Circadian rhythm of urinary pH in man with and without chronic antacid administration

Evaluation of urinary acidification in children: Clinical utility

The kidney plays a fundamental role in acid-base homeostasis by reabsorbing the filtered bicarbonate and by generating new bicarbonate, to replace that consumed in the buffering of non-volatile acids, a process that leads to the acidification of urine and the excretion of ammonium (NH₄ ⁺). Therefore, urine pH (UpH) and urinary NH₄ ⁺ (UNH₄ ⁺) are valuable parameters to assess urinary acidification. The adaptation of automated plasma NH₄ ⁺ quantification methods to measure UNH₄ ⁺ has proven to be an accurate and feasible technique, with diverse potential indications in clinical practice. Recently, reference values for spot urine NH₄ ⁺/creatinine ratio in children have been published. UpH and UNH₄ ⁺, aside from their classical application in the study of metabolic acidosis, have shown to be useful in the identification of incomplete distal renal tubular acidosis (dRTA), an acidification disorder, without overt metabolic acidosis, extensively described in adults, and barely known in children, in whom it has been found to be associated to hypocitraturia, congenital kidney abnormalities and growth impairment. In addition, a low UNH₄ ⁺ in chronic kidney disease (CKD) is a risk factor for glomerular filtration decay and mortality in adults, even in the absence of overt metabolic acidosis. We here emphasize on the need of measuring UpH and UNH₄ ⁺ in pediatric population, establishing reference values, as well as exploring their application in metabolic acidosis, CKD and disorders associated with incomplete dRTA, including growth retardation of unknown cause.

Dipstick Spot urine pH does not accurately represent 24 hour urine PH measured by an electrode

Objectives

To determine whether spot urine pH measured by dipstick is an accurate representation of 24 hours urine pH measured by an electrode.

Materials and Methods

We retrospectively reviewed urine pH results of patients who presented to the urology stone clinic. For each patient we recorded the most recent pH result measured by dipstick from a spot urine sample that preceded the result of a 24-hour urine pH measured by the use of a pH electrode. Patients were excluded if there was a change in medications or dietary recommendations or if the two samples were more than 4 months apart. A difference of more than 0.5 pH was considered an inaccurate result.

Results

A total 600 patients were retrospectively reviewed for the pH results. The mean difference in pH between spot urine value and the 24 hours collection values was 0.52±0.45 pH. Higher pH was associated with lower accuracy (p<0.001). The accuracy of spot urine samples to predict 24-hour pH values of <5.5 was 68.9%, 68.2% for 5.5 to 6.5 and 35% for >6.5. Samples taken more than 75 days apart had only 49% the accuracy of more recent samples (p<0.002). The overall accuracy is lower than 80% (p<0.001). Influence of diurnal variation was not significant (p=0.588).

Conclusions

Spot urine pH by dipstick is not an accurate method for evaluation of the patients with urolithiasis. Patients with alkaline urine are more prone to error with reliance on spot urine pH.

Aluminum Homeostasis in Man

Aluminum is the most prevalent metal found in nature and represents the third most abundant element of the earth's crust. In light of man's wide exposure to aluminum compounds, a review of the literature was undertaken to determine the extent of the available literature concerning the absorption, distribution, excretion, and metabolism of aluminum in man. In relative terms, the gastrointestinal tract is the major portal of entry for aluminum. The lungs play only a minor role, and there is no evidence to suggest that the dermal absorption of aluminum occurs. The gastrointestinal tract is only very slightly permeable to aluminum and provides a relatively effective barrier to its absorption. In the blood, aluminum is primarily bound to serum proteins (80%); however, a sufficient concentration of dialyziable or “free” (20%) aluminum exists to provide for its distribution. Aluminum can be found in every tissue and a normal body content of aluminum for reference man can now be calculated at 0.295 g. Present data suggest that bone may offer a major site of aluminum deposition. Urine provides at least one mechanism of aluminum excretion. However, aluminum's low renal clearance rate (2 ml/min) clearly suggests that other more efficient mechanisms for excretion exist. In fact, preliminary data indicate that bile may play some as yet undefined role in the removal process. The lack of a biologically convenient radiolabeled form of aluminum has severely handicapped the elucidation of aluminum metabolism. The chemical form of aluminum in blood, urine, or the tissues remains unknown. The liver is believed to play some role in aluminum metabolism, but no direct proof of this is available at present.

