An isotope dilution method, using 32P-labeled pyrophosphate, has been developed for the measurement of inorganic pyrophosphate (PP1) in human plasma. The specificity of the method was better than 90% as assessed by elution patterns during ion-exchange chromatography, by paper chromatography, and by incubation with inorganic pyrophosphatase. The 99% confidence limits for a single estimation of plasma PP1 was ±13%. There were no differences in plasma PP1 between men and women, but the values in young people (0-15 yr) were slightly higher than in older people. The mean concentration (±SE) of PP1 in the plasma of 73 men and women was 3.50 ±0.11 μmoles/liter (0.217 ±0.007 μg P/ml) and the normal range (99% limits) was 1.19-5.65 μmoles/liter (0.074-0.350 μg P/ml).
R. G. G. Russell, S. Bisaz, A. Donath, D. B. Morgan, H. Fleisch
In order to investigate the possible role of the renin-angiotensin system in the regulation of intrarenal hemodynamics in hemorrhagic hypotension (HH), seven mongrel dogs have been studied under the following conditions: (a) Control, (b) HH (mean arterial pressure 70 mm Hg), and (c) HH + alpha adrenergic blockade by phenoxybenzamine (HH + POB). The following parameters were obtained for the right kidney: Intrarenal distribution of blood flow and local blood flow rates (133Xe washout technique); total renal blood flow (RBF) on the basis of the clearance and extraction ratio of PAH and the arterial hematocrit; plasma renin concentrations in the renal artery and vein by the method of Boucher and his associates; and renin release into the renal circulation.
A. Grandchamp, R. Veyrat, E. Rosset, J. R. Scherrer, B. Truniger
The relation of neuraminidase to morbidity and mortality was examined in patients with Haemophilus influenzae, meningococcal, and pneumococcal meningitis. Ten strains of H. influenzae and eight strains of meningococci from infected cerebrospinal fluid (CSF) did not elaborate neuraminidase. Each of 27 strains of pneumococci from infected CSF elaborated both neuraminidase and N-acetylneuraminic acid (NANA) aldolase. There was no correlation between amount of neuraminidase secreted in vitro and survival of patients.
Richard D. O'Toole, Louise Goode, Calderon Howe
The utilization of circulating maltose was compared to that of glucose in six normal fasting subjects after intravenous injection of 25 g of either sugar. Blood samples were obtained over a 2 hr period and were assayed for free fatty acids (FFA), insulin, glucose, and total reducing substances. Urine was collected for 2 hr after maltose administration and assayed enzymatically for glucose and maltose. Blood glucose concentrations did not increase after maltose infusion, although a significant rise in total reducing substances was noted, indicating the presence of this disaccharide in the blood. Less than 3% of the administered maltose was excreted in the urine either as maltose or glucose. Initially, there was a fourfold increase in serum insulin concentration after glucose and a threefold increase after maltose infusion. Therefore, serum insulin concentrations gradually declined in a similar manner for both sugars. The plasma FFA at 15 min decreased 371 uEq/liter after glucose and 338 uEq/liter after maltose infusion.
Sister John M. Young, Elliot Weser
Influences of estrogen and progesterone on the development of hyperinsulinemia and augmented pancreatic islet insulin secretion during pregnancy were assessed in this study. Groups of female rats were injected subcutaneously for 21 days with varying daily dosages of estradiol benzoate or progesterone in oil. On day 21, pancreatic islets were isolated by a collagenase method. Total insulin secretion was measured after 90-min incubations of 10 islets in buffered medium containing glucose. Higher physiologic dosages of estradiol or progesterone, singly or in combination, significantly increased islet secretion above values of untreated control rats and were comparable to augmented islet responses of term, 3-wk pregnant rats. Diameter and protein content of islets obtained from steroid-treated and pregnant rats exceeded control measurements in these instances. However, 2-hr preincubations of control islets with 1 or 10 μg/ml of either steroid did not influence subsequent glucose-stimulated insulin output.
N. V. Costrini, R. K. Kalkhoff
Placental transport of vitamin B12 was studied in the pregnant rat in two series of experiments. In the first series animals were given cyanocobalamin-57Co intravenously at various stages of gestation. High specific activity tracer was used and doses of B12 were 1-2 ng per animal. The rats were killed from 15 min to 24 hr after injection and the fetuses, placentas, and serum were assayed for radioactivity. In the second series using uninjected animals, absolute amounts of vitamin B12 in fetuses and placentas were measured at stages of gestation from day 12 through day 20.
