Albert Quan

Prenatal Dexamethasone Programs Hypertension and Renal Injury in the Rat

Abstract—Dexamethasone is frequently administered to the developing fetus to accelerate pulmonary development. The purpose of the present study was to determine if prenatal dexamethasone programmed a progressive increase in blood pressure and renal injury in rats. Pregnant rats were given either vehicle or 2 daily intraperitoneal injections of dexamethasone (0.2 mg/kg body weight) on gestational days 11 and 12, 13 and 14, 15 and 16, 17 and 18, or 19 and 20. Offspring of rats administered dexamethasone on days 15 and 16 gestation had a 20% reduction in glomerular number compared with control at 6 to 9 months of age (22 527±509 versus 28 050±561, P <0.05), which was comparable to the percent reduction in glomeruli measured at 3 weeks of age. Six- to 9-month old rats receiving prenatal dexamethasone on days 17 and 18 of gestation had a 17% reduction in glomeruli (23 380±587) compared with control rats (P <0.05). Male rats that received prenatal dexamethasone on days 15 and 16, 17 and 18, and 13 and 14 of gestation had elevated blood pressures at 6 months of age; the latter group did not have a reduction in glomerular number. Adult rats given dexamethasone on days 15 and 16 of gestation had more glomeruli with glomerulosclerosis than control rats. This study shows that prenatal dexamethasone in rats results in a reduction in glomerular number, glomerulosclerosis, and hypertension when administered at specific points during gestation. Hypertension was observed in animals that had a reduction in glomeruli as well as in a group that did not have a reduction in glomerular number, suggesting that a reduction in glomerular number is not the sole cause for the development of hypertension.

Endogenous production of angiotensin II modulates rat proximal tubule transport.

There is evidence that angiotensin II is synthesized by the proximal tubule and secreted into the tubular lumen. This study examined the functional significance of endogenously produced angiotensin II on proximal tubule transport in male Sprague-Dawley rats. Addition of 10(-11), 10(-8), and 10(-6) M angiotensin II to the lumen of proximal convoluted tubules perfused in vivo had no effect on the rate of fluid reabsorption. The absence of an effect of exogenous luminal angiotensin II could be due to its endogenous production and luminal secretion. Luminal 10(-8) M Dup 753 (an angiotensin II receptor antagonist) resulted in a 35% decrease in proximal tubule fluid reabsorption when compared to control (Jv = 1.64 +/- 0.12 nl/mm.min vs. 2.55 +/- 0.32 nl/mm.min, P < 0.05). Similarly, luminal 10(-4) M enalaprilat, an angiotensin converting enzyme inhibitor, decreased fluid reabsorption by 40% (Jv = 1.53 +/- 0.23 nl/mm.min vs. 2.55 +/- 0.32 nl/mm.min, P < 0.05). When 10(-11) or 10(-8) M exogenous angiotensin II was added to enalaprilat (10(-4) M) in the luminal perfusate, fluid reabsorption returned to its baseline rate (Jv = 2.78 +/- 0.35 nl/mm.min). Thus, addition of exogenous angiotensin II stimulates proximal tubule transport when endogenous production is inhibited. These experiments show that endogenously produced angiotensin II modulates fluid transport in the proximal tubule independent of systemic angiotensin II.

Protein losses in children on continuous cycler peritoneal dialysis.

Abstract. Peritoneal dialysis can result in significant protein losses through the dialysate effluent. Although protein loss in chronic ambulatory peritoneal dialysis has been examined, it has not been extensively studied in patients on continuous cycler peritoneal dialysis. Such losses can contribute to protein calorie malnutrition, especially in infants and children, many of whom are on continuous cycler peritoneal dialysis. We measured protein loss during continuous cycler peritoneal dialysis in patients ranging in age from 2 months to 18 years. There was an inverse correlation between body surface area and peritoneal protein loss, expressed both as milligrams of protein per kilogram body weight per day (P<0.000l) and as milligrams of protein per meter square body surface area per day (P<0.05). Peritoneal fluid protein losses in patients greater than 50 kg were similiar to those previously reported in adults treated with chronic ambulatory peritoneal dialysis. In contrast, infants had nearly twofold greater peritoneal protein losses per meter square body surface area than older children weighing more than 50 kg. Such protein losses in infants impair normal growth and may contribute to permanent loss of growth potential. Infants on peritoneal dialysis require early and aggressive nutritional supplementation with higher caloric and protein intake to compensate for such dialysate protein losses and maximize growth.

