Impaired intestinal absorption of riboflavin in experimental uremia

Increased plasma and red blood cell concentrations of riboflavin have been reported in uremia. The possible role of altered intestinal absorption of riboflavin in the genesis of this abnormality is not known. For this reason we examined the intestinal absorption of riboflavin in rats made uremic by subtotal nephrectomy and sham-operated (control) rats in vivo using the recycling perfusion technique and in vitro using the everted-sac technique. Paradoxically, the results showed a significant impairment of intestinal absorption of riboflavin in vivo in uremic rats compared to the control group. However, no significant difference was observed in riboflavin transport in vitro. We conclude that the intestinal absorption of riboflavin is decreased in experimental uremia and cannot account for the reported increase in its plasma and red blood cell concentrations.     

Nicotinic acetylcholine receptor regulation of spinal norepinephrine release

BACKGROUND: Neuronal nicotinic acetylcholine receptor (nAChR) agonists produce antinociception in animals. nAChRs exist almost exclusively on presynaptic terminals in the central nervous system and stimulate neurotransmitter release. This study tested whether nAChR agonists stimulate spinal release of the neurotransmitter norepinephrine either by direct actions on noradrenergic terminals or indirectly by stimulating release of other neurotransmitters to induce norepinephrine release. METHODS: Adult male rats were anesthetized and microdialysis probes inserted in the L2-L4 dermatomes of the spinal cord. Probes were perfused with artificial cerebrospinal fluid containing nicotine, the specific alpha(4)beta(2*) nAChR agonist metanicotine, or nicotine plus nAChR antagonists and norepinephrine measured in the microdialysates. The effects of specific glutamate receptor antagonists and nitric oxide synthase inhibitors were also examined. To determine direct effects on noradrenergic terminals, synaptosomes were prepared from spinal cord and incubated with nAChR agonists and antagonists. RESULTS: Both nicotine and metanicotine induced norepinephrine release in spinal microdialsyates, an effect reduced by nicotinic antagonists but not glutamate antagonists or nitric oxide synthase inhibitors. Both of the nicotinic agonists stimulated norepinephrine release in synaptosomes, and the effect of metanicotine was blocked at lower concentrations of alpha(4)beta(2*)- than alpha(7*)-preferring nAChR antagonists. CONCLUSION: These results suggest that one mechanism by which nAChR agonists act for analgesia is to stimulate spinal norepinephrine release. They do so by actions on alpha(4)beta(2*) nAChRs, and perhaps other subtypes, most likely located on noradrenergic terminals, rather than by indirectly stimulating norepinephrine release through glutamate release or nitric oxide synthesis.     

Impaired metabolism of guanidinoacetic acid in uremia

In order to investigate the guanidinoacetic acid (GAA) metabolism in uremia, we have measured serum guanidino compounds in patients with chronic renal failure (CRF) in comparison with normal subjects, and the renal content of GAA and glycine amidinotransferase (GAT) activity in the kidney of experimental CRF rabbits. Serum concentrations of guanidinosuccinic acid (GSA) and methylguanidine (MG) in the patients with CRF were higher than those in the normal subjects, as well as serum urea nitrogen (BUN) and creatinine (Cr) levels. The serum GAA levels were however, significantly lower and showed a tendency to decrease inversely with the elevation of BUN in the patients with CRF under conservative therapy. On the contrary, in the patients under maintenance hemodialysis (MHD) therapy, the serum GAA level did not decrease in spite of the elevation of BUN. Four anephric patients under MHD therapy showed a level of serum GAA similar to the other MHD patients. In the CRF rabbits, the renal GAA content was significantly lower than in the sham-operated rabbits and showed an inverse correlation with BUN. Renal GAT activity was also significantly lower in the CRF rabbits, showing a positive correlation with serum GAA concentration and an inverse correlation with BUN. These results indicate that renal GAT activity decreases as the BUN level rises in the course of renal damage, resulting in lower concentration of serum GAA in the uremic state; in a more advanced stage of renal failure, the inability of the kidney to synthesize GAA may be compensated by other organ(s). Some dialyzable substances which might inhibit renal GAT activity may also be present.     

