Cyclosporine-induced hypertension and decline in renal function in healthy volunteers.

OBJECTIVE: To investigate the effect of cyclosporine A (CsA; Sandimmun Neoral) on systemic and renal hemodynamics, tubular function, and sodium excretion in healthy volunteers. Furthermore, we studied whether CsA enhances the systemic and renal hemodynamic sensitivity to norepinephrine. METHODS: Eighteen healthy volunteers were administered 10 mg/kg CsA or placebo capsules in a double-blind fashion. The mean arterial blood pressure (MAP), renal vascular resistance (RVR), glomerular filtration rate (GFR), and renal clearances of lithium (CLi) and sodium (CNa) were measured for 8 h after ingestion of the capsules. Norepinephrine (2 microg/kg per h) was infused intravenously for 1.5 h into nine subjects. RESULTS: CsA increased the MAP by 17+/-2 mmHg. The GFR decreased by 18+/-2% (P < 0.001) and the RVR increased by 37+/-4% (P< 0.001) after ingestion of CsA. The CsA-induced increase in MAP preceded the CsA-induced fall in GFR. The rise in MAP was followed by an early 35+/-8/0 increase in CNa (P < 0.001). At the end of the 8 h study period, CNa decreased by 25+/-7% (P < 0.001). Using CLi, it was found that the initial natriuresis had been caused by a relative decrease both in proximal and in distal tubular reabsorption of sodium, whereas the late sodium retention was secondary to the CsA-induced fall in GFR. Infusion of norepinephrine increased the MAP, RVR, and filtration fraction, and decreased the renal plasma flow, without CsA having any additional effect. CONCLUSION: It was demonstrated that a single oral dose of CsA caused a rise in blood pressure and transient natriuresis, followed by a fall in GFR and antinatriuresis. Thus, the present study confirms and extends earlier observations that renal dysfunction and sodium retention are not the initiating events in CsA-induced hypertension. The study also affords evidence suggesting that such rises in blood pressure are not mediated by an increased sensitivity to norepinephrine.

Effects of nitric oxide blockade and cyclosporin A on cardiovascular and renal function in normal man.

OBJECTIVE: The present study investigated whether the nitric oxide (NO) system is involved in cyclosporin A (CsA)-induced changes in cardiovascular and renal function in man. SUBJECTS AND METHODS: Ten healthy volunteers were investigated twice--with and without intake of a single dose of CsA (8 mg/kg). N(G)-monomethyl-L-arginine (L-NMMA; 3 mg/kg) was injected 4 h after study start on each day. RESULTS: There was no change in glomerular filtration rate (GFR) on the day without CsA. CsA alone did not change GFR, but after L-NMMA injection, GFR decreased significantly from 101 +/- 4 to 91 +/- 4 ml/min. L-NMMA increased renal vascular resistance with no difference between the two study days. CsA increased significantly the diastolic blood pressure (BP) by 8 +/- 2% and the heart rate (HR) by 30 +/- 4%, without changes in cardiac output L-NMMA further increased BP by around 8%, and decreased HR by 11% and cardiac output by 20% on both study days. L-NMMA decreased urinary flow rate by around 25% and renal sodium clearance from 1.1 to approximately 0.6 ml/min on both study days. CsA decreased plasma renin significantly and increased the urinary excretion rate of prostaglandin E2 (PgE2), 6-keto-prostaglandin F1alpha (6-keto-PgF1alpha) and thromboxane B2(TxB2) when compared to the control day. The urinary excretion rate of NOx and cGMP declined gradually on the control day. In contrast, there was a minor, non-significant increase in NOx and cGMP excretion after CsA, followed by a decrease (29 +/- 2 and 16 +/- 4%, respectively) after L-NMMA in parallel with the decrease in GFR. CONCLUSION: The present findings suggest that NO does not play a major role during acute CsA-induced changes in cardiovascular function and renal haemodynamics in man. Renal NO synthesis, however, may attenuate the acute CsA-induced decrease in GFR.

Renal clearance of an ionic high-osmolar and a nonionic low-osmolar contrast medium.

