Protein kinase C-α mediates hypertonicity-stimulated increase in urea transporter phosphorylation in the inner medullary collecting duct.

The UT-A1 urea transporter plays a critical role in the production of concentrated urine. Both vasopressin and hypertonicity increase urea permeability in rat terminal inner medullary collecting ducts (IMCD). Each agonist independently increases UT-A1 phosphorylation and apical plasma membrane accumulation. Vasopressin activates PKA and phosphorylates UT-A1 at serines 486 and 499. Hypertonicity stimulates urea permeability through protein kinase C (PKC) and intracellular calcium. To determine whether the hypertonic stimulation of urea permeability results from a PKC-mediated phosphorylation of UT-A1, rat IMCDs were metabolically labeled with [(32)P]. Hypertonicity stimulated UT-A1 phosphorylation, and this increase was blocked by preincubation with a PKC inhibitor. IMCDs were biotinylated to assess plasma membrane UT-A1. Hypertonicity increased biotinylated UT-A1, and this increase was blocked by preincubation with a PKC inhibitor. When PKC was directly activated using a phorbol ester, total UT-A1 phosphorylation increased, but phosphorylation at serine 486 was not increased, indicating that PKC did not phosphorylate UT-A1 at the same residue as PKA. Since PKC-α is a calcium-dependent PKC isoform and PKC-α knockout mice have a urine-concentrating defect, it suggested that PKC-α may mediate the response to hypertonicity. Consistent with this hypothesis, hypertonicity increased phospho-PKC-α in rat IMCDs. Finally, PKC-α knockout mice were used to determine whether hypertonicity could stimulate UT-A1 phosphorylation in the absence of PKC-α. Hypertonicity significantly increased UT-A1 phosphorylation in wild-type mice but not in PKC-α knockout mice. We conclude that PKC-α mediates the hypertonicity-stimulated increase in UT-A1 phosphorylation in the IMCD.

Effects of insulin on Na and K transporters in the rat CCD.

We tested the effects of insulin (2 nM, 30-60 min) on principal cells of isolated split-open rat cortical collecting ducts (CCD) using whole-cell current measurements. Insulin addition to the superfusate of the tubules enhanced Na pump (ouabain-sensitive) current from 18 ± 3 to 31 ± 3 pA/cell in control and from 74 ± 9 to 126 ± 11 pA/cell in high K-fed animals. It also more than doubled ROMK (tertiapin-Q-sensitive) K(+) currents in control CCD from 320 ± 40 to 700 ± 80 pA/cell, although it did not affect this current in tubules from K-loaded rats. Insulin did not induce the appearance of amiloride-sensitive Na(+) current in control animals, while in high K-fed animals the currents were similar in the presence (140 ± 30) and the absence (180 ± 70 pA/cell) of insulin. Intraperitoneal injection of insulin plus hypertonic dextrose decreased Na excretion, as previously reported. However, injection of dextrose alone, or the nonmetabolized sugar mannose, had similar effects, suggesting that they were largely the result of vascular volume depletion rather than specific actions of the hormone. In summary, we find no evidence for acute upregulation of the epithelial Na channel (ENaC) by physiological concentrations of insulin in the mammalian CCD. However, the hormone does activate both the Na/K pump and apical K(+) channels and could, under some conditions, enhance renal K(+) secretion.

In vitro protoscolicidal effects of hypertonic glucose on protoscolices of hydatid cyst.

To evaluate the protoscolicidal effects of various concentrations of hypertonic glucose, live protoscolices of sheep were exposed to 10%, 15%, 25% and 50% glucose solutions. Cetrimide (0.5%), silver nitrate (0.5%) and hypertonic saline (20%) were used as positive controls, while physiological saline was used as a negative control. After 1, 2 and 5 min, the protoscolicidal effects were determined by 1% eosin. A 25% glucose solution had no significant protoscolicidal effect. However, a 50% glucose solution revealed higher protoscolicidal effect than 0.5% silver nitrate but weaker effect than 0.5% cetrimide; the effect was comparable with that of 20% hypertonic saline. The results showed that hypertonic glucose solution is highly effective in killing protoscolices of Echinococcus granulosus in vitro.

Internalized GABA-receptor subunits are transferred to an intracellular pool associated with the postsynaptic density.

