The source of urinary epidermal growth factor in humans

To clarify the source of human urine EGF, we studied EGF renal clearance in 20 healthy, young adult subjects. Immunoreactive EGF was measured hourly in EDTA plasma, heparin plasma, serum and urine of 12 males and 8 females during a 3 h study period. Plasma and urine creatinine and creatinine clearance were measured and calculated hourly. Mean (and SEM) creatinine clearance was similar in males and females (118 +/- 12 vs 105 +/- 6 ml/min). EGF was not detectable in plasma, whereas relatively high levels were measured in serum (2.5 +/- 0.25 vs 1.5 +/- 0.18 ng/ml in males and females respectively p less than 0.05). Urine EGF excretion averaged 1641 +/- 233 ng/h in males and 1507 +/- 191 ng/h in females (p greater than 0.05). A significant correlation was observed between urine creatinine and urine EGF concentrations in both male (r = 0.98, p less than 0.01) and female (r = 0.94, p less than 0.01) subjects. EGF immunoreactivity in urine and serum eluted from G-75 sephadex columns similarly to recombinant 6000 Mr hEGF. Urine excretion of EGF approximated 1.5 micrograms/h or 25 ng/mg creatine. The high concentrations of EGF found in urine in the face of non-detectable levels of EGF in plasma favor the hypothesis that EGF in urine is derived from kidney synthesis and secretion. The significant positive correlation between urine creatinine and urine EGF suggests a functional correlation between glomerular filtration and the process of tubular EGF excretion.     

Role of the kidney in the metabolism of apolipoprotein A-IV: influence of the type of proteinuria

Increased plasma concentrations of apolipoprotein A-IV (apoA-IV) in chronic renal disease suggest a metabolic role of the kidney for this antiatherogenic protein. Therefore, we investigated patients with various forms of proteinuria and found increased serum concentrations of apoA-IV in 124 nephrotic patients compared with 274 controls (mean 21.9 +/- 9.6 vs. 14.4 +/- 4.0 mg/dl; P < 0.001). Decreasing creatinine clearance showed a strong association with increasing apoA-IV levels. However, serum albumin levels significantly modulated apoA-IV levels in patients with low creatinine clearance, resulting in lower levels of apoA-IV in patients with low compared with high albumin levels (21.4 +/- 8.6 vs. 29.2 +/- 8.4 mg/dl; P = 0.0007). Furthermore, we investigated urinary apoA-IV levels in an additional 66 patients with a wide variety of proteinuria and 30 controls. Especially patients with a tubular type of proteinuria had significantly higher amounts of apoA-IV in urine than those with a pure glomerular type of proteinuria and controls (median 45, 14, and 0.6 ng/mg creatinine, respectively). We confirmed these results in affected members of a family with Dent's disease, who are characterized by an inherited protein reabsorption defect of the proximal tubular system. In summary, our data demonstrate that the increase of apoA-IV caused by renal impairment is significantly modulated by low levels of serum albumin as a measure for the severity of the nephrotic syndrome. From this investigation of apoA-IV in urine as well as earlier immunohistochemical studies, we conclude that apoA-IV is filtered through the normal glomerulus and is subsequently reabsorbed mainly by proximal tubular cells.     

Effects of hydration state on hormonal and renal responses during moderate exercise in the heat

The effects of hydromineral hormones and catecholamines on renal concentrating ability at different hydration states were examined in five male volunteers while they performed three trials. Each of these trials comprised a 60-min exercise bout on a treadmill (at 50% of maximal oxygen uptake) in a warm environment (dry bulb temperature, 35°C; relative humidity, 20–30%). In one session, subjects were euhydrated before exercise (C). In the two other sessions, after thermal dehydration (loss of 3% body mass) which markedly reduced plasma volume (PV) and increased plasma osmolality (osm_pl), the subjects exercised either not rehydrated (Dh) or rehydrated (Rh) by drinking 600 ml of mineral water before and 40 min after the onset of exercise. During exercise in the Dh compared to C state, plasma renin, aldosterone, arginine vasopressin (AVP), noradrenaline and adrenaline concentrations were increased (P < 0.05). A reduction in creatinine clearance and urine flow was also observed (P < 0.05) together with a decrease in urine osmolality, osmolar clearance and sodium excretion, while free water clearance increased (P < 0.05). However, compared to Dh, Rh partially restored PV and osm_pl and induced a marked reduction in the time courses of both the plasma AVP and catecholamine responses (P < 0.05). Values for renal water and electrolyte excretion were intermediate between those of Dh and C. Plasma atrial natriuretic peptide presented similar changes whatever the hydration state. These results demonstrate that during moderate exercise in the heat, renal concentrating ability is paradoxically reduced by prior dehydration in spite of high plasma AVP levels, and might be the result of marked activation of the sympatho-adrenal system. Rehydration, by reducing this activation, could partially restore the renal concentrating ability despite the lowered plasma AVP. Accepted: 23 April 1997     