Stanley E. Graber, Ursula Scheffel, Barbara Hodkinson, Patricia A. McIntyre
Studies of adipose tissue cellularity were carried out in a group of nonobese adult male volunteers who gained 15-25% of their body weight as the result of prolonged high caloric intake. Adipose cell size (lipid content per cell) was determined in tissue obtained from three subcutaneous sites (gluteal, anterior abdominal wall, and triceps) and total adipose cell number estimated from measurement of total body fat.
Lester B. Salans, Edward S. Horton, Ethan A. H. Sims
Histamine has positive inotropic and chronotropic effects on the heart which are not abolished by beta adrenergic-blocking agents. Since the positive inotropic and chronotropic effects of other hormones on the heart are thought to be mediated by cyclic 3′,5′-AMP, we examined the effect of histamine on adenyl cyclase in particulate preparations of guinea pig, cat, and human myocardium. Histamine at the peak of its dose-response curve, 3 × 10-4moles/liter, produced approximately a 300% increase in cyclic 3′,5′-AMP accumulation in the guinea pig, 60% in the cat, and 90% in the human heart particles. Half-maximal activity for the histamine mediated activation of adenyl cyclase in the guinea pig was 9 × 10-6moles/liter, almost identical with that observed for norepinephrine in the same preparation. DL-Propranolol, 1 × 10-5moles/liter, did not abolish the activation of adenyl cyclase produced by histamine but did abolish the activation produced by norepinephrine. In contrast, diphenhydramine hydrochloride, Benadryl, 8 × 10-5moles/liter, abolished the activation of adenyl cyclase by histamine but not that produced by norepinephrine. These data suggest that there are at least two receptor sites in guinea pig heart mediating the activation of adenyl cyclase, one responsive to histamine, the other to norepinephrine. In addition, combined maximal doses of histamine and norepinephrine produced completely additive effects on the activation of adenyl cyclase, which suggests that at least two separate adenyl cyclase systems are present in the heart, each responsive to one of these hormones. However, definitive proof would require physical separation of the two enzymes.
Irwin Klein, Gerald S. Levey
The activation energy (EA) for the diffusion of water across the epithelial cell layer of the toad bladder was determined in the absence and presence of vasopressin. An experimental approach was employed which minimized the effects of unstirred layers and the thick supporting layer of the bladder on the measurement of water diffusion. EA in the absence of vasopressin was 11.7 ±1.4 kcal·mole-1; after vasopressin it was 10.6±1.1 kcal·mole-1. The difference between the two values was not significant. The results are consistent with an increase in the number rather than the size of aqueous channels in the cell membrane, a finding which differs from the generally held view that the hormone increases the radius of pores in the membrane.
Richard M. Hays, Nicholas Franki, Roy Soberman
The ability of heavy microsomes and mitochondria, isolated from the control and failing hearts of genetically dystrophic hamsters (BIO 14.6 strain), to accumulate calcium was examined. The rate and extent of energy-linked calcium binding (in the absence of oxalate) by the heavy microsomes of the failing heart were markedly depressed. The calcium uptake (in the presence of 5 mM oxalate) by the heavy microsomes of the failing heart was similar to that of the control heart. On the other hand, both the rate and extent of energy-linked calcium binding (in the absence of Pi and succinate) and calcium uptake (in the presence of 4 mM Pi and 5 mM succinate) by mitochondria were greatly reduced in the failing heart in comparison to the control. No difference in the total adenosine triphosphatase activities (Ca++-Mg++ stimulated) of heavy microsomes or mitochondria was observed between the control and failing hearts. These results indicate an abnormality of subcellular membranes of the failing heart to bind calcium and support the growing conviction concerning the defective “calcium pump” as a molecular abnormality associated with a moderate degree of congestive heart failure.
