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Biomedical subjects

S Dabbagh

Publications and source records attributed to S Dabbagh.

At least 19 recordsLinked to original sources
PubMed1998

Prevalence of microalbuminuria in children with sickle cell disease.

Renal involvement is common in homozygous sickle cell disease (HbSS), including glomerular hypertension and hypertrophy similar to that seen in rodent models of ablative nephrectomy and stage I diabetic nephropathy (DN). The proteinuria in the rodent models is attenuated by angiotensin converting enzyme inhibition (ACEI). Microalbuminuria (MA) is a sensitive marker for renal involvement in DN prior to the development of proteinuria, and is also attenuated with ACEI. Elevated urinary microalbumin/creatinine ratios (U Alb/Cr) >20 mg/g Cr are reported in 39%-43% of adults with HbSS, and studies are ongoing in this age group to assess the effect of attenuated proteinuria by ACEI on long-term renal function. The purpose of this study was to prospectively investigate the prevalence of MA in children with HbSS and determine factors which affect its expression. U Alb/Cr values were measured on spot urine samples in 102 children (aged 2-18 years, mean 9.47+/-4.62, M:F=53:49) by rate nephelometry. Children with prior known proteinuria, hypertension, or fever/pain episode in the last 15 days were excluded. MA was present in 26.5% of all children with HbSS. However, in children between the ages of 10 and 18 years, the prevalence was 46% (similar to the prevalence in adults). There was a strong correlation between patient age and prevalence of MA (P<0.0001) by both univariate and multivariate analysis. However, pain frequency, hospitalization, transfusion program, ferritin levels, and Cr clearance (C(Cr)) did not correlate with prevalence, although C(Cr) (as estimated by Schwartz formula) was elevated in all. We conclude that the prevalence of MA in the 2nd decade of life is similar to that in adults.

Adolescent↗
PubMed1998

Renal osteodystrophy.

Secondary hyperparathyroidism develops in most patients with chronic renal failure, and is associated with the histologic finding of osteitis fibrosa cystica. The disease is characterized by growth failure and severe bone deformities in children, especially the very young. The pathogenesis of renal osteodystrophy is related to phosphate retention, and its effect on calcium and calcitriol metabolism, in addition to roles played by metabolic acidosis, cytokines, and degradation of parathyroid hormone. Treatment includes restriction of dietary phosphorous intake, phosphate binders, and use of active metabolites of vitamin D.

Acidosis↗
PubMed1994

Alterations in plasma phosphorus, red cell 2,3-diphosphoglycerate and P50 following open heart surgery.

OBJECTIVES: To evaluate changes in and the correlation between plasma phosphorus, red cell 2,3-diphosphoglycerate (DPG) and adenosine triphosphate (ATP), and P50 in children following heart surgery. EXPERIMENTAL DESIGN: Prospective, observational study with factorial design. SETTING: A pediatric intensive care unit in a university hospital. PATIENTS: Twenty children undergoing open heart surgery for congenital heart defects. INTERVENTIONS: None. MEASURES: Red cell 2,3-DPG and ATP, P50, plasma phosphorus, and arterial lactate were obtained before and at 1, 8, 16, 24, 48, and 72 hours after surgery. The amount of intravenous fluid and glucose administered, and age of blood utilized were documented. Variables were analyzed by repeated measure analysis of variance followed by paired t-tests. To investigate the relationship between variables at each time point, scatterplot matrices and correlation coefficients were obtained. RESULTS: There was a reduction in plasma phosphorus, red cell 2,3-DPG, and P50 and an increase in arterial lactate at 1, 8, 16, 24, 48, and 72 hours after surgery. Red cell 2,3-DPG correlated with P50 at 1, 8 and 16 hours. The decrease in the plasma phosphorus correlated with the amounts of intravenous fluid and glucose administered on the day of surgery and on the first and second postoperative days. The age of the blood utilized correlated with the decrease in red cell 2,3-DPG on the day of surgery. CONCLUSIONS: Reduction in red cell 2,3-DPG, P50, and plasma phosphorus occurs after open heart surgery in children. These changes can potentially contribute to impaired oxygen utilization in the postoperative period, when adequacy of tissue oxygenation is critical.

