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It has long been recognized that acute respiratory alkalosis depresses the renal reabsorption of bicarbonate (1, 2), but the exact nature of the reabsorptive limit has not been defined. In the present studies, it has been demonstrated that acute reduction of plasma carbon dioxide tension depresses bicarbonate reabsorption to a rate which is essentially constant over a wide range of plasma bicarbonate concentrations. This pattern is analogous to that found in the normal but differs from that previously observed in acute respiratory acidosis, where reabsorption rises as a curvilinear function of plasma bicarbonate concentration (3). MATERIALS AND METHODSTwelve experiments were performed on female mongrel dogs anesthetized with sodium pentobarbital. Prior to each experiment, hydrochloric acid was infused in order to decrease the plasma bicarbonate concentration to roughly 10 mEq. per L. An endotracheal tube fitted with an inflatable balloon was introduced into the trachea and connected either to a calibrated volume displacement ventilator (Etsten Ventilator) or to a Mine Safety "Pneophore." Respiratory movements were inhibited by the administration of gallamine triethiodide (Flaxedil®) ments it was necessary to increase ventilation slightly in order to prevent the rise in CO2 tension that usually followed the rapid infusion of sodium bicarbonate. In most experiments there was a progressive reduction in blood pressure as blood pH approached 7.9 to 8.0. This hypotension was often accompanied by a drop in urine flow, as well as by hemoglobinemia and hemoglobinuria, and collection periods in which both hypotension and reduction in urine flow occurred were excluded from the study.The clearance of exogenous creatinine was used as a measure of glomerular filtration rate. Urine was collected under mineral oil through an inlying catheter, and the bladder was emptied by manual compression at the beginning and at the end of each 10 minute collection period. Heparinized blood samples were drawn anaerobically from the femoral artery. Plasma and urine were analyzed for creatinine by a modification of the method of Bonsnes and Taussky (4) and for total CO2 by the manometric method of Van Slyke. Blood and urine pH were measured anaerobically at 370 C. with a syringe type Cambridge Research Model pH meter. In a few experiments pH was measured at room temperature, using a factor of 0.01 unit per degrees C. for the correction to 37°C. Carbon dioxide tension in the blood and urine was calculated from the Henderson-Hasselbalch equation, using a pK' for carbonic acid of 6.1 and a solubility factor equal to 0.0301 for plasma and 0.0309 for urine. Bicarbonate concentration was calculated as the difference between total CO2 content and the dissolved carbon dioxide. Filtered bicarbonate was taken as the product of the filtration rate and the plasma bicarbonate concentration, corrected by a Donnan factor of 1.05. Tables I through III RESULTS

Après la perfusion intraveineuse de Polyfructosan, suivie d’une «equilibration» de 40 minutes, la décroissance plasmatique de cette substance est une fonction exponentielle du temps: Ct₂ = Ct₁ e^-η △^t. La pente η de la droite, dessinée par les logarithmes des taux plasmatiques successifs, représente la fraction du volume extracellulaire «fonctionnel» qui est épurée par unite de temps: η = clearance/volume min^-1 Chez trente-deux sujets, avec ou sans insuffisance rénale et exempts de retention aqueuse, nous trouvons une excellente corrélation (r > 0,9) entre cette constante η, que nous appelons clearance «relative», et la clearance classique telle qu’elle est mesurée en cours de perfusion continue. Cette corrélation est nettement supérieure à celle qui relie la clearance classique du Polyfructosan et la clearance de la créatiníne endogène de «routine». Ces résultats semblent conñrmer la possibilité d’un test simple, sans collection d’urines et sans perfusion continue, pour l’estimation de la fonction glomérulaire. Nos expériences préliminaires montrent cependant qu’après une injection unique de Polyfructosan, il faut attendre 70 min pour obtenir une «équilibration» suffisante et observer une décroissance exponentielle du taux plasmatique.