Jose A.L. Arruda

Hyperkalemic Distal Renal Tubular Acidosis Associated with Obstructive Uropathy

We studied renal function in 13 patients with obstructive uropathy and hyperkalemic metabolic acidosis to characterize the pathogenesis of this disorder. Base-line fractional potassium excretion was lower in all patients than in controls with similar glomerular filtration rates. Acetazolamide was given to 11 patients but failed to increase fractional potassium excretion to normal. In five patients, impaired potassium excretion was associated with decreased ammonium excretion, a urinary pH below 5.5 (5.18 +/- 0.07, mean +/- S.E.M.), and aldosterone deficiency. In the remaining eight patients, the urinary pH did not fall below 5.5 (6.4 +/- 0.2) with acidosis, and we failed to lower the urinary pH and increase fractional potassium excretion to normal by administering a mineralocorticoid and sodium sulfate. A syndrome of hyperkalemic distal renal tubular acidosis may occur in patients with obstructive uropathy. In some patients, this syndrome results from a defect in hydrogen and potassium secretion in the distal nephron rather than from aldosterone deficiency. Obstructive uropathy should be included in the differential diagnosis of hyperkalemic acidosis and renal insufficiency.

Role of Nitric Oxide in Cocaine-Induced Acute Hypertension

Cocaine causes acute hypertension by blocking catecholamine reuptake. There is evidence that it also impairs the peripheral endothelial nitric oxide system, which is normally vasodilatory. We further explored the role of nitric oxide in cocaine-induced vasoconstriction in anesthetized rats, and in vitro by using isolated carotid artery segments. Cocaine administered intravenously in rats increased mean arterial pressure by 30 to 40 mm Hg within 1 min. This effect was dose dependent and the maximum effect was observed at a dose of 1.25 mg/kg. The prototype catecholamine norepinephrine induced a similar increase in blood pressure. When rats were pretreated with NG-monomethyl-L-arginine (L-NMMA, a blocker of nitric oxide) and challenged with cocaine, the increase in blood pressure was blocked by 80%, whereas pretreatment with L-NMMA did not block norepinephrine-induced vasoconstriction. Both cocaine and norepinephrine also induced an immediate vasoconstriction in isolated carotid artery preparations. The in vitro vasoconstriction induced by cocaine was blocked by pretreatment with L-NMMA, whereas L-NMMA did not block the norepinephrine-induced vasoconstriction in vitro. Furthermore, carotid artery stripped of endothelium responded to norepinephrine but failed to respond to L-NMMA or cocaine. S-nitroso-N-acetyl-D,L-penicillamine (SNAP)-a precursor of nitric oxide- stimulated nitric oxide production in control coronary artery fragments. When these fragments were incubated with cocaine there was a 20% reduction in the production of nitrite oxide. These results suggest that cocaine exerts its peripheral vasoconstriction at least in part by inhibiting local vasodilator nitric oxide.

Activated omentum becomes rich in factors that promote healing and tissue regeneration.

In order to study the mechanism by which an omental pedicle promotes healing when applied to an injured site, we injected a foreign body into the abdominal cavity to activate the omentum. One week after the injection, we isolated the omentum and measured blood vessel density, blood content, growth and angiogenesis factors (VEGF and others), chemotactic factors (SDF-1α), and progenitor cells (CXCR-4, WT-1). We found that the native omentum, which consisted mostly of adipose tissue, expanded the mass of its non-adipose part (milky spots) 15– to 20-fold. VEGF and other growth factors increased by two– to four-fold, blood vessel density by three-fold, and blood content by two-fold. The activated omentum also showed increases in SDF-1α, CXCR-4, and WT-1 cells (factors and cells positively associated with tissue regeneration). Thus, we propose that an omentum activated by a foreign body (or by injury) greatly expands its milky-spot tissue and becomes rich in growth factors and progenitor cells that facilitate the healing and regeneration of injured tissue.

Hyperkalemic hyperchloremic metabolic acidosis in sickle cell hemoglobinopathies

This report describes the occurrence of hyperkalemic hyperchloremic metabolic acidosis in six patients with sickle cell hemoglobinopathies. Three patients had sickle cell anemia, two had sickle cell trait and one had S-C disease. In all patients, decreased renal potassium excretion was demonstrated by the finding of a fractional potassium excretion lower than that of control subjects with comparable glomerular filtration rates. Two patterns of impaired urinary acidification were discerned. Four patients had a urinary pH above 5.5 in the presence of systemic acidosis and, thus, were classified a having distal renal tubular acidosis. The remaining two patients had very low rates of ammonium excretion despite intact capacity to lower urinary pH below 5.5 during systemic acidosis; this pattern was ascribed to selective aldosterone deficiency. Sickle cell hemoglobinopathies should be included in the differential diagnosis of hyperkalemic hyperchloremic metabolic acidosis.