Bacterial translocation in experimental uremia

The aim of this study was to investigate whether or not experimental uremia would induce bacterial translocation. Forty male Wistar rats were randomized into two groups: uremic (n=20) and control (n=20). Under anesthesia, the upper and lower left renal poles and the marginal lateral parenchyma were excised in uremic group. Seven days later, in a second operation the whole right kidney was removed. In control animals, two sham operations with the same interval were performed. After 60 days from the first operation, the liver, spleen and the mesenteric lymph nodes (MLN) were excised and cultured. Blood samples were sent for biochemical analysis (BUN, creatinine, sodium and potassium) and cultured. Specimens of the jejunum (1 cm below the Treitz angle) and ileum (1 cm above the ileocecal valve) were collected and sent for histological examination and scored for the degree of inflammation of the mucosa using a classification proposed by Chiu et al. in 1970. Uremic rats presented higher BUN, creatinine and potassium than controls. Bacterial translocation was more frequent in uremic than in control animals (8/20 (40%) vs. 1/20 (5%); p=0.02). Translocation in uremic rats was observed mainly at the MLN (all eight cases). Both at the jejunum (uremic=3 [0–5] vs. control=2 [0–4]; p=0.04) and the ileum (uremic=2 [0–5] vs. control=0 [0–3]; p=0.01), inflammation score was higher in uremic rats than in controls. The intestinal mucosa barrier is impaired and bacterial translocation occurs in experimental uremia.     

Parathyroid hormone and the altered vascular response to norepinephrine in uremia

Patients with chronic renal failure manifest reduced pressor response to norepinephrine (NE); this abnormality is at least partly responsible for the autonomic nervous system dysfunction observed in these patients. Since uremia is associated with increased levels of parathyroid hormone (PTH) and since PTH blunts the pressor effect of NE most likely via activation of prostaglandins, we have studied the relationship between blood levels of PTH and the reduced pressor response to NE in 17 uremic patients and we examined the effect of treatment with indomethacin on the response to NE in 9 uremic and 5 normal subjects. There was a significant negative correlation (r = -0.63, p less than 0.01) between the changes in blood pressure and the blood levels of PTH in uremic patients. Treatment with indomethacin was followed by significant improvement or normalization of the pressor response to NE in uremic patients. These data are consistent with the notion that the decreased pressor response to NE in uremia is due to increased production of prostaglandins induced by excess PTH and provide a therapeutic tool for the treatment of some of the manifestations of autonomic nervous system dysfunction in uremia.     

Parathyroid growth and regression in experimental uremia

Early 1,25-dihydroxyvitamin D(3) (VD(3)) therapy during the course of renal failure prevents the downregulation of VD(3) receptor (VDR), calcium-sensing receptor (CaSR) or p21, and the parathyroid (PT) growth. We hypothesized that VD(3) could restore the decreased expressions of VDR and CaSR, and cause regression in enlarged PT glands. 5/6 nephrectomized rats fed high-phosphorus diet were killed at 1, 3, 5, or 7 days and at 2, 3, 4, 8, or 12 weeks. VD(3)-treated rats were given VD(3) intraperitoneally for 1, 2, 3, or 4 weeks, starting 8 weeks after 5/6 nephrectomy. PT glands were weighed and subjected to immunohistochemical analyses for VDR, CaSR, p21, Ki67, and Tdt-mediated dUTP nick end-labeling (TUNEL) assay. The area per cell was measured as the parameter of cell size. The expression of VDR and p21 began to decrease at day 1, and Ki67 increased at day 3, but decreased thereafter. There was a significant increase in PT gland weight to week 12 with the increase of cell size. VD(3) treatment significantly increased both VDR and CaSR expressions 2 weeks after the start of injection, and reduced the PT gland weight at week 3 with significant increase of TUNEL-positive cells and decrease of cell size. Our results suggest that PT growth in uremic rats involves both PT cell proliferation and hypertrophy, in association with the reduction of VDR, CaSR, and p21 expressions. In addition, VD(3) treatment could reverse PT hyperplasia and hypertrophy via restoration of these proteins.     

