Renal prostaglandins E2 and F2α throughout normal human pregnancy

Twenty-five normal pregnant women were studied sequentially at 4-week intervals, beginning from weeks 8-16 until delivery. In eighteen women the study was repeated 6 weeks after delivery. The 24-h urinary excretion of PGE2 and PGF2 alpha, plasma renin activity (PRA), plasma aldosterone and fractional excretion of sodium (FENa) were measured at each visit. PGE2 and PGF2 alpha increased progressively throughout pregnancy (867 +/- 81 and 1048 +/- 94 ng 24 h-1 respectively, before week 15 and 1581 +/- 175 and 2625 +/- 305 ng 24 h-1, respectively, after week 35) and returned to normal values 6 weeks after delivery (748 +/- 107 and 1503 +/- 165 ng 24 h-1, respectively). PRA and aldosterone increased in a similar fashion, but values of prostaglandins did not correlate with those of PRA or aldosterone. PGE2 correlated directly with FENa but this correlation was weak. These results may suggest that tubulo-interstitial prostaglandins play a role in the regulation of sodium homeostasis during pregnancy.     

Erythrocyte Li+/Na+ and Na+/H+ exchange, cardiac anatomy and function in insulin-dependent diabetics

It has been proposed that an increased activity of cell membrane Na+/H+ exchange, mirrored by increased erythrocyte Li+/Na+ exchange, may facilitate cell hypertrophy and hyperplasia. Patients with insulin-dependent diabetes mellitus may develop a specific cardiomyopathy with systolic and diastolic abnormalities and increased thickness of the left ventricle. Therefore, we have investigated the relationships between erythrocyte Li+/Na+ and Na+/H+ exchange and echocardiographic parameters in 31 male insulin-dependent diabetics (aged 17-68), in good metabolic control. Three had untreated mild hypertension. In all patients the urinary albumin excretion rate was less than 200 micrograms min-1. Ten patients had a Li+/Na+ countertransport higher than 0.37 mmol l-1 cell h-1, the upper normal limit for our laboratory (0.49 +/- 0.10, mean +/- SD). In comparison with the patients with normal countertransport, they had increased interventricular septum thickness and relative wall thickness (h/r). End diastolic volume and cardiac index were reduced while blood pressure and urinary albumin excretion rate were similar. In the whole study group, interventricular septum thickness was significantly correlated to Li+/Na+ exchange (r = 0.61, P less than 0.001) and Na+/H+ exchange (r = 0.35, P less than 0.05), independently of the effect of age and blood pressure. Posterior wall thickness was correlated to Li+/Na+ exchange (r = 0.38, P less than 0.05) and h/r to Li+/Na+ exchange (r = 0.41, P less than 0.05) and to Na+/H+ exchange (r = 0.44, P less than 0.05). Li+/Na+ exchange was negatively correlated to cardiac index (r = -0.37, P less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)     

Compared effects of ruthenium red and cis [Ru(NH3)4Cl2]Cl on the isolated ischaemic-reperfused rat heart

Summary— The sequence ischaemia-reperfusion is characterized by reperfusion damage. The calcium overload occurring at the beginning of reperfusion is one of the main mechanisms responsible for reperfusion damage. Ruthenium red, a blocker of the mitochondrial calcium uniport system, could prevent this damage by preserving the ATP synthesis in the mitochondria. We tested ruthenium red and another ruthenium compound, cis-tetrammine dichlororuthenium (III) chloride in our experimental model of ischaemic-reperfused rat hearts. After a 15 minute-stabilization period, the hearts were submitted to a 30 minute global ischaemia period and then reperfused for 45 minutes with the standard perfusion solution or with ruthenium red or cis-tetrammine dichlororuthenium (III) chloride at 1, 3 or 9 μM. Ruthenium red at 3 μM exerted a protective effect in our experimental conditions by showing a significant improvement of the contractility recovery at the end of reperfusion and a significant decrease of the malondialdehyde production, which reflects free radical production. The cis-tetrammine dichlororuthenium (III) chloride (containing 1 Ru ion per molecule) at 9 μM was slighty less efficient than ruthenium red at 3 μM (containing 3 Ru ions per molecule). The heart ruthenium binding was better for the ruthenium red than for the cis-tetrammine dichlororuthenium (III) chloride, suggesting a role of the ruthenium ion complexation in the crossing of the membrane, whereas the cardiac effect seemed to be linked to the ruthenium ion heart concentration, which was similar for the ruthenium red at 3 μM and for the cis-tetrammine dichlororuthenium (III) chloride at 9 μM. One can hope that ruthenium compounds would limit reperfusion damage and infarct size after ischaemia in in vivo models.     