Effect of Relaxin in Two Models of Renal Mass Reduction

Background: Relaxin (Rlx), a 6-kD protein hormone, belongs to the insulin growth factor family. We have previously shown that Rlx reduces interstitial fibrosis in a model of chronic papillary necrosis. Hypothesis: The purpose of this study was to extend these observations to a model of renal injury induced by mass reduction. Material and Methods: Renal mass was reduced by either infarction or surgical excision of both poles, with removal of the contralateral kidney. Two weeks later, creatinine clearance was done and animals from both groups implanted with osmotic pumps delivering either Rlx (2 µg/h) or vehicle (Veh). Treatment was continued for 4 weeks. The severity of the glomerular injury was quantified by planimetric measurements. Renal function was assessed by creatinine clearance and plasma creatinine. Results: Rlx significantly decreased systolic blood pressure in animals with infarction. This was accompanied by a decrease in serum creatinine and a slight improvement in creatinine clearance. The severity of the glomerular lesion was reduced by Rlx (sclerosis index, Veh 1.16 ± 0.13 vs. Rlx 0.74 ± 0.16, p = 0.037). In the excision group the animals were normotensive. In this group, Rlx treatment was accompanied by a decrease in serum creatinine (Veh 1.01 ± 0.03 vs. Rlx 0.81 ± 0.05 mg/dl, p = 0.02) and an increase in GFR (Veh 0.90 ± 0.14 vs. Rlx 1.33 ± 0.11 ml/min, p = 0.03). The sclerosis index was also reduced. Conclusion: Rlx decreases renal injury by at least two mechanisms, one by lowering blood pressure as seen in the infarction model, the other independent of blood pressure as seen in the normotensive excision model where there was also a significant functional improvement.

The pathogenesis of hyperchloremic metabolic acidosis associated with kidney transplantation

The mechanism of persistent hyperchloremic metabolic acidosis developing after kidney transplantation was investigated in six patients. In five patients in whom acidosis failed to lower the urine pH below 5.5, an infusion of sodium sulfate also failed to lower the urine pH. Neutral phosphate infusion failed to increase the urine minus blood (U-B) carbon dioxide tension (pCO2) difference normally in these patients. This abnormal response to both maneuvers indicates the presence of a tubular defect for distal hydrogen ion secretion. In the remaining patient, spontaneous acidosis lowered the urine pH below 5.5 and increased the U-B pCO2 normally with the administration of phosphate, demonstrating that this patients distal capacity for hydrogen secretion was intact. The plasma aldosterone level was low in this patient, and thus he had the acidification defect characteristic of aldosterone deficiency. Hyperkalemia developed in two patients; both were aldosterone-deficient, and they had a low fractional potassium excretion ion response to stimulation with sodium sulfate or acetazolamide. In all but one patient, who lost his kidney to accelerated rejection, chronic rejection developed. Homogeneous deposition of complement (C3) along the tubular basement membrane was found in three patients. Our data suggest that a secretory type of distal renal tubular acidosis can be an early sign of the immunologic process that leads to chronic rejection.

The Critical Importance of Urinary Concentrating Ability in the Generation of Urinary Carbon Dioxide Tension

Measurement of urine to blood (U-B) carbon dioxide tension (P(CO2)) gradient during alkalinization of the urine has been suggested to assess distal H(+) secretion. A fact that has not been considered in previous studies dealing with urinary P(CO2) is that dissolution of HCO(3) in water results in elevation of P(CO2) which is directly proportional to the HCO(3) concentration. To investigate the interrelationship of urinary HCO(3) and urinary acidification, we measured U-B P(CO2) in (a) the presence of enhanced H(+) secretion and decreased concentrating ability i.e., chronic renal failure (CRF), (b) animals with normal H(+) secretion and decreased concentrating ability, Brattleboro (BB) rats, and (c) the presence of both impaired H(+) secretion and concentrating ability (LiCl treatment and after release of unilateral ureteral obstruction). At moderately elevated plasma HCO(3) levels (30-40 meq/liter), normal rats achieved a highly alkaline urine (urine pH > 7.8) and raised urine HCO(3) concentration and U-B P(CO2). At similar plasma HCO(3) levels, BB rats had a much higher fractional water excretion and failed to raise urine pH, urine HCO(3) concentration, and U-B P(CO2) normally. At a very high plasma HCO(3) (>50 meq/liter), BB rats raised urine pH, urine HCO(3) concentration, and U-B P(CO2) to the same levels seen in normals. CRF rats failed to raise urine pH, urine HCO(3), and U-B P(CO2) normally at moderately elevated plasma HCO(3) levels; at very high plasma HCO(3) levels, CRF rats achieved a highly alkaline urine but failed to raise U-B P(CO2). Dogs and patients with CRF were also unable to raise urine pH, urine HCO(3) concentration, and U-B P(CO2) normally at moderately elevated plasma HCO(3) levels. In rats, dogs, and man, U-B P(CO2) was directly related to urine HCO(3) concentration and inversely related to fractional water excretion. At moderately elevated plasma HCO(3) levels, animals with a distal acidification defect failed to raise U-B P(CO2); increasing the plasma HCO(3) to very high levels resulted in a significant increase in urine HCO(3) concentration and U-B P(CO2). The observed urinary P(CO2) was very close to the P(CO2) which would be expected by simple dissolution of a comparable amount of HCO(3) in water. These data demonstrate that, in highly alkaline urine, urinary P(CO2) is largely determined by concentration of urinary HCO(3) and cannot be used as solely indicating distal H(+) secretion.

