Mechanisms of dopamine effects on Na-K-ATPase activity in Madin-Darby canine kidney (MDCK) epithelial cells

Dopamine decreases tubular sodium reabsorption, attributed in part to Na-K-ATPase inhibition in the proximal convoluted tubule (PCT). Because the final regulation of sodium excretion occurs in the collecting duct, where specific dopamine DA1 binding sites have been demonstrated, we examined the effects of dopamine, as well as of DA1 and DA2 receptor agonists on Na-K-ATPase activity and on the number of units in Madin-Darby canine kidney (MDCK) cells, which retain differentiated properties of the renal cortical collecting tubule epithelium. Dopamine (10(-5) M) inhibited pump activity (by 50%) and reduced the number of units. This effect was reproduced by the DA1 agonist SKF 38393, which inhibited pump activity in a dose- and time-dependent manner (maximum, 10(-5) M). The DA2 agonist quinpirole hydrochloride was without effect, either alone or in combination with SKF 38393. Inhibition of pump activity by dopamine was totally abolished by H7 (100 microM), an inhibitor of protein kinase (PK), but partially by 2',5'-dideoxy-adenosine (DDA) and H4, respective inhibitors of cAMP production and PKA, which suggests that the dopamine effect on Na-K-ATPase activity may be linked to activation of both PKC and PKA. In these cells, amiloride addition during preincubation did not alter the effect of dopamine on Na-K-ATPase activity; in contrast, furosemide increased further the inhibitory effect of dopamine on the enzyme activity. Monensin addition (10(-3) M) reversed the inhibitory effect of dopamine after a 30-min preincubation.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of lipoxygenase products of arachidonate metabolism on parathyroid hormone secretion

High extracellular Ca2+ (Ca2+ ec) stimulates the formation of inositol phosphates and diacylglycerol and activates phospholipase A2 in porcine parathyroid cells. Ca2+ ec action is also coupled to the formation of arachidonic acid, the precursor of both the cyclooxygenase and lipoxygenase (LO) pathways. We previously reported that LO pathway products might act as second messengers and play a part in regulating PTH secretion by Ca2+ ec. We have now investigated the effects of hydroxyeicosatetranoic acids (HETEs) on PTH secretion. Collagenase-dispersed porcine parathyroid cells were incubated in low [Ca2+] (0.5 mM, maximal stimulation) with or without HETEs for three 15-min periods. 12- and 15-HETEs inhibited PTH secretion in a dose-dependent manner from 10(-12) to 10(-9) M. Maximal inhibition was with 10(-9) M. Since 12- and 15-HETEs are the metabolic reduction products of 12- and 15-HPETEs, we also examined the effect of those precursors on PTH release. 12- and 15-hydroxyperoxyeicosatetranoic acids (HPETEs) were more potent inhibitors of PTH secretion. The threshold concentrations of both HPETEs that inhibited PTH release were lower than those for HETEs: 10(-9) M suppressed PTH secretion. This effect is comparable to that of high [Ca2+] (2 mM). This provides new evidence that products of 12-LO and 15-LO pathways are potent inhibitors of PTH secretion.

Endothelin-1 in children with chronic renal failure

Endothelin-1 (ET-1) was measured after extraction from plasma of normal adults (5.9 +/- 1.9 pg/ml, n = 22), normal children (7.1 +/- 1.86 pg/ml, n = 29), non-haemodialysed children with chronic renal failure (CRF) (11.1 +/- 1.8 pg/ml), n = 10), renal graft recipients (9.5 +/- 3.4 pg/ml, n = 37), haemodialysed children 24 h after a haemodialysis session (20.02 +/- 10.9 pg/ml, n = 26) and haemodialysed children before and after a haemodialysis session (15.31 +/- 10.6 and 13.8 +/- 8.5 respectively, n = 14). A sensitive and specific radioimmunoassay was used. ET-1 was significantly higher in non-haemodialysed CRF children and in renal graft recipients than in normal children (P < 0.001 and P < 0.01, respectively) and significantly higher in haemodialysed children when compared with normal children, non-haemodialysed CRF children and renal graft recipients (P < 0.001). ET-1 concentrations were similar in normal children and normal adults. ET-1 was inversely correlated with glomerular filtration rate in non-haemodialysed CRF children (r = -0.39, P < 0.01) and positively correlated with extracellular volume in haemodialysed children (r = 0.435, P < 0.03). After haemodialysis, ET-1 increased in 6 and decreased in 8 of the 14 children studied before and after a haemodialysis session.