2,3-Diphosphoglycerate↗
PubMed1994

Application since 1980 of antihypertensive agents to treat pediatric disease.

Strategies for using antihypertensive agents have changed significantly since 1980. This paper reviews clinical studies devoted to the use of antihypertensive agents in children beyond the newborn period. The availability of converting enzyme inhibitors and calcium channel blockers has significantly improved BP control in children with secondary forms of hypertension. The role of antihypertensive agents to chronically treat primary hypertension in children remains unclear. Additionally, some treatment protocols used in adults that apply to the treatment of hypertensive children and that have been used in the treatment of nonhypertensive disease are discussed. Preliminary studies suggest that the rate of decline of renal function in some forms of progressive renal disease may be retarded by the use of converting enzyme inhibitors.

Antihypertensive Agents↗
PubMed1993

Acute changes in endothelin-1 after hemodialysis for chronic renal failure.

Endothelin is a recently described, potent renal vascular and systemic vasoconstrictor peptide. To evaluate the response of this peptide to volume contraction, we measured eight baseline and posthemodialysis samples from seven children, aged 14.5 +/- 3 years, with chronic renal failure. Plasma was extracted and endothelin-1 was measured by radioimmunoassay. Dialysis was performed for a 3- to 3 1/2-hour period, and body weight decreased from 38.0 +/- 14.3 to 36.2 +/- 13.8 kg (p < 0.01) during this time. There were no significant changes in heart rate or respiratory rate after dialysis, but blood pressure fell from 127/80 +/- 22/16 to 114/72 +/- 20/21 mm Hg (p = 0.05 for the systolic pressure). Plasma endothelin-1 concentration increased from 1.5 +/- 1.2 pg/ml at baseline to 7.3 +/- 8.9 pg/ml (p = 0.06) after dialysis; the fall in body weight from dialysis correlated with the increase in endothelin (r = -0.75; p = 0.05). Thus volume contraction from hemodialysis is associated with a rise in plasma endothelin-1, which is related to the acute change in body weight.

Adolescent↗
PubMed1991

Adaptation to taurine deprivation in the phosphate-depleted rat.

The nonessential amino acid taurine, which is inert in renal tissue, was used to study renal adaptation in the presence of phosphate (P) depletion in the rat. Weanling rats were placed on the control diet (0.7% P, normal taurine) for 4 wk, then fed one of the experimental diets or continued on the control diet for 1 wk. The diets used were 1) P+T- (0.7% P, low taurine), 2) P-T+ (0.1% P, normal taurine); and 3) P-T- (0.1% P, low taurine). Taurine deficiency was associated with avid tubular reabsorption of taurine, irrespective of P status. This was associated with a 4- to 5-fold increase in the Vmax of uptake (p less than 0.001). On the other hand, P depletion increased the Km of taurine uptake by 6.6- to 9.5-fold, suggesting a decrease in the affinity of the taurine symport (p less than 0.001). This was independent of the taurine status of the animals. Although there was no effect of diet on the urinary excretion of beta-alanine, P depletion, irrespective of taurine status, resulted in a 2-fold increase in the Km of beta-alanine uptake. We conclude that the taurinuria of P depletion is reversed in taurine deprivation. The adaptive response involves an increase in the Vmax of uptake. However, the increase in Km of taurine uptake observed in P depletion does not reverse with taurine depletion.

Adaptation, Physiological↗
PubMed1991

The effect of aggressive nutrition on infection rates in patients maintained on peritoneal dialysis.

