The mechanism of decreased intestinal sodium and water absorption after acute volume expansion in the rat

Inulin reduces liver triacylglycerol by increasing lipid droplet lipolysis in fat-loaded mice

Increased consumption of high-fat low-fiber foods has been shown to contribute to the development of metabolic syndromes, such as fatty liver, obesity, diabetes, et al. Fermentable dietary fiber, such as inulin, is broadly used to mitigate host metabolic abnormalities. In this work, we studied systematically the effect of inulin on mice with metabolic disorders, induced by either short- or long-term high-fat feeding. As expected, inulin reduced the body weight of mice in both groups. However, it was found that inulin feeding could only increase energy expenditure, alleviate adiposity, and improve glucose intolerance in mice fed with high-fat diet (HFD) for 1 month but not for 4 months. Surprisingly, inulin supplementation could alleviate HFD-induced hepatic steatosis, mediated through increasing adipose triglyceride lipase (ATGL) on liver lipid droplets, in both groups. Gut microbiota in the short- and long-term fat-loaded mice were shown to be modulated differently, which may mediate the differential effects of inulin. These results may help in understanding the role and mechanism of fermentable fiber regulating host metabolism.

The male rectus diastasis: a different concept?

PURPOSE

More interest in the treatment of rectus diastasis has been evoked lately. Following the postpartum females from a great distance, the middle-aged males living with obesity are the second most common group of rectus diastasis patients. Although gender differences are considered frequently in regard to cosmetic appearance and symptoms, it is less obvious in classifications and subsequent treatment strategies. Is a unisex approach of rectus diastasis still applicable? The lack of a firm answer warrants this review of the current literature.

METHODS

An explorative free-text multi-database bibliographic search (Pubmed/CENTRAL/EMBASE/PEDro/Scholar) was performed with the focus on the rectus diastasis in males. Anticipating the limited references, the design was a non-systematic review. All studies, regardless of study type, language or time period, describing etiology, symptoms, classification and/or treatment options were eligible for inclusion. From the articles retrieved out of this search, additional references were identified by a manual search among the cited references.

RESULTS

The multi-database search resulted in a total of 7633 records. Based on the title and abstract 95 records were full text assessed for eligibility. Eleven studies were identified as relevant, six by cross-reference and another four by hand-search were added to provide an insight in gender-specific aspects in rectus diastase. Hereditary causes are differences in collagen-like composition of types and concomitant abdominal aneurysm as well as gender differences in the linea alba architecture. Acquired etiology is distributed into both absolute pressure by visceral obesity and relative pressure caused by weight lifting or improper exercises. Furthermore, the impact of muscle thickness and age are considered as influencers of biomechanics. Gender differences can also play a role in symptoms of body image and core stability. It is known that there are anatomical differences between male and female persons; more transverse fibers are found in infra-umbilical region in women. In classifications the awareness of male rectus diastasis is limited, treatment outcome studies are scarce on males.

CONCLUSION

An overview of male-specific aspects of rectus diastasis is provided, underlining that key aspects surrounding rectus diastasis in males differ from females. Although males are the minority of rectus diastasis patients, we recommend that the male rectus diastasis as a concept should be specifically acknowledged in classifications systems and study outcome reporting to evaluate this subgroup more accurately in the future.

Interaction with biliary and pancreatic fluids drives supersaturation and drug absorption from lipid-based formulations of low (saquinavir) and high (fenofibrate) permeability poorly soluble drugs

Drug absorption from lipid-based formulations (LBFs) in the gastrointestinal (GI) tract is the result of a series of processes, including formulation dispersion, interaction with biliary and pancreatic secretions, drug solubilisation and supersaturation, and finally intestinal permeability. Optimal formulation design is dependent on a good understanding of the limitations to, and drivers of, absorption, but for LBFs the complexity of these processes makes data interpretation complex. The current study has re-examined a previous in vitro digestion-in situ perfusion model to increase physiological relevance and has used this model to examine drug absorption from LBFs. The composition of rat bile and jejunal fluid was also characterised to identify in vivo-relevant conditions. Digestion was initiated using rat bile/pancreatic fluid and the formulation and digestive enzymes mixed immediately prior to entry into the jejunum (allowing dilution/digestion to occur at the absorptive site). These conditions were employed to study drug absorption from LBFs of high (fenofibrate, FFB) and low (saquinavir, SQV) permeability compounds. The impact of polymeric precipitation inhibitors (PPIs) was also evaluated. For FFB, supersaturation, initiated by formulation interaction with biliary/pancreatic fluids, appeared to drive absorption and the addition of the PPIs poly(glycidyl methacrylate) (PPGAE) and hydroxypropylmethyl cellulose (HPMC), reduced drug precipitation, increased FFB supersaturation and increased absorption from a Type IV LBF of FFB. For a Type IIIB LBF however, PPIs were ineffective at increasing absorption. The impact of PPIs on the absorption of a less permeable drug, SQV, was similarly evaluated and again drug absorption appeared to be related to the extent of supersaturation, although in this case PPI were unable to promote absorption. For both FFB and SQV, drug absorption patterns obtained with the in vitro digestion-in situ perfusion mode, correlated well with in vitro supersaturation data and in vivo drug exposure data from oral bioavailability studies. The data are consistent with a mode of drug absorption where rapid dilution of LBFs with biliary and pancreatic secretions at the absorptive site in the upper small intestine drives transient supersaturation, that supersaturation is a significant driver of drug absorption for both low and high permeability drugs, and that PPIs delay drug precipitation, enhance supersaturation and promote drug absorption in a drug and formulation specific manner.