Prakash V. Sulakhe, Naranjan S. Dhalla
The pulmonary vasopressor response to acidemia was studied in intact dogs in a hemodynamically separated lobe which was pump perfused with systemic arterial or venous blood at a fixed rate. The magnitudes of the lobar vasopressor responses to perfusion with blood rendered acidic by infusions of hydrochloric lactic, and acetic acids, and by hypercapnia (membrane oxygenator) were significantly different. Although the PH of the perfusing blood in each group fell to similar extents (pH 7.1-7.0), the lobar pressor response was greatest with hydrochloric acid (HCl), smaller with lactic and acetic acids, and absent with hypercapnia. A lobar vasopressor response also occurred during lobar perfusion with blood which had been extracorporeally acidified with HCl or acetic acid, but then returned to control pH by infusions of sodium bicarbonate and Tris before reaching the lung. A lobar vasopressor response also resulted from pump perfusion of the lobar artery with femoral venous blood during perfusion of the isolated ipsilateral femoral artery with similarly treated aortic blood. However, no lobar vasopressor response resulted from pump perfusion of the lobar artery with blood removed transseptally from a right pulmonary vein during acidification (HCl) of the right pulmonary artery (to pH 7.0).
Albert L. Hyman, William C. Woolverton, Paul S. Guth, Herbert Ichinose
Lysates of mixed human leukocyte suspensions released histamine from intact human leukocytes in vitro. Microgram quantities of leukocyte lysate protein released up to 90% of the total available histamine. The mixed leukocyte lysates were separated by differential centrifugation into nuclear (800 g pellet), lysosomal (25,000 g pellet), and postlysosomal supernatant (25,000 g supernatant) fractions. The degree of separation of the lysosomal from the other two fractions was assessed by measuring the relative activities of four lysosomal enzymes. The average distribution of enzyme activity was 11 ±2% (mean ±1 SD), 72 ±10%, and 17 ±8% for the nuclear, lysosomal, and supernatant fractions respectively. The histamine-releasing activity was equally distributed between the lysosomal and supernatant fractions, each of which had 5-fold greater activity than the nuclear fraction.
Michael T. Kelly, R. Russell Martin, Arthur White
A coordinate relationship between the activities of two sequential enzymes in the de novo pyrimidine biosynthetic pathway has been demonstrated in human red cells. The two enzymes, orotidylate phosphoribosyltransferase and decarboxylase are responsible for the conversion of orotic acid to uridine-5′-monophosphate. Fractionation of red cells, on the basis of increase of specific gravity with cell age, has revealed that these two enzymes have a marked but equal degree of lability in the ageing red cell. It is postulated that orotidylate phosphoribosyltransferase and decarboxylase form an enzyme-enzyme complex, and that the sequential deficiency of these two enzymes in hereditary orotic aciduria may reflect a structural abnormality in this complex.
Richard M. Fox, Margaret H. Wood, William J. O'Sullivan
An effort to examine certain aspects of the adaptation in potassium excretion associated with nephron reduction was made in dogs with unilateral remnant kidneys. A constant intake of potassium was maintained by tube feeding and studies were performed before and after removal of the intact control kidney. The removal of the intact kidney created the need for the remaining nephrons of the remnant kidney to increase their rate of potassium excretion markedly. Sodium intake was held constant either at a normal or a low level. Mineralocorticoid hormone activity was maintained either at a high level by the administration of 0.2 mg 9-α-fluorohydrocortisone daily or at a low level by performing bilateral adrenalectomy and administering a minimal maintenance dose of deoxycorticosterone acetate (DOCA) and cortisol. Potassium excretion per nephron increased strikingly within 18 hr of contralateral nephrectomy and by 7 days, excretion rates were 600% of control values for the remnant kidney. More potassium was excreted in the first 5 hr after administration of a test dose of potassium by the remnant kidney alone in the postnephrectomy state than by both the remnant and intact kidneys in the prenephrectomy state. 24 hr excretion of potassium by the remnant kidney postnephrectomy averaged 92% of the administered load of potassium. The adaptation in potassium excretion was independent of the concurrent rate of sodium excretion and of mineralocorticoid hormone activity and persisted during constriction of the renal artery, a stimulus which presumably decreased distal delivery of sodium. The adaptation and the continued modulation of potassium excretion could not be explained adequately by an increase in impermeant anion excretion per nephron. Finally, known changes in hydrogen ion excretion per nephron associated with nephron reduction are in a direction opposite to those which would explain the acquired kaliuresis per nephron.
Raymond G. Schultze, Dennis D. Taggart, Howard Shapiro, J. Phillip Pennell, Sali Caglar, Neal S. Bricker
In order to determine whether an adrenergic mechanism is involved in the secretion of growth hormone and insulin, the effect of adrenergic-blocking or -stimulating agents on plasma human growth hormone (HGH), immunoreactive insulin, blood free fatty acids (FFA), and glucose levels was studied in normal human subjects.