Renal responsiveness to aldosterone during exposure to simulated microgravity.

We measured renal functions and hormones associated with fluid regulation after a bolus injection of aldosterone (Ald) during head-down tilt (HDT) bed rest to test the hypothesis that exposure to simulated microgravity altered renal responsiveness to Ald. Six male rhesus monkeys underwent two experimental conditions (HDT and control, 72 h each) with each condition separated by 9 days of ambulatory activities to produce a crossover counterbalance design. One test condition was continuous exposure to 10 degrees HDT; the second was a control, defined as 16 h per day of 80 degrees head-up tilt and 8 h prone. After 72 h of exposure to either test condition, monkeys were moved to the prone position, and we measured the following parameters for 4 h after injection of 1-mg dose of Ald: urine volume rate (UVR); renal Na(+)/K(+) excretion ratio; renal clearances of creatinine, Na(+), osmolality, and free water; and circulating hormones [Ald, renin activity (PRA), vasopressin (AVP), and atrial natriuretic peptide (ANP)]. HDT increased Na(+) clearance, total renal Na(+) excretion, urine Na(+) concentration, and fractional Na(+) excretion, compared with the control condition, but did not alter plasma concentrations of Ald, PRA, and AVP. Administration of Ald did not alter UVR, creatinine clearance, Ald, PRA, AVP, or ANP but reduced Na(+) clearance, total renal Na(+) excretion, urinary Na(+)/K(+) ratio, and osmotic clearance. Although reductions in Na(+) clearance and excretion due to Ald were greater during HDT than during control, the differential (i.e., interaction) effect was minimal between experimental conditions. Our data suggest that exposure to microgravity increases renal excretion of Na(+) by a natriuretic mechanism other than a change in renal responsiveness to Ald.     

Beta 2-microglobulinaemia: a sensitive index of diminishing renal function in diabetics.

A sensitive single measure of diminishing renal function is of importance in attempts to modify the progression of diabetic nephropathy. In 12 insulin-dependent diabetics with proteinuria plasma concentrations of beta 2-microglobulin were found to correlate more closely than plasma creatinine concentrations or creatinine clearance with glomerular function as measured by clearance of 52Cr-EDTA. The plasma beta 2-microglobulin concentration was raised in all patients with diminished glomerular filtration rate (below 80 ml/min/1.73 m2). By contrast, in two of these patients plasma creatinine concentration was normal. Plasma beta 2-microglobulin concentrations were stable throughout the day and not affected by food intake, unlike plasma creatinine concentrations, which rose in the afternoon and evening and after a meat meal. Plasma beta 2-microglobulin concentrations were the same in venous and capillary blood, the capillary blood being readily self-collected. Concentrations of beta 2-microglobulin were stable for up to 24 hours when whole blood was stored at 4 degrees C; adding aprotinin inhibited loss of beta 2-microglobulin for up to seven days. The results of this study suggest, therefore, that measuring beta 2-microglobulin concentrations is a simple and accurate method of detecting minor degrees of renal impairment and monitoring the effects of treatment.     