Impaired muscle energy metabolism in uremia as monitored by 31P-NMR

Uremic patients often complain of fatigue and muscle weakness. In order to elucidate the abnormalities of energy metabolism in the muscles of such patients, we measured the concentrations of phosphocreatine (PCr), inorganic phosphate (Pi) and adenosine triphosphate (ATP) as well as the intracellular pH in skeletal muscles by 31P-NMR at rest, during aerobic and anaerobic exercise and during recovery in 15 uremic patients (7 non-dialyzed patients and 8 dialyzed patients) and 6 control subjects. At rest, there was no difference in intracellular pH between the uremic patients and controls, but the concentrations of PCr and ATP in the skeletal muscle were lower in the uremic patients. However, during aerobic exercise, the uremic patients showed a rapid decrease in intracellular pH and a delay in its recovery. They also revealed an increased PCr utilization during aerobic exercise and its delayed resynthesis during recovery. During anaerobic exercise, the uremic patients, especially non-dialyzed patients, displayed a slower decrease in pH than the controls and a delay in its recovery. An increased PCr utilization during anaerobic exercise and a delayed resynthesis during recovery were also demonstrated. These findings suggest that the aerobic and anaerobic energy productions in uremic patients are impaired and that the energy production of the muscle depends on anaerobic glycolysis during exercise. Hemodialysis apparently facilitates recovery of the inhibited enzyme activities of oxidative phosphorylation and glycolysis in uremic patients.     

Circulating inhibitor of gonadotropin releasing hormone secretion by hypothalamic neurons in uremia

BACKGROUND: Previous studies have suggested a neuroendocrine defect underlying uremic hypogonadism, characterized by a reduced secretion of gonadotropin-releasing hormone (GnRH) and luteinizing hormone (LH). METHODS: We studied the GnRH-producing GT1-7 cell line and the LH-producing LbetaT-2 pituitary cell line under uremic conditions to investigate whether substances circulating in uremic plasma directly affect hypothalamic or pituitary hormone secretion. The cells were incubated with serum from 5/6-nephrectomized or sham-nephrectomized castrated rats, respectively. Furthermore, GT1 cells were incubated with delipidated sera, serum subfractions separated by molecular weight, or several peptide hormones. Cellular viability, apoptosis rate and extracellular hormone degradation were assessed separately. GnRH and LH were measured by RIA in supernatants and cell lysates. GnRH gene expression was assessed by Northern blot. RESULTS: Uremic serum caused a reduction of extracellular GnRH concentration by 31%, whereas intracellular GnRH increased by 12%. This effect was independent of serum lipids and enzymatic GnRH degradation but was abolished by trypsin digestion. Cellular viability, apoptosis rates and GnRH gene expression did not differ between the two groups. The inhibitory activity was recovered from the high-molecular weight fraction, whereas the fraction <5 kD had stimulatory activity. In contrast, uremic serum did not affect LH secretion from LbetaT-2 cells, indicating that the hypoactivity of the hypothalamo-pituitary gonadotrope unit results from an inhibition at the hypothalamic rather than the pituitary level. CONCLUSIONS: Our results suggest that uremic serum contains macromolecular and hydrophilic peptide(s) able to specifically suppress the neurosecretion of GnRH from GT1-7 cells.     

Acidosis prevents growth hormone-induced growth in experimental uremia

The effects of 2 weeks of a daily injection (2 IU/day) of recombinant human growth hormone (GH) were studied in young (60-g) growing rats in two experiments. Experiment 1 was performed in uremic animals (mean plasma creatinine 65–71 mol/l) who were either acidotic (mean bicarbonate 11.5 mmol/l) or had acidosis corrected (mean bicarbonate 26 mmol/l) by addition of sodium bicarbonate to the diet. Experiment 2 used rats with normal renal function (plasma creatinine 25 mol/l) who were either non-acidotic but restricted to the dietary intake of uremic rats or rendered acidotic by ammonium chloride. GH induced an increase in body weight and length in nonacidotic uremic (+33% and +41%) and in non-acidotic food-restricted (+13% and +42%) rats, associated with an increased rate of protein synthesis and little change in plasma insulin-like growth factor 1 (IGF 1). In both acidotic rat groups, GH altered none of the parameters studied. Thus: (1) the presence of severe metabolic acidosis blunts the response to GH in uremic and non-uremic rats and (2) the increment of growth rate does not depend on a rise in plasma IGF 1.     

Skeletal changes and growth in experimental uremia.

Longitudinal growth; bone and growth zone histology; growth cartilage and bone mineralization (tetracycline technique); bone Ca content (neutron activation analysis); bone radiology; serum and urine chemistry; urinary cAMP and serum 25-OH-vitamin D3 were studied in a long-term model of experimental uremia in the rat. Uremia was induced by two-stage subtotal nephrectomy with irradiation of the remaining parenchyma. Ccr in the experimental group was 113 +/- 5.8 micron1/min X 100 g (19.8% of controls) and serum creatinine 1.67 +/- 0.04 mg% (5.1 X control value). Uremic animals were pair-fed with sham-operated controls. In the proximal tibia delayed transformation of cartilage into primary spongiosa with appearance of chondro-osteoid and delayed transformation of primary spongiosa into secondary spongiosa was observed (rickets). Increased amounts of osteoid were present although 25-OH-vitamin D3-levels were high. There were only modest signs of secondary hyperparathyroidism (osteoclast counts; urinary cAMP). In spite of the presence of bone disease, longitudinal growth was not reduced in uremic animals as compared with pair-fed sham-operated animals, but was significantly reduced as compared with ad lib fed control animals. In contrast, weight gain was significantly diminished in uremic animals as compared with pair-fed sham-operated control animals. It is concluded that diminished intake of food is the major determinant of growth retardation in preterminal experimental renal failure.     