Hiroo Imura, Yuzuru Kato, Masaki Ikeda, Masachika Morimoto, Mikio Yawata
In a series of 40 patients treated with L-asparaginase for various neoplastic diseases, 6 patients had generalized anaphylactic reactions to L-asparaginase. Each of these reactors had antibodies detectable by passive hemagglutination, but precipitins were detectable in only one of this group of six patients. That patient had received two courses of the enzyme. 1 wk after the anaphylactic reaction, complement-fixing antibodies were present in all the patients that were studied. Specific reagin antibodies (IgE) were demonstrated in one patient by the release of histamine from his leukocytes after incubation in vitro with L-asparaginase.
Robert G. Peterson, Robert E. Handschumacher, Malcolm S. Mitchell
Studies on bacteria have suggested that morphine-like drugs have effects on the cell membrane. To determine the effect of this class of drugs on a mammalian cell, we selected the rabbit peritoneal exudate granulocyte, which undergoes striking membrane changes during phagocytosis. We examined the effect in vitro of the morphine analogue, levorphanol on phagocytosis and metabolism by granulocytes incubated with and without polystyrene particles or live Escherichia coli. Levorphanol (1 or 2 mmoles/liter) decreased: (a) acylation of lysolecithin or lysophosphatidylethanolamine in the medium (which is stimulated about two-fold during phagocytosis) both at rest (40%) and during phagocytosis (60%); (b) uptake of latex particles and Escherichia coli, as judged by electron microscopy; (c) killing of live Escherichia coli (10-fold); (d) 14CO2 production from glucose-1-14C during phagocytosis by at least 80%; (e) K+ content of granulocytes (35%); (f) oxidation of linoleate-1-14C by 50%, and its incorporation into triglyceride by more than 80%. However, levorphanol stimulated 2 to 3-fold the incorporation of linoleate-1-14C or palmitate-1-14C into several phospholipids. Glucose uptake, lactate production, and adenosine triphosphate (ATP) content are not affected by the drug. Thus, levorphanol does not appear to exert its effects through generalized metabolic suppression.
Nancy Wurster, Peter Elsbach, Eric J. Simon, Penelope Pettis, Sharon Lebow
The mechanism of bacterial uptake of vitamin B12, the spectrum of microorganisms capable of such uptake, and the factors involved were the subject of this study. Bacterial uptake of vitamin B12 was found to be at least a two stage process. A primary uptake phase which was rapid (1 min or less), pH dependent, nontemperature dependent, did not require viable organisms and was insensitive to either the metabolic inhibitor dinitrophenol or to the sulfhydryl inhibitor N-ethyl-maleimide. Protein denaturation (formalin treatment or autoclaving) abolished all B12 uptake. This primary uptake phase is thought to represent adsorption to binding or “receptor” sites on the cell wall. Second stage uptake was slower, pH and temperature dependent, required living bacteria, and was abolished by either dinitrophenol or N-ethyl-maleimide. This phase is dependent upon metabolic processes and may reflect transfer of B12 from surface “receptor” sites into the bacterial cell. Although differences among organisms were observed in total 1 hr uptake, number of surface “receptor” sites, and relative avidities for B12, all organisms except Streptococcus fecalis shared the two stage mechanism. Two Gram-positive organisms. Bacillus subtilis and Group A streptococcus, demonstrated the highest 1 hr vitamin B12 uptake values; Gram-negative bacteria required 2,000-10,000 the number of organisms for comparable uptake. Binding constants (Km) varied from 5.05 ±1.67 × 10-10M for B. subtilis to 6.18 ±3.08 × 10-9M for Klebsiella pneumoniae which approximate the Km for human intrinsic factor (0.38 × 10-10M). Competition between bacteria and intrinsic factor for vitamin B12 may be inferred from the similarity of these constants.
R. A. Giannella, S. A. Broitman, N. Zamcheck
A new human antigen is reported which is present only on blood neutrophils. A neutrophil-specific antigen, designated NA1, has previously been identified in two unrelated families, and was shown to be involved in fetomaternal incompatibility and the development of isoimmune neonatal neutropenia in five newborns. In the present paper, a second antigen, designated NB1, is identified in four families with seven affected children. Antibodies that react with this second antigen are shown to produce selective agglutination of neutrophils but not other blood cells. They are neither absorbed by cells prepared from solid tissues nor by non-neutrophilic blood cells.
