Vasopressin Stimulation Research Articles

Vasopressin stimulates cortisol secretion and phosphoinositide catabolism in cultured bovine adrenal fasciculata/reticularis cells

Cells isolated from the zona fasciculata/reticularis (ZFR) of the bovine adrenal cortex and maintained in culture were found to secrete cortisol in response to vasopressin stimulation. The increased cortisol secretion was dose dependent, with a threshold response at 1 nM and a maximal response (1.68-fold over basal) at 0.1 microM. In cells cultured in the presence of [3H]inositol (to prelabel the membrane phosphoinositide pool), stimulation with vasopressin in the presence of LiCl (10 mM) resulted in a similar dose-dependent increase in labelling of the phosphoinositol fraction, with a maximal response (1.45-fold over basal) at 10 nM. The increased labelling of the phosphoinositol fraction was independent of extracellular Ca2+ as it was not abolished in medium with [Ca2+] buffered to intracellular resting levels. This suggests that vasopressin stimulation results in the activation of a phosphoinositidase C. It is probable that cortisol secretion by bovine ZFR cells in response to vasopressin is dependent upon activation of this Ca2(+)-independent phosphoinositidase C. However, the small magnitude of the cortisol secretory response makes it unlikely that vasopressin is a primary regulator of cortisol secretion in vivo.

Vasopressin stimulation of cell proliferation in the rat pituitary gland in vitro

Proliferative activity was measured in rat anterior pituitary cells in short-term culture by calculating the labelling index (LI), based on the immunohistochemical detection of cells incorporating the thymidine analogue bromodeoxyuridine. Basal LI was reproducible in the test system. Arginine vasopressin (AVP) induced a dose-related increase in LI up to 20 ng/ml. Corticotrophin-releasing factor-41 (CRF-41) had no effect at doses up to 20 ng/ml. However, in the presence of 10 ng CRF-41/ml, AVP induced a greater increase in LI at lower doses than did AVP alone. Fibroblast growth factor also induced a significant increase in LI. In the system used, epidermal growth factor and insulin had no effect on proliferation.

Vasopressin and norepinephrine stimulation of inositol phosphate accumulation in rat hepatocytes are modified differently by protein kinase C and protein kinase A

Rat hepatocytes were maintained in primary monolayer culture for 24 h in the presence of serum. Treatment of hepatocytes with 1 μM 4β-phorbol 12β-myristate 13α-acetate (PMA) for 5–15 min increased membrane-associated protein kinase C activity and concomitantly decreased soluble activity. Membrane protein kinase C activity returned to basal values within 1 h then decreased by more than 50% within 2 h. Prolonged (2–18 h) incubation with PMA did not further decrease protein kinase C activity. Pretreatment of hepatocytes with PMA for 5–15 min had little effect on the subsequent actions of 100 nM vasopressin but abolished the stimulation of inositol phosphate accumulation by 3 nM vasopressin and 20 μM norepinephrine. Long-term exposure (2–18 h) of hepatocytes to 1 μM PMA actually enhanced the effects of vasopressin and 20 μM norepinephrine. The stimulation by norepinephrine (20 μM) of inositol phosphate accumulation was abolished by the α 1-adrenergic antagonist prazosin (1 μM), whereas the β-adrenergic antagonist propranolol (30 μM) had little effect. Addition of 8Br-cAMP (100 μM) or glucagon (10 nM) for 5 min or 8 h had no significant effect alone, but enhanced the subsequent vasopressin stimulation of inositol phosphate accumulation. There was no effect of 8Br-cAMP or glucagon on norepinephrine stimulation of phosphoinositide breakdown. These data indicate that the stimulation of phospholipase C activity in rat hepatocytes by 3 nM vasopressin is enhanced by cyclic AMP-dependent kinase but inhibited by protein kinase C. In contrast, down regulation of protein kinase C markedly enhanced the maximal phosphoinositide response due to both vasopressin and norepinephrine.

