Glomerular-tubular balance for bicarbonate in the dog

1975 ◽  
Vol 228 (1) ◽  
pp. 98-106 ◽  
Author(s):  
CM Bennett ◽  
PD Springberg ◽  
NR Falkinburg
Keyword(s):  
Functional Relationship ◽  
Potassium Concentration ◽  
Extracellular Fluid ◽  
High Protein Diet ◽  
Plasma Potassium ◽  
Absolute Rate ◽  
Bicarbonate Concentration ◽  
Plasma Bicarbonate ◽  
Bicarbonate Reabsorption ◽  
The Absolute

Previous work that apparently showed a functional relationship between GFR and maximum bicarbonate reabsorption was done at a time when the effects on the latter of several factors (PCO2, plasma potassium concentration, and extracellular fluid volume expansion) were not recognized. The present study re-examines this relationship, while controlling these factors. In 14 hydropenic dogs, bicarbonate reabsorption per unt GFR increased linearly with increases in plasma bicarbonate concentration. At any level of plasma bicarbonate concentration,the absolute rate of bicarbonate reabsorption was functionally related to the GFR. In six volume-expanded dogs, bicarbonate reabsorption remained stable at 20-22 mmol/liter GFR as plasma bicarbonate was raised to greater than 40mM. The absolute rate of bicarbonate reabsorption increased with large increases in GFR induced by methylprednisolone and high-protein diet. In a third group of dogs, bicarbonate reabsorption varied directly with increases in GFR, while plasma bicarbonate concentration was held relatively constant above the threshold. We conclude there is a close functional relationship between the absolute rate of bicarbonate reabsorption and GFR in individual dogs.

Effect of carbonic anhydrase inhibition on proximal tubular bicarbonate reabsorption

1963 ◽  
Vol 205 (4) ◽  
pp. 693-696 ◽  
Author(s):  
James R. Clapp ◽  
John F. Watson ◽  
Robert W. Berliner
Keyword(s):  
Carbonic Anhydrase ◽  
Proximal Tubule ◽  
Intravenous Administration ◽  
Distal Portion ◽  
Bicarbonate Concentration ◽  
Plasma Bicarbonate ◽  
Bicarbonate Reabsorption ◽  
Carbonic Anhydrase Inhibition ◽  
Before And After ◽  
Proximal Tubular

Samples of fluid from the proximal tubule were collected for the measurement of pH and bicarbonate concentration before and after the administration of acetazolamide (Diamox). Samples collected before acetazolamide were consistently more acid than plasma with the most acid samples coming from the more distal portion of the proximal tubule. After the intravenous administration of acetazolamide, the pH and bicarbonate concentration were consistently higher than in plasma. Bicarbonate concentrations as high as 2.8 times that in plasma were observed. The rise in proximal tubular fluid bicarbonate concentration after acetazolamide is presumably due to a reduction in the rate of bicarbonate reabsorption out of proportion to any impairment in proximal tubular fluid volume reduction.

Effectiveness of the aldosterone-sodium and -potassium feedback control system

1976 ◽  
Vol 231 (3) ◽  
pp. 945-953 ◽  
Author(s):  
DB Young ◽  
RE McCaa ◽  
UJ Pan ◽  
AC Guyton
Keyword(s):  
Feedback Control ◽  
Potassium Concentration ◽  
Extracellular Fluid ◽  
Plasma Potassium ◽  
Sodium Concentration ◽  
Feedback Mechanism ◽  
Fluid Volume ◽  
The Body ◽  
Plasma Sodium ◽  
Aldosterone Secretion

This study was conducted to determine the quantitative importance of the aldosterone feedback mechanism in controlling each one of three major factors that have often been associated with aldosterone, namely, extracellular fluid sodium concentration, extracellular fluid potassium concentration, and extracellular fluid volume. To do this, the ability of the body to control these three factors in the face of marked changes in daily sodium or potassium intake was studied under two conditions: 1) in the normal dog, and 2) in the dog in which the aldosterone feedback mechanism was prevented from functioning by removing the adrenal glands and then providing a continuous fixed level of supportive aldosterone and glucocorticoids during the low and high electrolyte intake periods. Under these conditions, removal of feedback control of aldosterone secretion decreased the effectiveness of plasma potassium control by nearly fivefold (39% vs. 8% change in plasma potassium concentration), fluid volume by sixfold (12% vs. 2% change in sodium space) and had no effect on control of plasma sodium concentration (2% change with and without feedback control of aldosterone secretion.)