Creation of experimental urethral obstruction in utero: evaluation of fetal renal function

Management of obstructive uropathy diagnosed in utero would be markedly enhanced by the availability of a simple, safe and quantitative fetal renal function test to predict postnatal renal function. In order to allow experimental evaluation of such a parameter, we adjusted a model of complete urethral obstruction with urachal ligation in 30 fetal lambs at 79 or 99 days of gestation. The method described allows obstruction in male and female fetuses as early as 79 days of gestation, with an overall high survival rate (control: 12/14; obstructed: 23/29), although lower (6/12) when obstruction is performed early (79 days) during gestation. Consequences of obstruction were examined on the 121st day of gestation. Severe hydronephrosis, ureteral and calyceal dilatation, with or without ascites and pulmonary hypoplasia were observed in all fetuses; creatinine clearance determined in utero was decreased in both groups with obstruction (early and late) vs control group: 1.15 +/- 0.5, NS, and 0.58 +/- 0.4, p < 0.01 vs 1.61 +/- 0.8 ml/min/kg respectively. In both obstructed groups, fetuses with ascites displayed lower plasma creatinine concentration and higher creatinine clearance values when compared to fetuses without ascites. In conclusion, the experimental model of obstructive uropathy described appears efficient and easily reproducible, allowing therefore the evaluation of a predictive parameter of postnatal renal function. Our preliminary results suggest that renal fetal function is more dependent on the degree of obstruction than on the term of its creation.

Acute and early effects of aldosterone on Na-K-ATPase activity in Madin-Darby canine kidney epithelial cells

The time course and mechanism of early effects of aldosterone on renal Na-K-adenosinetriphosphatase (Na-K-ATPase) activity and number of units were studied in MDCK cells. Aldosterone induced a time- and dose-dependent stimulation of Na-K-ATPase activity. The stimulatory effect of aldosterone on activity and number of pump units increased progressively and was inhibited by spironolactone. In presence of cycloheximide, the stimulatory effect of aldosterone on activity and number of catalytic sites persisted to the same extent until 30 min and decreased by 20% after 60 min. In these cells, dimethylamiloride addition during preincubation abolished the aldosterone-induced stimulation in Na-K-ATPase activity up to 60 min. In contrast, furosemide addition did not alter the effect of aldosterone on Na-K-ATPase activity. The present study demonstrates an early effect of aldosterone on Na-K-ATPase activity that can be separated into the following two successive periods: 1) increase in pump number due to insertion of presynthetized units secondary to Na entry through an amiloride-sensitive apical pathway; and 2) an increase in pump number by de novo protein synthesis.

Attrition from an evening alcohol rehabilitation program

In recent years many groups have become interested in the potential cost savings and efficacy of outpatient treatment for chemical dependency. This study was originally conceived to answer questions of both patients and staff concerning graduation and attrition rates in an evening outpatient alcohol treatment program. Of particular interest were gender effects, rates of attrition across two progressive program levels, and whether alcohol-only users and self-initiated clients fared better in treatment than did polysubstance users and patients who were referred by others. Medical records were available for 103 of the 107 treated patients, and of these, 27 remained in the program until graduation. Women were more likely to graduate and remain in the program longer than men. Alcohol users were more likely to graduate than subjects with additional substance use disorders. Graduation rates did not differ significantly between contact initiators and noninitiators; however, the former dropped out of treatment more quickly. The study is an example of the potential use of data obtained from an existing agency data base.