Arginine vasopressin stimulation of prostaglandin F 2α release in heifers during the estrous cycle

The effect of arginine vasopressin on the stimulation of prostaglandin F 2α (PGF 2α) release has been examined in vivo. Fifty-eight heifers received one intravenous injection of 10 IU arginine vasopressin on either Day 0 (n = 14), Day 6 (n = 12), Day 13 (n = 14) and Day 18 or 19 or 20 (Day 18–20, n = 18) after the onset of oestrus (Day 0) to determine the effect of arginine vasopressin at different times of the oestrous cycle. Frequent blood samples were taken before and after arginine vasopressin injection for the measurement of 13,14-dihydro-15-keto-PGF 2α (PGFM) by radioimmunoassay (RIA). Blood samples for progesterone determinations were taken 2 hr before and 24 hr after arginine vasopressin to monitor luteal function. The data show that arginine vasopressin causes an increase (P < 0.005) in PGFM concentrations only at Day 18–20 of the cycle in 67% of the experimental heifers.

Roles of Intracellular and Extracellular Calcium in the Kinetic Profile of Adrenocorticotropin Secretion by Perifused Rat Anterior Pituitary Cells. II. Arginine Vasopressin, Oxytocin, and Angiotensin-II Stimulation*

We examined the effects of removing extracellular Ca2+ (Ca2+e), depleting intracellular Ca2+ (Ca2+i), inhibiting cAMP-dependent calmodulin, and blocking voltage-sensitive Ca2+ channels on the secretion of ACTH by perifused dispersed rat anterior pituitary cells. The cells were stimulated with synthetic arginine vasopressin (AVP), oxytocin (OT), and angiotensin-II (AII), all of which are thought to act via the Ca2+/inositol phosphate-dependent protein kinase-C pathway, with synthetic ovine CRF, which acts via the cAMP-dependent protein kinase-A pathway, and with dioctanoylglycerol, which directly activates protein kinase-C. All three secretagogues elicited an initial spike phase ACTH secretory response that peaked within 1 or 2 min and ended within 6 min. AVP and OT also elicited a sustained plateau phase response that lasted for as long as the cells were exposed to the secretagogue, but AII did not. Removal of Ca2+e diminished the initial spike phase by 30-50%, but depletion of Ca2+i virtually abolished it. In contrast, the sustained phase of the response to AVP and OT was abolished by removal of Ca2+e. The effect of dioctanoylglycerol, which elicits a sustained progressive increase in ACTH release, but no initial spike phase, was also greatly inhibited by Ca2+e removal; no greater effect was observed when Ca2+i was depleted. Blockade of L-type voltage-sensitive Ca2+ channels with nimodipine, a dihydropyridine drug, had the same effect as Ca2+e removal on both the initial spike and sustained plateau phases of the response to AVP. Inhibiting cAMP-dependent calmodulin with penfluridol had no effect on the initial spike phase, but reduced the sustained plateau phase of the response to AVP. Removal of Ca2+e or depletion of Ca2+i did not abolish the synergistic ACTH secretory response to the combination of AVP and CRF.(ABSTRACT TRUNCATED AT 400 WORDS)

Insulin, oxytocin, and vasopressin stimulate protein kinase C activity in adipocyte plasma membranes.

Incubation of isolated rat adipocytes with insulin, vasopressin, or oxytocin increased plasma membrane-bound protein kinase C (PKC) activity by 100-400%. PKC activity was assayed by a procedure that is virtually background-free, thus permitting assay of protein kinase activity in highly diluted samples of solubilized membranes. Hormone-dependent increases in PKC activity were limited to plasma membranes. Stimulation of the kinase was half-maximal with 70 pM insulin, and the hormone effect was rapid. Oxytocin and vasopressin produced effects on PKC similar to insulin, but the magnitude of the vasopressin stimulation exhibited seasonal variations. Treatment of cells with phorbol 12-myristate 13-acetate (PMA) resulted in a loss of PKC activity from the cytosol and a gain in plasma membrane activity, indicative of translocation of the enzyme. With activity measurements it was not possible to determine if insulin stimulated a translocation of the kinase. However, Western blot analysis of plasma membranes with polyclonal antibodies directed against PKC suggest that at least some of the insulin-stimulated PKC activity resulted from enzyme translocation.

Corticotropin Releasing Hormone and Arginine Vasopressin Stimulation of Acth and Substance P in Human Mononuclear Leukocytes

Bacterial lipopolysaccharide (LPS) and corticotropin releasing hormone (CRH) plus arginine vasopressin (AVP) induce immunoassayable (1-13)ACTH (alpha MSH) from mononuclear leukocytes. We studied the ability of LPS and CRH + AVP to in vitro stimulate native ACTH (not alpha MSH) and substance P (SP) production and thymidine incorporation in human mononuclear leukocytes. Neither CRH + AVP nor LPS stimulated detectable amounts of intracellular or extracellular ACTH (less than 15 pg/8 x 10(6) cells or total medium) or SP (less than 50 pg/8 x 10(6) cells or total medium) at 1, 2, 3 or 4 days of incubation. LPS, but not CRF + AVP, increased the amount of 3H-thymidine incorporation over controls. This data questions the importance of an immunoadrenal axis and the synthesis of SP by mononuclear leukocytes.

