[Relations between acid-base equilibrium and body temperature. Physiological concepts and practical applications]. / Relations entre équilibre acido-basique et température corporelle. Concepts physiologiques et applications pratiques.

In 1975 H. Rahn put forward a new concept of hydrogen ions regulation which explains acid-base regulation in relation to body temperature and applies to all animal species. At the root of this concept is the finding that maintenance of intracellular neutrality is governed by water dissociation and regulated by imidazole-rich protein buffers. The pH of the extracellular fluid, which receives acid by-products of cell activity, is kept higher than that of the intracellular fluid (relative alkalinity). The difference between extracellular pH and neutrality is constant for each species and ranges from 0.6 to 0.8 pH units. It is unaffected by changes in temperature, and the total CO2 content of extracellular fluid remains constant. The authors were able to confirm the value of this new concept in man by experimental studies of in vitro and in vivo blood of patients undergoing aorto-coronary bypass under controlled hypothermia. They draw the following practical conclusions: (1) in subjects under moderate or deep hypothermia for surgical purposes, the acid-base status can be controlled and the extracellular pH adjusted by ensuring intracellular neutrality; this is done by keeping PCO 2 at such a level that the arterial blood pH measured at 37 degrees C remains around 7.40; (2) the problem of correcting acid-base values (pH-PCO 2) according to body temperature is solved simply by using pH and PCO 2 values measured at 37 degrees C and interpreting them, as usual, in terms of metabolic or respiratory acidosis or alkalosis.

[Pharmacokinetics of antimalarials: quinine and mefloquine, halofantrine, qinghaosu, amino-4-quinolines]. / Pharmacocinétique des antipaludéens: quinine et méfloquine, halofantrine, qinghaosu, amino-4-quinoléïnes.

The development of new sensitive and specific assays (HPLC) have enabled the pharmacokinetics of antimalarial drugs to be studied. Parameters such as half-life distribution volume, clearance and bioavailability, are defined. In healthy subjects, quinine is rapidly eliminated (t1/2 beta: 6-12 h). Hepatic biotransformation accounts for approximately 80% of its total clearance. In malaria, the pharmacokinetic properties of quinine (decrease in the apparent volume of distribution, prolongation of the t1/2 beta, reduction in systemic clearance), are altered in proportion to the severity of infection. Red cell concentrations and plasma binding are increased. Parenteral quinine should be given by slow intravenous infusion and a loading dose is recommended in severe infections. Chloroquine (t1/2 beta: 6-50 days) and mefloquine (t1/2 beta: 6-33 days) have extensive tissue distribution and prolonged activity after a single dose. Both drugs are concentrated in erythrocytes and are bound considerably to plasma proteins. Amodiaquine is not found in the blood after oral administration. Hepatic biotransformation accounts for almost all orally administered drug. Its antiplasmodial activity is thus almost entirely due to monodesethylamodiaquine, the main metabolite. In healthy subjects, the t1/2 beta of this metabolite is 9 to 18 days in plasma. Amodiaquine is concentrated in erythrocytes. The protein binding of this drug has not been studied to date. For prophylaxis, it has been suggested that the dosage of 10 mg/kg/wk should be spread over the week (3.5 mg/kg every other day, or 1.5 every day). Halofantrine has an elimination half-life of between 1.3 and 6.6 days. This drug has been suggested as a single-dose treatment. No pharmacokinetic studies of qinghaosu have been reported in humans. In rabbits, the elimination half-life in plasma was found to be 40 min. Although rapidly eliminated, this drug appears to be highly effective. More information is required on the pharmacokinetics of these drugs in malaria, during pregnancy, in children and in renal and hepatic failure.

Assessment of Scholander micromethod for gas concentrations versus weighing method.

Three gaseous mixtures in N2, of varying concentrations of CO2 (3.60, 5.79, and 9.36%) and O2 (22.18, 15.12, and 6.82%), respectively, were prepared by precise weighings, which may serve as absolute measures. These mixtures were analyzed with two apparatuses by the Scholander micromethod. Taking into account the influence of several factors (apparatuses, order of analyses, etc, it appears that differences between apparatuses were not significant in five of six cases and the effect of order was significant in O2 (P less than 0.01) but not in CO2 for the set of measurements. When compared with weighings, measurements differed only in one apparatus (P less than 0.02) in two of six cases and by no more than 0.02%. The relation between weighings and measurements was highly significant (P less than 10(-9) and no lack of fit to linearity occurs. Side effects of the factors considered and interactions between them are discussed. In conclusion, the micromethod of Scholander gives accurate results, in very good agreement with the reference values provided that certain technical precautions are observed.

Nitric oxide effects on lung structure and blood oxygen affinity in rats.

