Role of Vasopressin in the Regulation of Renal Sodium Excretion: Interaction with Glucagon-Like Peptide-1.

The present study aimed to investigate the potential physiological role of vasopressin and the incretin hormone of the gastrointestinal tract (glucagon-like peptide-1; GLP-1) in the regulation of the water-salt balance in a hyperosmolar state as a result of sodium loadings. In rats, the administration of hypertonic NaCl solution resulted in a significant increase in natriuresis, which correlated with the vasopressin excretion rate. Natriuresis following an i.p. NaCl load (23.2 ± 1.4 µmol/min/kg) was enhanced by inhibition of V2 receptors (51.6 ± 3.7 µmol/min/kg, P < 0.05) and was reduced by a V1a antagonist injection (6.3 ± 1.1 µmol/min/kg, P < 0.05). Compared to i.p. salt administration, oral NaCl loading induced a significant increase in the plasma GLP-1 level within 5 min and resulted in more prominent natriuresis and a smaller increase in blood sodium concentration. It was hypothesised that the basis for the fast elimination of excess sodium following an oral NaCl load could be the involvement of GLP-1 in osmoregulation combined with vasopressin. It was demonstrated that GLP-1 mimetic exenatide (1.5 nmol/kg) produced a significant decrease in proximal reabsorption and an increase in fractional sodium excretion (from 0.15 ± 0.04% to 9 ± 1%). It was also shown that vasopressin at doses of 1-10 µg/kg and the selective V1a agonist (1 µg/kg) induced an increase in sodium fractional excretion to 10 ± 2% and 8 ± 2%, respectively. Combined administration of exenatide and V1a agonist revealed their cumulative natriuretic effect, and sodium fractional excretion increased by up to 18 ± 2%. These data suggest that GLP-1 combined with vasopressin could be involved in the regulation of sodium balance in the hyperosmolar state as a result of NaCl loading. Vasopressin regulates the reabsorption of a significant portion of filtered sodium in the distal segment of the nephron and modulates the natriuretic effect of GLP-1.

Excretion of proteins by rat kidney during various types of diuresis.

Experiments on healthy rats showed that increased diuresis induced by administration of water, polyethylene glycol 400, furosemide, or 1-desamino-arginine-vasotocin is associated with increased protein excretion by the kidneys. The results can be explained by enhanced filtration of plasma proteins in glomeruli during polyuria of various geneses.

Possible role of prostaglandins in pathogenesis of nocturnal enuresis in children.

OBJECTIVE: To compare excretion of ions and prostaglandins by the kidney in children with noctural enuresis. MATERIAL AND METHODS: Thirty-two children with primary nocturnal enuresis and 23 normal children were examined. Osmolality and sodium and potassium concentrations were measured in their urine and blood serum. Prostaglandins E2, E1, and F2alpha were determined using kits for immunoenzyme analysis. Luminal and contraluminal prostaglandin secretions were studied in frog urinary bladder. RESULTS: Children with nocturnal enuresis have increased nocturnal diuresis and renal sodium excretion, but no increase was found in excretion of prostaglandins E2, E1, and F2alpha. Administration of sodium diclofenac before bed-time eliminated episodes of nocturnal enuresis in 37% of children; intranasal administration of Adiuretin SD had a positive effect in 69% of enuretics. In children with nocturnal enuresis there is a correlation between renal excretion of PGE2 and sodium ions; this correlation is absent in the control group children, and disappears in enuretics treated with desmopressin. To evaluate the representativeness of the data on prostaglandin secretions to urine as compared with their release to extracellular fluid, experiments on frog urinary bladder were performed: a correlation was found between prostaglandin secretion to the urinary bladder lumen and to the extracellular fluid. CONCLUSIONS: The results of the study suggest that changes in renal function are due not to a higher secretion of prostaglandins in nocturnal enuresis but to the relative dominance of their effect as compared with other physiologically active substances that simultaneously act on renal tubular cells.

Nocturnal enuresis: correction of renal function by desmopressin and diclofenac.

