Improved mineral balance and skeletal metabolism in postmenopausal women treated with potassium bicarbonate

BACKGROUND

In normal subjects, a low level of metabolic acidosis and positive acid balance (the production of more acid than is excreted) are typically present and correlate in degree with the amount of endogenous acid produced by the metabolism of foods in ordinary diets abundant in protein. Over a lifetime, the counteraction of retained endogenous acid by base mobilized from the skeleton may contribute to the decrease in bone mass that occurs normally with aging.

METHODS

To test that possibility, we administered potassium bicarbonate to 18 postmenopausal women who were given a constant diet (652 mg [16 mmol] of calcium and 96 g of protein per 60 kg of body weight). The potassium bicarbonate was given orally for 18 days in doses (60 to 120 mmol per day) that nearly completely neutralized the endogenous acid.

RESULTS

During the administration of potassium bicarbonate, the calcium and phosphorus balance became less negative or more positive--that is, less was excreted in comparison with the amount ingested (mean [+/- SD] change in calcium balance, +56 +/- 76 mg [1.4 +/- 1.9 mmol] per day per 60 kg; P = 0.009; change in phosphorus balance, +47 +/- 64 mg [1.5 +/- 2.1 mmol] per day per 60 kg; P = 0.007) because of reductions in urinary calcium and phosphorus excretion. The changes in calcium and phosphorus balance were positively correlated (P < 0.001). Serum osteocalcin concentrations increased from 5.5 +/- 2.8 to 6.1 +/- 2.8 ng per milliliter (P < 0.001), and urinary hydroxyproline excretion decreased from 28.9 +/- 12.3 to 26.7 +/- 10.8 mg per day (220 +/- 94 to 204 +/- 82 mumol per day; P = 0.05). Net renal acid excretion decreased from 70.9 +/- 10.1 to 12.8 +/- 21.8 mmol per day, indicating nearly complete neutralization of endogenous acid.

CONCLUSIONS

In postmenopausal women, the oral administration of potassium bicarbonate at a dose sufficient to neutralize endogenous acid improves calcium and phosphorus balance, reduces bone resorption, and increases the rate of bone formation.

5 beta-Methyl-14 beta-(p-nitrocinnamoylamino)-7,8-dihydromorphinone and its corresponding N-cyclopropylmethyl analog, N-cyclopropylmethylnor-5 beta-methyl-14 beta-(p-nitrocinnamoylamino)- 7,8-dihydromorphinone: mu-selective irreversible opioid antagonists

5 beta-Methyl-14 beta-(p-nitrocinnamoylamino)-7,8-dihydromorphinone (MET-CAMO) and its corresponding N-cyclopropylmethyl analog, N-cyclopropylmethylnor-5 beta-methyl-14 beta-(p-nitrocinnamoylamino)- 7,8-dihydromorphinone (N-CPM-MET-CAMO) were tested in opioid receptor binding assays and in the mouse tail-flick test in order to characterize the affinity, selectivity and antinociceptive properties of these two compounds. Incubating bovine striatal membranes with either MET-CAMO or N-CPM-MET-CAMO produced a wash-resistant, concentration- and time-dependent inhibition of the binding of the mu-selective ligand, [3H]-[D-Ala2,MePhe4,Gly(ol)5]enkephalin, but with no change in delta or kappa binding. Preincubating membranes with N-CPM-MET-CAMO decreased the maximum binding value for [3H]-[D-Ala2,MePhe4,Gly(ol)5]enkephalin binding without changing the Kd value. In the mouse tail-flick assay, MET-CAMO and N-CPM-MET-CAMO did not produce any antinociception up to a dose of 100 nmol after i.c.v. administration. However, pretreatment of mice with either compound produced a time- and dose-dependent antagonism of morphine-induced antinociception. Analgesia mediated by delta or kappa opioids was not altered by either MET-CAMO or N-CPM-MET-CAMO at a dose of up to 100 nmol. The mu antagonistic effect of 1 nmol of MET-CAMO and N-CPM-MET-CAMO appeared at 8 hr and lasted up to 72 hr, with a maximal effect at 16 to 24 hr after i.c.v. administration. Pretreatment of mice with 1 nmol of MET-CAMO or N-CPM-MET-CAMO, given by i.c.v. administration at -24 hr, produced a rightward and downward shift of dose-response line of i.c.v. morphine.(ABSTRACT TRUNCATED AT 250 WORDS)

14 beta-[(p-nitrocinnamoyl)amino]morphinones, 14 beta-[(p-nitrocinnamoyl)amino]-7,8-dihydromorphinones, and their codeinone analogues: synthesis and receptor activity

A series of 14 beta-[(nitrocinnamoyl)amino]codeinones and morphinones, some of which contain a 5 beta-methyl group, were prepared from 14 beta-aminocodeinones and 14 beta-[N-(cyclopropylmethyl)-amino]norcodeinones. The affinities of the target compounds for the mu, delta, and kappa opioid receptors were determined by radiolabeled binding experiments using bovine brain membranes. An analogous series of 7,8-dihydrocodeinones and morphinones was prepared and assayed in the same systems. The 3-methoxy derivatives 3 and 4 were more selective than the corresponding morphinones for the mu receptor. The 5 beta-methylcodeinones 25 and 27 had lower affinity at all receptors than the corresponding morphinones, but the 5 beta-methylmorphinones had affinities similar to the morphinones 5 and 6. A similar pattern was observed in the 7,8-dihydro series. Two compounds, 5 beta-methyl-14 beta-[(p-nitrocinnamoyl)amino]-7,8-dihydromorphinone, 20 (MET-CAMO), and N-(cyclopropylmethyl)-14 beta-[(p-nitrocinnamoyl)amino]-7,8-dihydronormorphinone, 22 (N-CPM-MET- CAMO), acted as nonequilibrium ligands in antinociception and membrane binding studies. In mice after icv administration, neither ligand showed any agonist activity but 8-24 h after administration both compounds acted as potent mu antagonists. A Scatchard plot of the effect of N-CPM-MET-CAMO on [3H]DAMGO ([3H]D-Ala2, (Me)-Phe4, Gly(ol)5] enkephalin) binding to bovine striatal membranes showed that there was a significant decrease in the Bmax value and a marginal effect on the Kd value suggesting that the number of binding sites was reduced. When taken together, these results support the view that 20 and 22 bind covalently to the mu receptor. On the other hand, when N-acetylcysteine and 22 were allowed to react in a buffered solution, 22 was recovered unchanged. Under these conditions no Michael reaction was observed.

Precision and accuracy for rat whole body and femur bone mineral determination with dual X-ray absorptiometry

Precision and accuracy for rat whole body and excised femur bone mineral density (BMD) measurements were evaluated with two dual X-ray absorptiometry (DXA) systems. The 'small subject' mode on the Norland XR-26 (XR), and the 'ultra high resolution mode' on the Hologic QDR-1000/W(QDR) were used for the analysis. The whole body mode was only available on the XR. The lowest precision error for the whole body was found using a scan resolution of 1.0 x 1.0 mm and a scan speed of 15 mm/s. The scan spatial resolution of the femur measurement was approximately eight times higher on the QDR than on the XR. However, the XR allowed analysis of an arbitrary region of interest within the femur, which was not easily done with the QDR. Precision for the total femur measurement on the QDR (0.5-0.9%) was approximately two to four times superior to that of the XR (1.5-4.3%). The difference may be due to the superior scan resolution of the QDR. Bone mineral content and BMD on the QDR significantly declined with an increase of water depth (P < 0.001). No significant change was observed on the XR. Both DXA systems demonstrated an excellent correlation (r > or = 0.98) with ash weight under the scan conditions examined. The optimal scan condition for the excised femur measurement on the XR was obtained with 1.5-2.5 cm of perspex or water and a scan speed of 10 mm/s. For the QDR, we recommend scanning the rat femur with approximately 2.5 cm of perspex or water in terms of precision and accuracy.