Aggressive nutrition has been reported to improve growth parameters in children undergoing peritoneal dialysis. The current study reports the effect of a program of aggressive nutrition, started in 1/1988, on catheter-related infection rates in children undergoing chronic peritoneal dialysis. A combination of high calorie foods, supplements, "candy bar diets", and, when necessary, modular gastrostomy feedings, to provide 3-4 gm/kg/d and 100-120 kcal/kg/d was used. Peritonitis and catheter infection rates were assessed. A total of 37 pediatric patients underwent peritoneal dialysis from 1/1986-7/1990, with a total cumulative experience of 596 patient months. The peritonitis rate decreased from 1 episode/5.53 patient-month in 1987 to 1 episode per 46 patient-month in 1990. There was no significant effect on the catheter infections or the number of admissions/patient month. However, there was a 55% decline in the number of hospitalization days/patient month (p less than 0.01). The decrease in the peritonitis rate was independent of the modality of peritoneal dialysis or the usage of ultraviolet connecting devices. In 10 patients followed sequentially, the peritonitis rate was less (1 episode/23.5 patient months) after gastrostomy tube placement and feedings than before gastrostomy tube placement (1 episode/8.28 patient months) (p less than 0.01). There were no significant differences in serum albumin or total protein levels between the two observation periods. We conclude that adequate nutrition may play a role in decreasing the peritonitis rate in children maintained on peritoneal dialysis and speculate improved white cell function as a possible underlying mechanism.

Adolescent↗
PubMed1990

Perturbation of renal amino acid transport by brush border membrane vesicles in the vitamin D-deficient rat.

Vitamin D deficiency is characterized by secondary hyperparathyroidism, phosphaturia, bicarbonaturia, and generalized amino aciduria. While the site at which the phosphaturia ensues has been described to occur at the apical membrane of the renal proximal tubule, no studies are available for amino aciduria. Thus, weanling rats were fed five vitamin D-deficient diets for 4-6 weeks: (i) VLC, 0.02% Ca, 0.3% P; (ii) VLC + 1,25[OH]2D, same + 500 pmole ip for 2 days; (iii) LC, 0.45% Ca, 0.3% P; (iv) HC, 2.5% Ca, 0.3% P; and (v) VLP, 1.2% cA, 0.1% P. The normal diet contained 1.2% Ca, 0.7% P, and 2.5 micrograms% vitamin D. Amino acids, serum 25[OH]D, 1,25[OH]2D, and PTH, using a specific anti-rat PTH antibody, were measured. There were 4.65 +/- 1.1- and 10 +/- 1.39-fold increases in the urinary excretion of taurine and proline, respectively, irrespective of diet. Hypocalcemia, secondary hyperparathyroidism, and increased concentrations of urinary cAMP were demonstrated in all diets, except VLP. Taurinuria and prolinuria manifested at the renal brush border membrane. There was 21-25% and 26-39% attenuation in the peak of the overshoot of Na(+)-dependent uptake of taurine and proline, respectively, that was statistically significant as compared to that of normal diets (P less than 0.01). VLC resulted in a reduction in the Vmax of taurine (VLC, 78.26 +/- 6.88 vs normal, 115.4 +/- 6.26 pmole/mg protein/min, P less than 0.01) and proline (VLC, 402.06 +/- 31.26 vs normal, 589.49 +/- 37.42 pmole/mg protein/15 sec, P less than 0.01) uptake. Acute supplementation with pharmacological doses of 1,25[OH]2D normalized the Vmax of taurine and proline uptake, without affecting their renal excretion. The VLP diet induced and increase in the Km of taurine (VLP, 58.95 +/- 1.88 microM vs normal, 39.75 +/- 2.75 microM P less than 0.01) and proline (VLP, 116.75 +/- 8.87 microM vs normal, 76.82 +/- 7.27 microM P less than 0.01) uptake, without an associated perturbation in the Vmax of uptake. We conclude that the amino aciduria of vitamin D deficiency manifests at the apical membrane of the proximal tubule by an attenuation in the Na(+)-dependent uptake of amino acids. This is associated with a reduction in the initial rate of uptake or number of active transporters in the presence of secondary hyperparathyroidism and hypocalcemia, or a decrease in the affinity of the symport in the presence of P depletion. The data suggest the interplay of multiple factors in the causation of amino aciduria.

Amino Acids↗
PubMed1990

Aminoaciduria of phosphate depletion manifests at the renal brush border membrane.