Sixty-two children with nocturnal enuresis (43 boys, 19 girls aged 6-15 years) were treated with either desmopressin (Adiuretin-SD) (n = 32) or sodium diclofenac (n = 30). Desmopressin was effective in 85% of children and diclofenac in 33%. In children with primary nocturnal enuresis, the glomerular filtration rate was normal, whereas diuresis and solute excretion during the night were increased. Compared with healthy children, the nightly excretion of sodium was elevated by 43.7% and magnesium by 58.4%. A high correlation was found between the free water reabsorption and solute clearance (P < 0.001) in children with nocturnal enuresis. Changes in kidney function in nocturnal enuresis appear to be due to a decrease in the water and ion reabsorption in the thick ascending limb of Henle's loop because of a changed regulation of ion transport in this part of the nephron. Administration of desmopressin or a decrease in prostaglandin production after diclofenac administration restores the ion and water transport in the kidney, which results in the disappearance of nocturnal enuresis. The results indicate a role of changes in regulation of ion transport in renal tubules in the pathogenesis of one of the forms of primary nocturnal enuresis.

Study of the role of prostaglandin E2 in urine flow regulation in chronic renal failure.

OBJECTIVE: This study was carried out to investigate the role of prostaglandin E2 in the regulation of urine flow and ion excretion in patients with chronic renal failure. MATERIAL AND METHODS: Twenty patients with chronic renal failure (CRF) and 13 healthy people were studied. CRF develops as a terminal stage of glomerulonephritis, pyelonephritis or polycystic renal disease. Osmolality and sodium, potassium, magnesium, calcium and creatinine concentrations were measured in urine and blood serum. Urine prostaglandin E2 was determined using kits for imminoenzyme analysis. RESULTS: The average creatinine clearance was 19.9 +/- 6.3 ml/min, but it varied from 30 to 10 ml/min in different patients. In patients with CRF a correlation was revealed between diuresis and Na excretion (r = 0.78, p < 0.001) and between Na excretion and PGE2 excretion (r = 0.65, p < 0.001), a correlation that lacking in the healthy subject. A correlation was also found between diuresis and Mg excretion (r = 0.68, p < 0.001) and between Mg excretion and Na excretion (r = 0.83, p < 0.001) in patients with CRF but not in healthy subject. CONCLUSION: It is suggested that in patients with CRF who experience a decrease in the glomerular filtration rate (to 75-90% of the normal value) the increase in urine flow is due to prostaglandin-dependent inhibition of ion reabsorption in the thick ascending limb of the loop of Henle.

Defect of osmoregulatory renal function in nocturnal enuresis.

Renal function was studied in 62 children with primary nocturnal enuresis (PNE) and in 20 healthy children aged 6-15 years. During the night, children with PNE exhibited an increase in diuresis, free water reabsorption and solute excretion (including sodium and magnesium) in comparison to controls. Intranasal administration of Adiuretin-SD (10.5-24.5 micrograms) in the evening reduced diuresis and ion excretion to normal levels. During the treatment, 61% of the children became completely dry and, in 24% of the children, the number of wet nights was reduced by 50%. It is suggested that in the pathogenesis of PNE, the decrease in ion reabsorption in the thick ascending Henle's loop--resulting in a greater load of tubular fluid in the collecting ducts, an elevation of diuresis and increases in free water reabsorption and solute excretion--plays the leading role in disturbing renal function. Treatment of PNE with desmopressin is pathogenically justified, as it eliminates the principal defect of renal tubular function.

Ultrastructural correlates of the antidiuretic hormone-dependent and antidiuretic hormone-independent increase of osmotic water permeability in the frog urinary bladder epithelium.