Recommendation on sampling, transport, and storage for the determination of the concentration of ionized calcium in whole blood, plasma, and serum. IFC Scientific Division, Working Group on Ion-Selective Electrodes (WGSE)

The substance concentration of ionized calcium (cCa 2+) in blood, plasma, or serum preanalytically may be affected by pH changes of the sample, calcium binding by heparin, and dilution by the anticoagulant solution. pH changes in whole blood can be minimized by anaerobic sampling to avoid loss of CO 2, by measuring as soon as possible, or by storing the sample in iced water to avoid lactic acid formation. cCa 2+ and pH should be determined simultaneously. Plasma or serum: If centrifuged in a closed tube and measured immediately, the pH of the sample will be close to the original value. If there has been a delay between centrifugation and measurement, causing substantial loss of CO 2, equilibration of the sample with a gas mixture corresponding to pCO 2 = 5.3 kPa prior to the measurement is recommended. Conversion of the measured values to cCa 2+ (7.4) is only valid if the pH is in the range 7.2-7.6. Ca 2+ binding by heparin can be minimized by using either of the following: 1) a final concentration of sodium or lithium heparinate of 15 IU/mL blood or less; or 2) calcium-titrated heparin with a final concentration of less than 50 IU/mL blood. Dilution effect can be avoided by use of dry heparin in capillaries or syringes.(ABSTRACT TRUNCATED AT 250 WORDS)

Evaluation of capillaries for ionized calcium measurements

Commercially available capillaries containing calcium-titrated heparinate as an anticoagulant designed specifically for ionized calcium measurements in blood were tested with four serum pools with ionized calcium concentrations adjusted to 0.75, 1.25, 1.50 and 2.50 mmol/L. Although this is the best available anticoagulant for this purpose, the use of these capillaries induced a +/- 1% alteration of the original concentration around the titration level and changes of -2 to +10% at pathological values. The amount of heparinate released exceeded the recommended limit of 50 IU/mL of specimen with some variability (6% to 20%). Increasing the amount of anticoagulant with the objective of avoiding magnetic mixing did not seem to be a valid approach. Finally, Radiometer, IL and AVL capillaries gave the best available and acceptable results in terms of alterations in ionized calcium.

Protein kinase C activation causes inhibition of Na/K-ATPase activity in Madin-Darby canine kidney epithelial (MDCK) cells

To evaluate the influence of protein kinase C (PKC) activation on Na/K-ATPase activity in MDCK cells, we studied the effect of phorbol myristate acetate (PMA) and two diacylglycerol analogues, oleoylacetylglycerol and dioctanoylglycerol, on the enzyme activity. Na/K-ATPase activity was determined by cytochemistry. PMA induced a time- and dose-dependent inhibition of Na/K-ATPase activity and at 100 ng/ml decreased the enzyme activity by 55% of the initial value. These effects were mimicked by oleoylacetylglycerol and dioctanoylglycerol, and were abolished by two inhibitors of PKC, 1-(5-isoquinolinylsulphonyl)-2-methylpiperazine (H7) and sphingosine. A phorbol ester that does not activate PKC, 4 alpha-phorbol 12,13-didecanoate, did not inhibit Na/K-ATPase activity. PMA inhibition persisted in the presence of cycloheximide and actinomycin D but not in the presence of amiloride. Dopamine (10 microM) inhibition of Na/K-ATPase activity was abolished in a dose-dependent manner by sphingosine. Results suggest that in MDCK cells Na/K-ATPase is an effector protein for PKC and that dopamine inhibition of its activity may be mediated by PKC.

Effects of prolactin on Na+K(+)-ATPase activity in the nephron during maturation in the rat

The effect of prolactin (PRL) on renal Na+K(+)-ATPase was investigated in 7-d-old neonatal rats. Animals were treated by bromocriptine (Br; a blocker of endogenous PRL secretion), and the enzyme activity was compared with that of untreated controls. Na+K(+)-ATPase was determined in renal sections in the medullary thick ascending limb of Henle's loop and in the distal tubule by cytochemistry. In the distal tubule, Na+K(+)-ATPase activity was significantly lower in Br-treated animals than in controls (330 +/- 169 versus 558 +/- 146 pmol inorganic phosphate/mm/h, respectively); values did not differ in the medullary thick ascending limb of Henle's loop between Br-treated and control animals (132 +/- 74 versus 165 +/- 113 pmol inorganic phosphate/mm/h, respectively). In vitro effects of PRL were investigated by determining the enzyme activity after incubation of renal sections from Br-treated and untreated animals with different concentrations of PRL. Results suggest that PRL may affect renal Na+K(+)-ATPase activity in the distal tubule in the neonatal period but do not support a major role of PRL in the enzyme maturation.