Vitamin-D deficiency is associated with secondary hyperparathyroidism, hypophosphatemia, generalized aminoaciduria, phosphaturia and, late in its course, hypocalcemia. The tubulopathy has been attributed to the elevated levels of circulating parathyroid hormone. To further delineate the mechanisms responsible for aminoaciduria, vitamin-D deficiency and/or phosphate depletion were induced by placing weanling Sprague-Dawley rats on one of the following diets for 5 weeks: (1) control = 0.7% P, 5.5 micrograms % vitamin D; (2) D-P- = 0.1% P, 0 microgram % vitamin D; (3) D+P- = 0.1% P, 5.5 micrograms % vitamin D; (4) D-P+ = 0.3% P, 0 microgram % vitamin D, and (5) D-P++ = 0.7% P, 0 microgram % vitamin D. Short-term P depletion was produced in a group of animals fed D-P++ for 4 weeks, then fed D-P- for another week. To study the effects of acute supplementation with a pharmacological dose of calcitriol on the transport of amino acids by renal brush border membrane vesicles, the latter experimental group received 500 pmol of calcitriol (and is known as the SUPP group), or an equal amount of the vehicle (and is referred to as the ETH group). The uptake of taurine and proline by renal brush border membrane vesicles was blunted by 50 +/- 3 and 40 +/- 5%, respectively, at the peak of the overshoot, in all diets except D-P++. No changes were observed in vesicle size or Vmax.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1989

Cyclic AMP does not alter taurine accumulation by rat renal brush border membrane vesicles.

Secondary hyperparathyroidism has been attributed to be responsible for the generalized aminoaciduria and phosphaturia of vitamin D deficiency. Since PTH acts in the kidney to generate cAMP, we explored the possibility that its synthetic analog, dbcAMP, would alter the renal transport of taurine (an amino acid lost in the urine in vitamin D deficiency) and Pi. Exposure of renal BBMV prepared from normal and vitamin D-calcium-deficient rats to dbcAMP at concentrations ranging between 10(-4) and 10(-7) M did not alter taurine uptake by these vesicles. Higher dbcAMP concentrations blunted uptake, but these concentrations reduced intravesicular volume, thus representing an artifact of osmolarity. Preincubation of BBMV with dbcAMP for times between 0 and 60 min at 0 or 25 degrees C also did not alter taurine accumulation. Hypotonic lysis of BBMV, allowing entry of the cyclic nucleotide, followed by isotonic resealing did not influence taurine uptake. The addition of potassium fluoride (to inhibit phosphodiesterase activity) and ATP (as an energy source) did not alter taurine accumulation at 60 sec. The uptake of Pi, which is influenced by PTH, was decreased by 25% following exposure to dbcAMP on the internal surface of the vesicle. These data indicate that the taurinuria observed in vitamin D deficiency is unlikely to be related to a PTH-induced increase in intracellular cAMP, unlike the changes in Pi transport, which is sensitive to cyclic nucleotides.

Adenosine Triphosphate↗
PubMed1989

Aminoaciduria of vitamin D deficiency is independent of PTH levels and urinary cyclic AMP.