Electron and confocal microscopy, using immunocytochemical methods, was employed to assess osmotic water permeability of the frog (Rana temporaria) urinary bladder during transcellular water transport, induced by antidiuretic hormone (ADH) or by wash-out of autacoids from serosal, ADH-free Ringer solution. The increase of osmotic water permeability of the urinary bladder was accompanied by relevant ultrastructural changes, the most remarkable being: (1) the appearance of aggregates of intramembranous particles in the apical membrane of granular cells, and the extent of the membrane area covered by the aggregates proportional to that of the water flow; (2) redistribution of actin filaments in the cytoplasm of granular cells; judging from the anti-actin label density, the number of actin filaments in the apical region of cytoplasm was reduced by 2.5-4 times compared with normal; (3) a decrease in the total electron density of the cytoplasm due to the increased water content of granular cells.

Osmoregulatory function of the kidney in enuretic children.

Twenty children with primary nocturnal enuresis and 20 healthy children of the same age and sex were studied. Natural urination was used for the 24-h urine collection. It was found that urine osmolality and free water reabsorption during the night did not differ statistically significantly between the enuretic children and the healthy. The increased diuresis in the enuretic children was caused by a higher excretion of the osmotically active solutes, including sodium. Use of desmopressin reduced diuresis and natriuresis to normal levels. It is suggested that the main role in the pathogenesis of the studied form of nocturnal enuresis is played by a decrease in ion reabsorption, probably in the thick ascending Henle loop, which facilitates the increase in diuresis and occurrence of nocturnal enuresis.

Role of prostaglandin E2 in regulation of low and high water osmotic permeability in frog urinary bladder.

The water osmotic permeability of frog urinary bladder was found to be increased from 0.08 +/- 0.01 to 1.28 +/- 0.20 microl/min cm2 when serosal bathing medium was changed 4 times for a fresh Ringer solution. High epithelium permeability is accompanied by an increased content of cyclic AMP in the bladder tissue (by 42%, P < 0.01), higher activity of both basal and forskolin-stimulated membrane adenylate cyclase (AC) (by 109% and 74%, respectively, P < 0.05) and by appearance of aggregates of intramembranous particles in the apical membrane. The water flow was inhibited by 10(-9)-10(-5) M prostaglandin E2 (PGE2); the inhibitory effect was eliminated in the presence of 10(-4) M N-ethylmaleimide. The increase of water permeability due to changes of the bathing medium was accompanied by a decrease of serosal PGE2 concentration from 14.8 +/- 1.0 in the 1st solution to 0.6 +/- 0.1 nM in the 5th. 10(-6) M PGE2 in vitro inhibited the activity of membrane AC from highly permeable bladders by 33.4% (P < 0.02). Pretreatment of the membranes with 10 microg/ml pertussis toxin (PT) completely reversed this effect (+149%, P < 0.01). A significant activation of AC was also observed under 10(-10) M PGE2 (by 196%). These data demonstrate that the water permeability could be markedly increased independently of ADH, suggesting that the trigger role in activation of water transport is played by a decreased level of PGE2 which could stimulate AC.

AVP-independent high osmotic water permeability of frog urinary bladder and autacoids.

In the isolated frog urinary bladder a 20- to 50-fold increase of the osmotic water permeability has been revealed in the absence of arginine vasopressin (AVP) as a result of several successive changes of the serosal Ringer solution. This increase of the osmotic water permeability was of the same magnitude as that of the effect of 1 nM AVP. Similarly to the effect of AVP, the amount of adenosine 3',5'-cyclic monophosphate (cAMP) in the cells rose, and aggregates of intramembraneous particles were formed in the apical plasma membrane of granular cells (as shown by the freeze-fracture method). Immunocytochemical studies using anti-actin monoclonal antibodies indicated depolymerization of F-actin following the AVP-independent change in water permeability. It was possible to decrease the high level of osmotic permeability to the initial level if 10 microl/ml of frog blood serum or a lipid extract of this blood serum, or 1 microM arachidonic acid or 1 nM prostaglandin E2 was added to the serosal Ringer solution. The rapid restoration of the osmotic water impermeability of the epithelium after the AVP- evoked effect was achieved by the addition to the serosal Ringer solution of Ringer solution in which intact frog urinary bladders had been previously incubated for 1 h. The data obtained indicate that the maintenance of the impermeability to water of the osmoregulating epithelium and the restoration of the initial low level of the osmotic permeability after the effect of AVP are due to participation of prostaglandin E2 and other autacoids as well as, probably, some physiologically active substances of a lipid nature that are present in the blood serum.