An investigation into the relationship between small intestinal fluid secretion and systemic arterial blood pressure in the anesthetized rat

The effects of changes in the steady level of diastolic blood pressure on fluid flux across the jejunum has been investigated in the anesthetized rat during perfusion with a nutrient-free and Na⁺-free solution. Diastolic blood pressure was manipulated by intravenous infusions, during the jejunal perfusions, of vasodilators (vasoactive intestinal polypeptide, acetyl-β-methylcholine, and phentolamine) and a vasoconstrictor (arginine vasopressin), each of which acts through a different cellular mechanism. The outcome was that fluid flux was related by a parabolic relationship with diastolic blood pressure in which net secretion occurred over the range 40–100 mmHg, whereas net absorption was recorded at diastolic pressures exceeding 100 mmHg and below 40 mmHg. Against a background of normal absorption promoted by perfusion with 145 mmol L⁻¹ Na⁺/5 mmol L⁻¹ glucose solution, reductions in diastolic blood pressure markedly reduced the mean rate of fluid absorption by 58% overall, whereas the rate of glucose absorption remained unchanged. Our results were explained on the basis that vasodilatation led to increased capillary pressure and then to net filtration of fluid from the mesenteric capillary bed. Experiments in which Escherichia coli heat-stable toxin was added to the jejunal perfusate confirmed the absence of a secretory response, which was consistent with the absence of effect of the toxin on diastolic blood pressure.

Evaluation of sodium deficit in infants undergoing intestinal surgery

BACKGROUND

Sodium is a critical growth factor for children. Severe deficits cause growth impairment and cognitive dysfunction. Both the diagnosis and risk of sodium depletion in children undergoing intestinal surgery are poorly understood.

METHODS

With IRB approval, children undergoing intestinal surgery (2009-2012) who had a urine sodium measurement were retrospectively reviewed. Sodium deficits were defined: urine sodium <30 mmol/L and <10 mmol/L were deficient and severely deficient, respectively. Demographics, weight changes, and intake (sodium, fluid, and nutritional) were tabulated. Data were analyzed using regression analysis and Mann Whitney U tests.

RESULTS

Thirty-nine patients, 51.3% female, with a gestational age of 32.2 weeks and weight of 1.43 kg were identified. The most common diagnoses were NEC (38.5%), intestinal atresia (20.5%), and isolated perforation (10.3%). Sodium deficiency was documented in 36/39 (92%) and 92.9% for those in continuity. Severe deficiency occurred in 64%. Urine sodium was significantly correlated with weight gain (p=0.002). Weight gain in patients with urine sodium <30 mmol/L was significantly decreased vs. those ≥30 mmol/L (+0.58 g/d vs. +21.6 g/d, p=0.016).

CONCLUSION

In this population, sodium depletion is common in children undergoing intestinal surgery, even when the colon is in continuity. Correction of the sodium deficit to achieve urine sodium >30 mmol/L is associated with improved weight gain.

Exercise regulation of intestinal tight junction proteins

Gastrointestinal distress, such as diarrhoea, cramping, vomiting, nausea and gastric pain are common among athletes during training and competition. The mechanisms that cause these symptoms are not fully understood. The stress of heat and oxidative damage during exercise causes disruption to intestinal epithelial cell tight junction proteins resulting in increased permeability to luminal endotoxins. The endotoxin moves into the blood stream leading to a systemic immune response. Tight junction integrity is altered by the phosphoylation state of the proteins occludin and claudins, and may be regulated by the type of exercise performed. Prolonged exercise and high-intensity exercise lead to an increase in key phosphorylation enzymes that ultimately cause tight junction dysfunction, but the mechanisms are different. The purpose of this review is to (1) explain the function and physiology of tight junction regulation, (2) discuss the effects of prolonged and high-intensity exercise on tight junction permeability leading to gastrointestinal distress and (3) review agents that may increase or decrease tight junction integrity during exercise.

