Renal citrate metabolism and urinary citrate excretion in the infant rat

Renal citrate metabolism and urinary citrate excretion in the infant rat.BackgroundAlthough hypercalciuria has the same prevalence in children as adults, children rarely develop renal stones. This may be explained by a greater urinary citrate excretion in infants compared with adults. The present study examines the renal excretion of citrate and renal cortical citrate metabolism in infant and adult rats.MethodsAdult male and newly weaned infant rats were acclimated to metabolic cages and fed synthetic diets. Urine was collected after two days, and renal cortical citrate metabolism was assayed.ResultsInfant rats had a lower plasma [HCO3-] and higher plasma [K+] and had a fourfold higher urinary citrate:creatinine ratio and a twofold higher concentration of citrate in their urine compared with adult rats. This higher urinary citrate excretion was not due to a difference in renal proximal tubular Na/citrate cotransporter activity, nor renal cortical citrate synthase or ATP citrate lyase activities in infants as compared with adults. However, infant rat kidneys had significantly lower mitochondrial aconitase (m-aconitase) activity. Renal cortical citrate concentrations were comparable in infant and adult rats. Manipulation of plasma [K+] to adult levels did not affect the higher urinary citrate excretion in infant rats.ConclusionsUrinary citrate excretion in infant rats is greater than in adults but does not parallel tissue [citrate]. Thus, this higher urinary citrate is likely due to maturational differences in the proximal tubule, other than Na/citrate cotransport, that directly affect citrate transport

Renal citrate metabolism and urinary citrate excretion in the infant rat

Renal citrate metabolism and urinary citrate excretion in the infant rat.BackgroundAlthough hypercalciuria has the same prevalence in children as adults, children rarely develop renal stones. This may be explained by a greater urinary citrate excretion in infants compared with adults. The present study examines the renal excretion of citrate and renal cortical citrate metabolism in infant and adult rats.MethodsAdult male and newly weaned infant rats were acclimated to metabolic cages and fed synthetic diets. Urine was collected after two days, and renal cortical citrate metabolism was assayed.ResultsInfant rats had a lower plasma [HCO3-] and higher plasma [K+] and had a fourfold higher urinary citrate:creatinine ratio and a twofold higher concentration of citrate in their urine compared with adult rats. This higher urinary citrate excretion was not due to a difference in renal proximal tubular Na/citrate cotransporter activity, nor renal cortical citrate synthase or ATP citrate lyase activities in infants as compared with adults. However, infant rat kidneys had significantly lower mitochondrial aconitase (m-aconitase) activity. Renal cortical citrate concentrations were comparable in infant and adult rats. Manipulation of plasma [K+] to adult levels did not affect the higher urinary citrate excretion in infant rats.ConclusionsUrinary citrate excretion in infant rats is greater than in adults but does not parallel tissue [citrate]. Thus, this higher urinary citrate is likely due to maturational differences in the proximal tubule, other than Na/citrate cotransport, that directly affect citrate transport

Renal cortical mitochondrial aconitase is regulated in hypo- and hypercitraturia

Renal cortical mitochondrial aconitase is regulated in hypo- and hypercitraturia.BackgroundChronic metabolic acidosis and K+ deficiency increase, while alkali feeding decreases proximal tubule citrate absorption and metabolism. The present studies examined the regulation of mitochondrial aconitase (m-aconitase), the first step in mitochondrial citrate metabolism, in these conditions.MethodsRats were fed appropriate diets, and m-aconitase activity and protein abundance measured.ResultsIn chronic metabolic acidosis and chronic K+ deficiency, renal cortical m-aconitase activity was increased 17% and 43%, respectively. This was associated with respective 90% and 221% increases in renal cortical m-aconitase protein abundance. With chronic alkali feeding, there was a 12% decrease in renal cortical m-aconitase activity, associated with a 35% decrease in m-aconitase protein abundance. Hepatic m-aconitase activity was not regulated in a similar manner. There was no regulation of citrate synthase, the enzyme responsible for mitochondrial citrate synthesis.ConclusionsThese studies demonstrate tissue specific chronic regulation of renal cortical m-aconitase activity and protein abundance, which likely contributes to the hypocitraturia and hypercitraturia seen in these conditions. As m-aconitase is the only step in citrate transport and metabolism found to be regulated in alkali feeding, its regulation likely plays a significant role in mediating the hypercitraturia seen in this condition