COX-2 disruption leads to increased central vasopressin stores and impaired urine concentrating ability in mice

It was hypothesized that cyclooxygenase-2 (COX-2) activity promotes urine concentrating ability through stimulation of vasopressin (AVP) release after water deprivation (WD). COX-2-deficient (COX-2(-/-), C57BL/6) and wild-type (WT) mice were water deprived for 24 h, and water balance, central AVP mRNA and peptide level, AVP plasma concentration, and AVP-regulated renal transport protein abundances were measured. In male COX-2(-/-), basal urine output and water intake were elevated while urine osmolality was decreased compared with WT. Water deprivation resulted in lower urine osmolality, higher plasma osmolality in COX-2(-/-) mice irrespective of gender. Hypothalamic AVP mRNA level increased and was unchanged between COX-2(-/-) and WT after WD. AVP peptide content was higher in COX-2(-/-) compared with WT. At baseline, plasma AVP concentration was elevated in conscious chronically catheterized COX-2(-/-) mice, but after WD plasma AVP was unchanged between COX-2(-/-) and WT mice (43 ± 11 vs. 70 ± 16 pg/ml). Renal V2 receptor abundance was downregulated in COX-2(-/-) mice. Medullary interstitial osmolality increased and did not differ between COX-2(-/-) and WT after WD. Aquaporin-2 (AQP2; cortex-outer medulla), AQP3 (all regions), and UT-A1 (inner medulla) protein abundances were elevated in COX-2(-/-) at baseline and further increased after WD. COX-2(-/-) mice had elevated plasma urea and creatinine and accumulation of small subcapsular glomeruli. In conclusion, hypothalamic COX-2 activity is not necessary for enhanced AVP expression and secretion in response to water deprivation. Renal medullary COX-2 activity negatively regulates AQP2 and -3. The urine concentrating defect in COX-2(-/-) is likely caused by developmental glomerular injury and not dysregulation of AVP or collecting duct aquaporins.     

Dose-dependent elimination of 5-fluoro-2'-deoxyuridine in the monkey

The kinetics of 5-fluoro-2'-deoxyuridine (FdUrd) and 5-fluorouracil (FUra) disposition after bolus intravenous injection were determined in anesthetized rhesus and cynomolgus monkeys. FdUrd disappearance from plasma was an apparent triexponential process with average half-lives of 0.5, 2, and 8 min; FUra disappearance was biphasic with average half-lives of 2 and 13 min. After FdUrd injection, FUra reached peak plasma concentrations of 15-30% of the initial FdUrd concentrations within 3 min, and then disappeared more slowly than FdUrd. Total FdUrd clearance fell from 105 to 73 to 56 ml/kg/min as the dose increased from 10 to 20 to 40 mg/kg. Metabolic clearance was about 85% of total clearance and fell similarly with increasing dosage. Total and metabolic FUra clearances were about 30% of FdUrd values at an equimolar dose. Renal FdUrd clearance exceeded glomerular filtration rate and was decreased by probenecid, indicating tubular secretion; renal FUra clearance was close to glomerular filtration rate. There was no apparent correlation between dose and renal clearance or volume of distribution. It was concluded that FdUrd, like FUra, is eliminated primarily by a dose-dependent process. The metabolic basis of the dose-dependent kinetics remains to be determined.     

Renal resistance to vasopressin in poorly controlled type 1 diabetes mellitus

To investigate the hypothesis that diabetes induces nephrogenic diabetes insipidus, we studied the urine-concentrating ability in response to vasopressin (AVP) in 12 patients with insulin-dependent diabetes mellitus (IDDM) and 12 nondiabetic controls. Subjects were euglycemic-clamped, and after oral water loading, AVP was infused intravenously for 150 min. AVP induced a greater (P<0.001) rise in urine osmolality in controls (67.6+/-10.7 to 720+/-31.1 mosmol/kg, P<0.001) than in IDDM patients (64.3+/-21.6 to 516.7+/-89.3 mosmol/kg, P<0.001). Urinary aquaporin-2 concentrations after AVP infusion were higher in controls (611.8+/-105.6 fmol/mg creatinine) than in IDDM (462.0+/-94.9 fmol/mg creatinine, P = 0. 003). Maximum urine osmolality in IDDM was inversely related to chronic blood glucose control, as indicated by Hb A(Ic) (r = -0.87, P = 0.002). To test the hypothesis that improved glycemic control could reverse resistance to AVP, 10 IDDM subjects with poor glycemic control (Hb A(Ic) >9%) were studied before (B) and after (A) intensified glycemic control. Maximum urine osmolality in response to AVP increased with improved glycemic control (B, 443.8+/-49.0; A, 640.0+/-137.2 mosmol/kg, P<0.001), and urinary aquaporin-2 concentrations after AVP increased from 112.7 +/-69 to 375+/-280 fmol/mg creatinine (P = 0.006), with improved glycemic control. Poorly controlled IDDM is associated with reversible renal resistance to AVP.     