5 beta-Methyl-14 beta-(p-nitrocinnamoylamino)-7,8-dihydromorphinone: a long-lasting mu-opioid receptor antagonist devoid of agonist properties

5 beta-Methyl-14 beta-(p-nitrocinnamoylamino)-7,8-dihydromorphinone (MET-CAMO) suppressed morphine-induced antinociception but had no effect on antinociception mediated by delta- or kappa-opioid receptors after a single i.c.v. 1-nmol injection from 8 to 72 h before testing. MET-CAMO had no agonist effects in the mouse tail-flick assay in doses up to 100 nmol. MET-CAMO is the first N-methylated morphine derivative which shows such long-lasting mu-selective opioid receptor antagonism with no agonistic properties.

Diuretics, serum and intracellular electrolyte levels, and ventricular arrhythmias in hypertensive men

OBJECTIVE

To investigate the patterns of electrolyte abnormalities resulting from thiazide administration and whether they cause ventricular arrhythmias, and to help resolve the controversy over whether clinicians should routinely prescribe potassium-conserving therapy to all patients treated with thiazides.

DESIGN

Double-blind, randomized controlled trial.

PARTICIPANTS

A total of 233 hypertensive men aged 35 to 70 years.

INTERVENTIONS

Participants were withdrawn from prior diuretic treatment and were replenished with oral potassium chloride and magnesium oxide. They were then randomized to 2 months of treatment with (1) hydrochlorothiazide; (2) hydrochlorothiazide with oral potassium; (3) hydrochlorothiazide with oral potassium and magnesium; (4) hydrochlorothiazide and triamterene; (5) chlorthalidone; or (6) placebo.

MAIN OUTCOME MEASURES

Ventricular arrhythmias on 24-hour Holter monitoring and serum and intracellular potassium and magnesium levels.

RESULTS

Of the 233 participants, 212 (91%) completed the study. Serum potassium levels were 0.4 mmol/L lower in the hydrochlorothiazide group than in the placebo group (P less than 0.01), and this mean difference was not affected by supplementation with potassium, with potassium and magnesium, or with triamterene. However, the supplements did prevent the occasional occurrence of marked hypokalemia; all 12 of the men who developed serum potassium levels of 3.0 mmol/L or less were among the 90 who received diuretics without supplementation (P less than 0.01). Similarly, the overall proportion of men with ventricular arrhythmias was not affected by randomized treatment, but there was a twofold increase in the proportion with arrhythmias among the 12 men with serum potassium levels of 3.0 mmol/L or less (P = .02). Serum magnesium and intracellular potassium and magnesium levels were not reduced by hydrochlorothiazide, nor were they related to ventricular arrhythmias.

CONCLUSIONS

In the majority of hypertensive patients, treatment with 50 mg/d of hydrochlorothiazide does not cause marked hypokalemia or ventricular arrhythmias. However, because some individuals will develop hypokalemia after starting diuretic therapy, serum potassium levels should be monitored and potassium-sparing strategies should be used when indicated.

Synthesis and structure-activity relationships of a novel series of non-peptide angiotensin II receptor binding inhibitors specific for the AT2 subtype

Structure-activity relationships are reported for a novel class of 4,5,6,7-tetrahydro-1H-imidazo[4,5-c]pyridine-6-carboxylic acid derivatives that displace 125I-labeled angiotensin II from a specific subset of angiotensin II (Ang II) binding sites in rat adrenal preparations. This binding site is not the Ang II receptor mediating vascular contraction or aldosterone release, but, rather, is one whose function has not yet been fully elucidated. It has been identified in a number of tissues and has a similar affinity for Ang II and its peptide analogues as does the vascular receptor. The non-peptide compounds reported here are uniquely specific in displacing Ang II at this binding site and are inactive in antagonizing Ang II at the vascular receptor or in pharmacological assays measuring vascular effects. PD 123,319 (79), one of the most potent compounds, has an IC50 of 34 nM. Certain of these compounds may have utility in the definition and study of Ang II receptor subtypes.

Measurement of aortic blood flow by Doppler echocardiography: day to day variability in normal subjects and applicability in clinical research

To assess the reliability of Doppler ultrasound for detecting serial changes in cardiac output in response to experimental interventions, the day to day variability of the minute distance of aortic flow was determined in seven normal subjects maintained in a tightly controlled environment with regard to diet and activities. Measurements were made at the same time on 5 to 6 sequential days from an apical window with use of both continuous wave and pulsed wave Doppler techniques. Two statistical measures of reliability were calculated, the intraclass coefficient of correlation (R), which varies between 0 (null reliability) and +1 (perfect reliability), and the 95% confidence interval for the error-free value of a single measurement. For sequential measurements of arterial pressure, 24 h urinary volume and sodium excretion and body weight, the intraclass coefficients of correlation ranged from 0.85 to 0.99, indicating low day to day variability consistent with tight environmental control. Continuous and pulsed wave modes were proved equally and highly reliable for measuring minute distance of aortic flow. However, continuous wave Doppler ultrasound provided acceptable signals more frequently than did the pulsed wave technique. For continuous wave Doppler ultrasound, R was 0.87 (p less than 0.00001); the 95% confidence interval was +/- 1.81 m/min (or 11% of the mean of all measurements), which indicates that this method can be used in a single individual to detect a greater than 11% change in minute distance measured once before and after an intervention.(ABSTRACT TRUNCATED AT 250 WORDS)

Normal diet NaCl variation can affect the renal set-point for plasma pH-(HCO3-) maintenance

In humans who are ingesting abundant NaCl, blood pH (pHb) and plasma bicarbonate concentration [HCO3-)p) change little or imperceptibly in response to the ingestion of alkali salts. We tested the hypothesis that such tight homeostatic regulation is an artifact of eating a culturally imposed NaCl-enriched diet, not a fundamental physiological trait of humans. In five normal men ingesting a constant acid-producing diet with a low intrinsic NaCl content (0.15 mEq/kg of body weight per day), we measured plasma and urine acid-base composition during four 7-day periods in which the diet was supplemented as follows: no supplements----NaHCO3 only----NaHCO3 plus NaCl----NaCl only. Each sodium supplement was 2.0 mmol/kg body weight per day. With no supplements, pHb was 7.43 +/- 0.005 and (HCO3-)p was 25.0 +/- 0.4 mEq/L. When NaHCO3 only was added, pHb rose 0.02 (to 7.45 +/- 0.004; P less than 0.01) and (HCO3-)p rose nearly 4 mEq/L (to 28.9 +/- 0.6 mEq/L, P less than 0.001). The rise in (HCO3-)p was sustained predominantly by an increased rate of renal bicarbonate reabsorption. When NaCl was added, (HCO3-)p returned to the earlier level, despite continued NaHCO3 supplementation (24.9 +/- 0.6 mEq/L), and remained there when NaHCO3 supplementation was subsequently stopped (24.1 +/- 0.5 mEq/L). Thus, tight homeostatic regulation of plasma acid-base composition in response to a change in dietary base occurred only when dietary NaCl was abundant. To our knowledge, this is the first study in normal humans that demonstrates that diet NaCl variations within the normal range significantly influence plasma acid-base composition.(ABSTRACT TRUNCATED AT 250 WORDS)