Endocytosis represents an important mechanism regulating cell-surface expression of neurotransmitter receptors, including GABAA receptors, in neurons. Little is known, however, about trafficking of internalized receptors. Here, we used antibody tagging in living rat hippocampal neurons in culture to monitor GABAA receptor internalization. We show that cell-surface receptors have a homogeneous distribution reflecting their mobility in the membrane. Unexpectedly, internalized GABAA receptors were detected mainly in a subsynaptic pool associated with gephyrin at postsynaptic sites, whereas AMPA-type glutamate receptors were accumulated in the soma. This process was time-dependent and could be prevented by blocking clathrin-coated vesicle endocytosis. In control experiments, the existence of an intracellular pool of GABAA receptors associated with gephyrin was confirmed independently of internalization of surface receptors, and constitutive endocytosis, unrelated to antibody-tagging, could be demonstrated for both AMPA and GABAA receptors using a biotinylation assay. These results suggest that cycling of GABAA receptors between the cell surface and the subsynaptic pool provides a mechanism for the short-term regulation of GABAergic neurotransmission. Furthermore, the close association of gephyrin with internalized GABAA receptors suggests a role in intracellular receptor trafficking.

Comparative performance in the porcine esophagus of different solutions used for submucosal injection.

BACKGROUND: Before endoscopic mucosal resection and polypectomy of sessile lesions, injection of fluid into the submucosa cushions and isolates the tissue and thereby reduces thermal injury and the risk for perforation and hemorrhage. This study investigated the performance of 5 different solutions when used to form submucosal fluid cushions in the porcine esophagus. METHODS: Five groups of 5 pigs were studied. In each pig, 6 separate submucosal injections of 5 mL of a single test solution were performed within the distal third of the esophagus. The time required for the submucosal bleb to flatten completely was recorded after each injection. The solutions used were as follows: normal saline solution, normal saline plus epinephrine solution, 50% dextrose, 10% glycerine/5% fructose in normal saline solution, and 1% rooster comb hyaluronic acid. RESULTS: The normal saline solution and normal saline plus epinephrine solutions had the shortest disappearance times (respectively, median 2.4 and 3.0 minutes), which were significantly shorter compared with the other test solutions. The mean disappearance times for 50% dextrose and 10% glycerine were, respectively, 4.7 and 4.2 minutes. The mean disappearance time for hyaluronic acid was 22.1 minutes. CONCLUSIONS: A solution of hyaluronic acid appears to be ideal for producing a lasting submucosal cushion for prolonged procedures. Dextrose 50% is superior to normal saline solution and may serve as an alternative to hyaluronic acid in terms of availability and cost.

Cytokine expression profiling in human leukocytes after exposure to hypertonic and isotonic fluids.

BACKGROUND: Resuscitation from hemorrhagic shock causes profound immunologic changes. The tonicity of fluids used for resuscitation clearly influences the immune response. Our study was designed to determine whether isotonic and hypertonic fluids exert their differential effects on immune response by altering the cytokine gene profile of human leukocytes. The cDNA array method was used to profile transcriptional responses after exposure to hypertonic and isotonic fluids. METHODS: Blood from seven healthy volunteers was incubated for 30 minutes with isotonic (10% dextran-40 and lactated Ringer's [LR] solution) and hypertonic (7.5% hypertonic saline and hypertonic dextran [HTD]) fluids. The volumes of isotonic fluids used were equal to the volume of blood, whereas the volumes of hypertonic fluids were adjusted to keep the salt load identical to the LR group. The cDNA array technique was used to measure the gene expression of 23 common cytokines. RESULTS: Increased gene transcription of proinflammatory cytokines (interleukin [IL]-1alpha, IL-6, IL-10, and tumor necrosis factor-alpha) as well as others (IL-5, IL-7, and IL-16) was found after incubation with resuscitation fluids. Variances were noted depending on the type of fluid: HTD and LR solution did not induce expression of IL-5, and HTD also did not induce IL-1beta expression. Genes encoding IL-1alpha, IL-6, IL-9, and tumor necrosis factor-alpha had low level baseline expression in leukocytes isolated from unstimulated blood, and their expression increased markedly after exposure to resuscitation fluids. The inducible transcripts included IL-1beta, IL-7, IL-10, and IL-16. However, there was no difference in cytokine expression profile between isotonic and hypertonic fluids. CONCLUSION: Exposure of human leukocytes to resuscitation fluids causes an increase in cytokine gene expressions compared with undiluted blood. This expression profile is largely independent of the type of fluid used.