Steroid modulation of response of plasma bicarbonate concentration to NH4Cl loading: gamma distribution analysis

1983 ◽  
Vol 61 (6) ◽  
pp. 641-646 ◽  
Author(s):  
David Z. Levine ◽  
Robert A. McLeod ◽  
S. Raman
Keyword(s):  
Base Composition ◽  
Dynamic Assessment ◽  
Extracellular Fluid ◽  
Distribution Analysis ◽  
Bicarbonate Concentration ◽  
Acid Base ◽  
Plasma Bicarbonate ◽  
Fluid Compartment ◽  
Acid Load ◽  
Continuous Dynamic

Studies have been carried out in awake chronically cannulated adrenalectomized rats subjected to steroid replacement protocols. Our objective was to determine the effects of mineralocorticoid or glucocorticoid or combined replacement on acid–base composition of the extracellular fluid compartment in response to an acute ammonium chloride acid load. We obtained six blood samples from each animal over a 26-h period and, with the help of a specially derived mathematical model, we were able to obtain a continuous dynamic assessment of changes of plasma bicarbonate concentration during induction and recovery of the metabolic acidosis. Assessment of minimum values for plasma bicarbonate concentration, time to reach the minima, and time for 90% recovery showed that dexamethasone did not exert as much protection as aldosterone. The approach we have used, in a sense being a continuous display of plasma bicarbonate concentration, should be useful in further exploring the nature of the interrelations between acid production, net acid excretion, and the resultant plasma acid–base composition.

A model of proximal tubular bicarbonate absorption

1985 ◽  
Vol 248 (2) ◽  
pp. F272-F281 ◽  
Author(s):  
R. J. Alpern ◽  
F. C. Rector
Keyword(s):  
Extracellular Fluid ◽  
High Plasma ◽  
Bicarbonate Concentration ◽  
Solvent Interactions ◽  
Proton Secretion ◽  
Plasma Bicarbonate ◽  
Flow Dependence ◽  
Model Predictions ◽  
Proximal Tubular ◽  
Luminal Flow

A model is presented that utilizes determinants of acidification defined from microperfusion studies in the rat to stimulate the effect on absolute bicarbonate absorption along the entire proximal convoluted tubule. Net bicarbonate absorption is considered to consist of active transcellular proton secretion in parallel with passive paracellular bicarbonate diffusion. The rate of proton secretion is calculated as a function of luminal bicarbonate concentration using Michaelis-Menten kinetics. The K1/2 is modified by luminal flow rate and the Vmax by peritubular bicarbonate concentration. Solute-solvent interactions and axial heterogeneity are also included as determinants of proton secretion rate. The model demonstrates that a given percentage stimulation or inhibition of active proton secretion leads to a much smaller effect on absolute proximal bicarbonate absorption along the entire tubular length. This blunting of the stimulation or inhibition is greatest when filtered bicarbonate load is limited by decreases in glomerular filtration rate or plasma bicarbonate concentration. In addition, the model shows that flow dependence is greater at low plasma bicarbonate concentrations, whereas the effect of extracellular fluid volume expansion is greater at high plasma bicarbonate concentrations. Agreement between the model predictions and the results of free-flow micropuncture studies from our laboratory is good with the exception of the effect of raising plasma bicarbonate concentration. This discrepancy is resolvable by allowing the effect of peritubular pH to increase along the length of the tubule, a hypothesis that requires verification.

Relationship between plasma potassium concentration and renal potassium excretion

1982 ◽  
Vol 242 (6) ◽  
pp. F599-F603 ◽  
Author(s):  
D. B. Young
Keyword(s):  
Renal Excretion ◽  
Potassium Concentration ◽  
Sodium Intake ◽  
Extracellular Fluid ◽  
Plasma Potassium ◽  
Potassium Excretion ◽  
Potassium Intake ◽  
Arterial Ph ◽  
The Relationship ◽  
Renal Potassium Excretion

To study the relationship between extracellular potassium concentration and renal excretion of potassium, seven chronically adrenalectomized dogs were maintained on a constant intravenous infusion of aldosterone (50 micrograms/day), and constant sodium intake (30 meq/day ) while they received four levels of potassium intake--10, 30, 100, and 200 meq/day--for 7-10 days each. At the conclusion of each level of intake, plasma potassium and renal excretion as well as other variables known to influence potassium excretion were measured. There were minimal changes in arterial pH, mean arterial pressure, extracellular fluid volume, or glomerular filtration rate at any level of potassium intake. The values for plasma potassium and renal potassium excretion attained at each level of intake were: 3.13 +/- 0.24 and 10 +/- 2; 4.18 +/- 0.18 and 21 +/- 6; 4.31 +/- 0.11 and 66 +/- 10; and 4.75 +/- 0.10 meq/liter and 170 +/- 16 meq/day, respectively. Under these experimental conditions in which the levels of aldosterone, sodium intake, arterial pH, arterial pressure, extracellular fluid volume, and glomerular filtration rate remain constant, plasma potassium concentration appears to have a week effect on renal potassium excretion below the normal level of plasma potassium (approx. 11 meq/day change in excretion for each milliequivalent per liter change in concentration). Above the normal level, however, plasma potassium concentration has a powerful effect, 260 meq/day per milliequivalent per liter. The characteristics of the relationship between plasma potassium and renal potassium excretion make it ideally suited for controlling potassium excretion in response to greater than normal potassium intake.