Dietary potassium influences kidney maintenance of serum phosphorus concentration

In studying the metabolic effects of diet potassium (K+) variation in normal humans, we noted that varying diet K+ within its normal range influenced inorganic phosphorus (Pi) homeostasis and serum calcitriol (1,25-dihydroxyvitamin D) levels. In six men who ingested a constant whole-foods diet containing (per 70 kg body wt) 27 mmol/day Pi and 52 mEq/day K+, we increased diet K+ to 156 mmol/day with supplements first of potassium bicarbonate (KHCO3) alone and then of potassium chloride (KCL) alone, each for eight days interrupted by an eight-day recovery period of no K+ supplement. Urine Pi decreased promptly with either K(+)-salt, each inducing a persisting retention of 7 to 10 mmoles Pi, which was dumped during recovery. Fasting serum [Pi] increased with either K+ supplement (P = 0.022, repeated measures analysis of variance); the composite mean serum [Pi] for the two K(+)-supplement periods exceeded that for the two periods without supplements (P less than 0.01, paired t-test). Conversely, the concentrations of serum calcitriol decreased with either K+ supplement (P = 0.020). Among subjects, the diet K(+)-induced increases in serum [Pi] correlated with those in plasma [K+] (r = 0.64, P = 0.027); the decreases in serum calcitriol concentration correlated with the increases in serum [Pi] (r = -0.69, P = 0.014). There were no significant differences among periods in serum parathyroid hormone, ionized calcium, urine cyclic AMP excretion, plasma renin activity, body weight, serum albumin, or creatinine clearance; plasma volume decreased slightly during KCL but not during KHCO3 periods.(ABSTRACT TRUNCATED AT 250 WORDS)

Serial assessment of glomerular filtration rate in lupus nephropathy

In patients with lupus nephropathy (LN), previous studies have shown that creatinine clearance (CCr) overestimates true glomerular filtration rate as measured by inulin clearance (CIn), and that among patients the degree of overestimation is highly variable. We sought to determine whether the discrepancy between CCr and CIn remains constant over time (months, years) in each individual patient, and therefore whether serial measurements of CCr reliably reflect the direction and magnitude of change in CIn. Twenty-five patients with LN underwent simultaneous determinations of CCr and CIn performed two to four (mean 3.3) times over three years. In a given patient, it was found that the ratio of CCr/CIn changed substantially over time (mean SD 0.16 with 95% confidence interval of 0.12 to 0.20). Thus, in about 32% of cases the ratio of CCr/CIn will vary more than +/- 16% from a previously measured value of CCr/CIn. Patients with both high and low values of CIn showed similar variability in CCR/CIn over time. Variability in CCr/CIn was found regardless of whether CIn was increasing, decreasing, or constant over time. In nearly one-half of all measurements of CCr, the corresponding change in CIn was directionally discordant. Iothalamate and technetium-DTPA renal clearances correlated highly with CIn (R2 = 0.99). We conclude that the discrepancy between CCr and CIn can vary greatly over time in an individual patient. Consequently, serial CCr does not accurately measure the direction or magnitude of change in glomerular filtration rate in lupus nephropathy.

Food chloride distribution in nature and its relation to sodium content

Because of growing interest in the biological and clinical effects of dietary chloride as the anion accompanying the dietary cation sodium and because the standard food composition tables used in the United States to estimate sodium content do not contain data on chloride content, we analyzed the nutrient data base of the English workers Paul and Southgate, which contains an extensive listing of both chloride and sodium contents in foods. To examine food chloride distribution in nature, we focused on the uncooked, unadulterated, discrete, primitive foods in the data base (no. = 216 food items). The findings indicate the existence of both a large variability of chloride content among foods and a high degree of coupling of chloride with sodium. The contents of chloride and sodium varied over a similarly large range (coefficients of variation, 229% vs. 263%), differed very little from each other on the average (less than 20%), and correlated (r = 0.84, p less than 0.001) to the extent that greater than two-thirds of the overall variation of chloride content was linked to that of sodium content. Those findings accord with the often posited but untested assertion that the chloride content of foods approximates and parallels that of sodium.(ABSTRACT TRUNCATED AT 250 WORDS)

Dietary NaCl determines severity of potassium depletion-induced metabolic alkalosis

It is uncertain whether, in humans, potassium depletion can cause or sustain metabolic alkalosis of clinically important degree in the absence of coexisting known alkalosis-producing conditions. Previously we found, in normal humans ingesting abundant NaCl, that dietary K+ depletion alone can induce and sustain a small decrease in blood acidity and increase in plasma bicarbonate concentration; we hypothesized that more severe alkalosis was prevented by mitigating mechanisms initiated by renal retention of dietary NaCl that was induced by K+ depletion. To ascertain the acid-base response to dietary K+ depletion under conditions in which the availability of NaCl for retention is greatly limited, in the present study of six normal men we restricted dietary K+ as in the previous study except that intake of NaCl was maintained low (2 to 7 mEq/day, Low NaCl Group) instead of high (126 mEq/day, High NaCl Group). Plasma acid-base composition and renal net-acid excretion (NAE) did not differ significantly between groups during the control period. In the steady state of K+ depletion (days 11 to 15 of K+ restriction), neither plasma K+ concentration (2.9 +/- 0.9 mEq/liter vs. 3.0 +/- 0.1 mEq/liter) nor cumulative K+ deficit (399 +/- 59 mEq vs. 466 +/- 48 mEq) differed significantly between groups. During K+ restriction, persisting metabolic alkalosis developed in both groups, which was more severe in the Low NaCl Group: increment in [HCO3-]p, 7.5 +/- 1.0 mEq/liter versus 2.0 +/- 0.3 mEq/liter, P less than 0.001; decrement in [H+]p, 5.5 +/- 0.6 nEq/liter versus 2.9 +/- 0.4 nEq/liter, P less than 0.003. A significantly more severe alkalosis in the Low NaCl Group was evident at all degrees of K+ deficiency achieved during the course of the 15 days of K+ restriction, and the severity of alkalosis in the Low NaCl Group correlated with the degree of K+ deficiency. During the generation of alkalosis (days 1 to 7 of K+ restriction), NAE increased in the Low NaCl Group whereas it decreased in the High NaCl Group. During the maintenance of alkalosis (days 11 to 15), NAE stabilized in both groups after it returned to values approximating the control values. In both groups, urine Cl- excretion decreased during K+ restriction even though Cl- intake had not been changed, with the result that body Cl- content increased negligibly in the Low NaCl Group (28 +/- 6 mEq) and substantially in the High NaCl Group (355 +/- 64 mEq).(ABSTRACT TRUNCATED AT 400 WORDS)

Adrenocortical hormone secretory response to chronic NH4Cl-induced metabolic acidosis

We examined the effect of chronic metabolic acidosis on adrenocortical hormone production by administering NH4Cl for 5 days to four normal subjects. Plasma aldosterone concentration, aldosterone secretion, and urinary excretion of aldosterone-18-glucuronide increased significantly, whereas there were no significant changes in the plasma concentrations of cortisol, corticosterone, or deoxycorticosterone, or in the urinary excretion of 17-hydroxycorticoids. By day 2, plasma renin activity (PRA) and concentration (PRC) were not significantly different from control, and the slope of the regression line relating plasma aldosterone concentration to PRA was significantly greater than the slope in the control period, i.e., the sensitivity of aldosterone secretion to renin stimulation was increased. By day 5, however, PRA and PRC were increased above control. Plasma potassium concentration did not change significantly. Thus chronic NH4Cl-induced acidosis induces a sustained stimulation of aldosterone secretion in the absence of a change in adrenocorticotropin-dependent adrenocortical hormone secretion. Factors other than an increase in renin secretion and plasma potassium concentration may be involved in at least the early phase of aldosterone stimulation, suggesting that plasma hydrogen ion concentration might be a separate regulator of aldosterone secretion.