The diurnal variation in urine acidification differs between normal individuals and uric acid stone formers

Many biologic functions follow circadian rhythms driven by internal and external cues that synchronize and coordinate organ physiology to diurnal changes in the environment and behavior. Urinary acid-base parameters follow diurnal patterns and it is thought these changes are due to periodic surges in gastric acid secretion. Abnormal urine pH is a risk factor for specific types of nephrolithiasis and uric acid stones are typical of excessively low urine pH. Here we placed 9 healthy volunteers and 10 uric acid stone formers on fixed metabolic diets to study the diurnal pattern of urinary acidification. All showed clear diurnal trends in urinary acidification but none of the patterns were affected by inhibitors of the gastric proton pump. Uric acid stone formers had similar patterns of change through the day but their urine pH was always lower compared to healthy volunteers. Uric acid stone formers excreted more acid (normalized to acid ingestion) with the excess excreted primarily as titratable acid rather than ammonium. Urine base excretion was also lower in uric acid stone formers (normalized to base ingestion) along with lower plasma bicarbonate concentrations during part of the day. Thus, increased net acid presentation to the kidney and the preferential use of buffers, other than ammonium, result in much higher concentrations of un-dissociated uric acid throughout the day and consequently an increased risk of uric acid stones.

Novel insights into the pathogenesis of uric acid nephrolithiasis

PURPOSE OF REVIEW

The factors involved in the pathogenesis of uric acid nephrolithiasis are well known. A low urinary pH is the most significant element in the generation of stones, with hyperuricosuria being a less common finding. The underlying mechanism(s) responsible for these disturbances remain poorly characterized. This review summarizes previous knowledge and highlights some recent developments in the pathophysiology of low urine pH and hyperuricosuria.

RECENT FINDINGS

Epidemiological and metabolic studies have indicated an association between uric acid nephrolithiasis and insulin resistance. Some potential mechanisms include impaired ammoniagenesis caused by resistance to insulin action in the renal proximal tubule, or substrate competition by free fatty acids. The evaluation of a large Sicilian kindred recently revealed a putative genetic locus linked to uric acid stone disease. The identification of novel complementary DNA has provided an interesting insight into the renal handling of uric acid, including one genetic cause of renal uric acid wasting.

SUMMARY

The recognition of metabolic, molecular, and genetic factors that influence urinary pH, and uric acid metabolism and excretion, will provide novel insights into the pathogenesis of uric acid stones, and open the way for new therapeutic strategies.

Circadian changes in urinary bicarbonate, nitric oxide metabolites and pH in female player during handball camp involved in an exercise, rest and sleep cycle

Bicarbonate and nitric oxide levels are important humoral factors in the blood and are affected by the human body's physical condition. There are few reports, however, on changes in blood bicarbonate and nitric oxide levels during exercise and rest. Since urinary bicarbonate and nitric oxide metabolites reflect the levels of bicarbonate and nitric oxide in the blood, we studied circadian changes in 6 female athletes by monitoring their urinary pH and their levels of urinary bicarbonate and nitric oxide metabolites. Measurements were taken during exercise, rest and sleep. Six female athletes participated in a 3-day team handball training camp where they followed a schedule of exercise, rest and sleep. Urinary samples were collected immediately before and after handball training, at bed-time and upon waking. The urinary pH and levels of urinary bicarbonate and nitric oxide metabolites, including nitrite and nitrate, were examined with a blood gas analyzer and a NOx analyzer. The samples collected after handball training, as compared to the samples taken before exercise, showed a decreased pH, a decrease in levels of bicarbonate and little change in NO metabolites. During rest, urinary bicarbonate, NO metabolites and pH increased markedly in all 6 subjects. The levels of urinary bicarbonate, NO metabolites and pH significantly decreased upon waking. This study took into account the subjects' various physiological conditions when considering the significance of their changes in urinary bicarbonate, NO metabolites and pH during the 3 day handball training program. There were significant circadian changes in the urinary pH, and in the levels of urinary bicarbonate and nitric oxide metabolites, in the athletes involved in the exercise, rest and sleep program at team handball camp.