Evolutionary aspects of renal function.

In his hypothesis of the evolution of renal functions Homer Smith proposed that the formation of glomerular nephron and body armor had been adequate for the appearance of primitive vertebrates in fresh water and that the adaptation of homoiotherms to terrestrial life was accompanied by the appearance of the loop of Henle. In the current paper, the increase in the arterial blood supply and glomerular filtration rate and the sharp elevation of the proximal reabsorption are viewed as important mechanisms in the evolution of the kidney. The presence of glomeruli in myxines and of nephron loops in lampreys suggests that fresh water animals used the preformed glomerular apparatus of early vertebrates, while mechanisms of urinary concentration was associated with the subdivision of the kidney into the renal cortex and medulla. The principles of evolution of renal functions can be observed at several levels of organizations in the kidney.

Development of the hypothalamic vasopressin system and nephrons in Meriones shawi during ontogenesis.

This study has evaluated the development of the hypothalamic vasopressin system and nephrons of the kidney in desert rodents, Meriones shawi, which effectively retain water by excretion of highly concentrated urine. The vasopressin system was studied immunocytochemically at the 18th fetal day, at the 2nd, 13th, 27th postnatal days and in adulthood. The kidneys were investigated at the 2nd, 13th postnatal days and in adulthood using microdissection technique. Occasional vasopressin-immunoreactive neurons were observed as early as the 18th fetal day, only in the paraventricular nucleus. From the 2nd postnatal day onwards, vasopressin neurons increased progressively in number, being mainly concentrated in the supraoptic and paraventricular nuclei, as well as in the ventral retrochiasmatic region. Transient neuronal populations were also observed at the 13th postnatal day in the lateral preoptic area and anterior hypothalamic nucleus. Apart from the neurons, the glandular cells of the tuberal lobe showed immunostaining from the 18th fetal day, the first age studied, until the 13th postnatal day. The fibers of differentiating vasopressin neurons grew towards the circumventricular/neurohemal organs, terminating in the organum vasculosum of the lamina terminalis and the lateral ventricles as early as the 18th fetal day, as well as the third ventricle, the posterior lobe and the external zone of the median eminence between the 2nd and 13th postnatal days. The kidney in 2-day-old Meriones comprised nephrons at different stages of development from an S-shaped body to well-differentiated nephrons. At the 13th postnatal day, as in adulthood, the nephrons were well differentiated and characterized by long, thin loops descending to different levels of papilla. Thus, according to our morphological data the hypothalamic vasopressin neurons and nephrons in the kidney of Meriones reach the definitive state by the end of the 2nd postnatal week.

Modulation of the effect of arginine-vasopressin on water and ion transport in the newt early distal tubule and frog urinary bladder by V1-antagonists.

In the early distal tubule of the newt Triturus vulgaris L., 1 nM arginine-vasopressin (AVP) increased water reabsorption; the fractional reabsorption of Na+ was elevated from 46.2 +/- 6.9% to 67.8 +/- 3.9% (P < 0.001), of Cl- from 52.7 +/- 6.7% to 73.1 +/- 3.5% (P < 0.001), of Mg2+ from 48.0 +/- 7.7% to 71.7 +/- 6.3% (P < 0.001). When V1-receptors were blocked by 1 nM peptide V1-antagonist [1-(beta-mercapto-beta,beta-cyclopentamethylene propionic acid), 2-(O-methyl) Tyr]-[Arg8]vasopressin, 1 nM AVP increased the fractional reabsorption of fluid by 8.9% of Na+ by 10.7% and of Cl- by 11.2%, as compared with the effect of AVP alone. The fractional reabsorption of Ca2+ after addition of AVP did not differ from control; when V1-receptors were blocked in the presence of AVP, the fractional reabsorption of Ca2+ was increased by AVP. The V1-receptor block in the presence of AVP did not change the fractional reabsorption of Mg2+. Experiments on the urinary bladder of the frog Rana temporaria L. showed that 1 nM SR 49059, a non-peptide antagonist of V1a-receptors, like the peptide V1-antagonist, enhanced the AVP effect by 29%. Inhibition of protein kinase C activity by calphostin C (1 nM) mimicked the effect of V1-antagonists; the AVP hydroosmotic effect was increased by 60%. The results obtained indicate that V1-receptors modulate the effects of V2-receptor activation: their block is accompanied by an enhancement of the AVP hydroosmotic effect in the frog urinary bladder and by an increase of Na+ and Cl- reabsorption in the newt early distal tubule. The enhancement of the AVP effect owing to the V1-receptor activation seems to be mediated by a decrease in protein kinase C activity.