Effect of luminal angiotensin II on rabbit proximal convoluted tubule bicarbonate absorption

The present in vitro microperfusion study examined the effect of luminal angiotensin II on proximal convoluted tubule (PCT) volume absorption and bicarbonate transport. Neither 10(-11) M, 10(-10) M, nor 2 x 10(-8) M luminal angiotensin II significantly affected PCT transport. When tubules were first perfused with enalaprilat to inhibit endogenous angiotensin II production, addition of 10(-10) M luminal angiotensin II increased volume absorption (0.72 +/- 0.08 vs. 0.86 +/- 0.07 nl x mm(-1) xmin(-1), P < 0.01) and bicarbonate transport (52.3 +/- 3.7 vs. 67.9 +/- 4.2 pmol x mm(-1) min(-1), P < 0.01). Addition of 10(-6) M losartan, an AT1 inhibitor, to the luminal perfusate inhibited volume absorption (0.95 +/- 0.14 vs. 0.72 +/- 0.11 nl x mm(-1) x min(-1), P < 0.05) and bicarbonate transport (65.0 +/- 7.3 vs. 54.7 +/- 9.2 pmol x mm(-1) x min(-1), P < 0.05). Addition of 10(-4) M luminal PD-123319, an AT2 inhibitor, was without effect. In tubules perfused with 10(-4) M luminal enalaprilat and 10(-4) M luminal PD-123319, addition of 10(-10) M luminal angiotensin II in the experimental period resulted in a stimulation in volume absorption (0.61 +/- 0.08 vs. 0.81 +/- 0.10 nl x mm(-1) x min(-1), P < 0.01) and bicarbonate transport (49.9 +/- 6.3 vs. 77.4 +/- 14.3 pmol x mm(-1) x min(-1), P < 0.01). In tubules perfused with 10(-6) M losartan and 10(-4) M enalaprilat, addition of luminal 10(-10) M angiotensin II resulted in no change in transport. These data are consistent with endogenous angiotensin II affecting PCT bicarbonate transport in vitro via luminal AT1 receptors.The present in vitro microperfusion study examined the effect of luminal angiotensin II on proximal convoluted tubule (PCT) volume absorption and bicarbonate transport. Neither 10-11 M, 10-10 M, nor 2 × 10-8 M luminal angiotensin II significantly affected PCT transport. When tubules were first perfused with enalaprilat to inhibit endogenous angiotensin II production, addition of 10-10 M luminal angiotensin II increased volume absorption (0.72 ± 0.08 vs. 0.86 ± 0.07 nl ⋅ mm-1 ⋅ min-1, P < 0.01) and bicarbonate transport (52.3 ± 3.7 vs. 67.9 ± 4.2 pmol ⋅ mm-1 ⋅ min-1, P < 0.01). Addition of 10-6 M losartan, an AT1 inhibitor, to the luminal perfusate inhibited volume absorption (0.95 ± 0.14 vs. 0.72 ± 0.11 nl ⋅ mm-1 ⋅ min-1, P < 0.05) and bicarbonate transport (65.0 ± 7.3 vs. 54.7 ± 9.2 pmol ⋅ mm-1 ⋅ min-1, P < 0.05). Addition of 10-4 M luminal PD-123319, an AT2 inhibitor, was without effect. In tubules perfused with 10-4 M luminal enalaprilat and 10-4 M luminal PD-123319, addition of 10-10M luminal angiotensin II in the experimental period resulted in a stimulation in volume absorption (0.61 ± 0.08 vs. 0.81 ± 0.10 nl ⋅ mm-1 ⋅ min-1, P < 0.01) and bicarbonate transport (49.9 ± 6.3 vs. 77.4 ± 14.3 pmol ⋅ mm-1 ⋅ min-1, P < 0.01). In tubules perfused with 10-6 M losartan and 10-4 M enalaprilat, addition of luminal 10-10 M angiotensin II resulted in no change in transport. These data are consistent with endogenous angiotensin II affecting PCT bicarbonate transport in vitro via luminal AT1receptors.