Intoxication par l'eau chez des malades psychiatriques

Water intoxication mostly occurs in psychiatric patients. We observed 13 episodes of severe hyponatremia (less than 120 mmol/l) following a period of increased water consumption in 10 psychiatric patients (5 men, 5 women, mean age 48.8 years) treated with neuroleptics and/or benzodiazepines. Other causes of hyponatremia were excluded. The initial clinical signs were associated with severe gastrointestinal and neurological disorders requiring intensive care. In every case a gradual return to normal of natremia was obtained by creating a negative water balance while compensating for the sodium loss. From a study of urine and plasma osmolality ratio (U/P osm) on admission, several physiopathological mechanisms could be envisaged. A U/P osm ratio lower than 1 (6 cases) suggested a water intake exceeding the maximum dilution capacity of the kidneys (20-25 1), or a lesser water intake with little or no osmolal intake, or again an intrarenal disorder of urine dilution. When the U/P osm ratio was higher than 1 (7 cases), reflecting inappropriate secretion of the antidiuretic hormone, the hyponatremia could be explained by the psychosis itself, the treatment taken by the patients, a disorder of thirst regulation and/or a non-osmotic stimulation of vasopressin. This population, therefore, was heterogeneous: the mechanisms which contribute to this pathology are not fully elucidated, and they probably involve several factors.

Stimulation of atrial natriuretic peptide and vasopressin during percutaneous transluminal aortic valvuloplasty

The objective of this study was to determine the effects of transient aortic valve occlusion (balloon valvuloplasty) on vasoactive hormones in patients with heart failure. Plasma atrial natriuretic peptide, vasopressin, aldosterone, adrenocorticotropic hormone (ACTH), and plasma renin activity were measured before, immediately after, and 30 minutes and 18 to 24 hours following balloon inflation in 18 patients. Mean right atrial and pulmonary wedge pressures were 6 and 18 mm Hg before inflations, respectively, and were unchanged after balloon inflations (5 and 13 mm Hg, respectively). Systemic systolic/diastolic pressures were 139 ± 8 65 ± 4 mm Hg before occlusion, decreased to 47 ± 5 34 ± 3 mm Hg during occlusion, and returned to baseline after occlusions. Baseline atrial natriuretic peptide levels were 267 ± 43 pg/ml and increased to 513 ± 71 pg/ml after balloon inflations. Vasopressin levels before occlusion were 9.1 ± 2.2 pg/ml and increased to 21.4 ± 4.8 pg/ml after balloon inflations. Plasma renin activity was 5.4 ± 1.4 ng/ml/hr before inflations and was not significantly changed after balloon inflations. No clinically significant changes in plasma sodium, potassium, creatinine, and osmolality were observed after the procedure. Aldosterone increased from 23 ± 4 to 40 ± 7 ng/dl 10 minutes after the last inflation. Plasma ACTH measured in seven patients with increased aldosterone was 28 ± 8 pg/ml before and increased to 295 ± 157 pg/ml 10 minutes after balloon inflations. The increases in natriuretic peptide and vasopressin were likely due to elevated intracardiac and decreased arterial pressures, respectively; they persisted in spite of no clinically significant changes in filling pressures 12 to 24 hours after the procedure. Increased aldosterone secretion with no change in renin was likely due to elevated ACTH levels and may have attenuated the hyponatremic effects of atrial natriuretic peptide and vasopressin.