Reduced glomerular filtration rate can maintain a rise in plasma bicarbonate concentration in humans

In humans, deficiency of chloride and potassium were found to perpetuate the hyperbicarbonatemia that attends metabolic alkalosis induced by gastric aspiration partly by increasing renal bicarbonate reabsorption, commensurate with the attendant increase in filtered bicarbonate load, and partly by decreasing glomerular filtration rate (GFR), which minimizes the degree of which the filtered bicarbonate load increases and thereby minimizes the requisite increase in bicarbonate reabsorption. The relative contribution of stimulated renal bicarbonate reabsorption might increase, however, if the supply of extrarenal bicarbonate is increased, in which case a greater degree of hyperbicarbonatemia would be sustained. To investigate that possibility, we reexamined the mechanism of perpetuation of gastric alkalosis in normal subjects eating a low NaCl diet supplemented with bicarbonate salts. Prior to gastric aspiration, plasma bicarbonate concentration ([HCO3]p) and pH were higher than in similarly studied subjects not receiving bicarbonate: 29.9 +/- 0.6 vs. 25.3 +/- 0.1 and 7.43 +/- 0.008 vs. 7.41 +/- 0.002 mEq/l, respectively. With continued bicarbonate supplementation, gastric aspiration induced a further significant increase (p less than 0.05) in [HCO3]p of 10.8%, to values not significantly different from those in nonbicarbonate-loaded subjects with gastric alkalosis: 33.2 +/- 1.2 mEq/l. GFR decreased significantly by 8.4% (from 98 +/- 4 to 90 +/- 3 ml/min, p less than 0.025), offsetting nearly commensurately the increase in [HCO3]p so that total bicarbonate reabsorption was not significantly increased (2.90 +/- 0.12 vs. 2.97 +/- 0.19 mEq/min, p = NS).(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of dietary potassium depletion and mineralocorticoid excess on renal Cl-conservation in the dog

Preexisting dietary K+ depletion (KD) in dogs exaggerates the renal acid excretory response to mineralocorticoid hormone (MCH) and attenuates the renal Cl- reabsorptive response without altering the Na+ reabsorptive response. The exaggerated acid excretory response has been postulated to be an electrophysiological consequence of a defect in renal Cl- reabsorption caused by KD. To investigate the specific effects of KD on renal Cl- transport in dogs, we assessed renal Cl- conservation during dietary Cl- restriction in KD adrenalectomized dogs maintained on physiological replacement doses of MCH. After a 16-day period of dietary K+ restriction and physiological MCH replacement, reduction of dietary NaCl from 5.0 to 0.25 mmol X kg-1 X 24 h-1 was attended by reduction in urinary Cl- excretion to values less than intake and to significantly lower values than in K+ -replete controls. In a subsequent experimental period of continued Cl- restriction and administration of DOC (15 mg/24 h, i.m.), urinary Cl- excretion decreased further in both groups to stable values, but the values were significantly greater in KD (2.7 +/- 0.4 vs. 1.1 +/- 0.1 meq/24 h, P less than 0.05) and the cumulative retention of urinary Cl- was significantly less (10.3 +/- 1.4 vs. 29.5 +/- 6.7 meq, P less than 0.05). These findings demonstrate that preexisting dietary KD accelerates chronic renal Cl- conservation in response to dietary Cl- restriction under conditions in which MCH supply is normal and fixed but that it impairs maximal renal Cl- -conserving ability in response to MCH excess.

Reduced glomerular filtration and enhanced bicarbonate reabsorption maintain metabolic alkalosis in humans

The mechanism that sustains chloride-depletion metabolic alkalosis is presumed to be a stimulation of renal acidification, so that the elevated filtered bicarbonate load that attends hyperbicarbonatemia is completely reabsorbed. However, such enhancement of renal bicarbonate reabsorption is not necessary to maintain hyperbicarbonatemia if the filtered bicarbonate load is not increased owing to a concomitant reduction in glomerular filtration rate (GFR). To assess the relative contributions of enhanced renal bicarbonate reabsorption and reduced GFR in the maintenance of chloride-depletion alkalosis in humans, selective hydrochloric acid depletion was induced in five normal subjects. Plasma bicarbonate concentration increased by 27% (25.3 +/- 0.1 to 32.1 +/- 0.3 mEq/liter, P less than 0.005), whereas the rate of renal bicarbonate reabsorption increased by only 17% (2.7 +/- 0.1 to 3.2 +/- 0.2 mEq/min, P less than 0.05) owing to a 10% reduction in GFR (93.2 +/- 4.4 to 84.3 +/- 4.1 ml/min, P less than 0.01). Thus, in chloride-depletion metabolic alkalosis in humans, the increase in plasma bicarbonate concentration is not attended by a commensurate increase in filtered bicarbonate and rate of renal bicarbonate reabsorption. Both a reduction in GFR and an enhancement of renal bicarbonate reabsorption contribute to maintenance of the alkalotic state.

Effect of extracellular fluid volume depletion on renal regulation of acid-base and potassium equilibrium during prolonged mineral acid administration

Previous studies of the renal and systemic acid-base response to prolonged administration of mineral acids in dogs have suggested that during the steady state of acidosis, the level at which plasma bicarbonate concentration is regulated by the kidney is dependent on the degree of augmentation of "distal delivery" of sodium imposed by the increased filtered load of administered mineral acid anion with filtered sodium, and on the degree of augmentation of "distal avidity" for sodium reabsorption imposed by ECF volume ( ECFV ) contraction secondary to renal sodium losses accompanying the administered mineral acid anion. This formulation, however, fails to predict the level at which plasma bicarbonate concentration would be regulated under conditions of preexisting ECFV depletion, which would simultaneously limit distal delivery of sodium salts and yet increase distal avidity for sodium reabsorption. Our studies assessed the renal and systemic acid-base responses to prolonged daily administration of 5.0 mEq/kg of H+ as HCl (groups 1 and 2) or H2SO4 (groups 3 and 4) in dogs with normal ECFV (groups 1 and 3) vs. preexisting ECFV depletion (groups 2 and 4) induced by administration of ethacrynic acid. In response to HCl administration, dogs with depleted ECFV developed more severe acidosis than ECFV -replete dogs (delta[HCO-3,]p, -5.0 +/- 0.6 mEq/L, group 2 vs. -2.7 +/- 0.5 mEq/L, group 1, p less than 0.02). The exacerbated metabolic acidosis in group 2 persisted in the steady state, even though the steady-state net systemic acid load was not greater than in group 1. No exacerbation of acidosis was observed in H2SO4-fed dogs with depleted ECFV . In response to either HCl or H2SO4, persistent hypokalemia caused by increased renal potassium clearance occurred in ECFV -replete dogs but not in ECFV -depleted dogs. Our results indicate that preexisting ECFV depletion results in impaired renal hydrogen ion secretion during prolonged HCl feeding, but not during H2SO4 feeding. These results suggest that during prolonged HCl loading under conditions of preexisting ECFV depletion, hypovolemia-mediated restriction of the normal augmentation of distal delivery of sodium salts overrides the effects of enhanced distal cation secretory capacity that attends hypovolemia-mediated augmentation of distal avidity for sodium reabsorption.