Renal handling of NH3/NH4+: recent concepts

To be appropriately excreted in urine, NH4+, the major component of urinary acid excretion, must be synthesized by proximal tubular cells, secreted into the proximal tubular fluid, reabsorbed by the medullary thick ascending limb (MTAL) to be accumulated in the medullary interstitium, and finally secreted in medullary collecting ducts. Several targets have been identified to account at the gene expression level for the adaptation of renal NH4+ synthesis and transport in response to a chronic acid load. These targets are the key enzymes of ammoniagenesis (mitochondrial glutaminase and glutamate dehydrogenase) and gluconeogenesis (phosphoenolpyruvate carboxykinase) and the Na+/H+(NH4+) exchanger NHE3 in the proximal tubule, the apical Na+-K+(NH4+)-2Cl- cotransporter of the MTAL, the basolateral Na+-K+(NH4+)-2Cl- cotransporter, and likely the epithelial Rh B and C glycoproteins in the collecting ducts. An acid pH per se appears to be a major factor in the control of the expression of these genes during metabolic acidosis probably through activation of pH sensors. Glucocorticoids may also act in concert with an acid pH to coordinate the adaptation of various tubular cell types. The present review focuses on some new aspects of NH3/ NH4+ transport and of regulations of gene expression that have recently emerged.     

A comparison of the effects of glucose ingestion and NH4Cl acidosis on urinary calcium and magnesium excretion in man

Both glucose ingestion and NH(4)Cl acidosis have been reported to augment urinary calcium (U(Ca) V) and magnesium (U(Mg) V) excretion. Both also cause acidification of the urine and an increase in renal acid excretion. To examine whether a common mechanism of action was involved, the effects of glucose ingestion and NH(4)Cl acidosis on U(Ca) V and U(Mg) V were tested in the same subjects. Glucose ingestion caused significant increases in both U(Ca) V and U(Mg) V. During stable NH(4)Cl acidosis, U(Ca) V increased significantly, while U(Mg) V was unaffected. When a glucose load was given during acidosis, the separate effects of acidosis and glucose on U(Ca) V were additive, whereas U(Mg) V increased less than observed during normal acid-base balance. Although renal acid excretion increased and the urine was acidified after glucose in the normal steady state, when glucose was administered during NH(4)Cl acidosis urine pH rose and there was no change in renal acid excretion. We concluded that NH(4)Cl acidosis and glucose ingestion reduce the renal tubular reabsorption of magnesium and (or) calcium, but they act through separate mechanisms.     

Basophil Histamine Release and Leukotriene (LTB4 - LTC4) Production in Cluster Headache

Histamine release and leukotrienes (LTB4 and LTC4) production from circulating basophil have been studied in 13 patients with episodic cluster headache (CH) during the remission phase of symptoms, and in 9 normal subjects. Cell suspensions of basophils were stimulated with scalar dilutions of anti-IgE, f-met-peptide and Ca2+ ionophore A23187. Histamine was measured by an automated fluorimetric method; LTB4 and LTC4 with RIA in individual cases, and with Reverse-Phase HPLC in the two pools obtained from the supernatants of CH patients and controls. Mean values of histamine release in patients with CH were significantly lower when compared to those obtained in control subjects after stimulation with anti-IgE at the three dilutions used. LTC4 mean levels measured in CH patients were significantly lower than those of supernatants from controls after stimulation with 0.05 gamma/ml of A23187. A reduction of LTC4 and LTB4 levels in CH patients was also observed in R-P HPLC, which showed different elution patterns in the two groups. The histamine release in individual cases was related to leukotriene production: LTC4 levels were significantly (p less than .05) higher in "high histamine releasers" than in "low histamine releasers". Our results indicate that CH patients have complex abnormalities of histamine release and of leukotriene production during the painless phase of the disease.     