DDAVP effect on factor XII activity levels

Evaluation of the extent of response on factor XII and factor XI, and factor VIII coagulant activity, von Willebrand factor antigen and ristocetin cofactor after desamino-8-D-arginine vasopressin stimulation. Coagulation studies were performed on normals, thrombophilic patients and on a group of subjects affected by congenital factor XII and factor XI deficiencies

Variability of cellular responsiveness to ADH stimulation in toad urinary bladder

The hydrosmotic response of toad bladder to antidiuretic hormone (ADH) is quantitatively linked to the induced fusion of aggrephores with, and the appearance of aggregates of tightly packed intramembrane particles in the luminal membrane of granular cells. We used these morphological indexes of hormonally induced cell activation 1) to assess the variability of individual cell responsiveness to a maximally stimulating concentration of ADH and 2) to compare cell response patterns in paired tissues where the extent of whole tissue stimulation, as evidenced by transtissue water flow, was either maximal or submaximal. The results indicate that individual cell responsiveness within the same tissue to standardized maximal ADH treatment varies between two- and sevenfold, depending on the morphological endpoint measured. Furthermore, based on skewness in endpoint distribution, this variability appears to reflect inherent heterogeneity of granular cell reactivity to hormone. In relation to proportional tissue responses elicited by different stimulating concentrations of ADH, our observations of luminal membrane aggregate incidence suggest that the responding cells, whatever their sensitivity, participate in a graded, rather than "all-or-none," "on-off" manner.

Induction of c-fos protein by activation of vasopressin receptors in smooth muscle cells

Stimulation of vasopressin (V 1) receptors of rat aortic smooth muscle cells (A-10, ATCC CRL 1476) results in the hydrolysis of phosphatidylinositol 4,5-bisphosphate (PIP 2) to inositol 1,4,5-trisphosphate (IP 3) and diacylglycerol (DAG) with the mobilization of intracellular calcium. When A-10 cells are exposed to arginine vasopressin (AVP), there is an increase in the level of c-fos oncoprotein. The extent of induction of c-fos oncoprotein depends on both the time of exposure of the cells to AVP, reaching a maximum at 60 min after which there is a slow decline, and the concentration of AVP used, with an approximate EC 50 of 1 nM which corresponds well with the K d of vasopressin binding to these receptors. This vasopressin-mediated increase in c-fos protein level is inhibited by a V 1/V 2 antagonist (SKF 101498) suggesting that this is a receptor-mediated event. In addition dDAVP, a V 2 selective agonist, is much less effective than AVP in inducing c-fos protein suggesting that AVP mediates its effect via V 1 receptors. Desensitization of vasopressin receptors by prolonged exposure to AVP resulted in no additional induction of c-fos protein level in response to second challenge of AVP. In addition to AVP, phorbol dibutyrate (PDBu), an activator of protein kinase C (PKC), also stimulates the accumulation of c-fos protein although to a lesser extent than AVP. The above data suggest that c-fos protein levels in smooth muscle cells are regulated by AVP and the hormonal effect may be mediated through PI turnover and DAG, IP 3 and Ca 2+ signals.

Transient inositol (1,4,5) trisphosphate accumulation under vasopressin stimulation in WRK 1 cells: correlation with intracellular calcium mobilization

In the rat mammary tumoral cell line (WRK1 cells), vasopressin was previously described to stimulate a phospholipase C. In this study, we have analysed the effect of vasopressin both on intracellular calcium mobilization and on the accumulation of inositol phosphates. Maximal concentration of vasopressin simultaneously induces an accumulation of Ins(1,4,5)P3 and a rise of intracellular calcium concentration. Both these two phenomena are transient and exhibit similar kinetics. A sustained accumulation of InsP2, Ins(1,3,4)P3 and InsP are observed later. Yet no stimulation of InsP4 can be objectified. These results indicate that Ins(1,4,5)P3 is the major inositol phosphate involved in intracellular calcium mobilization.

Exposure of cultured hepatocytes to cyclic AMP enhances the vasopressin-mediated stimulation of inositol phosphate production

Isolated rat hepatocytes in primary monolayer culture were maintained for 18-24 h in the presence of 10% (v/v) serum and [3H]inositol. Vasopressin (100 nM) stimulated the production of inositol mono-, bis- and tris-phosphates (IP1, IP2, and IP3). Prior exposure of hepatocytes to 8-bromo cyclic AMP (8Br-cAMP; 100 microM), but not 8-bromo cyclic GMP, enhanced the vasopressin-mediated stimulation of inositol phosphate accumulation, but had no significant effect on their formation in the absence of vasopressin. The effect of the cyclic AMP analogue was mimicked by glucagon (10 nM), and was seen whether cyclic AMP or glucagon was added 5 min or 12 h before the addition of vasopressin. An 8 h incubation with dexamethasone (100 nM) enhanced the accumulation of IP3, but not that of IP2 or IP1, in the presence of 8Br-cAMP and vasopressin. Cycloheximide or actinomycin D had little effect on the vasopressin stimulation of inositol phosphate accumulation, after an 8 h incubation in the presence or absence of 8Br-cAMP.