Renal failure and nephrotoxic drug-induced disturbances in rat kidney tissue.

The injection to rats of glycerol, cisplatin, uranyl acetate, sodium dichromate, and mercuric chloride is followed on the third day by acute renal failure. A new approach for quantitative estimation of disturbance of excretory renal function is presented. The decrease in renal function due to uranyl acetate was 77%; sodium dichromate, 71%; mercuric chloride, 52%; cisplatin, 25%; and glycerol, 10%. The kidneys still maintained serum ion concentration close to normal values. Injection of nephrotoxic drugs increased kidney wet weight by 24-57%. This was caused by swelling of renal tissue and increases in dry weight of the kidneys. The sodium content increased in the renal cortex and decreased in the papilla. The potassium content of the renal cortex is increased. The effect of some nephrotoxic drugs is suggested to depend on an increased number of cells in the renal cortex (probably due to hemostasis and inflammation) and a decrease of renal medulla function. The above drugs induce disturbance of kidney tissue but have no effect on the ion and water content in liver and m. gastrocnemius.

Cisplatin nephrotoxicity: site of functional disturbance and correlation to loss of body weight.

We have investigated the effect of an intraperitoneal cisplatin injection (5 mg/kg body weight) into male Wistar rats on: (1) body weight; (2) proximal tubular transport of D-glucose and sulfate across the luminal membrane; (3) transport of p-aminohippuric acid (PAH) and sulfate across the contraluminal membrane; (4) urinary excretion of inulin; (5) urinary excretion and tissue accumulation of sulfofluorescein, and (6) effect of the 'protecting substances', N-Methyl-D-glucamine-dithiocarbamate (NaG), diethyldithiocarbamate, mercaptosuccinate (MS), probenecid, and glycine on parameters 1, 4 and 5. Five days after intraperitoneal application of cisplatin the following effects were observed: (1) body weight was reduced on average by 11% as compared to a 12% increase in control animals; (2) luminal sulfate and D-glucose transport was inhibited correlating with the degree of weight loss; (3) contraluminal PAH transport was also decreased in correlation to the loss of body weight, while contraluminal sulfate transport was not inhibited by cisplatin; (4) inulin excretion was reduced by 45%, the pattern for protection was the same as for the prevention of weight loss; (5) sulfofluorescein (SF) excretion in the urine was reduced by 43%, and (6) accumulation of SF into cortical tissue was augmented. Protecting substances prevented or mitigated weight loss, fall of urinary inulin and SF excretion as well as SF accumulation in cortical tissue with a similar pattern: N-glucamine-dithiocarbamate > mercaptosuccinate approximately probenecid approximately glycine. The data indicate: (1) that luminal (glucose and sulfate) and contraluminal (PAH) transport processes are affected by cisplatin; (2) that contraluminal transport (sulfate) can be unaffected or less affected than luminal transport processes (SF); (3) our method (SF) gives the possibility to monitor the balance between luminal and contraluminal transport steps in vivo; and (4) the correlation of body weight loss with decay of certain renal transport functions and their prevention with similar protecting patterns indicates that a simple index might be useful to monitor the cytotoxic status of an individual.

Tissue concentration and urinary excretion pattern of sulfofluorescein by the rat kidney.