Stromal cells cultured from omentum express pluripotent markers, produce high amounts of VEGF, and engraft to injured sites

When rat omentum becomes activated by intraperitoneal injection of inert polydextran particles, these particles are rapidly surrounded by cells that express markers of adult stem cells (SDF–1α, CXCR4, WT–1) and of embryonic pluripotent cells (Oct–4, Nanog, SSEA–1). We have cultured such cells, because they may offer a convenient source of adult stem cells, and have found that they retain stem cell markers and produce high levels of vascular endothelial growth factor for up to ten passages. After systemic or local injection of these cultured cells into rats with acute injury of various organs, the cells specifically engraft at the injured sites. Thus, our experiments show that omental stromal cells can be cultured from activated omentum, and that these cells exhibit stem cell properties enabling them to be used for repair and possibly for the regeneration of damaged tissues.

Angiotensin II Stimulation of Renal Epithelial Cell Na/HCO3 Cotransport Activity: A Central Role for Src Family Kinase/Classic MAPK Pathway Coupling

Angiotensin II (AII) plays an important role in renal proximal tubular acidification via the costimulation of basolateral Na/HCO3 cotransporter (NBC) and apical Na/H exchanger (NHE) activities. These effects are mediated by specific G protein-coupled AII receptors, but their corresponding downstream effectors are incompletely defined. Src family tyrosine kinases (SFKs) contribute to the regulation of both transport activities by a variety of stimuli and are coupled to classic mitogen-activated protein kinase (MAPK) pathway activation in this cell type. We therefore examined these signaling intermediates for involvement in AII-stimulated NBC activity in cultured proximal tubule cells. Subpressor concentrations of AII (0.1 nM) increased NBC activity within minutes, and this effect was abrogated by selective antagonism of AT1 angiotensin receptors, SFKs, or the classic MAPK pathway. AII directly activated Src, as well as the proximal (Raf) and distal (ERK) elements of the classic MAPK module, and the activation of Src was prevented by AT1 receptor antagonism. An associated increase in basolateral membrane NBC1 content is compatible with the involvement of this proximal tubule isoform in these changes. We conclude that AII stimulation of the AT1 receptor increases NBC activity via sequential activation of SFKs and the classic MAPK pathway. Similar requirements for SFK/MAPK coupling in both cholinergic and acidotic costimulation of NBC and NHE activities suggest a central role for these effectors in the coordinated regulation of epithelial transport by diverse stimuli.

Hyperkalemia and Renal Insufficiency: Role of Selective Aldosterone Deficiency and Tubular Unresponsiveness to Aldosterone

Hyperkalemia usually does not develop in chronic renal insufficiency until the glomerular filtration rate is very low. We studied 25 hyperkalemic patients with glomerular filtration rate ranging between 105 and 10 ml/min. 16 patients were unable to raise plasma aldosterone in response to hyperkalemia whereas the remainder of the patients increased plasma aldosterone to normal levels. Plasma cortisol levels were normal in both groups: At any given level of glomerular filtration rate, fractional potassium excretion, during baseline conditions, was significantly lower in both groups of patients than in controls. During stimulation of potassium excretion by NaHCO3, acetazolamide or Na2SO4 administration fractional potassium excretion was also lower in patients than in controls. Hyperchloremic metabolic acidosis was recognized in all but 2 patients of each group. These data indicate that hyperkalemia in patients with renal insufficiency, can arise either as a consequence of aldosterone deficiency or tubular unresponsiveness to this hormone.