Predictive Value of Quantitative PCR-Based Viral Burden Analysis for Eight Human Herpesviruses in Pediatric Solid Organ Transplant Patients

Human herpesviruses can cause significant morbidity and mortality in pediatric solid organ transplant recipients. It was hypothesized that viral burden quantification by polymerase chain reaction using an internal calibration standard could aid in distinguishing between viral disease and latency. Here we report the results of a 2-year prospective study of 27 pediatric solid organ (liver, kidney, or heart) transplant recipients in which multiple samples were analyzed for levels of all eight human herpesviruses by internal calibration standard-polymerase chain reaction. Herpes simplex viruses 1 and 2, varicella-zoster virus, and Kaposis sarcoma-associated herpesvirus were not detected in any of these samples. Human herpesvirus types 6 and 7 were detected in half of the patients, but were present at low levels, similar to those found in reference populations. Epstein-Barr virus (EBV) and cytomegalovirus (CMV) were detected in 89% and 56% of the patients, respectively. Viral burden analysis suggested distinct patient populations for CMV, with a natural cutoff of 10,000 viral targets/ml blood strongly associated with disease. In some cases, a dramatic increase in CMV levels preceded clinical evidence of disease by several weeks. EBV viral burden was relatively high in the only patient presenting with an EBV syndrome. However, two other patients without evidence of EBV disease had single samples with high EBV burden. Rapid reduction in both EBV and CMV burden occurred with antiviral treatment. These data suggest that viral burden analysis using internal calibration standard-polymerase chain reaction for CMV, and possibly other herpesviruses, is an effective method for monitoring pediatric transplant patients for significant herpesvirus infection and response to therapy.

Endogenous angiotensin II modulates rat proximal tubule transport with acute changes in extracellular volume

In the present study, we examined whether the effect of endogenously produced angiotensin II on proximal tubule transport in the male Sprague-Dawley rat is regulated by acute changes in extracellular volume. We measured the magnitude of endogenous angiotensin II-mediated stimulation of transport by sequentially perfusing proximal tubules in vivo, first with an ultrafiltrate-like solution, then by reperfusion of the same tubule with an ultrafiltrate-like solution containing 10(-8) M losartan (angiotensin II receptor antagonist). During volume contraction, 10(-8) M losartan decreased volume reabsorption from 4.20 +/- 0.50 to 1.70 +/- 0.30 nl . mm-1 . min-1 (P < 0.05), a decrease of 58.0 +/- 7.0%. In contrast, after acute volume expansion, 10(-8) M losartan decreased volume reabsorption from 1.84 +/- 0.20 to 1.31 +/- 0.20 nl . mm-1 . min-1 (P < 0.05), a decrease of 29.6 +/- 9.0%. In hydropenic rats, addition of exogenous luminal angiotensin II had no effect on transport. However, in volume-expanded rats, addition of 10(-8) M angiotensin II increased volume reabsorption from 2.10 +/- 0.34 to 4. 38 +/- 0.59 nl . mm-1 . min-1 (P < 0.005). These data are consistent with endogenously produced angiotensin II augmenting proximal tubule transport to a greater degree during volume contraction than after volume expansion.In the present study, we examined whether the effect of endogenously produced angiotensin II on proximal tubule transport in the male Sprague-Dawley rat is regulated by acute changes in extracellular volume. We measured the magnitude of endogenous angiotensin II-mediated stimulation of transport by sequentially perfusing proximal tubules in vivo, first with an ultrafiltrate-like solution, then by reperfusion of the same tubule with an ultrafiltrate-like solution containing 10-8 M losartan (angiotensin II receptor antagonist). During volume contraction, 10-8 M losartan decreased volume reabsorption from 4.20 ± 0.50 to 1.70 ± 0.30 nl ⋅ mm-1 ⋅ min-1( P < 0.05), a decrease of 58.0 ± 7.0%. In contrast, after acute volume expansion, 10-8 M losartan decreased volume reabsorption from 1.84 ± 0.20 to 1.31 ± 0.20 nl ⋅ mm-1 ⋅ min-1( P < 0.05), a decrease of 29.6 ± 9.0%. In hydropenic rats, addition of exogenous luminal angiotensin II had no effect on transport. However, in volume-expanded rats, addition of 10-8 M angiotensin II increased volume reabsorption from 2.10 ± 0.34 to 4.38 ± 0.59 nl ⋅ mm-1 ⋅ min-1( P < 0.005). These data are consistent with endogenously produced angiotensin II augmenting proximal tubule transport to a greater degree during volume contraction than after volume expansion.