Relationship between urinary prostaglandin E2 and F2α excretion and plasma arginine vasopressin during renal concentrating and diluting tests in renal transplant recipients

Urinary excretion of prostaglandin E2 (PGE2 and F2 alpha (PGF2 alpha) and plasma concentration of arginine vasopressin (AVP) were determined during urinary concentrating and diluting tests in renal transplant recipients and control subjects. During the concentrating test PGE2 and PGF2 alpha remained unchanged in the renal transplant recipients, whereas both PGE2 and PGF2 alpha were significantly reduced in the control subjects. During the diluting test PGE2 and PGF2 alpha increased in both groups but, contrary to PGF2 alpha, PGE2 was significantly higher in all periods in the transplant recipients compared to the controls. However, the prostaglandin excretion rates per kidney were significantly higher in the renal transplant recipients than control subjects, for all periods during both the concentrating and the diluting test. Arginine vasopressin was significantly higher in renal transplant recipients than control subjects during basal conditions, increased to a significantly higher level in the transplant recipients after thirst, but was reduced to the same levels in the two groups during the diluting test. It is concluded that the increased excretion of prostaglandins in renal transplant recipients may be a compensatory phenomenon representing an adaptation to a reduced renal mass in order to maintain adequate renal water excretion. Although a direct relationship between the prostaglandin excretions of PGE2 and PGF2 alpha and AVP does not seem to exist, it is possible that the higher prostaglandin excretion in the renal transplant recipients may be a counterbalancing mechanism to the higher AVP level, which most likely is secondary to a decreased responsiveness to vasopressin of the renal collecting ducts in the transplanted kidney.     

Histamine differentially interacts with tumor necrosis factor-α and thrombin in endothelial tissue factor induction: the role of c-Jun NH2-terminal kinase

BACKGROUND: Histamine plays an important role in vascular disease. Tissue factor (TF) expression is induced in vascular inflammation and acute coronary syndromes. OBJECTIVES: This study examined the effect of histamine on tumor necrosis factor-alpha- (TNF-alpha-) vs. thrombin-induced endothelial TF expression. METHODS AND RESULTS: Histamine (10(-8)-10(-5) mol L-1), TNF-alpha (5 ng mL-1), and thrombin (1 U mL-1) induced TF expression in human endothelial cells. Although TF expression by TNF-alpha and thrombin was identical, histamine augmented TNF-alpha-induced expression 7.0-fold, but thrombin-induced expression only 2.6-fold. Similar responses occurred with TF activity. The H1-receptor antagonist mepyramine abrogated these effects. Differential augmentation by histamine was also observed at the mRNA level. Histamine-induced p38 activation preceded a weak second activation to both TNF-alpha and thrombin. Histamine-induced c-Jun NH2-terminal kinase (JNK) activation was followed by a strong second activation to TNF-alpha, and less to thrombin. Selective inhibition of this second JNK activation by SP600125 reduced TF induction to histamine plus TNF-alpha by 67%, but to histamine plus thrombin by only 32%. Histamine augmented TNF-alpha- and thrombin-induced vascular cell adhesion molecule 1 (VCAM-1) expression to a similar extent. Consistent with this observation, VCAM-1 induction to TNF-alpha and thrombin was mediated by p38, but not by JNK. CONCLUSIONS: Histamine differentially augments TNF-alpha- vs. thrombin-induced TF expression and activity, which is mediated by the H1-receptor, occurs at the mRNA level, and is related to differential JNK activation.     