One hundred patients with normal serum creatinine concentration underwent intravenous urography with either an ionic high-osmolar (diatrizoate) or a nonionic low-osmolar (iopamidol) contrast medium after randomization. Before injection of the contrast medium, a blood sample was drawn for determinating serum creatinine concentration, and a urine sample for measurement of urine osmolality. Using x-ray fluorescence, the plasma concentration of iodine (contrast medium) was determined on blood samples drawn approximately 3 and 4 hours after injection of the contrast medium. The glomerular filtration rate was calculated by two different formulas: one requiring only a single sample and one requiring at least two samples (standard). There were poor correlations between the standard contrast medium clearance and the serum creatinine concentration, the estimated creatinine clearance (calculated from a nomogram), as well as the urine osmolality. The 3-hour and the 4-hour single-sample values correlated well with the two-sample values for both contrast media. In patients with normal serum creatinine, the glomerular filtration rate determined by measuring the contrast medium concentration in a single plasma sample obtained at 3 hours, is almost identical to the value determined from two samples. Consequently, two samples are unnecessary.

Effects of PTH(1-34) on blood pressure, renal function, and hormones in essential hypertension: the altered pattern of reactivity may counteract raised blood pressure.

As it has been suggested that parathyroid hormone (PTH) is implicated in the pathophysiology of essential hypertension, the effects of PTH(1-34) were assessed during infusion over 120 min in ten men with essential hypertension and in ten healthy men. Ionized calcium was kept constant by a clamping technique. Mean arterial blood pressure fell slightly in the patients (116 mm Hg, median, before, and 108 mm Hg during the infusion, P < .01), but remained unchanged in the controls (median 87 mm Hg). The pulse rate rose to a similar extent in the two groups, but cardiac output, measured by the CO2 rebreathing technique, was unchanged. The glomerular filtration rate (GFR) was slightly lower in the hypertensives than in the controls at baseline (92 v 109 mL/min, P < .02), but it increased similarly during PTH infusion in both groups (+13% v +9%, medians), as did the effective renal plasma flow (+50% v +38%). The urinary rate of sodium excretion, which was similar at baseline, increased more in the patients than in the controls (+191% v +46%, P < .05); this was mainly attributable to a reduction in the tubular reabsorption of sodium. Calculations based on lithium clearance indicated that mainly the proximal tubular reabsorption of sodium decreased during PTH infusion. Baseline plasma PTH(1-84) was higher in the patients than in the controls (20.5 ng/L v 16.5 ng/L, P < .05). The baseline plasma values of renin, aldosterone, atrial natriuretic peptide, endothelin, and noradrenaline were similar in the two groups. During infusion of PTH, renin increased less in the patients than in the controls (P < .02), and aldosterone increased only in the controls (P < .01). The other hormonal values remained unchanged. In conclusion, the patients with essential hypertension had increased baseline PTH values, but nevertheless PTH had more marked vasodilative and natriuretic effects than in the controls. PTH thus seems to counteract rather than aggravate elevation of blood pressure in these patients.

Acute cardiovascular effect of 1,25-dihydroxycholecalciferol in essential hypertension.

A role for vitamin D in the pathophysiology of essential hypertension has frequently been suggested, but acute direct effects on blood pressure, cardiac output, renal hemodynamics, or hormones have not previously been demonstrated. The rapid effects of 1,25-dihydroxycholecalciferol (1,25-D) were assessed over 120 min after a bolus injection (0.02 microg/kg body weight) in eight men with essential hypertension and in nine healthy men. A placebo group of 10 healthy men was also included. Ionized calcium was monitored closely during the study, and was kept constant with a clamping technique. In the hypertensive patients, a transient increase in blood pressure and a reciprocal fall in cardiac output measured by a CO2 rebreathing technique (-15%, P < .05) were observed after 1,25-D injection. In the control group, both blood pressure and cardiac output remained unchanged. The glomerular filtration rate, effective renal plasma flow, and urinary sodium and water excretions were unchanged in both groups. Plasma levels of atrial natriuretic peptide at baseline were higher in the hypertensive patients than in the control subjects (P < .02); plasma levels of renin, aldosterone, norepinephrine, endothelin, and parathyroid hormone(1-84) were similar in the two groups. None of these hormones was affected during the observation time after the injection of 1,25-D. In conclusion, acute administration of 1,25-D caused a fast and likely nongenomic-mediated decrease in cardiac output in patients with essential hypertension, which together with a transient BP increase implies a 1,25-D-induced increase in total peripheral resistance. These data suggest an enhanced cardiovascular responsiveness to 1,25-D in hypertensive compared to healthy normotensive subjects.

Increased parathyroid hormone as a consequence of changed complex binding of plasma calcium in morbid obesity.