Shuttle-box avoidance learning in mice: improvement by glucose combined with stimulant drugs.

Glucose was tested alone or in combination with two stimulant drugs, amphetamine and nicotine, in mice of the CD-1 strain subjected to five daily shuttle-box training sessions. Pretraining intraperitoneal administration of glucose (50 or 100 mg/kg) had no effect, while amphetamine and nicotine, given alone, significantly improved avoidance acquisition at a dose of 0.5 mg/kg, but not 0.025 mg/kg. Significant improvement of avoidance learning was also produced by a combination of glucose with the lower dose of amphetamine or nicotine. This enhancing action, produced by a combination of glucose and stimulant drugs, at doses ineffective by themselves, might be due to a concomitant cholinergic and dopaminergic activation, induced by glucose and stimulant drugs, respectively.

The effects of electrolyte, lactate, high-concentrated glucose, and dialysate on peritoneal mesothelial cells.

In order to investigate which component of dialysate is responsible for mesothelial cell damage, we studied the chronic cytotoxicity to mesothelial cells by using four types of solution. Four different types of solution (Ringer's solution, lactate, high-concentrate glucose, and 4.25% Dianeal) were prepared and injected into the abdominal cavity of five ddY-mice, 5 mL every day for one month. The monolayer of the mesothelial cells was carefully removed from the liver surface by the imprint technique. Then, the mesothelial cell damage was evaluated by using trypan blue staining and comparing the results. Trypan blue-stained cells in 100 mm2 were observed in 7.0% of the control, 15.4% of the Ringer's solution, 18.7% of the lactate, 23.2% of the high-concentrate glucose, and 22.4% of the 4.25% Dianeal group, respectively. The damaged cells were significantly (p < 0.05) greater in the 4.25% Dianeal group than in the control group, and those in the high-concentrate glucose group also appeared to be greater in number compared to the control group It is concluded from these results that damage to the mesothelial cells is induced by chronic exposure to high-glucose dialysate, and its pathogenesis is deeply related to high concentration of glucose.

Pyruvate infusions into the septal area attenuate spontaneous alternation impairments induced by intraseptal morphine injections.

Glucose infusions into the medial septal area attenuate memory impairments produced by concurrent intraseptal morphine injections. One possible explanation for these effects of glucose on memory is that the treatment modulates regional energy metabolism. As a test of this hypothesis, the present experiment determined whether intraseptal pyruvate injections could attenuate a spontaneous alternation impairment seen after intraseptal morphine injections. Intraseptal injections of morphine (4.0 nmol) 30 min prior to testing produced spontaneous alternation scores significantly lower than those in control groups. Morphine injections near, but outside, the septal region did not impair spontaneous alternation performance. The morphine-induced impairment was similarly reversed by coadministration of either glucose (18 nmol) or pyruvate (18 nmol) into the septum. These findings suggest that glucose may act through the tricarboxylic acid cycle by increasing the availability of ATP, augmenting the synthesis of certain neurotransmitters, or both.

Timing of hypertonic glucose and thermochemotherapy with 1-(4-amino-2-methylpyrimidine-5-yl) methyl-3-(2-chloroethyl)-3-nitrosourea (ACNU) in the BT4An rat glioma: relation to intratumoral pH reduction and circulatory changes after glucose supply.