Amelioration of metabolic acidosis by dietary potassium restriction in hyperkalemic patients with chronic renal insufficiency

Hyperkalemia has been implicated in the pathogenesis of metabolic acidosis in chronic renal insufficiency because acidosis is ameliorated after administration of medications that correct hyperkalemia: mineralocorticoids, diuretics, intestinal K+-binding agents. However, the acidosis-ameliorating effect of these medications may be a consequence not of their ability to correct hyperkalemia, but of their ability to directly stimulate renal or intestinal excretion of acid. To investigate the specific effect of correcting hyperkalemia, balance studies were performed wherein hyperkalemia was corrected solely by restriction of dietary K+ in three patients with moderate chronic renal insufficiency (Ccreat 36, 44, and 58 ml/min/1.73 m2, respectively). Reduction of K+ intake was effected by substitution of Na+ for K+ in the electrolyte supplement to a whole-food diet of low K+ content. This maneuver resulted in correction of hyperkalemia and sustained amelioration of metabolic acidosis in each patient. Net acid excretion increased only transiently, and not enough to fully account for the magnitude of the increment in plasma [HCO3-], suggesting that an extrarenal mechanism of HCO3- input to the systemic circulation was the major factor that ameliorated the systemic acidosis. Evidence of an extrarenal mechanism was obtained only during the phase of decreasing plasma [K+]. Subsequently, during sustained normokalemia, the increased plasma [HCO3-] was maintained as a consequence of a sustained increase in total renal H+ secretion, evidenced by complete reabsorption of the increased filtered load of HCO3- and no reduction in net acid excretion from control values. These results indicate that in some patients with moderate chronic renal insufficiency, metabolic acidosis is ameliorated when hyperkalemia is corrected by restriction of dietary K+ (Na+ substitution) without otherwise changing diet composition and without administration of medication. Amelioration of the acidosis is predominantly effected by extrarenal mechanisms, and is sustained by an increase in the set point at which plasma [HCO3-] is regulated by the kidney.

Amelioration of hyperchloremic acidosis with furosemide therapy in patients with chronic renal insufficiency and type 4 renal tubular acidosis

In hypoaldosteronemic patients with chronic renal insufficiency, administration of a mineralocorticoid steroid such as fludrocortisone can ameliorate hyperkalemia and metabolic acidosis, but this therapy is not always safe owing to the deleterious consequences of extracellular fluid volume expansion resulting from mineralocorticoid-induced sodium chloride retention. In the present study of 8 patients with renal hyperchloremic acidosis, mild hyperkalemia and chronic glomerular insufficiency, we evaluated the therapeutic effect of chronic administration of a natriuretic/chloruretic agent, furosemide, a renoactive drug that is known to increase renal acid excretion in experimental animals without increasing body content of sodium chloride. 4 patients had hyporeninemic hypoaldosteronism. During 8 days of treatment in 6 patients who received furosemide alone, metabolic acidosis was significantly ameliorated. Urinary net acid excretion increased, except in the 2 patients who had the most severe hypoaldosteronism. For the group as a whole, the cumulative change in net acid excretion correlated positively with the rate of aldosterone excretion (r = 0.94, p less than 0.01). Thus, the aciduric response to furosemide is attenuated by aldosterone deficiency. When furosemide was administered in combination with fludrocortisone (4 subjects), an amelioration of metabolic acidosis occurred that was greater than that observed in the group treated with furosemide alone. Combined therapy ameliorated acidosis in the patient with the most severe degree of hypoaldosteronism, the same patient in whom administration of furosemide without fludrocortisone was ineffective even after 6 months of treatment. The findings in this study indicate that chronic furosemide therapy, alone or in combination with fludrocortisone, is a safe and effective means of ameliorating metabolic acidosis in patients with chronic renal insufficiency, including those with hypoaldosteronism.

Renal tubular acidosis induced by dietary chloride

Previous studies have demonstrated that dietary intake of anions with high renal reabsorbability (Cl- greater than SO4=) can result in either exacerbation of chronic metabolic acidosis or correction of chronic metabolic alkalosis. These results, however, fail to predict the renal acid-base response to Cl- administration when systemic acid-base composition is initially normal, but accompanied by an extracellular fluid (ECF) volume-mediated renal avidity for Cl- reabsorption; that is, the renal options include HCl retention, KCl retention, and phosphaturia. Accordingly, the present metabolic balance studies evaluated the response to substitution of dietary Cl- (2.5 mEq/kg/day) for Pi in five dogs previously ECF-depleted with diuretics and maintained on a dietary K+ supplement, 5.0 mEq/kg daily as neutral Pi (electrolyte-free diet) during a steady-state control period. Dietary Cl- resulted in a decrease in arterial plasma [HCO3-] from 21.2 +/- 0.7 to 17.8 +/- 0.8 mEq/liter, (P less than 0.01) and increase in [H+] from 38.5 +/- 0.7 to 43.3 +/- 0.8 nEq/liter (P less than 0.001). Urine pH increased (P less than 0.01), the cumulative change in net acid excretion decreased (-79 mEq, P less than 0.05), and Cl- retention (39 mEq, P less than 0.05) occurred. No change in Na+, K+, or Pi excretion occurred. The renal acidosis was fully corrected when SO4= was substituted for dietary Cl- and redeveloped when Cl- was resubstituted . Superimposition of a large oral buffer load (creatinine) did not ameliorate Cl- -induced renal acidosis. The results indicate that dietary reabsorbable anions can result in renal acidosis when Cl- reabsorption is stimulated and suggest that anion reabsorbability characteristics and not anion buffer properties are responsible.

Effect of diet on plasma acid-base composition in normal humans

Steady-state plasma and urine acid-base composition was assessed in 19 studies of 16 normal subjects who ingested constant amounts of one of three diets that resulted in different rates of endogenous noncarbonic acid production (EAP) within the normal range. Renal net acid excretion (NAE) was used to quantify EAP since the two variables are positively correlated in normal subjects. A significant positive correlation was observed between plasma [H+] and plasma PCO2, and between plasma [HCO3-] and plasma PCO2, among the subjects. Multiple correlation analysis revealed a significant interrelationship among plasma [H+], plasma PCO2, and NAE (r = 0.71, P less than 0.001), and among plasma [HCO3-], plasma PCO2, and NAE (r = 0.77, P less than 0.001). The partial correlation coefficients indicated a significant positive correlation between plasma [H+] and NAE, and a significant negative correlation between plasma [HCO3-] and NAE, when plasma PCO2 was held constant. These findings indicate that two factors influence the level at which plasma [H+] is maintained in normal subjects: (1) the steady-state rate of endogenous noncarbonic acid production, and (2) the setpoint at which plasma PCO2 is regulated by the respiratory system. Plasma [HCO3-] is also co-determined by these two factors. In disease states, therefore, both factors must be known before a disturbance in acid-base homeostasis can be excluded.