Aminoaciduria and secondary hyperparathyroidism accompany vitamin D deficiency. However, the degree of aminoaciduria and PTH elevation have not been studied relative to different calcium and phosphorus dietary intakes. Weanling rats were fed 5 vitamin D deficient diets for 4-6 weeks: very low Ca (VLC) 0.02% Ca, 0.3% P; VLC + 1,25-dihydroxyvitamin D [1,25(OH)2D3], same + 500 pmol i.p. for 2 days; low Ca (LC) 0.45% Ca, 0.3% P; very low P (VLP) 1.2% Ca, 0.1% P; high Ca (HC) 2.5% Ca, 0.3% P, and control 1.2% Ca, 0.70% P + 2.5 micrograms% vitamin D. Amino acids, serum 25-hydroxyvitamin D [25(OH)D3], 1,25(OH)2D3, and PTH, using a specific antirat PTH antibody, were measured. A significant generalized aminoaciduria (11 amino acids) was found in all vitamin D-deficient groups. Furthermore, it was independent of plasma Ca and PTH, and urinary cAMP excretion irrespective of diet. Serum 25(OH)D and 1,25(OH)2D were significantly reduced in all vitamin D-deficient groups. VLC and VLC + 1,25(OH)2D3 were associated with the highest PTH levels (10- and 13-fold increase, respectively) and urinary cAMP (2.3-fold increase in each) and the lowest serum Ca. LC rats had an 8.8- and a 1.7-fold increase in PTH and urinary cAMP, respectively. Phosphate depletion was found in VLP rats documented by insignificantly elevated PTH, normal urinary cAMP, hypercalciuria, and percent tubular reabsorption of phosphate of greater than 99%. While dietary Ca and P affect plasma and urinary Ca and P plasma PTH and urinary cAMP, it appears that dietary P affects the aminoaciduria observed in this study via mechanisms that remain unclear. The possibility that the mechanism for the tubulopathy is multifactorial should be entertained.

Amino Acids↗
PubMed1989

Effect of vitamin D deficiency on amino acid excretion in the phosphate-depleted rat.

Vitamin D deficiency is associated with a generalized aminoaciduria which has been shown to be independent of parathyroid hormone (PTH) and urinary cyclic AMP excretion. To further characterize the mechanism underlying the tubulopathy, weanling rats were placed on one of the following diets for 5 weeks: (1) control [0.7% phosphorus (P), 5.5 micrograms % vitamin D]; (2) D-P- (0.1% P, 0 vitamin D); (3) D+P- (0.1% P, 5.5 micrograms % vitamin D); (4) D-P+ (0.3% P, 0 vitamin D); (5) D-P++ (0.7% P, 0 vitamin D). All diets contained 1.2% calcium (Ca). A group of rats raised on D-P++ for 4 weeks were fed D-P- for 7 days after which they received 500 pmol of 1,25-dihydroxyvitamin D3 [1,25(OH)2D3; SUPP] or an equal volume of the vehicle (ETH). The above diets resulted in partial vitamin D depletion in that 1,25(OH)2D levels were 50.25-79 pg/ml in the presence of very low 25(OH)D concentrations. Augmentation in the urinary excretion of 6 out of 8 amino acids measured was observed in P depletion irrespective of vitamin D status. For the most part, acute supplementation with 1,25(OH)2D3 did not ameliorate the tubulopathy. Plasma PTH and Ca concentrations remained normal in all diets, except D+P-, where plasma Ca was 15.88 +/- 0.54 mg/dl. P depletion was associated with hypercalciuria, hypophosphatemia, avid reabsorption of P and growth retardation, irrespective of vitamin D status. Using taurine as a representative of the amino affected, there was a strong correlation between urinary taurine on the one hand and dietary P content (r = 0.613), plasma P (r = 0.399) and 1,25(OH)2D levels (r = -0.576) on the other. The present study suggests that the aminoaciduria of vitamin D deficiency is not related to elevated levels of PTH. A similar defect may be produced by P depletion, suggesting the possibility of a common pathway for the effect.

Amino Acids↗
PubMed1988

Development of beta-amino acid transport in the kidney.

This study focuses on the maturation of the renal beta-amino acid transport system and uses dietary manipulation as a probe. The epithelial surface of the renal proximal tubule is responsible for the conservation of ions and organic solutes including beta-amino acids. This beta-amino acid transport system is stimulated during periods of reduced dietary intake and permits increased excretion following dietary excess. We have examined transport of the sulfur-containing beta-amino acid, taurine, as a measure of this renal adaptive response to fluctuations in dietary sulfur amino acid intake and as a substrate for the beta-amino acid transport system. A precession of taurine uptake values by brush border membrane vesicles (BBMV) prepared from nursing rats from youngest to oldest was evident. However, these membranes demonstrate the full renal adaptive response to altered sulfur amino acid intake after the first week of life. This adaptive response is expressed at the brush border surface by transport changes in both directions ("up regulation" and "down regulation"), through changes in the initial rate (15 sec) of Na+-taurine cotransport. No alterations in the lipid microenvironment of the membrane, as detected by altered membrane fluidity, were uncovered. Although vesicles from 7-day-old pups demonstrate adaptation and accumulate taurine to a limited extent, the accumulation of Na+, which energizes uptake, may be altered, thereby preventing full expression of the adaptive response and of transport capacity at this age.

