabolism in chylomicron and VLDL were examined in daunomycin-induced nephrotic rats. 1) There was no difference in intestinal cholesterogenesis between the control rats and daunomycin-induced nephrotic rats. 2) The apoprotein content of chylomicron and VLDL increased in daunomycin-induced nephrotic rats. 3) Daunomycin-induced nephrotic rats showed increases in the content of apo B-48 and C-III, and a decrease in that of apo E in chylomicron. The apoprotein composition of VLDL in daunomycin-induced nephrotic rats showed increased apo B and decreased apo E. These results suggest that increased chylomicron-cholesterol is not due to increased intestinal cholesterogenesis, but to decreased chylomicron catabolism in daunomycin-induced nephrotic rats. Increased apoprotein in VLDL may contribute to the decreased catabolism by reducing LPL activity in the plasma and increased secretion from the liver of daunomycin induced nephrotic rats.

Adsorption of human recombinant erythropoietin on dialysis membranes in vitro

The adsorptive characteristics of 5 dialysis membranes for recombinant human erythropoietin (EPO) were studied in vitro in a closed circuit system. For 120 min, EPO added with bovine serum was significantly adsorbed by polymethylmethacrylate (PMMA) and polyacrylonitrile (PAN) membranes but not by Cuprophan, ethylene vinyl alcohol (EVAL), or polysulfone (PS) membranes. In addition the EPO adsorptive rate, as well as that of beta 2-microglobulin (beta 2-MG), was greater with a PMMA membrane than with a PAN membrane. EPO was not detected in the ultrafiltrate at 15 min with 5 membranes. These results indicate that EPO was eliminated by membrane adsorption only with some dialysis membranes.

[Lipid metabolism in daunomycin-induced nephrotic rats (Part 6)]

Lipid metabolism in tissues and HDL were examined in daunomycin-induced nephrotic rats. 1) Daunomycin-induced nephrotic rats showed the decreased phospholipids, the increased cholesterol content in heart. Phospholipids, triglycerides and cholesterol content in brain, lung and spleen were similar in daunomycin-induced nephrotic rats and control rats. 2) Triglycerides content in hepatocytes was decreased in daunomycin-induced nephrotic rats. But, cholesterol esters content in hepatocytes was higher in daunomycin-induced nephrotic rats than control rats. 3) LCAT activity in serum was increased in daunomycin-induced nephrotic rats. 4) Apolipoproteins composition of HDL in daunomycin-induced nephrotic rats showed the increased apoA-I and the decreased apo E. These results show that the increased cholesterol esters in liver tissue are due to hepatocytes in daunomycin-induced nephrotic rats. The increased HDL cholesterol content may contribute to the increase of LCAT activity in daunomycin-induced nephrotic rats. The increase of LCAT activity in serum results in the increased apo A-I content in daunomycin-induced nephrotic rats. No direct evidence about the incorporation of HDL into liver is obtained from the present experiments and further study will be necessary to clarify this evidence.

[Lipid metabolism in daunomycin-induced nephrotic rats (5)]

Lipid metabolism of intestine, liver and kidney was examined in daunomycin-induced nephrotic rats. 1) Phospholipids, triglycerides and cholesterol contents in chylomicrons were increased in daunomycin-induced nephrotic rats. 2) Cholesterol absorption in intestine (in vivo and situ) was similar in daunomycin-induced nephrotic rats and control rats. 3) Total bile acids levels in bile and portal vein were similar in two groups. 4) There was no difference in incorporation of 14C-mevalonate into cholesterol by liver and kidney slices in two groups. The oxidation of 14CO2 from 14C-mevalonate in kidney slices was decreased in daunomycin-induced nephrotic rats. These results show that the hypercholesterolemia in daunomycin-induced nephrotic rats are not caused by increased absorption of cholesterol in intestine. The increased cholesterol esters in liver are not derived from decreased bile acids catabolism. The increased cholesterogenesis in the liver of daunomycin-induced nephrotic rats may be due to an increased rate at the step prior to mevalonate. The oxidation of 14CO2 from mevalonate by shunt pathway may be decreased in the kidney of daunomycin-induced nephrotic rats.