Distal tubule bicarbonate reabsorption during rebound metabolic alkalosis

1991 ◽  
Vol 69 (11) ◽  
pp. 1784-1788 ◽  
Author(s):  
David H. Vandorpe ◽  
Steven P. Nadler ◽  
David Z. Levine
Keyword(s):  
Metabolic Acidosis ◽  
Metabolic Alkalosis ◽  
Distal Tubule ◽  
Bicarbonate Transport ◽  
Bicarbonate Concentration ◽  
Plasma Bicarbonate ◽  
Bicarbonate Reabsorption ◽  
Collecting Ducts ◽  
Persistent Elevation

Rebound metabolic alkalosis is a transient alkalemia that is seen during recovery from NH4Cl-induced metabolic acidosis. The persistent elevation of plasma bicarbonate concentration is the result of continuing excretion of net acid by the kidney. Bicarbonate transport by inner medullary collecting ducts has been reported by others to proceed normally (i.e., bicarbonate reabsorption continues in this segment) during rebound metabolic alkalosis. No other segmental responses have been evaluated. Since the surface distal tubule of the rat is known to both reabsorb and secrete bicarbonate in vivo, it was of interest to determine the response of this segment. Our results show that the distal tubule microperfused in vivo during rebound metabolic alkalosis continues to reabsorb significant amounts of bicarbonate, despite the presence of systemic alkalemia that we have previously shown to be associated with distal tubule bicarbonate secretion.Key words: rebound metabolic alkalosis, distal tubule, micropuncture, bicarbonate reabsorption.

Extrarenal action of the adrenal cortex on electrolyte metabolism in nephrectomized and nephrectomized-eviscerated rats

1958 ◽  
Vol 196 (1) ◽  
pp. 141-144 ◽  
Author(s):  
Mary Jane Tompkins ◽  
Edward Eckman ◽  
Leonard Share
Keyword(s):  
Adrenal Gland ◽  
Adrenal Cortex ◽  
Opposite Effect ◽  
Potassium Concentration ◽  
Extracellular Fluid ◽  
Plasma Potassium ◽  
Electrolyte Metabolism ◽  
Series Of Experiments ◽  
Sodium And Potassium ◽  
Potassium Metabolism

A study was made of the extrarenal action of the adrenal cortex on sodium and potassium metabolism in the rat. There was a reduction in the plasma potassium concentration 24 hours after the administration of desoxycorticosterone, 2 mg/rat, in the adrenalectomized-nephrectomized rat. Treatment with hydrocortisone, 5 mg rat, resulted in the opposite effect. Corticosterone and 2-methyl-9α-fluorohydrocortisone were without effect. In another series of experiments, adrenalectomy resulted in an elevation in the plasma potassium concentration in nephrectomized-eviscerated rats. This change could be detected as early as two hours after operation. The intravenous administration of large doses of desoxycorticosterone, hydrocortisone, corticosterone and aldosterone were without effect. It is suggested that there is a movement of potassium into the extracellular fluid in the absence of the secretions of the adrenal gland.

Extrarenal Factors in Diabetes Insipidus in the Rat

1958 ◽  
Vol 192 (2) ◽  
pp. 401-404 ◽  
Author(s):  
Sydney M. Friedman ◽  
Harald F Scherrer ◽  
Miyoshi Nakashima ◽  
Constance L. Friedman
Keyword(s):  
Renal Function ◽  
Diabetes Insipidus ◽  
Potassium Concentration ◽  
Extracellular Volume ◽  
Extracellular Fluid ◽  
Plasma Potassium ◽  
Fluid Volume ◽  
Extracellular Fluid Volume ◽  
Plasma Sodium ◽  
Sodium Potassium

Using inulin as indicator of the extracellular volume, the distribution of sodium, potassium and water was studied in rats with diabetes insipidus produced by interrruption of the supraoptico-hypophyseal tract. A well defined increase in the extracellular fluid volume associated with normal plasma sodium and reduced plasma potassium concentration was uniformly present in the rats with diabetes insipidus. These changes occurred in nephrectomized animals and were thus independent of renal function, but were in some degree referable to an increase in adrenal function since they could be partially reversed by adrenal ablation.

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