PURPOSE: Intraperitoneal hypertonic glucose has previously been shown to induce hyperglycemia, hemo-concentration, and to influence systemic and tumor circulation, and, thus, enhance the effect of thermochemotherapy with 1-(4-amino-2-methylpyrimidine-5-yl)methyl-3-(2-chloroethyl)-3-nitrosoure a (ACNU) and 1,3-bis(2-chloroethyl)-1-nitrosourea (BCNU). However, the optimal timing and the precise mechanisms responsible are not known. The effect of different time intervals between glucose load and thermochemotherapy with ACNU in the treatment of BT4An tumors, therefore, was investigated. Changes of serum glucose (Se-glucose), hemoglobin, systemic circulation parameters, tumor pH, and tumor temperature, induced by intraperitoneal glucose and/or hyperthermia, were measured to assess their effect on tumor growth. METHODS AND MATERIALS: (a): Inbred BD IX rats with BT4An tumors on the hind leg were treated with ACNU 7 mg/kg intravenously just before waterbath hyperthermia, and intraperitoneal hypertonic glucose (6 g/kg) at different time intervals before (240-0 min) or immediately after thermochemotherapy. (b): Intratumoral pH and temperature were measured at different intervals after intraperitoneal glucose, and during hyperthermia with or without previous glucose. (c): Hemoglobin, hematocrit, and Se-glucose were measured at different times after intraperitoneal glucose. (d): Mean arterial pressure, pulse pressure, and heart rate were measured for 120 min after intraperitoneal glucose. RESULTS: (a): The number of tumor controls and the growth delay was greatest with glucose 45 min before thermochemotherapy, and least with a time interval of 240 min. Glucose after thermochemotherapy delayed tumor growth. (b): After intraperitoneal glucose alone, intratumoral pH decreased gradually from 6.76 to 5.86 after 240 min. Hyperthermia 120 min after glucose induced a rapid further pH drop, while hyperthermia alone had no significant influence on pH. Intratumoral temperature was higher during hyperthermia in animals given glucose. (c): A substantial rise of Se-glucose and hemoglobin developed. The hemoconcentration was maintained also after reduction of Se-glucose towards normal values. (d): An initial tachycardia, and a reduction of the mean arterial pressure of about 10% 5-45 min after was measured. CONCLUSION: The data indicate that a complex interaction between gradually reduced tumor pH, hyperglycemia, hemoconcentration, and reduced tumor blood flow, and not a breakdown of systemic circulation, is responsible for the effect of intraperitoneal glucose on thermochemotherapy with ACNU. Interestingly, enhancement of thermochemotherapy effect was also seen when intraperitoneal glucose was given after heat and ACNU.

The effects of supercooling chemicals on myocardial ultrastructure: a transmission electron microscopy case study.

Extended ischemia results in organ infarction which limits the availability of donor hearts. Hypothermic storage extends heart preservation by effectively stopping cellular metabolism, thereby preventing toxic accumulations of metabolic wastes and depletion of energy stores. However, cell swelling as a result of ion concentration changes and cell laceration due to ice crystal growth are consequences of hypothermic ischemia. Supercooling successfully preserves hearts for an extended time without associated myocardial necrosis. The efficacies of four supercooling preservative solutions, containing hypertonic glucose, polyethylene glycol, and or winter flounder antifreeze protein, are assessed using the Langendorff isolated organ perfusion apparatus and transmission electron microscopy. Polyethylene glycol seems the most effective in preventing myocardial necrosis possibly by dehydrating, minimizing cellular ice formation, protecting against cell swelling, and functioning as an antioxidant. Hypertonic glucose seems the most effective in reducing cell swelling; it may also depress solution freezing points, bind water, adjust both intra- and extracellular osmolarities, stabilize proteins, and assist in adenosine triphosphate (ATP) production. Antifreeze protein seems to bind effectively to ice and inhibit its growth; it may also reduce membrane permeabilities to Ca2+ and K+ ions.

Effects of glucose on rat lung preservation: report of a study conducted on an isolated lung reperfusion model utilizing. Another isolated lung as a "deoxygenator".

We describe herein a new experimental model in which an isolated rat lung was ventilated with a mixture of 95% nitrogen and 5% carbon dioxide to decrease the oxygen and increase the carbon dioxide in the perfused blood to create and maintain a gas composition similar to that of venous blood. By utilizing this system as a "deoxygenator," pulmonary functions, including gas exchange, could be measured for at least 60 min in isolated and preserved lungs on reperfusion. When the effects of glucose in the flushing and storage solution were examined, 5 mM glucose in the solution resulted in better preservation of the lung, as shown by a higher uptake of oxygen and a lower intratracheal pressure, than when no glucose was given. However, the presence of 50 mM glucose was not beneficial, but rather increased the wet/dry weight ratio of the tissue.

[Growth characteristics of bovine retinal pericytes in culture]. / Wachstumscharakteristika von bovinen retinalen Perizyten in Kultur.