Radioimmunoassay of Prostaglandins Fα, E1 and E2 in Human Plasma

Abstract. Antibodies against prostaglandins (PG)F₂α, E₁ and E₂ were obtained in rabbits immunized with respectively PG F₂α, PG E₁ and PG E₂ conjugated to bovine serum albumin by carbodiimide. A radioimmunoassay capable of measuring 7 pg of PG Fα, 2 pg of PG E₂ and 14 pg of PG Ej in human peripheral plasma is described. Plasma samples (pH 3, citric acid) are extracted with cyclohexane: ethyl acetate, 1:1 and then chromatographed on silicic acid columns to separate the prostaglandins into three fractions: fraction I, PG A, PG B and some unknown immunoraactive compounds; fraction II, PG E and fraction III PG Fα. The recovery is 80 %± 6. 2. Mean plasma levels iu adults of PG Fa and PG E, expressed in pg/ml: -PG Fα 12 ± 2. 8 (n = 25 men), 8 ± 2. 3 (n = 18 women, follicular phase), 7 ± 1. 4 (n = 18 women, luteal phase). -PG E₁ 40. 5 + 7. 6 (n = 13 men), 38 + 17. 1 (n = 10 women). -PG E₂ 4. 5 ± 1 (n = 12 adult subjects).
The major characteristics of the method described herein are the following: - a large volume of plasma has to be processed (10 ml or more for PG Fa and PG E₁, 5 ml or more for PG E₂). - a chromatographic step is necessary to separate the different prostaglandins which makes it possible to circumvent problems of immunological cross reactivity and interference with unknown immunoreactive compounds. - great care has been taken in collection of blood samples, especially to insure complete removal of blood cells namely platelets.     

The 13C-mixed triglyceride breath test in healthy adults: determinants of the 13CO2 response

Defects in lipolysis due to pancreatic insufficiency can be diagnosed by the mixed triglyceride (MTG) ¹³CO₂ breath test. However, the effects of various test conditions on the ¹³CO₂ response have only been partially elucidated. In healthy adults, we performed the ¹³CO₂ mixed triglyceride breath test and we compared (a) the inter- and intra-individual variation in the ¹³CO₂ response; (b) the effect of two different test meals; (c) the effect of an additional meal during the test; and (d) the effect of physical exercise during the test. Upon repeating the test in the same individual (test meal cream), repeatability coefficients were large, with respect to either time to maximum ¹³C excretion rate (3.8 h), maximum ¹³C excretion rate (4.9% ¹³C dose h^?1) or cumulative recovery of ¹³C over the 9-h study period (22.7% ¹³C dose). The cumulative ¹³C expiration over 9 h obtained with the test meal composed of cream was quantitatively similar to that obtained with bread and butter: 42.2 ± 8.4% and 47.7 ± 6.3% respectively. Fasting for 9 h during the test resulted in similar ¹³C expiration rates and cumulative ¹³C expiration (43.4% ± 7.2%) when compared with consumption of an additional meal 3 h after the start of the test (38.3 ± 5.3%). The ¹³CO₂ response increased in five out of seven subjects, but decreased in the other two, when moderate exercise was performed (bicycle ergometer, 50 W for 5 h). We conclude that the repeatability of the MTG test in healthy adults is low. The present results indicate that a solid and a liquid test meal, containing a similar amount of fats, give similar cumulative ¹³CO₂ responses, and that stringent prolonged fasting during the test is unnecessary. Standardization of physical activity seems preferable, since the unequivocal effects of moderate exercise on the ¹³CO₂ response were observed in the individuals studied.     

Urinary dopamine in man and rat: effects of inorganic salts on dopamine excretion.

1. Plasma and urine free dopamine (3,4-dihydroxyphenethylamine) were measured in six normal male volunteer subjects and the urinary clearance of dopamine was calculated for each subject. 2. The excretion rates for free dopamine in man were greater than could be explained by simple renal clearance. It was concluded that free dopamine must, therefore, be formed in the kidney. 3. Changes in urinary dopamine excretion were studied in four groups of rats initially maintained on low sodium diet and then given equimolar dietary supplements of NaCl, NaHCO3, KCl or NH4Cl, to study the specificity of the previously observed increase in dopamine excretion after increased dietary NaCl. 4. The mean dopamine excretion increased significantly in rats given NaCl, KCl and NH4Cl, whereas dopamine excretion decreased in those given NaHCO3. 5. The failure of dopamine excretion to rise in response to loading with NaHCO3 was unexpected, and argues against a simple effect of volume expansion by the sodium ion. The increase in dopamine excretion with KCl and NH4Cl showed that this response was not specific to the sodium ion.     