Fluorescence labeling of proteins related to ADH‐induced change in frog bladder luminal membrane

Sulfhydryl (SH) reactive reagents, such as eosin derivatives, have been found to be useful in labeling water pathways in red cells. In the present study we used an impermeable SH-reagent, a fluorescent maleimide analogue EMA (eosin-5'-maleimide), in order to identify proteins involved in water permeability response to antidiuretic hormone (ADH). We observed that: 1) EMA (1 mM) mucosal pretreatment did not modify either the basal water flux or the subsequent ADH-induced hydrosmotic response; 2) EMA added to the mucosal bath at the maximum response to ADH, significantly decreased net water flux by about 40%; similar results were obtained when 10(-5) M forskolin was used as a hydrosmotic agent. These results suggest that the inhibitory effect of EMA occurs at a post cAMP step, possibly at the level of the sulfhydryl groups of the water channels themselves. Fluorescence distribution in SDS-PAGE of Triton X-100 extracted proteins from bladder labeled with EMA in both control conditions and under ADH stimulation allowed us to identify apical membrane proteins, labeled during ADH stimulation and not labeled in water impermeable controls. Of particular importance are four proteins of 52, 32-35, 26, 17, kDa. These polypeptides are probably involved in ADH-stimulated water transport and may be components of the water channels.

Fluorescence labeling of proteins related to ADH-induced change in frog bladder luminal membrane

Sulfhydryl (SH) reactive reagents, such as cosin derivatives, have been found to be useful in labelling water pathways in red cells. In the present study we used an impermeable SH-reagent, a fluorescent maleimide analogue EMA (eosin-5′-maleimide), in order to identify proteins involved in water permeability response to antidiuretic hormone (ADH). We observed that: 1) EMA (1 mM) mucosal pretreatment did not modify either the basal water flux or the subsequent ADH-induced hydrosmotic response; 2) EMA added to the mucosal bath at the maximum response to ADH, significantly decreased net water flux by about 40%; similar results were obtained when 10−5 M forskolin was used as a hydrosmotic agent. These results suggest that the inhibitory effect of EMA occurs at a post cAMP step, possibly at the level of the sulfhydryl groups of the water channels themselves. Fluorescence distribution in SDS-PAGE of Triton X-100 extracted proteins from bladder labeled with EMA in both control conditions and under ADH stimulation allowed us to identify apical membrane proteins, labeled during ADH stimulation and not labeled in water impermeable controls. Of particular importance are four proteins of 52, 32–35, 26, 17, kDa. These polypeptides are probably involved in ADH-stimulated water transport and may be components of the water channels.

Intramembrane particle structures in epithelial cells of the toad urinary bladder: a quantitative freeze‐fracture study

Freeze-fracture electron microscopy reveals intramembrane particle arrays in basal membranes of granular epithelial cells as well as both upper and lower plasma membranes of the underlying basal cells in the toad urinary bladder. These particle arrays are morphologically indistinguishable from the luminal membrane aggregates which are known to be associated with antidiuretic hormone (ADH)-stimulated water transport. In both granular and basal cells particle arrays are frequently located in and/or around the openings of vesicular and/or tubular structures fused to the plasma membranes, suggesting that they may be transferred from the cytoplasm by membrane fusion. Quantification of cytoplasmic aggrephores in control granular cells shows that they can be numerous and as close to the basolateral membrane as they are with the luminal membrane, to which they are known to fuse and deliver aggregates upon ADH stimulation. Aggrephore-like tubules were also found in the basal cells. Particle array densities were quantified for 6 pairs of control and ADH-stimulated hemibladders. At least 1440 microns 2 area of plasma membrane for each membrane domain was examined. Results indicate that the presence of these particle arrays in granular and basal cell membranes is highly variable and that exposure to ADH does not cause a statistically significant increase in their frequency.