Escherichia coli Heat Stable (STa) Enterotoxin and the Upper Small Intestine: Lack of Evidence in Vivo for Net Fluid Secretion

Heat stable (STa) enterotoxin from E. coli reduced fluid absorption in vivo in the perfused jejunum of the anaesthetized rat in Krebs-phosphate buffer containing lactate and glucose (nutrient buffer), in glucose saline and in glucose free saline. Bicarbonate ion enhanced fluid absorption of 98 +/- 7 (6) microl/cm/h was very significantly (P < 0.0001) reduced by STa to 19 +/- 4 (6) microl/cm/h, but net secretion was not found. When impermeant MES substituted for bicarbonate ion, net fluid absorption of 29 +/- 3 (6) microl/cm/h was less (P < 0.01) than the values for phosphate buffer and bicarbonate buffer. With STa in MES buffer, fluid absorption of 3 +/- 2 (6) microl/cm/h was less than (P < 0.001) that in the absence of STa and not significantly different from zero net fluid absorption. E. coli STa did not cause net fluid secretion in vivo under any of the above circumstances. Neither bumetanide nor NPPB when co-perfused with STa restored the rate of fluid absorption. In experiments with zero sodium ion-containing perfusates, STa further reduced fluid absorption modestly by 20 microl/cm/h. Perfusion of ethyl-isopropyl-amiloride (EIPA) with STa in zero sodium ion buffers prevented the small increment in fluid entry into the lumen caused by STa, indicating that the STa effect was attributable to residual sodium ion and fluid uptake that zero sodium-ion perfusates did not eradicate. These experiments, using a technique that directly measures mass transport of fluid into and out of the in vivo proximal jejunum, do not support the concept that E. coli STa acts by stimulating a secretory response.

Gastroduodenal resistance and neural mechanisms involved in saline flow decrease elicited by acute blood volume expansion in anesthetized rats

We have previously demonstrated that blood volume (BV) expansion decreases saline flow through the gastroduodenal (GD) segment in anesthetized rats (Xavier-Neto J, dos Santos AA & Rola FH (1990) Gut, 31: 1006-1010). The present study attempts to identify the site(s) of resistance and neural mechanisms involved in this phenomenon. Male Wistar rats (N = 97, 200-300 g) were surgically manipulated to create four gut circuits: GD, gastric, pyloric and duodenal. These circuits were perfused under barostatically controlled pressure (4 cmH2O). Steady-state changes in flow were taken to reflect modifications in circuit resistances during three periods of time: normovolemic control (20 min), expansion (10-15 min), and expanded (30 min). Perfusion flow rates did not change in normovolemic control animals over a period of 60 min. BV expansion (Ringer bicarbonate, 1 ml/min up to 5% body weight) significantly (P < 0.05) reduced perfusion flow in the GD (10.3 +/- 0.5 to 7.6 +/- 0.6 ml/min), pyloric (9.0 +/- 0.6 to 5.6 +/- 1.2 ml/min) and duodenal (10.8 +/- 0.4 to 9.0 +/- 0.6 ml/min) circuits, but not in the gastric circuit (11.9 +/- 0.4 to 10.4 +/- 0.6 ml/min). Prazosin (1 mg/kg) and yohimbine (3 mg/kg) prevented the expansion effect on the duodenal but not on the pyloric circuit. Bilateral cervical vagotomy prevented the expansion effect on the pylorus during the expansion but not during the expanded period and had no effect on the duodenum. Atropine (0.5 mg/kg), hexamethonium (10 mg/kg) and propranolol (2 mg/kg) were ineffective on both circuits. These results indicate that 1) BV expansion increases the GD resistance to liquid flow, 2) pylorus and duodenum are important sites of resistance, and, 3) yohimbine and prazosin prevented the increase in duodenal resistance and vagotomy prevented it partially in the pylorus.

Meal-stimulated canine jejunal ionic absorption. Effect of direct jejunal meal delivery and premeal intravenous hydration

The ingestion of a meal stimulates water and ion absorption from the small intestine. The administration of nutrient substances directly to the small bowel can cause dumping symptoms, with intraluminal fluid accumulation and relative systemic hypovolemia. This study compared the effect of oral versus direct jejunal meal delivery on jejunal water and ion absorption, with and without premeal intravenous saline infusion. Jejunal absorption studies (N = 40) were performed on dogs with 25 cm proximal jejunal Thiry-Vella fistulas and feeding jejunostomies. Luminal perfusion with [14C]PEG was used to calculate fluxes of water and electrolytes. Five groups were randomly studied: (1) intravenous 0.9% saline alone, (2) oral meal alone, (3) intravenous 0.9% saline plus oral meal, (4) jejunal meal alone, and (5) intravenous 0.9% saline plus jejunal meal. Hydration status was assessed hourly by measurement of hematocrit. Water and electrolyte absorption was significantly stimulated by both oral and jejunal meal delivery (P less than 0.01). Intravenous saline hydration significantly reduced the hematocrit (P less than 0.05) but did not alter the proabsorptive response to an oral or jejunal meal. In conclusion, a postprandial signal for proximal jejunal water and electrolyte absorption was stimulated equally by orally or jejunally administered nutrients and was not affected by premeal hydration. These data support the hypothesis that the proabsorptive signal that stimulates water and ion absorption is an enteroenteric phenomenon originating from the small intestine, without implicating pathophysiologic events such as hypovolemia or dumping.