To evaluate whether changed plasma calcium binding might lead to a secondary increase of parathyroid hormone in morbid obesity, fasting measurements of serum ionized, ultrafiltrable and total calcium, calcium binding substances, and parathyroid hormone were undertaken in age- and sex-matched groups of obese (n = 44) and normal weight subjects (n = 52). The 24-hour urinary calcium excretion and clearance of creatine were also measured. Calcium binding to proteins was changed. Serum total proteins and protein-bound calcium did not differ, but serum albumin was decreased in obesity. Consequently, obese subjects did not reveal the normal dependency of protein-bound calcium upon albumin. Calcium binding to other substances was also changed. Serum phosphate and bicarbonate were decreased, while the concentrations of citrate, lactate, acetoacetate, 3-hydroxybutyrate, free fatty acids, and urate were all increased, leaving the total concentration of plasma complex-bound calcium unchanged. Nevertheless, these reciprocal changes increase the concentrations of less readily reabsorbable anions in the renal ultrafiltrate. The changed pattern of calcium binding in serum of the obese subjects may serve to explain our findings of increased urinary calcium excretion, lowering of serum ionized calcium and increased parathyroid hormone levels, changes being significantly correlated with degree of overweight.

Secondary hyperparathyroidism of morbid obesity regresses during weight reduction.

In order to test the relation between obesity and the secondary hyperparathyroidism found in markedly overweight subjects, 24 morbidly obese patients were studied before and after a weight loss of 35.9 kg obtained by a nutritionally adequate, intermittent very-low-calorie diet. Overweight was reduced from 98 +/- 34% to 44 +/- 19%. Serum total calcium did not change, but serum ionized calcium (Ca2+) increased from 1.22 +/- 0.04 mmol/L to 1.25 +/- 0.04 mmol/L (P less than .001). A corresponding fall was observed in serum parathyroid hormone (s-PTH), which decreased from 47.2 +/- 21.7 pmol/L to 35.2 +/- 19.4 pmol/L (P = .01). The change of s-PTH was positively associated with the reduction of body weight (r = .50, P less than .05) and with the reduction of overweight (r = .55, P less than .01). Regarding calcium binding substances, serum albumin remained low. The initially lowered serum phosphate and bicarbonate both rose (P less than .001). Plasma lactate and plasma free fatty acids (FFAs) decreased (P less than .001). The study supports our hypothesis that the change profile of calcium complexing anions in obesity interferes with the tubular reabsorption of calcium, which in turn lowers serum Ca2+, thus promoting hyperparathyroidism. Along with weight loss, concentrations of calcium complexing anions returns towards normal values and the secondary hyperparathyroidism regresses.

Clinical evaluation of a prototype glucose electrode.

A new prototype direct reading glucose electrode working with glucose oxidase and hydrogen peroxide was preliminarily tested clinically during insulin-induced hypoglycemia in eight healthy subjects, and during hyperglycemia in five dysregulated diabetic patients. The results for 282 whole blood samples were compared to those of our routine method, which measures the glucose concentration in whole blood. The correlation was: y = 1.05.x - 0.05 mmol/L, r = 0.99. The glucose electrode measured a glucose concentration of 10.5 mmol/L +- 0.49 mmol/L (between-day imprecision) in a control serum (glucose 10.0 mmol/L). The glucose electrode supposedly responds to the activity of glucose that equals the molality (mmol glucose per kg water). The ratio of results with the glucose electrode and our routine method was lower than the expected ratio between water concentration in calibrator and whole blood, which is 1.18. A steep gradient from blood sample to glucose electrode, depending on the diffusion coefficient and hematocrit might explain the discrepancy.

Relation between ionised calcium and pH in infants with acute acid-base disturbances.

Plasma ionised calcium, [Ca2+], and pH were negatively correlated in 21 infants with disturbed acid-base homeostasis. The slopes of the individual regression lines indicated a mean decrease in [Ca2+] of 42% per pH increase. (Mean delta log[Ca2+]/delta pH = -0.184, SEM = 0.050, p less than 0.001). The value was not significantly different from the relation between [Ca2+] and pH in vitro, when whole blood or plasma was equilibrated with CO2-air mixtures. pH and [Ca2+] must be measured and considered together to allow a proper interpretation of the result.

Direct reading glucose electrodes detect the molality of glucose in plasma and whole blood.