Metabolic alkalosis in models of primary and secondary hyperparathyroid states

Hyperchloremic metabolic acidosis has been reported in clinical states of primary and secondary hyperparathyroidism (HPT). Acute administration of parathyroid hormone (PTH) decreases renal acidification in humans and dogs, but the renal and systemic acid-base effects of chronic HPT have not been extensively investigated. In chronically thyroparathyroidectomized (TPTX) dogs (group I), bPTH 1-5 U/kg twice daily resulted in sustained hypophosphatemia, hypercalcemia, and Cl- -resistant metabolic alkalosis that was of renal origin at least in part: delta [HCO3-]p + 4.1 +/- 0.8 meq/liter, P less than 0.01; delta [H+]p -4 +/- 1 neq/liter, P less than 0.001, days 10-12. The cumulative change (sigma delta) in net acid excretion (NAE) was +44 meq (day 9, P less than 0.05). Similarly, metabolic alkalosis of renal origin, at least in part, occurred when PTH was administered by chronic continuous intravenous infusion (group II). Since chronic administration of calcitriol in dogs results in metabolic alkalosis, plasma calcitriol concentration was measured and found not to be increased by chronic intravenous PTH administration. In intact dogs (group III), a continuous chronic intravenous infusion of the Ca2+ chelator, Na4EGTA (3.0 mmol/kg daily), substituted for an equimolar amount of prechelated EGTA (CaNa2EGTA), resulted in a model of hypocalcemic HPT and severe Cl- -resistant metabolic alkalosis: delta [HCO3-]p +9.1 +/- 1.9 meq/liter, P less than 0.05; delta [H+]p -5 +/- 1 neq/liter, P less than 0.01, days 6-8. NAE decreased significantly. Thus, whereas metabolic alkalosis induced by PTH administration could be accounted for by increased NAE (group I), EGTA-induced metabolic alkalosis was accounted for by an extrarenal mechanism of base input to extracellular fluid (group III). Neutralization of the extrarenal base input by chronic administration of HCl during the period of EGTA-induced HPT did not preclude the development of metabolic alkalosis (group V), suggesting that a renal component was present in EGTA-induced metabolic alkalosis as well as in models of primary HPT (groups I and II). During the steady state, in this group as in the groups administered PTH, the net endogenous load of acid to the systemic circulation requiring renal excretion was unchanged from control, as indicated by stable values of NAE not significantly different from control. Yet metabolic alkalosis persisted in the steady state.(ABSTRACT TRUNCATED AT 400 WORDS)

Incidence of radiographically evident bone disease, nephrocalcinosis, and nephrolithiasis in various types of renal tubular acidosis

The syndrome of renal tubular acidosis has been categorized into three physiologic types that have different clinical findings and prognostic and therapeutic implications. We reviewed radiographs of the skeleton and kidneys in 92 patients (56 children and 36 adults) with renal tubular acidosis in order to determine whether the radiologic findings could be related to the type of syndrome. Forty-four patients had Type 1 renal tubular acidosis, 18 had Type 2, and 30 had Type 4. Evidence of skeletal abnormalities was uncommon (17 per cent) and was confined to patients who had the Type 2 disorder or azotemia. The children with Type 2 and skeletal abnormalities had rickets; the adults had osteopenia without pseudofractures. Nephrocalcinosis was evident in approximately one fourth of the group (29 per cent) and was restricted to patients with the Type 1 syndrome. In patients with Type 4, osteopenia was evident in 12 per cent, all of whom were azotemic. Our observations indicate that the radiographic manifestations of renal tubular acidosis are influenced by the physiologic type of renal tubular acidosis.

Disorders of distal nephron function

In this review, the distal nephron is considered to be that portion of the renal tubule commencing with the thick ascending limb of the loop of Henle and ending with the papillary collecting duct. The collecting duct, including its subdivisions in the cortex and medulla, originates from a different embryologic anlage than more proximal nephron segments, which may explain its morphologic and functional dissimilarities from the thick ascending limb and the distal convoluted tubule. This review summarizes selected aspects of the physiology of the distal nephron, with particular emphasis on the physiology of distal nephron transport of sodium, potassium, chloride and hydrogen ion. The pathophysiologic features of the following disorders of distal nephron function are reviewed: (1) pseudohypoaldosteronism, a heterogenous group of disorders in which the signs and symptoms are suggestive of aldosterone deficiency, but in which aldosterone levels are supernormal and administration of exogenous mineralocorticoid is not ameliorative; (2) pseudohyperaldosteronism (Liddle syndrome), a familial disorder in which the clinical manifestations closely resemble those resulting from an aldosterone-producing adenoma of the adrenal gland (primary aldosteronism), but in which the measured rate of aldosterone secretion and excretion is greatly subnormal; (3) Bartter syndrome and related syndromes of renal potassium wasting; (4) type 1 renal tubular acidosis (classic, distal); (5) type 4 renal tubular acidosis (hyperkalemic). Reference citations are generally to articles reporting recent advances in these areas and to review articles that contain comprehensive bibliographies.

Renal and systemic acid-base effects of chronic hypoparathyroidism in dogs

MEtabolic alkalosis has been reported in patients with chronic hypoparathyroidism under conditions of uncontrolled diet and medication intake. Hypoparathyroidism has also been reported to result in increased renal bicarbonate reabsorptive capacity in acutely bicarbonate-loaded dogs. However, the acid-base effects of experimentally induced chronic hypoparathyroidism have not been investigated in any species. Accordingly, we investigated the chronic effects of hypoparathyroidism by thyroparathyroidectomy (TPTX) plus thyroxine replacement on renal regulation of plasma acid-base composition under metabolic balance conditions of normal dietary acid load (group I) and alkali load (group II, 9.0 meq/kg HCO3(-) daily) in dogs ingesting a normal Cl-, high Ca2+ diet throughout study. For groups I and II pre-TPTX: [HCO3(-)]p, 19.7 +/- 1.0, 20.1 +/- 0.9 meq/liter. Plasma acid-base composition (days 5-10) was unchanged by TPTX: delta [HCO3(-)]p, -0.7 +/- 0.4, 0.0 +/- 0.2 meq/liter; delta [H+]p, 0 +/- 1, -1 +/- 0 neq/liter, NS from control. A reduction in plasma total calcium concentration ([CaT]p) occurred and persisted (group I: [CaT]p, -1.6 +/- 0.2 mg/100 ml, P less than 0.01, day 1 and -1.2 +/- 0.9, days 5-10; group II: -1.4 +/- 0.3 mg/100 ml, P less than 0.01, day 1 and -2.3 +/- 0.4, days 5-10). No significant change in net acid or Cl- excretion occurred following TPTX. Thus, chronic hypoparathyroidism characterized by a chronic reduction in [CaT]p does not result in significant alterations in renal regulation of plasma acid-base composition in the dog.

Mineralocorticoid-resistant renal hyperkalemia without salt wasting (type II pseudohypoaldosteronism): role of increased renal chloride reabsorption

A rare syndrome has been described in which mineralocorticoid-resistant hyperkalemia of renal origin occurs in the absence of glomerular insufficiency and renal sodium wasting and in which hyperchloremic acidosis, hypertension, and hyporeninemia coexist. The primary abnormality has been postulated to be a defect of the potassium secretory mechanism of the distal nephron. The present studies were carried out to investigate the mechanism of impaired renal potassium secretion in a patient with this syndrome. When dietary intake of sodium chloride was normal, renal clearance of potassium was subnormal (CK/GFR = 3.6 +/- 0.2%; normal subjects, 9.0 +/- 0.9%, N = 4) despite high normal or supernormal levels of plasma and urinary aldosterone. The fractional clearance of potassium remained subnormal (CK/GFR = 5.1 +/- 0.2%) during superimposed chronic administration of superphysiologic doses of mineralocorticoid hormone. Little increase in renal potassium clearance occurred when the delivery of sodium to distal nephron segments was increased further by the i.v. infusion of sodium chloride, despite experimentally sustained hypermineralocorticoidism. But potassium clearance increased greatly when delivery of sodium to the distal nephron was increased by infusion of nonchloride anions: sulfate (sodium sulfate infusion, low sodium chloride diet; CK/GFR = 63.7 +/- 0.4%) or bicarbonate (sodium bicarbonate plus acetazolamide infusion; CK/GFR = 81.7 +/- 1.7%). These findings indicate that mineralocorticoid-resistant renal hyperkalemia in this patient cannot be attributed to the absence of a renal potassium secretory capability or to diminished delivery of sodium to distal nephron segments; instead it may be dependent on chloride delivery to the distal nephron. We suggest that the primary abnormality in this syndrome increases the reabsorptive avidity of the distal nephron for chloride, which (1) limits the sodium and mineralocorticoid-dependent voltage driving force for potassium and hydrogen ion secretion, resulting in hyperkalemia and acidosis and (2) augments distal sodium chloride reabsorption resulting in hyperchloremia, volume expansion, hyporeninemia, and hypertension.