Only pharmacological doses of atrial natriuretic peptide affect intestinal ion transport in non-volume expanded rats

Pharmacological doses of atrial natriuretic peptide were infused into rats to study its effect on intestinal transport. Saline control or two concentrations of rat alpha atrial natriuretic peptide (0.06 or 1.0 nmol/min/kg) were administered intravenously (1 ml) over one hour. Jejunal net transport of water and electrolytes was measured with a plasma-like luminal electrolyte solution using a 'closed loop' technique. Distal colonic potential difference and arterial blood pressure were monitored continuously. Blood samples for analysis of plasma atrial natriuretic peptide concentrations were taken at the end of the experiments. Plasma concentrations were increased (mean (SD) (2.1 (0.5) and 24.0 (1.1) nmol/l respectively) compared with the controls (0.023 (0.016) nmol/l). Blood pressure dropped by 30% (p less than 0.05) in both groups of rats receiving atrial natriuretic peptide but remained unchanged when control saline was infused. Jejunal net absorption was reduced (p less than 0.01) only in animals receiving the higher concentration of peptide (H2O from 173 (33) to 64 (69) microliters.h-1.cm-2, Na from 25.7 (5.3) to 10.9 (8.9) mumol.h-1.cm-2). Distal colonic potential difference was not affected by atrial natriuretic peptide. In conclusion massive doses of atrial natriuretic peptide are required to produce any change in intestinal salt and water transport in normal, non-volume expanded rats; these effects could be a non-specific or 'toxic' response.

The effect of atrial natriuretic peptide on intestinal electrolyte transport

The effect of atrial natriuretic peptide (ANP) on rat small intestinal electrolyte transport was examined. In vivo, intravenous administration of rat ANP(99-126) induced diuresis and natriuresis in conjunction with a significant decrease in intestinal water (basal, 37.1 +/- 5.7 versus ANP 28.5 +/- 6.0 microliters/cm per 20 min, P less than 0.05) and Na+ (4.0 +/- 0.7 versus 2.8 +/- 0.9 mumol/cm per 20 min, P less than 0.05) absorption (n = 9). In vitro, in Ussing chambers, in both jejunum and ileum, addition of 1.0 microM ANP to short circuited, stripped tissue produced a maximal increase in short circuit current and stimulated net Cl- secretion due to a significant increase in the unidirectional serosal to mucosal flux (JCl-sm: jejunum 17.4 +/- 1.3 versus 19.8 +/- 1.3 microEq/cm2 per h, P less than 0.01, n = 6; ileum 13.4 +/- 0.5 versus 17.2 +/- 0.6, P less than 0.01, n = 6) which was inhibited by the calcium channel antagonist verapamil (82 +/- 26%, P less than 0.05) and by the 5-HT2 receptor antagonist cinanserin (72 +/- 44%, P less than 0.05). Guanylate cyclase activity was stimulated by ANP in intact epithelium, but not in isolated crypt and villus enterocytes.

The effect of atrial natriuretic peptide on small intestinal contractility and transit

Isometric tension in response to ANF (10(-10) to 10(-4) M) was recorded from longitudinally and circularly oriented rat jejunal smooth muscle strips. Conscious, fasted rats received an IV infusion of 1.25 nmol ANF/100 g body weight in 0.5 ml normal saline and controls received saline alone. Five minutes later 10 muCi Na2 51CrO4 in 0.5 ml saline was instilled through a jejunostomy. Fifteen minutes later animals were sacrificed, and the gut divided into 8 equal segments of small intestine, cecum and remaining colon. The radioactivity of each segment was measured and a geometric center of transit determined for each group. ANF induced relaxation of longitudinally oriented strips (Tm = -72.3 +/- 10.7 mN/g, ED50 7.3 +/- 3.6 x 10(-8) M), and contraction of circularly oriented strips (Tm = 35.0 +/- 5.0 mN/g, ED50 1.3 +/- 1.0 x 10(-8) M). This response was unaffected by 10(-6) M tetrodotoxin. The geometric mean center of transit was significantly (p less than 0.001) further aboral in ANF-treated compared to control animals (intestinal segment 4.2 +/- 0.2 vs. 3.2 +/- 0.2).

Atrial natriuretic peptide and water and electrolyte transport in the human jejunum

The effects of atrial natriuretic peptide were investigated on water and electrolyte transport in the human jejunum. Six healthy male volunteers (aged 21-33 years) were studied using a triple lumen perfusion technique. A plasma like electrolyte solution containing polyethylene glycol (5 milligrams) as a non-absorbable marker was perfused into the jejunum at 10 ml/min, and net water and electrolyte transport and transepithelial potential difference were measured. Subjects were studied single blind on two occasions with either intravenous atrial natriuretic peptide (6 pmol/min/kg for 90 minutes) or placebo (saline), both after controlled sodium intake over three days. Plasma atrial natriuretic peptide concentrations rose from (mean (SD)) 10.3 (3.6) pmol/l to a peak of 96.0 (61.8) pmol/l. Jejunal net water and electrolyte fluxes and potential difference were identical in both the atrial natriuretic peptide and the control studies. Compared with placebo atrial natriuretic peptide induced a significantly greater diuresis (peak 10.2 (6.0) v 1.8 (1.0) ml/min, p less than 0.05) and natriuresis (peak 1069 (351) v 376 (208) mumol/min, p less than 0.01) and haemoconcentration (haematocrit 0.405 (0.040) v 0.368 (0.018), p less than 0.01). There was no difference in blood pressure, pulse rate, plasma electrolytes, and plasma osmolality between the two studies. There was no evidence to suggest an effect of atrial natriuretic peptide on jejunal water and electrolyte transport in healthy human subjects.