Abnormal renal response to twenty-four-hour dehydration and fasting in Nagase analbuminemic rats.

We assessed renal function in fasting adult Nagase analbuminemic rats (NAR). Sodium output in male and female NAR was 68% and 46%, respectively, of the output of age- and sex-matched normal Sprague-Dawley (SD) rats. Potassium excretion was significantly greater in female NAR but there was no difference between male NAR and SD rats. The renal clearances of urea and creatinine were reduced in NAR with corresponding increases in plasma concentrations; however, the urea and creatinine concentrations were not different in plasma samples taken from normally fed and hydrated SD and NAR rats. Exchangeable body sodium and sodium space was significantly larger in normally fed and hydrated NAR than in SD but there were no differences in plasma sodium concentrations or plasma volumes. Although plasma concentrations of albumin in NAR were only about 0.07% of the concentration in SD rats, the renal clearance of albumin in NAR was threefold greater. Kidney weights in NAR were 10 to 16% less than in SD rats but liver weights were 22 to 42% greater. Clearly, renal function was markedly abnormal in Nagase rats during a 24-hour fast.     

Indomethacin increases plasma lithium.

The effects of indomethacin on plasma lithium concentrations and renal lithium clearance were investigated in three psychiatric patients and four normal volunteers. After steady-state plasma lithium concentrations had been reached, the subjects received indomethacin placebo for three to seven days, indomethacin (50 mg thrice daily) for seven days, and placebo again for three to seven days. Indomethacin increased plasma lithium concentrations by 59% in the psychiatric patients and 30% in the volunteers. Renal lithium clearance was reduced by indomethacin by 31% in the group as a whole, and prostaglandin synthesis, determined by measuring the major metabolite of PGE2 with mass spectrometry, was reduced by 55%. These results show that indomethacin reduces renal lithium clearance to an extent which may be clinically important. They also suggest that the renal clearance may be affected by a prostaglandin-dependent mechanism, possibly located in the distal tubule.     

Renal function in patients receiving long-term lithium therapy.

Renal function was assessed in 42 stable outpatients who had been taking lithium for an average of 4 1/2 years. Impaired ability to concentrate the urine was found in 61% of the 41 patients who provided a urine sample for an osmolality measurement, and a moderate reduction in creatinine clearance was present in 12% of the entire group; 1 patient showed both defects. Urine microscopy revealed an excess of cells in 40%. It is suggested that lithium therapy produces a self-limiting lesion of the distal nephron that does not usually progress to chronic renal failure. The lesion is not dangerous, except that it may predispose to acute neurotoxic effects in the event of intercurrent illness or dehydration.     

High Dosage Metolazone in Chronic Renal Failure

Metolazone is a modified quinazolinesulphonamide and in a dose of between 4 and 7·5 mg is an effective diuretic in man with normal renal function. Fourteen patients with non-oedematous stable chronic renal failure (creatinine clearance ranging from 1·2 to 12 ml/min) were given metolazone in doses ranging from 20-150 mg. A noticeable increase in urine flow and sodium excretion occurred, free water clearance increased, and there was a small but significant increase in potassium excretion. No side effects were noted.     

Inhibition by angiotensin II of some vasopressin effects on renal function in sheep.

The effects of intravenous infusions of arginine vasopressin (AVP) alone and with angiotensin II (AII) on renal function were studied in conscious Merino ewes. AVP at 11.5 pmol.min-1 caused an increase in water and electrolyte output which was associated with a rise in glomerular filtration rate (GFR), solute clearance, solute-free water reabsorption and tubular sodium reabsorption. Addition of AII of 100 ng.min-1 generally reversed all of these effects. The filtration fraction, which rose during AVP infusion, increased further when AII was added due to a greater fall in renal plasma flow than in GFR. The diuretic and electrolyte-excreting effects of infused AVP appeared to be brought about by an increase in GFR. It is suggested that this inappropriate effect of AVP, which is secreted in response to water deprivation, could be countered by the simultaneous production of AII.     