Two month-old Wistar rats were exposed continuously for six weeks, either to 2.0 +/- 0.1 ppm nitric oxide (NO) mixed homogeneously with air for tests, or to ambient air for controls. Oxyhemoglobin dissociation curve (ODC), erythrocytic variables, methemoglobin (MetHb) concentration and lung structure, particularly through electron microscopy studies, were investigated each week of exposure. The hemoglobin affinity for oxygen was not modified, probably as a result of both pH and 2,3-diphosphoglycerate (2,3-DPG) stability. Moreover MetHb formation was not found in treated rats. The few ultrastructural alterations found under electron microscopy may not prove NO-induced since they were found similarly in both groups. Slight emphysematous changes were found only in 1 micrometer-thick sections of lungs from NO-treated rats.

Lack of effect of methemoglobinemia on the plasma-erythrocyte pH relationship.

A stable and reproducible methemoglobinemia is induced by small concentration of an oxidizing gas (NO). Under such conditions we evidenced that plasma pH (pHe) to erythrocyte pH (pHi) relationship is unchanged. A strong acidity bound to the changes of NO in water occurs. But we may conclude that the buffer capacity of erythrocyte is not modified by the oxydation of ferro into ferrihemoglobin within the erythrocyte.

Ccomparison of cisternal and lumbar cerebrospinal fluid pH in high altitude natives.

Samples of cisternal or lumbar cerebrospinal fluid were obtained from 20 young male volunteers born and living at high altitude (3500 to 4800 m). The pH, carbon dioxide and oxygen tensions, and bicarbonate concentration were measured and compared with those in the arterial and jugular venous blood. A consistent difference between the two CSF compartments was noted, particularly a lower pH (0.05), a higher PCO2 (7 Torr), and a lower PO2 (7 Torr) at the lumbar site. Mean bicarbonate concentration was not significantly different at the two sites. The main factor is PCO2, which controls the pH variation. These differences were more marked in high-altitude natives than in man at sea level. The existence of a consistent inhomogeneity of CSF acid-base content emphasizes the inaccuracy of using lumbar CSF pH to estimate the ECF pH as regulator of pulmonary ventilation and determinant of cerebral blood flow.

Control of acid-base status during hypothermia in man.

Rahn's concepts of acid-base balance during hypothermia were tested in humans by studying eleven men who required extra-corporeal cooling for surgery. Hypothermia was moderate (27-28 degrees C) and maintained for 60-70 min. Extracorporeal blood perfusion (ECBP) was performed with a bubble-oxygenator which allowed changes in blood flow and gas concentrations. Arterial pH (pHa) at the person's body temperature was controlled by varying CO2 flow to the oxygenator in order to maintain in vitro pH measured at 37 degrees C in the normal range. During hypothermia and after rewarming to 37 degrees C, bicarbonate concentration and total CO2 content of arterial and mixed venous blood remained constant. A physiologic solution was introduced into the peritoneal cavity which was used as a tonometer; the values of equilibrated CO2 content in peritoneal fluid were constant. Neither metabolic acidosis nor hypercapnia developed. Blood acid-base balance in vivo during hypothermia was therefore identical to the behavior of blood in vitro. In addition, the interpretation of the results of acid-base studies, in humans with abnormal central temperature is facilitated when measurements are performed at 37 degrees C.

[Pharmacokinetics of amodiaquine and prevention of Plasmodium falciparum malaria]. / Pharmacocinétique de l'amodiaquine et prophylaxie du paludisme à Plasmodium falciparum.

Amodiaquine might appear as an alternative in prophylaxis of chloroquine-resistant P. falciparum malaria. In an attempt to explain the discrepancy between its in vivo-in vitro activity, a pharmacokinetic study was conducted in healthy subjects with HPLC assays. The results showed that: amodiaquine was no more detected in the blood, a main metabolite (monodesethyl derivative) appeared as the active form of the drug in vivo, metabolite's half-life had a mean value of 15.6 +/- 5.4 days. This study shows that monodesethylamodiaquine (and not amodiaquine) must be monitored in vitro. Furthermore the high individual variations of blood levels and half-life's values suggest that the weekly prophylactic schedule must be eventually re-evaluated.

Simultaneous determination of chloroquine, amodiaquine and their metabolites in human plasma, red blood cells, whole blood and urine by column liquid chromatography.

A column liquid chromatographic method for the simultaneous determination of chloroquine, amodiaquine and their monodesethyl metabolite in human plasma, red blood cells, whole blood and urine is described. The drugs and internal standard were extracted as bases with methylene dichloride and then re-extracted into an acid aqueous phase. Separation was obtained using a reversed-phase column and a mobile phase of phosphate buffer (pH 3.0)-acetonitrile (88:12). The absorbance of the drugs was monitored at 340 nm with a sensitivity limit of 10 pmol/ml. No endogenous compound interfered at this wavelength. The mean overall recovery from each biological fluid was greater than 75%. This method can be applied to therapeutic, pharmacokinetic and epidemiological studies. The metabolism of these two amino-4-quinolines in humans is compared.