Effect of phosphate depletion on vasopressin secretion and kidney tissue vasopressin concentration in rats

The effects of chronic phosphate depletion on vasopressin (ADH) secretion and kidney tissue ADH concentration were examined in rats fed on a diet containing 0.26% phosphorus (LP) or 0.99% phosphorus (NP). The concentration of plasma phosphorus (P) fell significantly in the LP rats after a 4-week period on the experimental diet. There was no significant difference between the LP and NP rats as regards their plasma ADH concentrations and kidney tissue ADH concentrations in normal hydration after a 4-week period on the experimental diets. Following hypertonic saline tests, the plasma ADH concentrations increased significantly in the LP and NP rats, but there was no significant difference between the groups. The kidney medulla and papilla ADH concentrations increased significantly with plasma ADH elevations in both groups. Again, no difference could be found in the cortico-medullary ADH concentration gradients between the two groups. These results indicate that chronic hypophosphatemia in phosphate depleted rats may not be related to ADH secretion and the distribution or tissue concentration of ADH in the kidney. Further, our data suggest that a low plasma P does not influence the ability of ADH to bind to kidney receptor in rats.

Effect of magnesium deficiency on lipid metabolism in uremic rats

The effects of acute magnesium deficiency on lipid metabolism were examined in five-sixths nephrectomized uremic rats and sham-operated rats. Three weeks after the surgery, both groups were divided into two subgroups. Half of the uremic and sham-operated rats received a magnesium-deficient diet. The rest of the experimental animals received a control diet. After 2 weeks on this regimen, all animals were sacrificed. In uremic rats, magnesium deficiency increased serum triglyceride levels and decreased high-density lipoprotein cholesterol levels as in sham-operated rats. Total serum cholesterol levels were higher in uremic rats than in sham-operated rats with or without magnesium deficiency. Serum free fatty acid levels were increased only in uremic rats with magnesium deficiency. These results suggest that magnesium deficiency worsens several parameters of lipid in uremic rats.

Effect of 1,25-dihydroxyvitamin D3 on intestinal disaccharidases in uremic rats

The effect of 1,25-dihydroxyvitamin D3 (1,25-D) on the activity of intestinal disaccharidases, maltase, sucrase, trehalase and lactase, was studied in five-sixths nephrectomized uremic rats. In uremic rats, maltase, sucrase and trehalase activities were lower than in sham-operated rats. Administration of 1,25-D produced significant improvement of maltase, sucrase, trehalase and lactase activities in uremic rats. These results suggest that activities of intestinal disaccharidases are reduced in uremic rats and these activities are normalized after 1,25-D administration.

Liver 3-hydroxy-3-methylglutaryl-coenzyme A reductase activity in pyridoxine-deficient rats

The activities of 3-hydroxy-3-methylglutaryl-CoA reductase [EC 1.1.1.34] in the livers of pyridoxine-deficient and control rats were compared. The reductase activity, which is known to show a circadian rhythm, was about twice as high in pyridoxine-deficient rats during both the light and dark periods. After administration of cycloheximide the rate of decrease in reductase activity was similar in pyridoxine-deficient and control rats. The Km values from the two groups for DL-DMH-CoA, the heat stabilitied and the microsomal lipid compositions were also similar. The effects of cytosolic activator and inactivator proteins on the reductase activities were also similar. These results show that the increased activity in pyridoxine-deficient rats is due to increased enzyme synthesis or increased specific activity induced by some unknown mechanism, but not to change in the state of phosphorylation of the enzyme.

Metabolism of fatty acids and the levels of ketone bodies in the livers of pyridoxine-deficient rats

Lipid metabolism was examined in rats fed a high-protein pyridoxine-deficient diet, and their livers were found to contain large amounts of lipids, mainly in the forms of triglycerides and cholesteryl ester. The contents of ketone bodies in the livers of pyridoxine-deficient and the control rats were similar. Their NAD+/NADH ratios, calculated from the amounts of ketone bodies, were also similar in pyridoxine-deficient and control groups when the animals were fed, but the ratio in pyridoxine-deficient rats was lower than that of control rats when the animals were starved. After injection of 14C-linoleic acid, the amounts of expired 14CO2 in pyridoxine-deficient and control rats were similar. The pattern of incorporations of 14C-linoleic acid into various lipid components of the livers were examined; incorporation into the phospho-lipid fraction was similar in control and deficient rats, but the incorporation into the triglyceride fraction was slower, and the incorporation into cholesterol was faster in deficient animals than in controls.