Parviz Lalezari, Georgette B. Murphy, Fred H. Allen Jr.
The question of whether the carotid sinus baroreceptors modulate myocardial performance remains controversial. Several studies that have stressed their importance have been criticized because the possible role of cerebral ischemia and of other important variables was not eliminated. To reinvestigate this problem, we studied 21 dogs placed on total cardiopulmonary bypass. In each of these animals the carotid sinus regions were isolated and perfused with fully oxygenated blood at a constant flow rate; perfusion pressure was changed by varying the resistance to outflow from the isolated segments. Several indices of myocardial performance were assessed: right and left ventricular contractile force with Walton-Brodie strain gauge arches; the maximal rate of change in contractile force, dF/dt; the pressure developed within an isovolumic balloon inserted into the left ventricle; and the maximal rate of change of this pressure, dP/dt. When the pressure distending the carotid sinuses was raised from an average value of 34.1 ±2.8 (SEM) mm Hg to 190.1 ±4.7 mm Hg, right ventricular contractile force fell 14.9 ±2.3% (P < 0.001); right ventricular dF/dt decreased 16.7 ±3.0% (P < 0.01); left ventricular contractile force declined 14.9 ±3.3% (P < 0.01); left ventricular dF/dt fell 19.3 ±4.0% (P < 0.01); peak systolic pressure in the isovolumic balloon declined 18.2 ±3.7% (P < 0.001); and dP/dt decreased 34.1 ±4.0% (P < 0.01). Prior adrenalectomy and vagotomy and maintenance of heart rate at a constant level did not influence these results. The inverse relation between carotid sinus perfusion pressure and the indices of contractility that was observed in this investigation strongly suggests that the carotid sinus baroreceptors are an important regulatory mechanism in the control of myocardial performance.
Studies of the rate of extrathyroidal conversion of thyroxine (T4) to 3,5,3′-triiodo-L-thyronine (T3) were carried out in rats. Total body homogenates were prepared and extracted with ethanol 48, 72, and 96 hr after the intravenous injection of 125I-T4. 131I-T3 was added, and the paper chromatographic purification of T3 was effected by serial elution and rechromatography in three paper and one thin-layer cycles. The ratio of 131I-T3 and 125I-T3 counting rates in the final chromatograms, which was identical in three different paper chromatography systems, was used to calculate the proportion of 125I-T3 to 125I-T4 in the original homogenates. In order to discount the effects of in vitro monodeiodination of T4 during extraction and chromatography, we killed control animals immediately after injection of 125I-T4 and processed them in a similar fashion to the experimental groups. The average ratio of 125I-T3 to 125I-T4 in carcass extracts of animals killed between 48 and 96 hr after isotopic injection was 0.08 whereas the average ratio of 125I-T3 to 125I-T4 in chromatograms of control animals was 0.01. On the basis of the proposed model, calculations indicated that about 17% of the secreted T4 was converted to T3. Assuming values cited in the literature for the concentration of nonradioactive T3 in rat plasma, these findings would suggest that about 20% of total body T3 is derived by conversion from T4. Moreover, since previous estimates have suggested that in the rat, T3 has about 3 to 5 times greater biologic activity than T4, these results also raise the possibility that the hormonal activity of T4 may be dependent in large part on its conversion to T3.
Harold L. Schwartz, Martin I. Surks, Jack H. Oppenheimer
Low density lipoproteins (LDL) and high density lipoproteins (HDL) from the plasma of patients with familial lecithin: cholesterol acyltransferase (LCAT) deficiency have been characterized by gel filtration, analytical ultracentrifugation, and gel electrophoresis, and their relative content of lipid and protein has been determined. The LDL of d 1.019-1.063 g/ml show marked heterogeneity. A subfraction of the LDL emerges from columns of 2% agarose gel with the void volume, has corrected flotation rates (Sf°) in the range of 20-400, and contains 4-10 times as much unesterified cholesterol, phosphatidylcholine, and triglyceride per mg protein as normal LDL. A major subfraction of the LDL emerges from the gel in the same general position as normal LDL, but exhibits somewhat higher flotation rates and contains 1.5-3 times as much unesterified cholesterol and phosphatidylcholine and 13 times as much triglyceride per mg protein. The HDL, shown to be heterogeneous in earlier studies, are mainly comprised of molecules which have flotation rates of F1.20 3-20, migrate in the α1-α2 region on electrophoresis, and contain about 12 times as much unesterified cholesterol and 5 times as much phosphatidylcholine per mg protein as normal HDL. Smaller molecules are also detected, which have flotation rates of F1.20 0-3, migrate in the prealbumin region on electrophoresis, and contain only slightly more unesterified cholesterol and phosphatidylcholine per mg protein than normal HDL.