A study of nephron function in normal tropical residents using the creatinine and lithium clearances

 The kidney bears the brunt of the demands of a tropical climate for water and electrolyte homeostasis. We hypothesised that a tropical climate may cause adaptive changes in the entire organism leading to altered renal function in our subjects. Hence renal function data for residents of a temperate climate may not be applic- able to tropical residents. We therefore sought to elucidate renal function in subjects residing in a tropical climate. We used lithium clearance, C _Li, a non-invasive tool for assessing proximal tubular function in humans, and endogenous creatinine clearance, C _Cr, to estimate proximal tubular function and glomerular function, respectively, in our subjects. We did this in order to establish whether or not nephron function in our subjects differs from that for residents of a temperate climate. Nineteen male and 12 female Ghanaian subjects aged between 15 and 48 years were studied. The estimated G _Cr was 117.3±6.6 ml/min for male subjects and 97±6.4 ml/min for female subjects. C _Li was 20.3±1.6 ml/min for male and 19.1±0.4 ml/min for female subjects, respectively. The estimated absolute reabsorption rate of fluid of proximal tubules was 97.0±6.0 ml/min for males and 78.1±6.0 ml/min for females. The percentage proximal fluid reabsorption for male and female subjects was 81.2±1.4 and 79.5±1.6, respectively. The differences between male and female values (mean±SEM) were not statistically significant. The data suggest that the proximal tubule in residents of a tropical climate may reabsorb more fluid compared to that in residents of a temperate climate. Our values for proximal tubular reabsorption are higher than those reported for residents of a temperature climate. Our estimate of glomerular filtration, however, is similar to published data for Caucasians. The difference in proximal tubular function may reflect possible renal adaptation to a hot, humid climate. We conclude that renal function of tropical residents differs from that of residents of a temperate climate. This difference may be due to renal adaptation to the hot, tropical climate. Received: 1 July 1996 / Revised: 22 December 1996 / Accepted: 8 January 1997     

Aluminium bone disease in patients receiving plasma exchange with contaminated albumin.

Aluminium balance studies were carried out on eight patients with various immunological disorders who were receiving plasma exchange with albumin solutions known to be contaminated with aluminium. Four patients with impaired renal function (creatinine clearance less than 50 ml/min) retained between 60% and 74% of the aluminium infused during a single plasma exchange. Transiliac bone biopsy specimens from three patients in this group had a high content of aluminium and showed histological evidence of current or previous bone disease related to aluminium. Two of these patients suffered intermittent bone pain. The main route of excretion of injected aluminium was in urine, only a small proportion of the total input being removed in the "plasma bag" during plasma exchange. The extent of aluminium retention and bone deposition was not reflected by the plasma aluminium concentration before or after plasma exchange. Treatment of five patients with intravenous desferrioxamine increased the plasma aluminium concentration and urinary output of aluminium in those with evidence of aluminium retention. These studies show that patients with poor renal function receiving treatment with albumin contaminated with aluminium retain the metal and deposit it in bone, where it may eventually cause aluminium bone disease. Plasma exchange should be used with caution in patients with renal impairment.     

Renal Excretion of Digoxin in Swine and Goats

In experiments on swine and goats the renal excretion of digoxin was examined, and it was found that the renal clearance of non-protein-bound digoxin in swine was lower than creatinine clearance which expresses filtration clearance. Correlation analysis showed that the renal clearance of digoxin in swine was not significantly influenced by the concentration of non-protein-bound digoxin in plasma and the pH of the urine, while there was a significant positive correlation between the clearance and the urine flow rate (Table 4). On the other hand, the renal clearance of digoxin in goats was significantly influenced by the concentration of non-proteinbound digoxin in plasma and by urine pH (Table 4). From these results it is concluded that glomerular filtration and back-diffusion are involved in the renal handling of digoxin in both swine and goats. In addition active tubular secretion is also involved in the renal excretion of digoxin in goats.     