Acute hypervolaemia increases gastroduodenal resistance to the flow of liquid in the rat

The effect of volume expansion of extracellular fluid on gastroduodenal resistance to the flow of isotonic saline was assessed in three groups of rats using intravenous infusions of isotonic, isotonic-isoncotic, and isotonic-isoncotic-isohaemic solutions. The gastroduodenal segment of 29 male Wistar rats was barostatically perfused at a constant pressure gradient of 4 cm H2O and changes in flow (ml/minute) were taken as a reflection of changes in gastroduodenal resistance. Isotonic expansion led to a 33% drop in gastroduodenal flow compared with the normovolaemic period in the same animals (p less than 0.01). Extracellular fluid expansion with isotonic-isoncotic and isotonic-isoncotic-isohaemic solutions was associated with reductions in gastroduodenal flow of 29% (p less than 0.05) and 31% (p less than 0.01) respectively. The increase in gastroduodenal resistance is due to hypervolaemia per se and not to haemodilution, decreases in plasma oncotic pressure, or electrolyte imbalance. The effect of hypervolaemia on gastroduodenal resistance, which was reversed by small haemorrhages (0.5-1.0 ml per 100 g body weight), may be due to changes in tonus or phasic motor activity, or both, and may be part of the homeostatic processes that help the organism minimise liquid volume excess.

Rat intestinal cell atrial natriuretic peptide receptor coupled to guanylate cyclase

The present studies were initiated to determine if cells of intestinal origin possess the molecular components supporting a response to atrial natriuretic peptides. Specific binding in cultured rat ileal cells with 125I-labeled atrial natriuretic peptide was saturable and of high affinity. Scatchard analyses showed a single population of binding sites with a Kd of 2.1 nmol/L and a Bmax of 300 fmol/mg protein. Atrial natriuretic peptide activated particulate guanylate cyclase 5- to 10-fold in a concentration- and time-dependent fashion. The EC50 for activation of enzyme by atrial natriuretic peptide was 6 nmol/L. Accumulation of cyclic guanosine monophosphate stimulated by atrial natriuretic peptide was observed in the intracellular (25-fold) and extracellular (50-fold) compartments and was dependent on concentration and time. Half-maximum intracellular accumulation was observed with 10 nmol/L atrial natriuretic peptide. These data suggest a role for atrial natriuretic peptides in the gastrointestinal tract.

Effects of atrial natriuretic peptide (ANP) on jejunal net fluid absorption in the rat

The role of atrial natriuretic peptide (ANP) on jejunal net fluid transport was studied in intact rats as well as in rats subjected to a perivascular denervation of the intestinal segment. In rats with intact nerves, an acute volume expansion with 5% albumin (10% of estimated blood volume) decreased jejunal net fluid absorption by approximately 70% compared to control animals not subjected to volume expansion. After a perivascular denervation of the intestinal segment, the acute volume expansion reversed net fluid absorption into a net fluid secretion. In order to reduce the volume expansion-induced endogenous release of ANP, one group of rats was subjected to a right atrial appendectomy 7 days prior to the experiments. In these animals, the intestinal response to the same 10% volume load was blunted compared to controls. Administration of rat alpha-ANP (99-126; 5 micrograms kg-1 i.v.) induced effects similar to those of volume expansion both in rats with intact perivascular nerves as well as in denervated animals. Volume expansion increased mean arterial pressure (MAP) as well as central venous pressure and decreased heart rate (HR) in all groups. When exogenous ANP was administered, a fall in MAP was seen, while HR remained unchanged. In conclusion, these data strongly indicate a physiological role for ANP in jejunal fluid transfer in response to acute volume expansion.

Intravenous atrial natriuretic peptide does not affect water and ion transport in the human small intestine

Atrial natriuretic peptide (ANP) increases renal sodium and water excretion in several species including man. In rats ANP was also found to influence water and electrolyte transport in the small intestine. In the present study we investigated whether ANP can alter transport in the jejunum and ileum of healthy volunteers using a triple-lumen perfusion technique. The small intestine was perfused under steady-state conditions with a plasma-like electrolyte solution using polyethylene glycol as a nonabsorbable volume marker. After an initial control period with intravenous saline infusion ANP was administered intravenously at a dose of 400 pmol kg-1 h-1. This dose led to a significant (P less than 0.05) increase in the plasma levels of ANP (up to 22-fold) and cGMP (up to 15-fold), and of urine volume. Intestinal water and electrolyte transport were, however, not affected by ANP. Our results suggest that circulating ANP does not play a role in the regulation of mucosal water and ion transport in the human small intestine.