Amino Acids↗
PubMed1988

Good outcome in prune-belly syndrome despite associated severe anomalies.

A boy aged 4.5 years with prune-belly syndrome and associated urethral stenosis, oligohydramnios, imperforate anus and vesicosigmoid fistula is described. In contrast to the anticipated poor prognosis, vesicostomy and divided transverse colostomy performed after birth followed by prophylaxis of infection and bicarbonate supplementation have resulted in a good outcome. The vesicosigmoid fistula might have served in utero as a "natural diversion" protecting from pressure-induced renal damage. It is suggested that the main determinant of prognosis in PBS is the presence and degree of kidney dysplasia at birth as reflected by the neonatal renal function after performance of an indicated urinary diversion procedure rather than the presence of severe associated anomalies.

Anus, Imperforate↗
PubMed1987

Studies on renal adaptation to altered dietary amino acid intake: reduced renal cortex taurine content increases the Vmax of taurine uptake by brush border membrane vesicles.

Rats were placed on a normal taurine diet (NTD), low taurine diet (LTD) or a high taurine diet (HTD) for 14 days. beta-Alanine was fed to half of the animals in each group and resulted in a lowered renal cortex taurine content. Brush border membrane vesicle (BBMV) uptake of taurine was higher after beta-alanine feeding and was associated with an increase in Vmax of uptake. beta-Alanine feeding to HTD animals also altered the Km of uptake, possibly since the load of sulfur amino acids (6% of diet) was high. As a control, glycine (3%) feeding for 8 days along with each diet did not alter the plasma or renal cortex content; BBMV uptake as well as Km and Vmax of taurine accumulation were minimally altered. Accordingly, ingestion of a non-sulfur-containing alpha-amino acid did not change beta-amino acid transport. This study provides evidence that whole body taurine homeostasis is maintained in the presence of a taurine-depleting agent (beta-alanine feeding) by an increase in the number of Na(+)-taurine uptake sites.

Amino Acids↗
PubMed1987

Moderate hypocalcemia due to normal serum 1,25-dihydroxyvitamin D levels in an asymptomatic kindred with familial hypoparathyroidism.

Hypoparathyroidism was diagnosed in nine members of a kindred of three generations. This study investigated why these persons were asymptomatic and without developmental abnormalities, in contrast to the common presentation of idiopathic hypoparathyroidism. In the hypocalcemic subjects, serum calcium level was 7.4 +/- 0.8 mg/dl (mean +/- SD) and ionized serum calcium level was 3.48 +/- 0.21 mg/dl. Immunoreactive parathyroid hormone values were inappropriately low. Injection of EDTA in one patient lowered ionized calcium levels, but immunoreactive parathyroid hormone values did not rise. Serum levels of 1,25-dihydroxyvitamin D and other vitamin D metabolites were normal or elevated and substantially higher than in other hypoparathyroid states. The normally observed positive correlation between the fasting urinary calcium/creatinine ratio and serum 1,25-dihydroxyvitamin D that reflects the dependence of net bone resorption on 1,25-dihydroxyvitamin D was upheld in hypoparathyroid patients. It is proposed that the subjects with familial hypoparathyroidism in this kindred had moderate asymptomatic hypocalcemia without developmental abnormalities because normal or elevated serum 1,25-dihydroxyvitamin D levels enhanced intestinal calcium absorption. This may represent one point in the spectrum of idiopathic hypoparathyroidism. Alternately, both the moderate degree of hypocalcemia and the normal serum calcitriol values could have been related to mild, partial hypoparathyroidism, which could have been inherited in this kindred.

Calcium↗