PREVENTION OF CCL4-INDUCED LIVER CIRRHOSIS BY SILYMARIN

The efficacy of silymarin treatment in preventing biochemical and histological alterations in CCL4-induced liver cirrhosis in rats was studied. Four groups of rats were treated with: (1) CCL4; (2) mineral oil; (3) CCL4 + silymarin; and (4) silymarin. All animals were sacrificed 72 h after the end of treatments. The activities of alkaline phosphatase (alk. phosp.), gamma-glutamyl transpeptidase (GGTP), glutamic pyruvic transaminase (GPT) and glucose-6-phosphatase (G6Pase), and bilirubin content were determined in serum. Na+, K+-ATPase and Ca++-ATPase activities were measured in isolated plasma membranes. Lipoperoxidation, triglycerides (TG), and glycogen contents were also measured in liver homogenates. Liver cirrhosis was evidenced by significant increases in liver collagen, lipoperoxidation, serum activities of alk. phosp., GGTP, GPT, G6Pase, bilirubin content, and liver TG. Activities of ATPases determined in plasma membranes were significantly reduced, as was liver glycogen content. Silymarin cotreatment (50 mg/kg b.wt) completely prevented all the changes observed in CCL4-cirrhotic rats, except for liver collagen content which was reduced only 30% as compared to CCL4-cirrhotic rats. Silymarin protection can be attributed to the agent's antioxidant and membrane-stabilizing actions.     

The urinary excretion of prostaglandins E2 and F2α in essential hypertension

The 24 h urinary excretions of prostaglandins E2 (E2/d) and F2 alpha (F2 alpha/d) were measured in twenty-five normal subjects and in thirty-five patients with essential hypertension [seventeen with low renin (LRH) and eighteen with normal renin (NRH) hypertension]. E2/d was lower in patients with LRH than in normal subjects (P less than 0.01), whereas no difference was found between patients with NRH and the controls. F2 alpha/d was similar in patients with LRH and in the normal subjects, but was significantly greater in patients with NRH (P less than 0.02). The ratio of prostaglandin E2 to prostaglandin F2 alpha was decreased in hypertensive patients (P less than 0.02), although in the NRH subgroup the difference was not statistically significant. It appears that LRH is associated with impaired production of prostaglandin E2, while a deranged relationship between the two prostaglandins exists in all the patients with essential hypertension. These changes in prostaglandin production could possibly contribute to the pathogenesis of hypertension, by increasing renal vascular resistance and decreasing sodium excretion. Alternatively, they might be a secondary phenomenon, reflecting changes in renal prostaglandin metabolism induced by the hypertensive state.     

Hyperparathyroidism and abnormal 1,25(OH)2vitamin D3 metabolism in experimental lead intoxication

Clinical evidence points to disturbed calcium metabolism in lead (Pb) intoxication. To further clarify the mechanisms involved, serum levels of 1,25(OH)2D3, receptors for 1,25(OH)2D3 as well as size and ultrastructure of parathyroid glands were examined in Wistar Kyoto rats exposed to 1% lead (Pb) acetate in drinking water for 10 weeks (short-term study) or 0.001-1% Pb acetate for 24 weeks (long-term study). After administration of Pb for 10 weeks, bone Pb was significantly increased (641 +/- 66.9 (SD) vs. 0.648 +/- 0.39 mg kg-1 ash in controls). Total serum calcium and ionized Ca2+ (1.15 +/- 0.031 vs. 1.25 +/- 0.03 mmol l-1) were significantly decreased. Renal function (Ccr) was unchanged, but urinary cAMP excretion and circulating 1,25(OH)2D3 (177 +/- 10.9 vs. 232 +/- 18.9 pmol l-1) were diminished. Specific binding of 1,25(OH)2D3 was increased in parathyroids (Bmax 128 +/- 4.7 vs. 108 +/- 0.6 fmol mg-1 protein) and intestinal muscosa; Bmax failed to adequately rise in response to pretreatment with 1,25(OH)2D3 (2 x 10 ng day-1 for 4 d) in Pb-exposed animals. Receptor characteristics (sedimentation constant, KD, DNA affinity) were unchanged. Parathyroid weight was significantly increased (178 +/- 25 vs. 96 +/- 34 micrograms) with no change of estimated nuclear volume, cell volume or cell ultrastructure. After 24 weeks of Pb exposure, a dose-dependent but non-linear increase of parathyroid weight was noted between 0.001% and 1% Pb in drinking fluid. The present study documents secondary hyperparathyroidism associated with, and presumably caused by, hypocalcaemia and low 1,25(OH)2D3 levels, in experimental Pb intoxication.     