Evidence for sympathetic regulation of the hydraulic conductance of rat jejunal mucosa in vivo

The aim of the study was to test the hypothesis that sympathetic nerve stimulation inhibits jejunal fluid secretion by decreasing the hydraulic conductance (Lp) of the mucosa. Jejunal segments of anaesthetized rats were mounted in a specially constructed chamber which makes it possible to measure net fluid transport together with transmural potential difference or short circuit current in vivo. Lp was estimated by measuring the effects on net fluid transport rate elicited by stepwise changes in luminal pressure. Lp was measured in four groups of animals: (1) under control conditions; (2) after hexamethonium administration, to block intramural secretory neurons; (3) during efferent stimulation of the mesenteric nerves, to activate sympathetic neurons, and (4) during mesenteric nerve stimulation (MNS) after pre-treatment with phentolamine, an alpha-adrenergic antagonist, to block the sympathetic effector mechanism. Lp measured at positive luminal pressures in control animals was approximately 4 microliters min-1 cmH2O-1 100 cm-2 serosal surface area. When measured at negative luminal pressures, this value increased approximately threefold. Hexamethonium did not significantly influence Lp. At positive luminal pressures, MNS decreased Lp to a value not significantly different from zero. This effect was abolished by phentolamine. At negative luminal pressures, MNS decreased Lp by approximately 50% and this effect was partly antagonized by phentolamine. The results suggest that a decrease in mucosal hydraulic conductance may contribute to the antisecretory effect of sympathetic nerve stimulation in vivo.

Hypoproteinemia-induced mucosal albumin leakage. Influence of luminal nutrients

Previous studies indicate that a peptide enteral formula significantly attenuates the intestinal water and albumin loss in volume-expanded rats with acute hypoproteinemia. The purpose of this study was to determine the relative abilities of the fat, carbohydrate, and protein components of the peptide enteral formula to stimulate water absorption and attenuate albumin turnover in intact jejunal segments during hypoproteinemia induced by intravenous infusion of Tyrode's solution (2.5 ml/min/kg) in Sprague-Dawley rats. Radio iodinated albumin movement from blood to lumen was used to estimate mucosal albumin clearance. Net transmucosal water was measured using a volume recovery method. When compared to luminal perfusion with Tyrode's solution (control animals), protein (as a protein hydrolysate) or protein combined with fat significantly enhanced fluid absorption (P less than 0.05) before and during volume expansion. This did not occur with carbohydrates or when carbohydrate was combined with the protein hydrolysate. However, the hypoproteinemia-induced increase in mucosal albumin clearance was significantly (P less than 0.05) attenuated by all solutions containing the carbohydrate component of the diet. These findings indicate that the protein component of the enteral formula is responsible for the enhanced net transmucosal water movement in hypoproteinemic animals. However, the carbohydrate component is largely responsible for the decrease in intestinal albumin clearance.

The role of albumin in nutritional support

Hypoalbuminemia is considered one of the hallmarks of protein-calorie malnutrition and chronic liver disease. Recently, serum albumin has also been proposed as a critical predictor of the response to nutritional support and tolerance to enteral feeding in critically ill patients. Albumin is essential for maintenance of plasma colloidal osmotic pressure, prevention of edema, and transport of certain drugs and nutrients. Experimental studies have shown that rapid plasma expansion and reduced plasma protein concentration and osmotic pressure induce a net secretion of sodium and water into the small intestinal lumen. However, the effects of chronic hypoalbuminemia per se on intestinal absorption, independent of malnutrition, have not been fully studied. It is documented that both chronic illness and malnutrition may profoundly affect intestinal anatomical structure and function, inducing some degree of malabsorption. In the last few years, some have advocated albumin infusion to improve clinical response to patients with hypoalbuminemia receiving parenteral nutritional support or to reduce intestinal intolerance and diarrhea in patients receiving enteral tube feeding. A review of the literature shows that both clinical and experimental data to support these suggestions are scarce and further investigations are needed. Hypoalbuminemia is one of many parameters of malnutrition, and it is unlikely that correction of a single parameter for a short time would lead to major clinical benefits.

Presence of atrial natriuretic peptide-like material in guinea pig intestine

Acidic extracts of guinea pig jejunum and colon contain atrial natriuretic peptide-like material (IR-ANP) detected by radioimmunoassay after purification by Sephadex G-50 gel filtration. Immunohistochemical analysis of guinea pig colon also revealed IR-ANP to be located directly beneath the lamina muscularis mucosae. High performance gel permeation chromatography (HP-GPC) and reverse phase high performance chromatography (RP-HPLC) of the IR-ANP showed correspondence to the 15 kD ANP precursor molecule (pro-ANP). No low molecular weight forms of ANP were detected. The extracted pro-ANP could be converted to alpha-ANP-like material by incubation with serum or supernatant of colonic homogenate. These data indicate the intestine to be a further site of ANP synthesis.