Adverse reactions and interactions with aspirin. Considerations in the treatment of the elderly patient

Aspirin (acetylsalicylic acid) is probably the most frequently used medication, and its use is generally uneventful. However, aspirin is also noted for numerous side effects and drug interactions that can complicate the course of therapy. The elderly, especially those with complicated medical histories, are more prone to the adverse effects of salicylates and may develop gastrointestinal tract bleeding, renal insufficiency, asthma and CNS toxicity. In the clinical situation, important drug interactions can occur with concurrent use of anticoagulants, sulphonylureas, diuretics, methotrexate and antacids. In long term aspirin therapy, enteric-coated or nonacetylated forms of aspirin are associated with fewer side effects and may be better tolerated. Monitoring of therapy (especially in the higher risk patient), with frequent assessments of the clinical state and measurements of serum creatinine, electrolytes and salicylate concentrations, may diminish the likelihood of toxicity.

The effects of urine pH modification on the pharmacokinetics and pharmacodynamics of phenylpropanolamine

To determine whether urinary alkalinization had an effect on the plasma pharmacokinetics and pharmacodynamics of phenylpropanolamine, a double-blind crossover study was conducted in four healthy, normotensive male volunteers. The subjects received 25 mg immediate-release phenylpropanolamine and either placebo or sodium bicarbonate in a balanced randomized order. The bicarbonate treatment consisted of 6 g sodium bicarbonate 30 min prior to the phenylpropanolamine and then 3 g sodium bicarbonate every 4 hr for the next 16 hr. During the control treatment, phenylpropanolamine and a placebo for bicarbonate (lactose) were given on the same schedule. Blood and urine samples were collected over 24 hr and analyzed by HPLC. A supine blood pressure and pulse were obtained before each blood sample. The bicarbonate treatment significantly increased the urine pH throughout the study period and decreased phenylpropanolamine renal clearance by 33.5%. The apparent total-body clearance was also decreased by 31.5% and resulted in higher postabsorptive plasma phenylpropanolamine concentrations in each subject as compared to the control treatment. Both systolic and diastolic blood pressures changed significantly from baseline in both treatments. The bicarbonate treatment was accompanied by significantly higher diastolic blood pressures than in the control treatment, but there was no effect on systolic blood pressures. Generally, when the blood pressure-concentration pairs were plotted chronologically, clockwise hysteresis curves resulted. Heart rates did not change significantly from baseline values for either treatment. In this small group of normotensive healthy male volunteers, urinary alkalinization significantly depressed the renal clearance of phenylpropanolamine, producing higher postabsorptive phenylpropanolamine plasma concentrations and a small but significant increase in the diastolic blood pressure.

Effect of routine doses of antacid on renal acidification

Ten healthy volunteers took a magnesium and aluminium hydroxide antacid for 4 days, and their urinary acid excretion was measured. During antacid ingestion, blood bicarbonate levels did not change significantly, but there were highly significant rises in urine pH and bicarbonate excretion and falls in the 24 h excretion of titratable acid, ammonium, and net acid; the average change in net acid excretion was 41 +/- 4 mmol (72 +/- 9%) per 24 h. This large reduction in net acid excretion appears to result from neutralisation of more hydrochloric acid than sodium bicarbonate in the gastrointestinal tract rather than from absorption of exogenous alkali. Although metabolic alkalosis does not occur with their use in normal individuals, these antacids should not be termed "non-systemic". They might cause important changes in renal drug handling, solubility of excreted substances, or acid-base status in patients at risk.

Effect of antacid and ascorbic acid on serum salicylate concentration

To determine the effect of antacid or ascorbic acid administration on plateau serum salicylate concentrations, nine healthy subjects were given each of the following treatments by balanced block design: choline salicylate (equivalent to 3.76 or 5.62 Gm/day of aspirin); choline salicylate plus magnesium-aluminum hydroxide (120 ml/day); or choline salicylate plus ascorbic acid (3 Gm/day). In subjects developing a control serum salicylate level above 10 mg/dl, antacid administration produced a decrease in serum salicylate level (mean 19.8 mg/dl vs. 15.8 mg/dl) (P less than 0.01). Ascorbic acid administration was not associated with a significant change in serum salicylate. The reduction in serum salicylate following antacid appears to be due to antacid-induced alkalinization of the urine with resultant increase in renal salicylate clearance. Antacid administration should be considered a potential cause of altered serum salicylate concentration in patients receiving large doses of salicylate.