Renal and systemic acid-base effects of chronic spironolactone administration

Studies in dogs were carried out to investigate the effects of chronic administration of the mineralcorticoid antagonist spironolactone (15 mg/kg orally) on renal and systemic acid-base metabolism. In adrenalectomized dogs administered fixed mineralocorticoid and glucocorticoid replacement, spironolactone resulted in a definite renal antimineralocorticoid effect, as evidenced by natriuresis and chloruresis, and sustained metabolic acidosis and hyperkalemia due in part to impaired renal secretion of hydrogen and potassium. In adrenalectomized dogs receiving physiological glucocorticoid without mineralocorticoid, metabolic acidosis also occurred, but a marked stimulatory effect of spironolactone on net acid excretion occurred in association with increased urinary SO4-2 and total nitrogen excretion. Accordingly, spironolactone results in sustained renal tubular acidosis when administered in the presence of constant physiological levels of mineralocorticoid and glucocorticoid steroids. When administered under conditions of complete lack of mineralocorticoid activity, spironolactone exerts systemic and renal acid-base effects similar to those of a glucocorticoid steroid, namely, increased protein catabolism and sulfuric acid production with resultant extrarenal metabolic acidosis associated with increased net acid excretion.

Effect of mineralocorticoid replacement therapy on renal acid-base homeostasis in adrenalectomized patients

Chronic balance studies were performed in six adrenalectomized patients to investigate the renal and systemic acid-base consequences of mineralocorticoid deficiency in the absence of either glucocorticoid deficiency or parenchymal renal disease. Constant glucocorticoid replacement was provided with dexamethasone, 750 to 875 micrograms/day, administered orally. Creatinine clearance averaged 98 +/- 8 ml/min/1.73 m2. Following a control period, mineralocorticoid replacement with fludrocortisone (100 to 200 micrograms/day) was either discontinued (N = 3) or initiated (N = 2). In an additional patient, mineralocorticoid replacement was initiated and sustained (5 days) by continuous i.v. infusion of aldosterone, at a dose approximating the normal secretion rate (120 micrograms/day). Net acid excretion (NAE) and plasma total carbon dioxide decreased in each patient in whom mineralocorticoid was discontinued and increased in each patient in whom mineralocorticoid was initiated. The cumulative change in NAE (sigma delta NAE) independent of direction averaged 66 +/- 20 mEq (P less than 0.05) by the fifth experimental day in the six patients, and the corresponding change in plasma total CO2 averaged 1.2 +/- 0.3 mmoles/liter (P less than 0.02). The magnitude of sigma delta NAE correlated with the basal rate of NAE (r = 0.87, P less than 0.05), which averaged 0.9 +/- 0.1 mEq/kg body wt per day. The change in plasma total CO2 correlated with sigma delta NAE (r = 0.83, P less than 0.05). The changes in NAE correlated positively with the corresponding changes in sodium balance and negatively with the corresponding changes in potassium balance. These findings provide the first evidence that renal acidification is under tonic stimulation by mineralocorticoid at levels not exceeding those in normal subjects ingesting acid-producing diets of normal sodium and potassium content. The extent to which the tonic stimulation of renal acidification is mediated by a direct effect of mineralocorticoid on renal hydrogen ion transport or by an indirect effect dependent on altered renal sodium and/or potassium transport requires further investigation. The findings implicate mineralocorticoid deficiency as a significant renal acidosis-producing condition not dependent on the presence of renal disease or glucocorticoid deficiency, and potentially amplified when endogenous acid production is increased by diet or disease.

Renal and systemic acid-base effects of chronic dichloroacetate administration in dogs

Dichloroacetate (DCA) increases metabolic disposal of lactic acid secondary to activation of pyruvate dehydrogenase and consequent acceleration of pyruvate oxidation. DCA has thus been proposed as a therapeutic agent for clinical states of lactic acidosis. Yet, DCA has a potential metabolic acidosis-producing effect by virtue of reported effects of (A) increasing blood ketoacid concentration, (B) decreasing tubular reabsorption of filtered ketoacid anions, and (C) decreasing renal NH3 production. In the present study chronic administration of DCA, 50 mg/kg p.o. daily for 6-8 days, resulted in a cumulative increase in renal net acid excretion (NAE) (sigma delta NAE, +61 meq, p < 0.05). The increase in NAE was accounted for entirely by increased NH4+ excretion. Production of ammonia by the kidney appeared to be increased since the increased excretion of NH4+ was accompanied by an increase in urine pH (delta UpH, +0.18 +/- 0.07, p < 0.05). The increase in NAE was accompanied by a nearly identical increase in urinary anion gap (UAG) (UAG = [NH4+ + Na+ + K+] - [Cl- + HCO3- + HPO4(2-) + H2PO4-]). The increase in UAG was caused by increased urinary total organic anions, accounted for at least in part by a significant increase in urinary acetoacetate. No significant increase in urinary potassium or sodium excretion occurred. A change in plasma acid-base composition occurred that was consistent with a mild respiratory acidosis without associated primary metabolic acidosis or alkalosis. These findings indicate that chronic DCA administration results in (1) increased steady state endogenous noncarbonic organic acid production, and (2) retention of carbonic acid. Further investigation of the potential metabolic and respiratory acidosis-producing effects of DCA is required to determine its clinical efficacy in the treatment of clinical lactic acidosis.

Effects of glucocorticoid steroids on renal and systemic acid-base metabolism

Clinical states of hyperglucocorticoidism are associated with renal metabolic alkalosis, yet the systemic and renal acid-base response to chronic administration of glucocorticoid steroids (dexamethasone, triamcinolone) possessing little or no mineralocorticoid activity has not been investigated. In balance studies studies in dogs administration of triamcinolone (Tcn), 1.0 mg . kg-1 . day-1 for 6-9 days (group I, n = 5), resulted in a persistent reduction in urine pH and increase in net acid excretion (NAE), and in the excretion of urinary unmeasured anions (C+NH4,Na;K minus A-Cl,HCO3,Pi), which were identified as organic anions and sulfate. A significant degree of metabolic acidosis occurred initially (delta [HCO3-]p, -3.4 meq/liter, P less than 0.05, day 1). As Tcn administration was continued, the cumulative increment in net acid excreted exceeded the cumulative increment in urinary unmeasured anion excreted and [HCO-3]p returned to pre-Tcn control values and remained stable thereafter. In the steady state of Tcn administration plasma potassium concentration and renal potassium clearance were not significantly different from pre-Tcn control, in contrast to the findings of hypokalemia and increased renal potassium clearance during chronic administration of deoxycorticosterone (DOC). Triamcinolone did not result in antinatriuresis or antichloruresis. Chronic administration of a 10-fold smaller dose of Tcn (0.1 mg . kg-1 . day-1) in an additional group (group III) also resulted in a persisting reduction in urine pH and an increase in net acid excretion that exceeded unmeasured anion excretion and resulted in a small increase in steady-state plasma bicarbonate concentration. These results suggest that chronic administration of potent glucocorticoid steroids results in 1) a persisting increase in endogenous acid production, and 2) stimulation of renal hydrogen ion secretion that was of greater degree than accounted for by the increment in endogenous acid production and that was not accompanied by renal mineralocorticoid effects on sodium and potassium transport.