Effects of nitric oxide on resistance to bacterial infection in mice.

Continuous exposure to 2 ppm nitric oxide (NO) for as long as 4 wk did not reduce the resistance of male mice to infection by aerosol inoculation with Pasteurella multocida. In contrast, mortality was slightly enhanced and survival shortened in NO-exposed compared to control female mice; however, the importance of these small differences is uncertain. These results suggest only that male and female mice did not react similarly to the infectious challenge after exposure to NO.

Effects of low-concentration NOxSO2 gas mixtures on lung structure and blood-oxygen affinity in rats.

The respiratory effects of low levels of SO2 alone or associated with NO or NO2 were studied in rats exposed for periods of one day to thirteen weeks. Control rats were exposed to ambient air. Both control and treated rats appeared similarly active and grew uniformly. Erythrocytic variables (hemoglobin, hematocrit, red cell counts, 2,3-DPG, glucose, lactate, methemoglobin) and oxyhemoglobin dissociation curves were determined at different times throughout exposure to the gaseous mixture. Blood variables of the exposed rats were not significantly different from those of controls, and hemoglobin affinity was not modified. Bronchiolar and tracheal epithelia were studied by scanning (TEM) to detect a possible loss of cilia. The alveolar walls were investigated by Light Microscopy and TEM after each period of exposure. No striking changes were observed in rat lung structures under Light Microscopy or TEM. Bronchiolar and tracheal epithelia were normally ciliated. No synergistic effects were produced by either SO2 + NO or SO2 + NO2.

[Distribution of chloroquine and desethylchloroquine in blood, plasma and erythrocytes of healthy subjects and malaria patients. Assay using HPLC]. / Distribution de la chloroquine et de la déséthyl-chloroquine dans le sang, le plasma et les érythrocytes de sujets sains et paludéens. Dosage en HPLC.

Chloroquine (Cq) and desethyl-chloroquine ( CqM ) levels were measured by HPLC in the blood, plasma, and erythrocytes of 9 healthy subjects under standard prophylactic treatment (100 mg/day for 10 days) and 8 malarial patients given a therapeutic regimen (10 or 25 mg/kg). Chloroquine levels in various fractions of the healthy subjects were as follows: whole blood: 1 265 +/- 598 nmol/l; plasma: 145 +/- 63 nmol/l of whole blood; erythrocytes: 827 +/- 460 nmol/l of whole blood. The CqM /Cq ratio in malarial patients varied from 0.4 to 0.8. These results show that Cq levels and Cq metabolization varied significantly from one individual to the next. Above all, they demonstrate the presence of Cq in other types of blood cells. This underlines the practical importance of the conditions of chloroquine assay in blood.

Chloroquine uptake by Plasmodium falciparum-infected human erythrocytes during in vitro culture and its relationship to chloroquine resistance.

Chloroquine uptake by Plasmodium falciparum-infected human erythrocytes (RBC) was studied in vitro before and during culture by measuring the chloroquine gradient between the cells and medium (C/M) by high-pressure liquid chromatography. The C/M values were 5.9 +/- 2.7 (n = 23) for uninfected RBC, 13 to 34 for six chloroquine-susceptible isolates (concentration required to inhibit 50% of parasite growth, less than 100 nmol/liter) in partially infected RBC (parasitemia from 0.3 to 5%) (n = 28), and 8.4 to 4.9 for four chloroquine-resistant isolates (concentration required to inhibit 50% of parasite growth, 320 to 1,500 nmol/liter) in partially infected RBC (parasitemia from 0.4 to 5%) (n = 26). Two isolates were studied before and after adaptation to continuous culture. C/M was found to decrease (34.2 to 2.1 and 19.3 to 4.9), whereas the concentration required to inhibit 50% of parasite growth increased (35 to 1,400 and 54 to 1,500 nmol/liter), thus indicating the acquisition of chloroquine resistance. These results demonstrate that chloroquine uptake decreased in RBC in which the infective strain, initially susceptible, became resistant in culture and imply that the drug is bound to ferriprotoporphyrin IX to a lesser extent or that a parasite protein competes with ferriprotoporphyrin IX to a greater extent. We suggest that genotypic modifications in the mechanism of chloroquine uptake might occur in the parasite.

[Biotransformation of amiodaquine and prophylaxis of Plasmodium falciparum malaria]. / Biotransformation de l'amodiaquine et prophylaxie du paludisme à Plasmodium falciparum.