Fetal origins of cardiovascular disease

Several epidemiologic studies have shown that intrauterine growth retardation is a risk factor for the development of cardiovascular disease in later life. In this review, we discuss these epidemiologic studies and animal models that have been developed to investigate the pathophysiology of this phenomenon. We discuss data suggesting that intrauterine growth retardation leads to fetal exposure to maternal glucocorticoids. In addition, we present other data showing that fetal exposure of glucocorticoids during specific times of fetal development results in focal and segmental glomerulosclerosis, a reduced number of nephrons, hypertension, and diabetes. These studies suggest that at critical times during fetal development fetal injury programs the development of cardiovascular disease and diabetes in later life.

Effect of luminal angiotensin II receptor antagonists on proximal tubule transport.

The proximal tubule can endogenously synthesize and secrete luminal angiotensin II at a concentration approximately 100- to 1000-fold higher than that in the systemic circulation. We have recently shown that this endogenously produced and luminally secreted angiotensin II regulates proximal tubule volume reabsorption, which is a reflection of sodium transport within this segment. In this study, we use in vivo microperfusion of angiotensin II receptor antagonists into the lumen of the proximal tubule to examine the role of the luminal AT1 and AT2 receptor in the regulation of volume reabsorption. Systemically administered (intravenous) AT1 and AT2 receptor antagonists, acting through basolateral angiotensin II receptors, have previously been shown to inhibit proximal tubule transport. Luminal perfusion of 10(-6) mol/L Dup 753 (AT1 antagonist) and 10(-6) mol/L PD 123319 (AT2 antagonist) decreased proximal tubule volume reabsorption from 2.94 +/- 0.18 to 1.65 +/- 0.18 and 1.64 +/- 0.19 nL/mm x min, respectively, P < .01. Luminal perfusion of 10(-4) mol/L CGP 42112A, another AT2 antagonist, similarly decreased volume reabsorption to 1.32 +/- 0.36 nL/nm x min, P < .01. The inhibition of transport with AT1 and AT2 antagonist was additive, as luminal perfusion of 10(-6) mol/L Dup 753 plus 10(-6) mol/L 123319 resulted in a decrease in volume reabsorption to 0.41 +/- 0.31 nL/mm x min, P < .001 v control, P < .05 v Dup 753, and P < .01 v PD 123319. These results show that endogenously produced angiotensin II regulates proximal tubule volume transport via both luminal AT1 and AT2 receptors.

Renal Tubular Acidosis and Deafness: Report of a Large Family

The syndrome of distal renal tubular acidosis (dRTA) and sensorineural deafness has been reported in consanguineous families and is believed to be inherited in an autosomal recessive pattern. All affected patients also have nephrocalcinosis. We report here a family with 6 of 12 children affected with this syndrome. The parents are unaffected and are not blood related. This is the largest family described to date with distal renal tubular acidosis and sensorineural deafness.

Late onset seizures, hemiparesis and blindness in hemolytic uremic syndrome.

Neurologic complications of hemolytic uremic syndrome, including seizures, usually occur early during the acute phase of the illness. We report a3-year-old girl with classic diarrhea-associated hemolytic uremic syndrome who developed late onset seizures, hemiparesis and transient blindness on the 17th hospital day, at which time her recovery was characterized by improvement in her blood pressure, serum electrolytes, renal function, hematocrit and platelet count. A CT and MR revealed brainstem and posterior parietal and occipital infarct/edema. The association of these radiologic findings within the posterior distribution along with visual loss and seizures are unique to posterior reversible encephalopathy syndrome. Within 7 days, she regained motor function and vision and had no further seizure activity. At 6 months follow-up, physical examination revealed normal motor function and vision and a repeat MR showed near resolution of the previous findings with minimal occipital lobe gliosis. This case report describes the uncommon finding of late onset seizures occurring during the recovery phase of hemolytic uremic syndrome with MR findings consistent with posterior reversible encephalopathy syndrome.