Pathophysiology of chronic renal tubular acidosis induced by administration of amiloride

Amiloride is a "potassium-sparing" diuretic agent of moderate natriuretic potency with site of action in postmacula densa segments of the distal nephron. In isolated segments of mammalian cortical distal nephron, amiloride diminishes sodium reabsorption and transtubular electrical PD and inhibits potassium secretion. We investigated the effects of long-term administration of a demonstrably maximal dose of amiloride (1.0 mg/kg b.i.d.) on plasma and urine acid-base and electrolyte composition in fixed steroid-replaced ADX dogs. Amiloride administration resulted in potassium retention and hyperkalemia and reduced net acid excretion and caused chronic hyperchloremic metabolic acidosis. The cumulative reduction in net acid excretion and severity of systemic acidosis were not significantly different in additional groups in which potassium retention was prevented by restriction of dietary potassium during amiloride administration or in which amiloride was administered to animals with pre-existing dietary potassium depletion. The response of urine pH and ammonium excretion, however, differed among groups. In the steady state of chronic acidosis, urine pH and ammonium concentration were lowest in the hyperkalemic group and highest in the hypokalemic group, and among the three groups pH and ammonium were positively correlated (r = 0.67, p less than 0.001). Ammonium concentration varied inversely with plasma potassium concentration. Net acid excretion rates returned to control levels during the steady state of chronic amiloride-induced acidosis in the three groups. During continued amiloride administration, sustained correction of acidosis by long-term oral administration of sodium bicarbonate did not result in negative values of net acid excretion; that is, amiloride did not cause net wasting of base at normal plasma bicarbonate concentration. The results of these studies suggest that chronic amiloride administration results in a sustained impairment of renal hydrogen ion secretion restricted to the distal nephron and not dependent on alterations in potassium balance. Differences in potassium balance (positive or negative) appeared to influence only the availability of ammonia for diffusion into urine and steady-state urine pH, but not the steady-state net rate of renal hydrogen ion secretion during amiloride. These studies identify an experimental model of chronic distal renal tubular acidosis in which external hydrogen ion balance is re-established during chronic acidosis even when the availability of ammonia for excretion is decreased.

The use of dragonfly nymphs in the control of Aedes aegypti

The predatory rates of the dragonfly nymphs on Aedes aegypti were studied in the laboratory and under field conditons. Labellulid nymphs were found to predate on Ae. aegypti larvae and pupae readily. The rate of consumption was found to be 133 +/- 21 all stages of larvae per medium size nymph per 24 hours. In container habitats complete elimination of all larvae and pupae were achieved between day 4 and 9 depending on density of aquatic stages. The dragonfly nymphs as predators could be used in biological control of Aedes mosquitoes.

Pathogenesis of renal hyperchloremic acidosis resulting from dietary potassium restriction in the dog: role of aldosterone

In dogs dietary K+ restriction (16 days) results in diminished urinary net acid excretion (NAE) and systemic hyperchloremic metabolic acidosis (sigma delta NAE, -200 meq; delta[HCO3-]p, -2.9 +/- 0.3 meq/liter, P less than 0.05). Urinary aldosterone (aldo) excretion decreased by 34 +/- 3% (P less than 0.001) and metabolic clearance rate of aldo increased by 80 +/- 17% (P less than 0.02) during K+ restriction. Daily subcutaneous injection of a small amount of exogenous aldo (20 micrograms) during K+ restriction significantly attenuated the reduction in NAE (sigma delta NAE -51 vs. -200 meq, P less than 0.05) without raising plasma aldo concentrations to levels greater than control. These findings suggest that hypoaldosteronism induced by potassium depletion is at least in part the cause of the observed renal tubular acidosis. In adrenalectomized (ADX) dogs maintained on fixed mineralocorticoid and glucocorticoid replacement (aldo dose 60 micrograms/day), K+ restriction resulted in a significant degree of renal metabolic acidosis (delta[HCO3-]p, -1.4 +/- 0.3 meq/liter, P less than 0.01). In these ADX dogs, the exogenous supply of aldo was fixed but hypoaldosteronism may have developed owing to increased metabolic clearance rate of aldo caused by dietary K+ depletion. When mineralocorticoid replacement was withheld in ADX dogs, the steady-state degree of renal metabolic acidosis was no more severe in animals with preexisting dietary K+ depletion (16 days) than in the same animals when mineralocorticoid was withheld without preexisting K+ depletion. Thus, when neither endogenous nor exogenous aldo is present, K+ depletion does not result in a renal acidosis-producing effect that exacerbates that of aldo deficiency. The results of these studies suggest that the reduction in NAE and consequent metabolic acidosis induced by dietary K+ depletion is at least in part a consequence of aldo deficiency, and provide no evidence of an additional defect in acidification not caused by aldo deficiency.

Prevalence, pathogenesis, and functional significance of aldosterone deficiency in hyperkalemic patients with chronic renal insufficiency

Our findings indicate that hypoaldosteronism occurs commonly (23/31 patients) in hyperkalemic patients with chronic renal insufficiency and that the deficiency of aldosterone contributes to the pathogenesis of the hyperkalemia. In most patients (83%), hypoaldosteronism could be accounted for by deficient renal secretion of renin, but in some patients (17%) overt renin deficiency did not appear to be present, and therefore other (unidentified) causes of aldosterone deficiency must be invoked. The results also indicate that the urinary excretion rate of aldosterone secretion rate in this group of patients.

Correction of metabolic acidosis by the kidney during isometric expansion of extracellular fluid volume

In dogs with chronic hypochloremic metabolic alkalosis associated with ECFV contraction, plasma [HCO-3] ([HCO-3]p) normalizes during expansion of ECFV with a solution containing Cl- and HCO-3 in concentrations duplicating those in the plasma before expansion (isometric expansion). The kidney selectively rejects administered HCO-3 and retains Cl-. If this preferential Cl- less than HCO-3 reabsorptive selectivity were a characteristic renal response to ECFV expansion, isometric expansion during hyperchloremic acidosis would exacerbate the acid-base disturbance rather than correct it as it does in alkalosis. We examined the effect of isometric expansion in dogs with chronic hyperchloremic metabolic acidosis induced by HCl feeding or mineralocorticoid hormone deficiency. During expansion, as the expected decrease occurred in the fractional reabsorption of Na+, a lesser decrease occurred in fractional reabsorption of HCO-3, whereas a greater decrease occurred in fractional reabsorption of Cl-. The kidney selectively retained administered HCO3 and rejected Cl-. [HCO-3]p normalized. The shift to bicarbonate-selective from chloride-selective anion reabsorption during ECFV expansion in metabolic acidosis vs. metabolic alkalosis indicates that in response to ECFV expansion- the kidney selectively alters the ratio of bicarbonate to chloride concentration in the tubular reabsorbate in the direction that tends to normalize plasma acid-base composition, irrespective of the direction of deviation of the initial plasma bicarbonate concentration. The signal that initiates the shift in anion reabsorptive selectivity remains to be identified.