Acid regulation of NaDC-1 requires a functional endothelin B receptor

Metabolically generated acid is the major physiological stimulus for increasing proximal tubule citrate reabsorption, which leads to a decrease in citrate excretion. The activity of the Na-citrate cotransporter, NaDC-1, is increased in vivo by acid ingestion and in vitro by an acidic pH medium. In opossum kidney cells the acid stimulatory effect and the ability of endothelin-1 (ET-1) to stimulate NaDC-1 activity are both blocked by the endothelin B (ETB) receptor antagonist, BQ788. Acid feeding had no effect on brush border membrane NaDC-1 activity in mice in which ETB receptor expression was knocked out, whereas a stimulatory effect was found in wild-type mice. Using ETA/ETB chimeric and ETB C-terminal tail truncated constructs, ET-1 stimulation of NaDC-1 required a receptor C-terminal tail from either ETA or ETB. The ET-1 effect was greatest when either the ETB transmembrane domain and C-terminal tail were present or the ETB C-terminal tail was linked to the ETA transmembrane domain. This effect was smaller when the ETB transmembrane domain was linked to the ETA C-terminal tail. Thus, the acid-activated pathway mediating stimulation of NaDC-1 activity requires a functional ETB receptor in vivo and in vitro, as does acid stimulation of NHE3 activity. Since increased NaDC-1 and NHE3 activities constitute part of the proximal tubule adaptation to an acid load, these studies indicate that there are similarities in the signaling pathway mediating these responses

Nepafenac 0.3% after Cataract Surgery in Patients with Diabetic Retinopathy: Results of 2 Randomized Phase 3 Studies

Purpose To demonstrate the efficacy and safety of once-daily nepafenac 0.3% ophthalmic suspension versus vehicle, based on clinical outcomes, after cataract surgery in patients with diabetes. Design Two prospective, randomized, multicenter, double-masked, vehicle-controlled phase 3 studies. Participants Total, 615 patients in study 1 and 605 patients in study 2. Methods Patients were randomized (1:1) to topical nepafenac 0.3% or vehicle once-daily starting the day before surgery and continuing for 90 days thereafter. Main Outcome Measures Key efficacy variables were: patients (%) in whom macular edema (ME) developed (≥30% increase from preoperative baseline central subfield macular thickness) within 90 days after cataract surgery and the patients (%) with a best-corrected visual acuity (BCVA) improvement of ≥15 letters from preoperative baseline through day 14 maintained through day 90. Secondary end points included: patients (%) with a BCVA improvement of ≥15 letters from preoperative baseline through days 90 and 60 and safety over 3 months. Results A significantly lower percentage of patients demonstrated ME within 90 days after surgery with nepafenac 0.3% versus vehicle (study 1: 2.3% vs. 17.3%; P P = 0.001; pooled: 4.1% vs. 15.9%; P P P = 0.671) in study 2, and 55.4% versus 46.7% ( P = 0.003) in the pooled analysis. A greater percentage of patients treated with nepafenac 0.3% versus vehicle in study 1 and similar percentage in study 2 had a BCVA improvement of ≥15 letters from preoperative baseline through day 90 (77.2% vs. 67.7% [ P = 0.009] and 65.4% vs. 65.9% [ P = 0.888]) and through day 60 (76.2% vs. 64.7% [ P = 0.002] and 68.9% vs. 62.1% [ P = 0.092]). No unanticipated adverse events were observed. Conclusions These studies demonstrated the clinical benefits of nepafenac 0.3% over vehicle in reducing the risk of postoperative ME, with the integrated analysis showing improved BCVA after cataract surgery in patients with diabetic retinopathy, with no unanticipated safety events

Effect of phenylephrine on static and dynamic accommodation.

PURPOSE: We tested the hypothesis that changes in accommodation after instillation of Phenylephrine Hydrochloride (PHCl) observed in some studies could be caused by changes in optics. METHODS: We performed two experiments to test the effects of PHCl on static and on dynamic accommodation in 8 and 6 subjects, respectively. Objective wavefront measurements were recorded of the static accommodation response to a stimulus at different distances or dynamic accommodation response to a sinusoidally moving stimulus (between 1 and 3 D of accommodative demand at 0.2Hz). The responses were characterized using two methods: one that takes into account the mydriatic optical effects on the accommodation produced by higher-order aberrations of the eye and another that takes into account only power changes paraxially due to the action of the ciliary muscle and regardless of the pupil size. RESULTS: When mydriatic optical effects were taken into account, differences in responses before and after PHCl instillation were 0.51±0.53 D, and 0.12±0.15, for static and dynamic accommodation, respectively, and were statistically significant (p0.313). CONCLUSIONS: The mydriatic effect of the PHCl causes optical changes in the eye that can reduce the objective and subjective measurement of accommodation