Phospholipase-A2 action and arachidonic acid metabolism in calcium-mediated parathyroid hormone secretion

The involvement of arachidonic acid (AA) and its metabolites in the control of PTH secretion by porcine parathyroid cells was investigated. Increasing the extracellular calcium concentration from 0.5 to 2 mM increased free [3H]AA release and decreased PTH secretion from labeled parathyroid cells as a function of time (1-30 min). Free [3H]AA in the medium was significantly increased (+153 +/- 6%) after 5 min, while PTH secretion was significantly decreased (-75 +/- 7%) only after 15 min, suggesting a link between the two. [3H]AA release was associated with a decrease in [3H]AA incorporated into phosphatidylinositol, phosphatidic acid, and phosphatidylcholine, suggesting that these phospholipids are the major source of AA. Exogenous phospholipase-A2 (PL-A2; 1-500 mU/ml) and AA (5-40 microM) inhibited PTH secretion in a dose-dependent manner. PTH secretion inhibited by 2 mM Ca2+ was restored by two PL-A2 inhibitors, indomethacin (30 microM) and mepacrine (50 microM). The cyclooxygenase pathway inhibitor ibuprofen (20 microM) did not restore PTH secretion of affect high Ca(2+)-, AA-, or PL-A2-inhibited PTH secretion. Two inhibitors of the lipoxygenase pathway (LO), phenidone (1 microM) and baicalein (0.1 microM), a relatively selective 12-LO inhibitor, blunted high Ca(2+)-induced inhibition of PTH secretion (+101 +/- 10% and +105 +/- 6%, respectively), but nordihydroguaiaretic acid, which inhibits the 5-LO pathway, did not restore PTH secretion inhibited by high Ca2+, AA, or PL-A2. These results suggested that AA and agents that cause its liberation inhibit PTH secretion. AA may act via the 12-LO, but not via the 5-LO or cyclooxygenase, pathway. Thus, 12-LO products may be second messengers in parathyroid cells.

International Federation of Clinical Chemistry (IFCC), scientific division: IFCC recommendation on sampling transport and storage for the determination of the concentration of ionized calcium in whole blood, plasma and serum

The substance concentration of ionized calcium (cCa2+) in blood, plasma or serum preanalytically may be affected by pH changes of the sample, calcium binding by heparin, and dilution by the anticoagulant solution. pH changes in whole blood can be minimized by anaerobic sampling to avoid loss of CO2, by measuring as soon as possible or by storing the sample in iced water to avoid lactic acid formation. cCa2+ and pH should be determined simultaneously.

The sleep apnoea syndrome in obesity: risk of sudden death

A total of 34 severely obese men with a history of heavy snoring and excessive daytime sleepiness indicative of obstructive sleep apnoea syndrome (OSAS) were studied prospectively. Their mean age was 46 years, and mean body mass index was 41.6 kg m-2. During a 4-year follow-up, 15% (5/34) of these subjects died (three cases of acute myocardial infarction and two cases of pulmonary oedema), all of them suddenly and unexpectedly, outside hospital. On autopsy the degree of atherosclerosis was found to be moderate in all cases. In 68% (15/22) of the men a pathological apnoea index (mean value 46 +/- 20) confirmed the OSAS diagnosis. Exercise tests and neurological examinations did not reveal any other causes of daytime sleepiness. Mean blood pressure at rest and during exercise was normal, and mean serum lipid and blood glucose levels were normal. Spirometry revealed intrapulmonary restrictive changes that could not be attributed to the heavy thoracic wall. Compliance was reduced to about 50% of reference values, and the mean pCO2 level (5.8 kPa) was close to the upper reference limit. Blood tests suggested that high alcohol consumption may be an important factor contributing to OSAS. These results demonstrate that morbidly obese men with a history of OSAS have a high risk of sudden cardiovascular death, despite the absence of other conventional risk factors.