Influence of Medetomidine on Acid-base Balance and Urine Excretion in Goats

Seven goats were given medetomidine 5 μg/kg as an iv bolus injection. Venous blood samples were taken repeatedly and urine was collected continuously via a catheter up to 7h after the injection. Medetomidine caused deep clinical sedation. Base excess, pH and PCO2 in venous blood rose after medetomidine administration. There were no significant changes in plasma concentrations of sodium, calcium, magnesium, creatinine or osmolality, whereas potassium and bicarbonate concentrations increased, and phosphate and chloride decreased. Medetomidine increased plasma glucose concentration, and in 4 of 7 goats glucose could also be detected in urine. Medetomidine did not influence urine flow rate, free water clearance, bicarbonate and phosphate excretion or pH, but renal chloride, sodium, potassium, calcium, magnesium and creatinine excretion were reduced. The results suggest that the metabolic alkalosis recorded after medetomidine administration is not caused by increased renal acid excretion.     

Glomerular filtration rate and blood pressure monitoring in awake baboons

Minimally invasive techniques were used to collect urine with an external catheter together with automated intermittent monitoring of arterial blood pressure in awake male baboons. Using endogenous creatinine, 24-hour creatinine clearances were measured for 2 to 3 consecutive days in four intact and in four uninephrectomized baboons. Despite large differences in urinary volume and sodium excretion, reproducibility of 24-hour creatinine clearances was within 15% in 15 of 19 studies obtained from 6 of 8 animals. Arterial blood pressure was monitored intermittently at 30 to 60 minute intervals over 24 hours with a Dinamap monitor and recorder. Mean blood pressure averaged 71 +/- 4.4 to 89 +/- 5.5 mm Hg in different animals. Blood pressure tended to be lower at night than during the day. In separate studies using 15 to 60 minute urine collection periods, inulin clearance was compared in awake and in anesthetized animals with endogenous or exogenous creatinine clearance measured simultaneously. The clearance of creatinine systematically exceeded the clearance of inulin, even in intact animals with a normal serum creatinine. The creatinine-to-inulin clearance ratio averaged 1.16 +/- 0.03 at a serum concentration of 0.7 to 0.8 mg/dl; 1.27 +/- 0.03 at a serum creatinine of 1.0 to 1.1 mg/dl and 1.56 +/- 0.04 at a serum creatinine greater than 10 mg/dl. All values exceed unity significantly (p less than 0.001). Thus, renal function, including inulin clearance, can be measured in awake baboons. Duplicate or triplicate 24-hour urine collections are needed to assess the reliability of creatinine excretion. However, creatinine clearance overestimates glomerular filtration rate, as it does in humans.     

Stimulation of renal phosphate secretion in the stenohaline freshwater teleost: Carassius auratus gibelio Bloch

1. Renal excretion of phosphate in the Prussian carp was modulated by tubular reabsorption and tubular secretion. 2. Under the conditions of an i.v. phosphate-load during which the plasma concentration of phosphate was doubled, 65% of the phosphate load was excreted by the kidney, mainly by tubular secretion. 3. The renal clearance of PAH markedly exceeded the clearance of polyfructosan which could be used for the measurement of the GFR. 4. A transport maximum for tubular PAH secretion was reached at plasma concentrations of about 250 mumol/l.     

Renal excretion of urea in a small east African antelope, the dik-dik (Rhynchotragus kirkii)

1. A study on the renal handling of urea by the dik-dik antelope (Rhynchotragus kirkii) was conducted. 2. Plasma and urine samples were analysed for osmolality, urea and creatinine concentrations during dehydration and intra-ruminal loading of potassium and sodium solutions. 3. The glomerular filtration rate (GFR) of the dik-dik was found to be 182.6 +/- 11.7 ml/min/100 kg body mass. 4. Dehydration was observed to increase tubular urea reabsorption and increase plasma and urine osmolalities, but had no effect on the amount of urea filtered at the glomerulus. 5. Potassium loading increased both GFR and urine flow rate.