The loss of retinal pericytes is one of the earliest changes in diabetic retinopathy. In order to study this phenomenon in vitro, an optimal isolation and cultivation system has to be established. Therefore, pericytes from bovine retinae were isolated enzymatically with 0.4% collagenase in phosphate-buffered saline and identical immunologically by positive staining with antibodies against smooth muscle alpha-actin. Routine cultivation of pericytes was performed by using DMEM supplemented with 10% fetal calf serum. Dependent on the in vitro age of cells, the effect of the following reagents on proliferative activity was determined: fetal calf serum, heparin, ECGF, ECGF+heparin, and glucose. Increasing serum concentrations stimulated the proliferation of pericytes, although the degree of stimulation was reduced with increasing in vitro age. Heparin inhibited the growth in a dose-dependent manner; the achieving 50% inhibition was extrapolated to be 25 micrograms/ml. ECGF increased pericyte proliferation significantly, with a maximum at 10 microliters/ml. In addition, ECGF reversed the inhibitory effect of heparin. Furthermore, all tested glucose concentrations (5.5-27.75 mmol/l) did not show any influence on growth rates of pericytes. The results demonstrate that routine cultivation of retinal pericytes is possible. Moreover, they indicate that enhanced blood glucose concentrations, as observed in diabetic patients, are not the only important factor in the loss of retinal pericytes.

Release of angiotensin in the paraventricular nucleus in response to hyperosmotic stimulation in conscious rats: a microdialysis study.

Angiotensin peptides are thought to act as neurotransmitters or neuromodulators in central osmoregulation. We tested the hypothesis that angiotensin peptides are released in the paraventricular nucleus (PVN) of the hypothalamus upon local osmotic stimulation. Brain microdialysis and radioimmunoassay (RIA) techniques were used to measure the release of immunoreactive angiotensin II (irANG II) in the PVN following direct stimulation of this area with hyperosmotic solutions. In conscious rats, perfusion of the PVN with 0.3 M and 0.6 M NaCl in artificial cerebrospinal fluid (aCSF) elicited concentration-dependent increases in irANG II release to 5.52 +/- 0.53, (P < 0.01, n = 8) and 9.01 +/- 1.03 pg/100 microliters, (P < 0.001, n = 7), respectively, from basal values of 3.04 +/- 0.46 pg/100 microliters. Local perfusion of the PVN with 1.2 M glucose in aCSF also resulted in an increased release of irANG II from 3.07 +/- 0.87 to 6.24 +/- 0.45 pg/100 microliters (P < 0.05, n = 5). Fractionization of angiotensin peptides by HPLC followed by RIA revealed that ANG II (1-8) and ANG III (2-8) were released in similar amounts in the perfusate collected during 0.6 M NaCl stimulation (4.79 +/- 0.69 and 3.45 +/- 0.76 pg/100 microliters, respectively). Our results show that both, ANG II and ANG III are released in the PVN in response to local hyperosmotic stimulation. They support the concept that angiotensin peptides in the PVN are involved as neurotransmitters in central osmotic control.

Effects of betaines and urine on the antibacterial activity of aminoglycosides.

Urine has long been known to inhibit the activity of aminoglycosides against urinary tract pathogens. Glycine betaine which is present in urine confers resistance against high osmolarity to Gram-negative organisms. We postulated that glycine betaine might contribute to the aminoglycoside resistance found in hypertonic urine. Escherichia coli became extremely resistant to gentamicin (40 x MIC in 0.9 M sodium chloride) when cultured in minimal medium supplemented with 10(-4) M glycine betaine and 0.1-1.0 M sodium chloride. Resistance was increased in the presence of high glucose concentrations but to a lesser extent (3 x MIC in 1.0 M glucose). This effect was not produced by other polyols or urea. These results suggest the observed synergism is mediated by the osmoprotective effects of glycine betaine and the inhibitory effect of sodium chloride or glucose against the aminoglycoside. Other betaines tested had a less marked effect. The betaines in urine permit the expression of increased resistance to aminoglycosides in concentrated urine.

In vivo exposure to the currently available peritoneal dialysis fluids decreases the function of peritoneal macrophages in CAPD.