The authors have devised a specific HPLC method for amodiaquine assay which demonstrated that the drug disappeared rapidly from the blood of subjects under prophylaxis for malaria (10 mg/kg/week in a single oral dose). The main metabolite was identified as the monodesethyl derivative which is the only active form of the drug. The low erythrocytic levels of the metabolite, observed at day +7, might account for the failure in the prophylaxis of P. falciparum malaria with amodiaquine in a few cases. The in vitro activity of monodesethyl amodiaquine should be evaluated during the chemosensitivity tests and the chemoprophylaxis schedule, re-evaluated.

Continuous intravascular monitoring of pO2 and pCO2. A comparative in vitro-in vivo study.

Two electrodes placed at the tip of catheters for in vivo determinations of PCO2 and PO2 respectively, were tested in dogs. Results were satisfactory when compared to a highly accurate reference method, correlation coefficients were close to 1 (P less than 10(-9)). Means of the differences were respectively --1.74 +/- 1.14 toor for the PO2 probe (P less than 0.01) and --1.62 +/- 0.72 torr for the PCO2 sensor (P less than 0.0001). While no drift was detected in the PCO2 electrode, that of the PO2 was significant but negligible compared to the variability of measurements. Thus, for PCO2 values between 20 and 85 torr, and PO2 values between 20 and 140 torr, in vivo monitoring is sufficiently reliable for clinical use.

Methaemoglobinemia induced by nitric oxide in whole blood. Quantitative relationship.

We studied in vitro the effects of nitric oxide (NO) in human and rat blood and in human erythrolysate. Using NO in the tonometric technique allows to predict through an experimental model the amount of methemoglobin formed. At known oxygen and carbon dioxide pressures, methaemoglobinemia is all the more important as NO concentration is great and tonometry duration is long. Moreover methaemoglobin concentration is greater in saturated (P02 congruent to 500 Torr) than in desaturated blood (P02 congruent to O Torr) while only slight changes occur for small P02 variations. Thus the study of the oxygen dissociation curve should be possible in presence of NO. Methaemoglobin is responsible for the drop in the oxygen combining capacity and thus impairs blood oxygen transport. Results are similar in human and in rat blood.

Arterial blood gases and acid-base status in awake rats.

Arterial blood gases and acid-base balance were measured in adult rats using a cannula implanted in the aortic arch. These measurements were performed both in awake, unrestrained animals and in animals submitted to various circumstances i.e. (a) different diet: high and low sodium chloride intake, (b) anesthesia by pentobarbital or inactine and, (c) repeated blood sampling with concomitant replacement with the same volume of blood. For each group investigated the [HCO3 -]a vs. PaCO2, [H+] vs. PaCO2, PaCO2 vs. PaO2 relationships were determined. The values obtained (m +/- SD) from awake, unrestrained adult rats were respectively 7.47 +/- 0.02 for arterial pH, 34.5 +/- 3.0 Torr for PaCO2 and 90 +/- 5.5 Torr for PaO2; the calculated [HCO3 -]a concentration was 25.5 +/- 1.5 mmol . 1-1. The present results indicate that plasma bicarbonate concentration, within normal range, highly depends on the prevailing resting level of PaCO2 (n = 202; r = 0.82; P less than 10(-3)). In addition, the PaCO2 versus PaO2 relationship was highly statistically significant (n = 202; r = -0.43; P less than 10(-3). In the other experimental groups of rats, these relationships were virtually the same as above although mean values (+/- SD) for PaCO2, PaO2, pHa and [HCO3 -]a might vary with the group investigated. The mean value for whole pHi, obtained by the DMO method, reached 6.81 for pHa = 7.47 and was not correlated to PaCO2 level in normal conditions. The present data argue for the existence of a respiratory component mediating individual acid-base variations in a normal population of rats. Arterial carbon dioxide partial pressure, by determining bicarbonate ions reabsorption rate, would ensure pH regulation under normal circumstances.

Respiratory effects of normobaric oxygen toxicity in awake guinea-pig.

We studied the time course of the respiratory events in awake guinea-pigs catheterized with a chronic arterial cannula, exposed to 100% O2 during 48 hr and after air return breathing. 2. The oxygen toxicity has a pulmonary and respiratory expression: clinical, histological and biochemical data show that death is related to the asphyxia generated by acute pulmonary edema. 3. The O2 toxicity respiratory effects show striking differences in rats and guinea-pigs; the differences belong to a specific and particular lymphatic system in the rat. 4. Rat and guinea pig offer two different models of pulmonary edema, (the first is characterized by absence of arterial hypoxemia) and in consequence two different models of lung oxygen toxicity.