Ammonia and glutamine metabolism in human liver slices: new aspects on the pathogenesis of hyperammonaemia in chronic liver disease

Ammonia and glutamine metabolism was studied in slices from normal, fatty and cirrhotic human livers. The liver disease was evaluated by histological examination. With respect to ammonia removal, urea and glutamine synthesis in human liver represent low and high affinity systems with k0.5(NH4+) values of 3.6 and 0.11 mM, respectively. Compared with normal control livers, cirrhotic livers showed a decreased glutamine synthesis from NH4Cl by about 80%. The same was true for urea synthesis. Conversely, flux through hepatic glutaminase was increased in cirrhosis 4-6-fold. These changes in hepatic glutamine and ammonia metabolism were observed regardless of whether reference was made to liver wet weight, DNA or protein content. Acetazolamide inhibited urea synthesis in cirrhotic liver slices by about 50%, indicating that mitochondrial carbonic anhydrase is required for urea synthesis also in cirrhosis. There was a significant correlation between the in-vitro determined capacity for urea synthesis from NH4Cl and the in-vivo determined plasma bicarbonate concentration.(ABSTRACT TRUNCATED AT 250 WORDS)     

Leukotriene B4 metabolism in neutrophils of patients with chronic granulomatous disease: phorbol myristate acetate decreases endogenous leukotriene B4via NADPH oxidase-dependent mechanism

We studied the effect of phorbol myristate acetate (PMA) on endogenous leukotriene B4 (LTB4) metabolism of calcium ionophore A23187-stimulated human neutrophils. Preincubation of normal neutrophils with PMA significantly suppressed the recovery of endogenous LTB4 induced by A23187. PMA did not suppress the recovery of LTB4 produced by neutrophils from patients with chronic granulomatous disease (CGD), which is known to be defective in NADPH oxidase activation to produce reactive oxygen species (ROS). PMA inhibited the formation of omega-oxidation products of LTB4, but enhanced arachidonic acid release in normal and CGD neutrophils. Furthermore, 5-lipoxygenase activity of 10,000 x g supernatants from normal neutrophils pretreated with PMA was equivalent to that of the controls. Decrease in LTB4 recovery was not attributed to the suppression of the intracellular Ca2+ increase. Thus, it is suggested that reactive oxygen species (ROS) produced by PMA may directly affect endogenous LTB4 and convert it into metabolite(s) distinct from omega-oxidation products.     

In vivo nitrogen metabolism in ornithine transcarbamylase deficiency.

We developed a new technique that monitors metabolic competency in female heterozygotes for ornithine transcarbamylase deficiency (OTCD). The method uses mass spectrometry to measure conversion of (15)NH4Cl to [15N]urea and [5-(15)N]glutamine following an oral load of (15)NH4Cl. We found that heterozygotes converted significantly less NH3 nitrogen to urea, with this difference being particularly obvious for symptomatic carriers, in whom the blood [15N]urea concentration (mM) was significantly less than control values at most time points. The blood concentration of [5-(15)N]-glutamine (microM) was significantly higher in both asymptomatic and symptomatic heterozygotes than it was in the control subjects. The administration of a test dose of sodium phenylbutyrate to the control group did not affect the rate of [15N]urea formation. We conclude: (a) This test effectively monitors in vivo N metabolism and might obviate the need for liver biopsy to measure enzyme activity in OTCD; (b) Asymptomatic OTCD carriers form urea at a normal rate, indicating that ureagenesis can be competent even though enzyme activity is below normal; (c) Although ostensibly asymptomatic OTCD carriers form urea at a normal rate, their nitrogen metabolism is still abnormal, as reflected in their increased production of [5-(15)N]glutamine; and (d) This new test may be important for monitoring the efficacy of novel treatments for OTCD, e.g., liver transplantation and gene therapy.     