Protein-metabolism kinetics and energy-substrate utilization in infants fed parenteral solutions with different glucose-fat ratios

The relative effect of glucose and lipids on whole-body protein-metabolism kinetics was assessed in seven infants undergoing parenteral feeding. Protein intake was kept constant and nonprotein energy was either provided as glucose alone or as an isoenergetic glucose-lipid mixture according to a randomized crossover trial. Protein metabolism and energy-substrate utilization were assessed by a primed, constant L-[13C]leucine infusion, combined with indirect calorimetry. There was a significant difference in the pattern of energy-substrate utilization according to regime. Protein turnover (11.3 +/- 0.7 vs 9.8 +/- 0.4 g.kg-1.d-1; P less than 0.05), protein breakdown (8.4 +/- 0.6 vs 7.1 +/- 0.4 g.kg-1.d-1; P less than 0.05), and amino acid oxidation rates (2.7 +/- 0.4 vs 1.4 +/- 0.5 g.kg-1.d-1; P less than 0.05) were higher for the glucose than the glucose-lipid treatment, whereas protein-synthesis rates did not significantly differ. These results suggest that the nature of energy substrates delivered to parenterally fed infants may affect protein metabolism.

Autonomic nervous system function in patients with primary obstructive sleep apnoea syndrome

Ten patients with obstructive sleep apnoea syndrome cured by uvulopalatopharyngoplasty were compared to nine patients considered as surgical failures, using cardiovascular reflex tests--Valsalva manoeuvre, respiratory sinus arrhythmia, isometric handgrip and head-up tilt. Two patients had signs of moderate vagal dysfunction, but no case of definite autonomic nervous dysfunction was diagnosed. The overall results indicated sympathetic overreactivity, positively correlated to oxygen desaturation indices and remaining after successful treatment. Four patients did not exhibit bradycardia during sleep apnoea. Two of them had decreased respiratory sinus arrhythmia when awake, but two had normal values. This implies a difference in vagal responsiveness between the awake and sleeping states, or that other factors besides vagus function influence the bradycardia response to apnoea. The group mean values were all within normal limits. There was no significant difference between the two groups in any test. Autonomic nervous dysfunction therefore does not seem to contribute to surgical failure, nor to occur with increased incidence among patients with primary obstructive sleep apnoea syndrome.

The exploding head syndrome: polysomnographic recordings and therapeutic suggestions

Attention has recently been drawn to a condition termed the exploding head syndrome, which is characterized by unpleasant, even terrifying sensations of flashing lights and/or sounds during reported sleep. Nine patients complaining of sensations of explosions in the head during sleep or drowsiness were investigated with polysomnographic recordings. None of them had any neurological disorder. Five patients reported explosions during the recording sessions. According to the recordings, the attacks always took place when the patients were awake and relaxed. In two cases abrupt electroencephalographic (EEG) and electromyographic changes indicating increasing alertness were recorded at the time of the reported attacks. In the remaining three cases no EEG changes were seen. Thus, there were no indications of an epileptic etiology to the condition. In all patients the symptoms ameliorated spontaneously with time. The severity of the symptoms was reduced by reassurance of the harmlessness of the condition. Clomipramine was prescribed to three patients who all reported immediate relief of symptoms. It is concluded that symptoms of this type are probably not true hypnagogic phenomena but may be an expression of emotional stress in the awake state.

Use of calcium-titrated sodium heparinate for ionized calcium determination on plasma and whole blood (heparinized blood sampler B-129 Radiometer)

We report modifications of ionized calcium as observed on specimens collected in a commercially available sampling device (Radiometer B-129). When the sampler is used as recommended, errors are non-significant around 1.25 mmol l-1. There is a +3% increase for low (0.75 mmol l-1) values and a -2% decrease for high (2.50 mmol l-1) values. Incomplete syringe-filling increases these errors.