Previous in vitro studies have revealed that the currently available peritoneal dialysis fluids (PDF) inhibit several functions of phagocytic cells. To investigate the clinical relevance of those in vitro findings, we compared the in vivo effect of PDF pH on peritoneal macrophage (PMO) function in chronic peritoneal dialysis patients. In a randomized crossover setting, each of eight patients used exclusively PDF at pH five (D5) or pH seven (D7) on day one. The next day the patients who used D5 were switched to D7 and vice versa. Likewise the effect of glucose-mediated hypertonicity was studied in eight other patients, using PDF with 1.36% glucose (D136) or 3.86% glucose (D386). PMO were isolated from the effluents and studied for their phagocytic and killing capacity, and their ability to mount a respiratory burst (chemiluminescence response). PMO obtained after the intraperitoneal instillation of D7 were significantly better able to phagocytize both S. epidermidis (65 +/- 9 vs 37 +/- 8% uptake, p < 0.005) and E. coli (43 +/- 8 vs 25 +/- 4% uptake, p < 0.005). In addition, PMO harvested from D7 effluents revealed a significantly higher killing capacity than PMO derived from D5 effluents for S. epidermidis (60 +/- 5 vs 38 +/- 6%, p < 0.005) as well as for E. coli (51 +/- 10 vs 25 +/- 9%, p < 0.025). Moreover, PMO derived from D7 effluents mounted a significantly higher respiratory burst as compared to PMO in vivo exposed to D5 for the same time.(ABSTRACT TRUNCATED AT 250 WORDS)

Avaliaçäo clínica do esvaziamento gástrico com glicose a 50 em pacientes submetidos à vagotomia troncular com antrectomia parcial e gastroduodenostomia ao nível da curvatura menor / Clinical evaluation of gastric emptying with glucose at 50

Faz-se um estudo do evaziamento gástrico após a vagotomia troncular com antrectomia parcial e gastroduodenostomia pela curvatura menor (VAGDPC). Em 32 pacientes portadores de úlcera cloridropéptica duodenal complicada e com indicaçäo cirúrgica, usou-se o teste oral com soluçäo de glicose hipertónica a 50% (SGH 50) antes e após a cirurgia. Faz-se uma aaliaçäo clínica e conclui-se que os pacientes operados desta forma (VAGDPC) näo apresentam, com o teste, a síndrome de esvaziamento gástrico rápido com expressäo clínica

Uso da glicose hipertônica na intoxicaçäo alcoólica aguda: um estudo duplo-cego / Use of hypertonic glucose solution in acute alcoholic intoxication: a double-blind study

Os autores realizaram um estudo duplo-cego, avalindo a glicemia, a alcoolemia e o estado neurológico de 83 pacientes que procuraram atendimento no Pronto Socorro Municipal de Porto Alegre por se apresentarem alcoolizados. A aferiçäo foi realizada no momento do ingresso no serviço e repetida 40 minutos após. A glicemia média foi 90,16mg/dl, com desvio-padräo 21,15, a maior parte dentro da faixa normal de 70 a 105mg/dl. Apenas um paciente apresentou sintomatologia compatível com hipoglicemia, acompahada de níveis glicêmicos de 63mg/dl. Näo foi encontrada correlaçäo linear entre a glicemia e a alcoolemia. Após a avaliaçäo inicial, foram administrados 20ml de soluçäo fisiológica, como placebo. Näo foi verificada diferença significativa entre os dois grupos quanto à queda da alcoolemia após o intervalo controlado. O estado neurológico dos pacientes foi aferido por um teste adaptado pelos autores. Os dois grupos apresentaram melhora semelhante no escore do teste. Os resultados obtidos pelos autores reforçam a idéia de que a administraçäo de glicose a pacientes alcoolizados deve ser indicada pela presença de sinais de hipoglicemia

Studies on the pathogenesis of the early dumping syndrome induced by intraduodenal instillation of hypertonic glucose.

A reaction indistinguishable from the early dumping syndrome was induced in four of nine normal volunteers by intraduodenal instillation of a hypertonic glucose meal. Tachycardia and marked peripheral vasodilatation were demonstrated in 'dumpers' by Doppler ultrasound measurements of the arterial blood flow signal. The dumping reaction was not detectably altered by the addition of guar to the meal. Plasma VIP concentration rose and plasma volume fell to a similar degree in 'dumpers' and 'non-dumpers', suggesting that neither event is an integral component of the dumping mechanism. In contrast, the rates of rise of blood glucose and enteroglucagon concentration were markedly greater in 'dumpers'. The results are inconsistent with the conventional explanation that the early dumping syndrome is caused by a large osmotic fluid shift, but are compatible with a mechanism involving an initial period of intestinal hypermotility.