Maximal Rates of Excretion and Synthesis of Urea in Normal and Cirrhotic Subjects

When normal individuals eat 0.33 g protein N/kg body weight (BW)((3/4)) per day, they excrete 10-15 mg urea N/h per kg BW((3/4)). If they now ingest (at 0 h) 0.27 (dose A), 0.40 (dose B), 0.53 (dose C), 0.94 (dose D), or 1.33 (dose E) g protein N/kg BW((3/4)) (in the form of casein, ovalbumin, or lactalbumin), the rate of urea N excretion accelerates within 4 h. At dose C a maximal rate of urinary urea N excretion (MRUE) is reached, which averages 55 mg urea N/h per kg BW((3/4)) and which persists for 16 h. Higher doses of protein do not further accelerate urea excretion, but prolong the duration of MRUE to 28 h (after dose E). Blood urea N (BUN) rises by 7-20 mg/100 ml during the first 8 h after dose C to E, and remains stable within +/-5 mg/100 ml during the ensuing 8-28 h of MRUE. Each increment of protein above dose C causes a further increment in plasma alpha-amino N. During infusion of free amino acids at a rate of 110 or 165 mg amino acid N/h per kg BW((3/4)) for 12 h, rate of urea excretion increases to the MRUE value produced by dose C-E of oral protein.These findings indicate that MRUE corresponds to a period of maximal rate of urea synthesis (MRUS). MRUS is greater than MRUE because one fraction of newly formed urea is hydrolyzed in the gastrointestinal tract, and another fraction may accumulate temporarily in body water during the MRUE period. Oral neomycin reduces the proportion of urea hydrolyzed in the gut to less than 20%; its extent is measured by recovery in the urine of a tracer dose of [(14)C]urea injected intramuscularly during determination of MRUE. Accumulation of urea in body water is estimated from increment in BUN during the period of MRUE measurement (8-24 h after dose E of casein) and from body water measured with (3)H(2)O. Then MRUS is calculated as: ([mg urea N excreted between 8 and 24 h after dose E] + [BUN at 24 h - BUN at 8 h] x [body water]) x (100/% recovery [(14)C]urea) x (1/kg BW((3/4))) x (1/16 h).MRUS in 10 normal subjects averaged 65 mg urea N/h per kg BW((3/4)) (range 55-76), and in 34 cirrhotics 27 mg urea N/h per kg BW((3/4)) (range 6-64). Among 19 cirrhotic patients fed 40, 60, 80, or 100 g protein daily for successive 10 day periods, the occurrences of hyperammonemia, hyperaminoacidemia, and encephalopathy at each level of protein intake were inversely related to MRUS value.     

THE NUMERICAL LAWS GOVERNING THE RATE OF EXCRETION OF UREA AND CHLORIDES IN MAN : I. AN INDEX OF UREA EXCRETION AND THE NORMAL EXCRETION OF UREA AND CHLORIDES.

1. The excretion of urea and of chlorides in the normal individual is carried out according to definite laws, capable of numerical expression. 2. The rate of excretion of urea and of sodium chloride is determined by the concentration in the blood, the rate of water output, and indirectly by the weight of the individual. 3. The threshold of sodium chloride excretion is practically constant at about 5.62 grams of sodium chloride per liter of plasma. Slight variations in the threshold occur in normal individuals. 4. The rate of excretion of urea under the conditions found at any time can be measured directly in terms of the normal by an index of urea excretion.     

CHLORIDE RETENTION IN EXPERIMENTAL HYDRONEPHROSIS

1. In acute experimental hydronephrosis chloride retention occurs as well as retention of water, urea, and phenolsulfonephthalein. 2. If both water and chlorides are retained there may be no appreciable rise in the plasma chloride content. 3. When chlorides are retained, but not water, the chloride content of the plasma rises strikingly. 4. After the removal of the ureteral obstruction in acute hydronephrosis all renal functions, water, urea, and chloride excretion, may be rapidly restored in equal degree, or the chlorides may be retained temporarily while there is free excretion of water and urea. 5. In chronic hydronephrosis adequate daily excretion of urea and chlorides may be maintained by a compensatory polyuria. 6. Chloride retention or an abnormal chloride excretion may occur in certain renal lesions when there is no change in the urea, phenolsulfonephthalein, or water excretion.