Regulation of parathyroid cell gene expression in experimental uremia

The secondary hyperparathyroidism of renal failure is an important component of renal osteodystrophy. We studied PTHmRNA levels and their regulation in control and subtotal nephrectomized (5/6 NX) rats at 3 wk, as well as levels of the 1,25(OH)2D3 receptor mRNA in parathyroids. Serum 1,25(OH)2D levels were decreased in 5/6 NX, whereas PTHmRNA levels were increased (7 +/- 0.7 OD U, N = 4) compared to controls (2.1 +/- 1.2, P less than 0.01); both decreased after 1,25(OH)2D3 (100 pmol/100 g body weight). Similar results were found in 5/6 NX rats after 3 months. There was no change in actin mRNA levels. PTHmRNA levels were highest in 5/6 NX rats with the most severe renal failure. The parathyroid gland 1,25(OH)2D3 receptor mRNA levels were not different between 5/6 NX rats and controls and were not affected by 1,25(OH)2D3 (100 pmol/100 g body weight daily) at 1 or 3 days. PTHmRNA levels of 5/6 NX rats did not increase when the serum calcium was decreased from 2.8 +/- 0.05 mmol/L to 0.9 +/- 0.15 mmol/L at 3 or 5 h, which contrasted with the marked increase in PTHmRNA in normal rats after hypocalcemia. As in normal rats, after hypercalcemia (4.8 mmol/L at 1 h) there was no change in the 5/6 NX rats' PTHmRNA levels. These results show that 5/6 NX rats have increased PTHmRNA levels that are normally regulated by injected 1,25(OH)2D3 but not by calcium. Parathyroid gland 1,25(OH)2D receptor mRNA levels are not increased in 5/6 NX in contrast to the increased PTHmRNA, which reflects the larger glands of uremia. 1,25(OH)2D receptor mRNA levels were not regulated by 1,25(OH)2D3.(ABSTRACT TRUNCATED AT 250 WORDS)     

Red blood cell sodium transport and phosphate release in uremia

Red blood cell (RBC) phosphate release was linear for more than 1 h and dependent on the intracellular hydrolysis of organic phosphate esters. In uremics on chronic hemodialysis total phosphate release was significantly increased suggesting an elevated RBC energy metabolism. Ouabain-sensitive phosphate release, however, was decreased. For RBCs of controls and uremic subjects approximately 80% of inorganic phosphate liberated within the cell was recycled. Thus, RBC phosphate release represents 20% of intracellular phosphate ester metabolism. In uremia active electrolyte transport was diminished, suggesting an impaired Na-K-ATPase activity. It resulted in an increased RBC sodium and a decreased potassium concentration. The positive correlation between ouabain-sensitive rate constant for sodium efflux and ouabain-sensitive RBC phosphate release indicates that ouabain inhibition of phosphate elimination might be related to Na-K-ATPase. In RBCs of uremic subjects almost 4% of the increased energy metabolism was needed for active electrolyte transport mechanisms, in control RBCs 12% was required.     

Effect of experimental uremia upon the estrous cycle in rats

By daily vaginal smears, uremic rats showed significantly greater prevalence of irregular estrous cycles compared with sham-operated controls (p less than 0.02). There seems to be a correlation between the degree of renal failure and estrous cycle abnormalities. The lack of LH surge on the afternoon of proestrus, found in uremic animals, suggests a defect in the positive hypothalamic steroid feedback.     

Impaired phagocytic activity of human monocytes in respect to reduced antibacterial resistance in uremia.

Resistance to bacterial infection, particularly septicemia and pneumonia, is decreased in patients with uremia. Tests of monocyte function in 21 patients with chronic uremia and in 21 normal healthy subjects showed an increase in attachment rate, spreading activity and Nirtoblue-tetrazolium reduction in the uremic subjects. In contrast, phagocytosis of IgG-coated red cells was impaired.