Intramembrane particle structures in epithelial cells of the toad urinary bladder: a quantitative freeze-fracture study

Freeze-fracture electron microscopy reveals intramembrane particle arrays in basal membranes of granular epithelial cells as well as both upper and lower plasma membranes of the underlying basal cells in the toad urinary bladder. These particle arrays are morphologically indistinguishable from the luminal membrane aggregates which are known to be associated with antidiuretic hormone (ADH)-stimulated water transport. In both granular and basal cells particle arrays are frequently located in and/or around the openings of vesicular and/or tubular structures fused to the plasma membranes, suggesting that they may be transferred from the cytoplasm by membrane fusion. Quantification of cytoplasmic aggrephores in control granular cells shows that they can be numerous and as close to the basolateral membrane as they are with the luminal membrane, to which they are known to fuse and deliver aggregates upon ADH stimulation. Aggrephore-like tubules were also found in the basal cells. Particle array densities were quantified for 6 pairs of control and ADH-stimulated hemibladders. At least 1440 μm2 area of plasma membrane for each membrane domain was examined. Results indicate that the presence of these particle arrays in granular and basal cell membranes is highly variable and that exposure to ADH does not cause a statistically significant increase in their frequency.

Phosphorylation of a single subunit of the epithelial Na+ channel protein following vasopressin treatment of A6 cells.

Arginine vasopressin (antidiuretic hormone, ADH) stimulation of sodium transport in high electrical resistance epithelia is accompanied by adenylate cyclase stimulation and cAMP accumulation. The hypothesis of direct phosphorylation of the purified amiloride-blockable epithelial Na+ channel protein by cAMP-dependent protein kinase A after ADH treatment of cultured cells was investigated in this study. Phosphate-depleted A6 cells (a cell line derived from toad kidney) were exposed to 32PO4(3-) in the absence or presence of basolateral ADH (100 milliunits/ml). After 20 min (the time needed for ADH to increase maximally Na+ transport), the Na+ channels were extracted from the cells and purified. At every stage of purification, only one subunit of the Na+ channel, namely, the 315-kDa subunit, was specifically phosphorylated as assessed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and autoradiography or scintillation counting. In addition, a polyclonal antibody raised against purified epithelial Na+ channel protein was able to immunoprecipitate the phosphorylated channel protein from a detergent-solubilized fraction of vasopressin-treated A6 cells. This same subunit was also specifically phosphorylated in vitro when the purified Na+ channel protein was incubated with gamma-[32P]ATP and the purified catalytic subunit of the cAMP-dependent protein kinase. Thus, only a single component, the 315-kDa subunit, of the Na+ channel protein complex (which is composed of six subunits) can be phosphorylated both in vivo and in vitro. This subunit is selectively phosphorylated by the catalytic subunit of cAMP-dependent protein kinase to a level of 2-3 mol of 32P/mol of protein.

Role of diuretics, hormonal derangements, and clinical setting of hyponatremia in medical patients.

Because hyponatremia is frequently associated with preceding diuretic treatment and unrestricted fluid intake--conditions which have not been addressed sufficiently in published literature--we studied the pathophysiology and the clinical setting of such hyponatremia in a large group of internal medicine patients. We observed: a) Of an initial 310 patients with chemical hyponatremia only 204 (64%) had an associated plasma hypoosmolality. Since a normal plasma osmolality excludes a disturbance of water metabolism only the 204 patients with hypoosmolar hyponatremia were included in the study. This data shows that plasma osmolality is an essential measurement in any evaluation of hyponatremia. b) In 204 consecutive patients with hypoosmolar hyponatremia the electrolyte disturbance was related to advanced congestive cardiac failure in 25%, decompensated liver cirrhosis in 18%, volume contraction in 28%, syndrome of inappropriate antidiuretic hormone secretion in 19% and renal insufficiency in 4%. c) Plasma vasopressin was measurable in 90% of the 204 patients. It is known that radioimmunoassays to measure vasopressin fail to reliably detect low concentrations of circulating vasopressin (less than 0.5 pg/ml). It may therefore be stated that hypoosmolar hyponatremia was generally characterized by a failure of antidiuretic hormone suppression. d) Mean daily fluid intake of hyponatremic patients was 2.35 +/- 0.15 l. In the presence of stimulated vasopressin this large a fluid intake is bound to worsen the severity of hyponatremia. e) Of 204 patients 126 were treated with diuretics at the time of study. In these patients hyponatremia worsened during such treatments and was associated with evidence of prerenal azotemia. However there were no significant differences between diuretic-treated and -untreated patients with respect to plasma vasopressin stimulation and amount of fluid intake.(ABSTRACT TRUNCATED AT 250 WORDS)