In vitro evaluation of a heparinized blood sampler for ionized calcium measurement

When ionized calcium measurements are needed urgently blood has to be sampled with an anticoagulant to allow rapid specimen processing. Heparinate salts cause a decrease in ionized calcium by binding which is clinically significant when the concentration exceeds 15 IU/mL of whole blood. The use of an anticoagulant in an aqueous state induces 'solution-dilution' errors. To avoid these two types of error the use of calcium-titrated sodium heparinate in a dry state has been proposed. However, in this situation the actual calcium concentration could be modified if its value were different from the titration level. This possibility has been studied using a commercially available sampler (Radiometer B-129). When the sampler was used as recommended, errors were non-significant around 1.25 mmol/L. There was a +3% increase for low (0.75 mmol/L) values and a -2% decrease for high (2.50 mmol/L) values. Incomplete syringe filling increased these errors.

Preanalytical errors in ionized calcium measurements induced by the use of liquid heparin

The use of heparin in a liquid form to measure ionized calcium (Ca++) in plasma or whole blood can induce preanalytical errors by dilution and by changing the original Ca++ value by binding or by re-equilibration with calcium in the anticoagulant solution. To quantify these errors, Ca++ was measured on serum pools under different sampling conditions. Incomplete syringe filling and specimen volume/syringe nominal volume ratio effects were tested. Syringes were rinsed with saline to yield pure dilution effects, with sodium heparinate to study binding and with calcium-titrated heparinate to evaluate 'calcium-distortion'. Detailed tables provide percentage error values for all sampling conditions. Dilution errors could reach -5% and binding was always important (-14 to -50%). Distortion was minimal around 1.25 mmol/L but could reach -4% for high and +8% for low Ca++ values. Errors increased when syringes were not filled to their nominal volume, especially with small-sized specimens.

Protein A-sepharose used to measure free insulin in plasma

Diabetic patients receiving insulin therapy generally develop anti-insulin antibodies that must be eliminated, usually by extraction with polyethylene glycol (PEG), before determining the concentration of free (active) insulin in plasma. We describe a new method for removing such antibodies, with the use of Protein A coupled to Sepharose microspheres. The results correlate well with those by the PEG method, although values are systematically higher or lower for given samples, according to the initial titer of the antibody measured in terms of binding capacity. Further studies are required to clarify this observation.

Simulated long-term driving performance before and after uvulopalatopharyngoplasty

To investigate whether automobile drivers with the clinical features of sleep apnea syndrome (SAS) perform worse than controls in a simulated long-term test drive, and to see if their driving improves after uvulopalatopharyngoplasty (UPPP), 15 male drivers with SAS, suffering from sleep spells whilst driving, and 10 matched controls without a history of SAS or hypersomnia at the wheel were tested in an advanced driving simulator. Brake reaction time, lateral position deviation and off-road episodes were measured during a 90-min rural drive at twilight conditions. The clinical evaluation was made by a questionnaire scoring symptoms of snoring, sleep disturbances and diurnal sleepiness before and after surgery. Before UPPP the patient group showed impaired performance in all three effect measures compared to controls. UPPP resulted in improved reaction time performance (average mean improvement: 0.5 s, average 90th percentile improvement 0.8 s). Furthermore, 12 of the 15 patients reported a marked improvement regarding sleepiness whilst driving. For these clinically successful cases the number of off-road episodes decreased substantially. We conclude that most patients improve their long-term driving performance as a result of UPPP.

Does Swedish amateur boxing lead to chronic brain damage? 1. A retrospective medical, neurological and personality trait study

Sweden banned professional boxing in 1969 and has also considered banning amateur boxing. We therefore analysed possible chronic brain damage in 47 former amateur boxers who started their careers after the introduction of stricter Swedish amateur boxing rules. The boxers were compared with three control groups--25 soccer players, 25 track and field athletes and 19 conscripts. All athletes were interviewed about their sports career, medical history and social variables. They then underwent a physical and a neurological examination, including a mini-mental state examination. Personality traits were investigated and related to their platelet MAO activity in the athletes as well as in the conscripts. No significant differences were found between the groups in any of the physical or neurological examinations. All had a normal mini-mental state examination. Thus, results from these test methods did not reveal any signs of chronic brain damage from Swedish amateur boxing. Neither were any significant differences found with regard to platelet MAO activity, while significant differences were found in some of the social and personality traits variables.