It is the activity that determines the direction of chemical processes, transport, etc. and thus provides the clinically more relevant information. Direct reading glucose electrodes consume glucose at a rate proportional to the glucose activity in the sample. The activity equals the molality (mmol glucose per kg water), so results from direct reading glucose electrodes must differ from the conventionally measured glucose concentration. This was observed in 159 whole blood samples which gave higher results from a direct reading glucose electrode than by our conventional method (y = 1.21x - 0.37 mmol/l). However, adjustment for the different water concentration due to salt, plasma proteins, and hemoglobin occupying space, gave results equal to the concentrations (y = 1.00x - 0.28 mmol/l, r = 0.997). Furthermore, results for samples with constant glucose concentration and varying albumin concentration correlated with the albumin concentration (r = 0.989), but not after adjustment for water concentration (r = 0.037, n.s.).

Diode-array spectrophotometry for simultaneous measurement of hemoglobin pigments.

A prototype oxygen saturation meter was used to measure the concentrations of deoxygenated hemoglobin (rHb), oxyhemoglobin (HbO2), carboxyhemoglobin (HbCO), methemoglobin (MetHb), and sulfhemoglobin (SHb) in 35 microliter blood. Simultaneous absorbance measurements at 535, 560, 577, 622, 636, and 670 nm permitted the composition of any hemoglobin pigment mixture to be determined more accurately, precisely and easily than before. The inclusion of 670 nm, where the hemoglobin pigments have low absorption coefficients, allowed correction for turbidity.

Spectrophotometric determination of hemoglobin pigments in neonatal blood.

Fetal and adult hemoglobin pigments have slightly different light absorption coefficients. Blood from newborns therefore gives inaccurate results with a direct spectrophotometric determination of hemoglobin pigments (Radiometer's OSM3), if the absorption coefficients for adult blood are used. We determined an absorption coefficient matrix for hemoglobin pigments in twenty full term newborns' blood. This matrix yielded results accurate to within 0.2% in 40 further newborns, but the accuracy of the results varied with the individual ratio of fetal to total hemoglobin, which was 80 +/- 5% (SD) in the examined samples. The OSM3's inaccuracy with the adult absorption coefficients can be used to directly estimate the ratio of fetal to total hemoglobin in an infant.

IFCC recommendation on reporting results for blood glucose.

In human beings, glucose is distributed like water between erythrocytes and plasma. The molality of glucose (amount of glucose per unit water mass) is the same throughout the sample. Different water concentrations in calibrator, plasma, and erythrocyte fluid can explain some differences that are dependent on sample type, methods requiring sample dilution, and direct reading biosensors detecting molality. Different devices for the measurement of glucose detect and report fundamentally different analytical quantities. The differences exceed the maximum allowable error of glucose determinations for diagnosing and monitoring diabetes mellitus, and they complicate the treatment. The goal of the International Federation of Clinical Chemistry, Scientific Division, Working Group on Selective Electrodes (IFCC-SD WGSE) is to reach a global consensus on reporting results. The document recommends harmonizing to the concentration of glucose in plasma (with the unit mmol/l), irrespective of sample type or technology. A constant factor of 1.11 will convert measured concentration in whole blood to the equivalent concentration in plasma.

Donnan effect or protein interference in ionised calcium measurements?

The observation that the ionised calcium concentration is higher if measured in the original serum sample than in an ultrafiltrate is examined by means of a theoretical model. It is concluded that this difference is a predictable consequence of the Donnan equilibrium and is not a result of protein interference with the calcium-specific electrode.

Parameter estimation in six numeric models of transperitoneal transport of glucose.

Six competing kinetic models of transperitoneal glucose transport were formulated and validated. The models were designed to elucidate the presence or absence of diffusive, nonlymphatic convective and lymphatic convective solute transport. The validation procedure included an assessment of theoretical and practical identifiability, goodness of fit, residual error analysis, and plausibility of parameter estimates. Experimental results were obtained from 21 patients without diabetes. The validation procedure demonstrated that the model that only included diffusion was superior to the other models. Theoretically, both nonlymphatic convective and lymphatic convective transports might exist. However, neither the ultrafiltration sieving coefficient nor the lymphatic flow rate were practically identifiable, probably because any amount of glucose transported by nonlymphatic convective and lymphatic convective transport mechanisms was negligible compared with the amount transported by diffusion. Based on these results, there appear to be problems measuring convective solute transport parameters when the solute transport is in the dialysate-to-blood direction while the fluid transport is in the blood-to-dialysate direction.

Standardizing and reporting results from Mg2+ ISEs, with some notes on sample handling.