Influence of right atrial stretch and atrial natriuretic factor on rat intestinal fluid content

1. Studies were made on the effects of right atrial stretch and atrial natriuretic factor (ANF) infusion on fluid movement into the intestinal tract. 2. Stimulation of the atrial volume receptors by inflation of an intracardiac balloon in the conscious, unrestrained rat did not change intestinal fluid content under normovolaemic conditions. 3. When the rat was rendered hypovolaemic by peritoneal dialysis (34% deficit in extracellular fluid volume), right atrial stretch significantly increased intestinal fluid content. Under these conditions, inflation of the balloon restored large intestinal fluid content to the pre-dialysis state, i.e. right atrial stretch completely abolished that component of fluid absorption attributable to the extracellular fluid volume deficit. 4. These data suggest that stimulation of the right atrial receptors inhibits intestinal fluid reabsorption but probably does not initiate fluid secretion. 5. There was no evidence that this might be mediated by ANF since rat ANF (twenty-eight residue peptide, Ser-99-Tyr-126), infused for 1 h at doses of 0, 0.05, 0.1 and 0.5 microgram/min, did not cause any detectable changes in the fluid content of the large or small intestine of similarly prepared hypovolaemic rats.

Radioautographic localization of 125I-atrial natriuretic factor (ANF) in rat tissues

Rats were injected either with synthetic 125I-Arg 101-Tyr 126 atrial natriuretic factor (ANF) or with 125I-ANF together with an excess of cold Arg 101-Tyr 126 ANF. Binding sites in various tissues were accepted depending on two criteria: displacement of radioactivity by cold ANF and absence of localization of silver grains on putative target cells in the presence of cold ANF. Binding sites were localized on zona glomerulosa cells and on adrenergic and noradrenergic cells of adrenal medulla, on hepatocytes, on the base of mature epithelial cells of villi in the small intestine, on smooth muscle cells of the muscularis layer of the colon and on the base of epithelial cells of the ciliary bodies. In addition, binding sites were localized in the vasculature of kidney, adrenal cortex, lung and liver. Binding sites were particularly numerous on renal glomerular endothelial cells. These results indicate that ANF may have important hemodynamic effects in kidney, lung, liver and adrenal cortex, may regulate water and ion transport in small intestine and ciliary bodies and may have metabolic effects in the liver. The presence of binding sites on the zona glomerulosa is in agreement with the important inhibitory effect of the peptide on aldosterone secretion.

Inhibition of upper gastrointestinal secretions by reinfusion of succus entericus into the distal small bowel. A clinical study of 30 patients with peritonitis and temporary enterostomy

We prospectively studied peritonitis secondary to small bowel leakage in 30 critically ill patients, each of whom had complete diversion of intestinal continuity by stoma, fistula, or both. All patients received total parenteral nutrition during implementation of the protocol. The proximal intestinal effluent was collected and recycled into the distal small bowel. During reinfusion of succus entericus, a significant reduction in the output of the proximal stoma was observed (mean 30.2%, p less than 0.001). The reinfusion also significantly reduced the volume from isolated small bowel loops in six patients (32.6%, p less than 0.001). When isotonic dialysate solution was infused into the distal intestine, a lesser though significant reduction in stoma output occurred (mean 20.3%, p less than 0.001). These findings demonstrate a consistent inhibitory effect upon upper gastrointestinal secretions by reinfusion of succus entericus. Clinical benefits of this technique include simplified control of fluid and electrolyte balance in patients with high output stomas and optimal utilization of remaining absorptive capacity for enteral nutrition.

Ethacrynic acid facilitates gentamicin entry into endolymph of the rat

Influence of ethacrynic acid (EA) upon gentamicin kinetics in perilymph and endolymph was studied in rats that were given a constant-infusion of gentamicin (150 micrograms/min) and EA (140 micrograms/min). Inner ear fluids and plasma were sampled up to 5 h. The purity of the endolymph was ensured by measurement of sodium and potassium concentrations. Gentamicin assay was done with a modified radioimmunoassay. Results show that EA facilitates the entry of gentamicin into endolymph, while it does not affect the kinetics of the drug in perilymph. Although the mechanism of this facilitation remains unclear, this result may account for the ototoxic potentiation reported between EA and aminoglycoside antibiotics.