In order to find a fluorescein analog that is excreted in a way similar to p-aminohippurate (PAH) and is suitable to register excretion into the urine and also to monitor continuously the concentration within cortical tissue, the interference of fluorescein, sulfofluorescein (SF), and fluorescein-5(6)-sulfonate with the contraluminal transport systems of PAH, succinate, and sulfate and with the luminal transport system of sulfate and lactate was evaluated. All three substances exerted a strong inhibitory potency against contraluminal PAH uptake (apparent Ki, 0.06 to 0.1 mmol/L) and also showed a moderate to small inhibitory potency against contraluminal sulfate transport (apparent Ki, 0.7 to 5.3 mmol/L). None of the three substrates interacted with the contraluminal dicarboxylate transport. Luminally, fluorescein and SF interacted with the lactate transporter (apparent Ki, approximately 3.0 mmol/L), whereas SF and fluorescein-5(6)-sulfonate had a very weak inhibitory potency against luminal sulfate transport (apparent Ki, 30 to 40 mmol/L). Because of its relatively low interference with the contraluminal sulfate transport, we preferred SF in the following study (protein binding, 88%) over fluorescein-5(6)-sulfonate (protein binding, 43.3%) and fluorescein (protein binding, 77.3%). A bolus injection of SF was given together with [14C]inulin into the jugular vein to rats in mannitol diuresis. Excretion of both substances in the urine was measured in 5-min samples. Fluorescence of the kidney surface was monitored at the exposed kidney with a photocell (excitation light, 470 nm; emission light, 530 nm). The effect of interfering substances was evaluated by their application 1 min before, simultaneously, or 1 min after SF bolus injection. PAH < probenecid < apalcillin inhibited SF excretion in the urine and, to a similar degree, SF fluorescence in cortical tissue. Inhibition was strongest when the substances were given simultaneously with SF. With the injection of alpha-ketoglutarate, glutarate, and succinate, an increase of SF excretion in the urine and, partially also, of SF content in tissue was seen. Tetrafluorosuccinate and mercaptosuccinate inhibited urinary SF excretion and tissue fluorescence strongly. Therefore, SF secretion is completely inhibited whereas filtration remained unaffected. The injection of acetate, lactate, and pyruvate as well as of 2-chloropropionate and thiosulfate did not change urinary excretion and tissue fluorescence of SF significantly. In SF-preloaded animals, the injection of probenecid, apalcillin, tetrafluorosuccinate, and mercaptosuccinate caused an immediate decrease of cellular SF content, whereas the injection of glutarate caused an increase. SF fluorescence in tissue was linearly related to urinary excretion of SF, whereas urinary excretion of inulin was barely affected.(ABSTRACT TRUNCATED AT 400 WORDS)

Renal function and renal platinum content in uninephrectomized rats following cisplatin administration.

The changes in renal function and renal platinum content were assessed in uninephrectomized and sham-operated female Wistar rats on the third day after treatment with 2.5 mg/kg BW or 5 mg/kg BW cisplatin. Treatment of control and nephrectomized rats with 2.5 mg/kg BW cisplatin resulted in indices of renal function which were not significantly different from those of animals which had received no cisplatin, though the renal platinum contents in nephrectomized rats were practically the same as in two-kidney animals given 5 mg/kg BW cisplatin. Treatment with 5 mg/kg cisplatin resulted in much less severe changes in kidney weight and renal function compared to two-kidney animals, in spite of much more substantial (by 49-58%) platinum accumulation.

Chelating agent reversal of cadmium effects on ionic transport in the isolated frog skin (Rana temporaria).

1. The application of 1 mM CdCl2 to the outside surface of frog skin causes a large increase in the potential difference (PD) across the skin and in the short-circuit current (SCC); the subsequent addition of selected dithiocarbamate chelating agents (which by themselves have no effect on PD or SCC) restored both electrical parameters to values close to initial levels. 2. The response observed on addition of the chelating agents indicates that the effect of CdCl2 is reversible and that the complexed ions do not possess the ability to initiate corresponding changes in the transepithelial ion transport processes in the frog skin.