Mg2+ by ion-selective electrode (ISE) is a direct measure of the reactivity of magnesium ions in plasma, which may be clinically and physiologically more relevant than the concentration of total magnesium. The Mg(2+)-ISE will build up an electric potential which exactly matches the chemical potential of Mg2+ in the sample. Chemical potential (= chemical work per unit of Mg2+) has no absolute value and is difficult to visualize. The results must be standardized, either to the magnesium concentration in a protein-free calibrator or to the concentration of total magnesium in plasma. The constant factor relationship will assure identical clinical discrimination, no matter how the Mg(2+)-ISE results are reported. The general opinion of a conference held in Orlando, Florida in March of 1993 was to define free Mg2+ in plasma as the concentration of magnesium in a saline standard with the same magnesium activity as the sample, and report it in SI units (mmol/L). The small differences in liquid junction potential and water concentration will provide a value for free Mg2+ in plasma of approximately 103% of the true concentration, or 96% of the true molality. Differences between plasma and interstitial fluid and Donnan equilibria across the vascular endothelium will effect the result, so sampling should take place with the patient at rest to assure a stable plasma volume. Since heparin binds magnesium, it is preferable to use serum or plasma with a minimum of heparin which has been titrated with magnesium. Binding of Mg2+ depends on pH, and pH of circulating plasma is not constant.(ABSTRACT TRUNCATED AT 250 WORDS)

What is "ionized calcium"?

"Ionized calcium", in clinical chemistry, designates the free calcium ions which are present in the biological fluids as hydrated ions: Ca2+, 12 H2O. The calcium ion selective electrode measures differences in activity, however, values are reported not as the activity, but as the activity divided by the activity coefficient (gamma) of Ca2+ in "normal plasma". The latter is assumed to be equal to the activity coefficient (gamma) in a calibration solution of CaCl2 + NaCl with an ionic strength of 0,16 mol X kg-1. We have estimated the activity coefficient in this calibration solution to be gamma Ca2+ = 0,3040 (molal basis) or gamma Ca2+ = 0,3048 (substance concentration basis). The derivation of gamma Ca2+ is based on a convention for derivation of the activity coefficient of the chloride ion. We have used the Debye-Hückel equation extended by the Stokes-Robinson hydration theory plus the Bates-Staples-Robinson convention that the hydration number for Cl- is zero. International consensus is needed concerning the convention to be used for deriving the activity coefficient of Ca2+ in the calibration solutions and concerning the most appropriate value for gamma Ca2+ in normal plasma.

Ionized calcium during dialysis and ultrafiltration.

The changes in ionized calcium during dialysis and ultrafiltration with albumin containing solutions were highly dependent on the total electrolyte concentration. Protein interference on the calcium electrode could not explain the observation, which was, however, consistent with the Donnan theory. The uneven distribution of sodium ion also agreed with a Donnan membrane potential.

Elimination of the erythrocyte effect on the liquid junction potential in potentiometric measurements on whole blood using mixed salt bridge solutions.

An effect of erythrocytes on the liquid junction potential of the junction "concentrated KCl whole blood" has previously been described, the effect being a positive bias of +1,4 mV with a high erythrocyte volume fraction (0.75). We have studied the erythrocyte effect with different concentrated salt solutions, and found a similar positive bias with KBr, KJ, KNO3, K2SO4, but a negative bias with NaCl, NaNO3, LiCl and CaCl2. The erythrocyte bias may be eliminated by mixing salts with opposite effect, e.g. KCl + NaCl (1.0 + 7.0 mol/l), KNO3 + NaNO3 (1.0 + 3.0 mol/l) KNO3 + Li-acetate (0.15 + 4.0 mol/l). The use of a mixed salt bridge solution may be advantageous for eliminating the erythrocyte bias when measuring ionic activity (e.g. Na+, K+, Ca2+) directly in whole blood.

Nomograms for calculating the concentration of ionized calcium of human blood plasma from total calcium, total protein and/or albumin, and pH.

Two nomograms are described. One is a Cartesian nomogram similar to the original McLean-Hastings nomogram but supplemented by an albumin scale and a pH scale to allow calculations in case of an abnormal albumin/globulin ratio or an abnormal pH. The other is an alignment nomogram. The underlying arithmetic equations, which are slightly different for the two nomograms are described. Both refer to 37 degrees C. Calculated and measured ionized calcium are compared for 24 specimens and it is concluded that the calculated value may be subject to a considerable bias amounting to 0.2 mmol/l in the worst cases. Nomograms size A4 and BASIC program are available on request.