Kaare R. Norum, John A. Glomset, Alex V. Nichols, Trudy Forte
The low density lipoproteins (LDL) of d 1.019-1.063 g/ml of patients with familial lecithin: cholesterol acyltransferase (LCAT) deficiency show marked heterogeneity when viewed with the electron microscope. At least two types of particles are present, one large and the other small. The large particles predominate in a LDL subfraction of large molecular weight isolated by gel filtration on 2% agarose gel. They appear to be flattened structures with diameters mainly in the range of 900-1200 A. The small particles predominate in a LDL subfraction of smaller molecular weight isolated by filtration on the same type of gel. They are 210-250 A in diameter and are similar to normal LDL in size and shape.
Trudy Forte, Kaare R. Norum, John A. Glomset, Alex V. Nichols
The sequential changes in the concentration and pattern of circulating luteinizing hormone (LH) and follicle-stimulating hormone (FSH)1 following bilateral ovariectomy were determined in 10 premenopausal women. The initial (1st wk) and delayed (3 wk) secretory responses of serum LH and FSH as related to the phases of the menstrual cycle were examined. Ovariectomy during follicular phase was accompanied by a prompt and much greater rise in both LH and FSH during the 1st wk. This rapid rise was followed by a transient decline between the 7th and 10th day which resulted in a biphasic pattern. In contrast, a slower and progressive rise in serum LH and FSH was observed in subjects ovariectomized during luteal phase of the cycle. The quantitative secretion (area under the curve) during the 1st wk after ovariectomy was significantly greater in patients operated on during the follicular phase than during the luteal phase for both LH (P < 0.05) and FSH (P < 0.01). Thereafter, a similar pattern of gonadotropin rise was observed for patients ovariectonized during either phase of the cycle and reached a plateau by the end of the 3rd wk. At this time, the mean LH concentration increased 6-fold for follicular phase surgery and 8-fold for luteal phase surgery. The mean serum FSH concentration increased 8-fold for follicular phase surgery and 12-fold for luteal phase surgery. The net increase in serum FSH level was higher than that in the serum LH level after surgery in both phases of the cycle and thus a reversal of FSH/LH ratio occurred. These data provide indirect evidence that the phase of ovarian steroid secretion may exert a quantitative influence on the gonadotropin turnover rate within the hypothalamic-pituitary system. The augmented gonadotropin release and the reversal of FSH/LH ratio following ovariectomy presumably could be due to an increased gonadotropin net synthesis which is more pronounced for FSH than for LH.
S. S. C. Yen, C. C. Tsai
After the relief of 24 hr of complete unilateral ureteral obstruction in the dog, the experimental kidney is characterized by a decrease in filtration rate and an increase in fractional and often absolute excretion of sodium before and after the administration of mannitol. In the hydrated state, the failure to conserve sodium is associated with increases in fractional free water clearance and fractional sodium supply to water-freeing sites signifying that the augmented sodium excretion is derived from a proximal source. In the hydropenic state there is decreased fractional free water reabsorption, and sometimes free water excretion, in the postobstructive kidney. An early plateau in free water reabsorption is associated with an increased fractional excretion of sodium. These findings are attributed to the early development of distal nephron impermeability to water as a result of enhanced distal tubular supply and transport of sodium. There is a decrease in maximal tubular reabsorptive capacity (Tm) of glucose in the post-obstructive kidney which is, however, less marked than the decrease in filtration rate. The fall in filtration rate is to some extent likely due to a dropping out of nephrons from the circulation while the remaining nephrons are hypoperfused. The magnitude of the sodium reabsorptive defect is markedly exaggerated as the concentration of nonreabsorbable solute (mannitol) in the glomerular perfusate is increased. It is concluded that the postobstructive increase in sodium excretion during mannitol administration is in part due to a limit in the capacity to reabsorb sodium against a concentration gradient in the proximal tubule.
D. Danny Bercovitch, Leonard Kasen, Laurence Blann, Marvin F. Levitt