Appearance of 14C-polyethylene glycol 4000 in intestinal venous blood: influence of osmolarity and laxatives, effect on net water flux determination

In anaesthetized rats the appearance rate of 14C-polyethylene glycol 4000 (14C-PEG 4000) was measured in the intestinal venous blood after intraluminal administration into a jejunal, ileal, and colonic segment. The absorption rate was small, especially in the colon (0.5-4.2% within 60 min in an intestinal segment of about 300 mg wet tissue weight depending on the batch of 14C-PEG 4000). The absorbed PEG in the plasma consisted mainly of molecules with lower molecular weight than 4000 which were included in the commercial batches of 14C-PEG 4000. The appearance rate of 14C-PEG decreased with time after single dose but remained constant, when a 14C-PEG solution was perfused continuously through the intestinal lumen. A hypotonic solution increased and a hypertonic one decreased slightly the absorption of PEG in the jejunum and ileum but not in the colon. The influence of bisacodyl (100 mgl(-1)) and ricinoleate (10 mmol l(-1)) on the absorption of PEG was small or absent, while deoxycholate (5 mmol 1(-1)) raised the absorption rate considerably, predominantly of the high molecular weight fraction. If in intestinal absorption studies a batch of commercial 14C-PEG 4000 with a small low molecular weight fraction is used, the error in the determination of net water flux caused by the absorption of PEG can be neglected. The influence of osmolarity and laxatives is insignificant. Bile acids increase the intestinal permeability of PEG 4000, so that the net water flux determination can be biased considerably.

Techniques and applications of extracellular space determination in mammalian tissues

This review summarizes the ways in which the extracellular space (ECS) may be estimated in mammalian tissues, and briefly describes some of the uses to which the EC confinement of certain molecules (markers or tracers) may be put in the elucidation of physiological functions. The introductory section is followed by a description of the more commonly used marker molecules and their functional characteristics, and of factors likely to lead to the spurious over- or under-estimation of the ECS. Certain alternative methods are also described, in particular those based on morphological and electrical criteria which seek to demonstrate small, functionally important, changes in the size of specialized regions of the ECS (e.g. lateral cellular interspaces) without necessarily being required to provide a quantitatively precise estimate of their size. Section III describes the results of measurements of ECS in various mammalian tissues (muscle, gastro-intestinal tract, nervous tissue, crystalline lens, placenta, lung and kidney) and some applications of EC markers to investigation of cellular function (e.g. uptake of metabolic substrates and epithelial transport) and, in outline, characterization of capillary permeability. The available literature in this field is very extensive, and in the interests of brevity the reader is, where appropriate, referred to previous reviews covering specialized aspects of ECS determination and related topics.

Mechanism of glomerulotubular balance in the setting of heterogeneous glomerular injury. Preservation of a close functional linkage between individual nephrons and surrounding microvasculature

Autologous immune complex nephropathy (AICN), an experimental model for human membranous glomerulopathy, is characterized by marked heterogeneity in function from glomerulus to glomerulus. However, the fraction of the filtered load of fluid reabsorbed by the proximal tubule remains nearly constant from nephron to nephron, despite wide variation in single nephron glomerular filtration rate (SNGFR). To define the physiological mechanisms responsible for this marked variation in SNGFR values within a given kidney and for the remarkable preservation of glomerulotubular balance, the various determinants of fluid exchange across glomerular and peritubular capillary networks were evaluated in Munich-Wistar rats with AICN. For comparison, similar measurements were obtained in rats with the functionally more homogeneous lesion of heterologous immune complex nephropathy. In AICN rats studied approximately 5 mo after injection of renal tubule epithelial antigen (Fx1A), a high degree of glomerulus-proximal tubule balance was found, despite marked variations in SNGFR values within a single kidney. These changes were associated with marked heterogeneity in immunoglobulin and complement deposition within and among glomeruli. Although mean capillary hydraulic pressure and Bowman's space hydraulic pressure ranged widely from glomerulus to glomerulus, the mean glomerular transcapillary hydraulic pressure difference was remarkably uniform among these functionally diverse glomeruli and could not, therefore, be implicated as the cause of the dispersion in SNGFR values. The two remaining determinants of SNGFR, namely, glomerular plasma flow rate (Q(A)) and ultrafiltration coefficient (K(f)), varied markedly from glomerulus to glomerulus, but always in direct proportion to SNGFR, and proved to be responsible for the marked variation in SNGFR. The mean net peritubular capillary reabsorptive force ( P(r)) correlated closely with the absolute rate of fluid reabsorption in adjacent proximal tubules (APR) in AICN. Of the factors determining P(r), peritubular capillary hydraulic pressure was essentially constant in a given AICN kidney, whereas peritubular capillary plasma protein concentration and oncotic pressure varied directly with APR and largely accounted for the observed tight correlation between P(r) and APR. ON THE BASIS OF THESE OBSERVED CORRELATIONS, WE SUGGEST THAT THE CLOSE QUANTITATIVE COUPLING BETWEEN SNGFR AND APR IN INDIVIDUAL NEPHRONS IN AICN IS DUE TO THE FUNCTIONAL RESPONSE OF INDIVIDUAL GLOMERULI: those with the most pronounced declines in SNGFR are characterized by the most pronounced declines in Q(A) and K(f). The resultant low peritubular capillary oncotic pressure favors a decline in APR, thus favoring nearly perfect glomerulotubular balance. In glomeruli with higher SNGFR values, Q(A) and K(f) values are also higher. These changes in K(f) once again are capable of establishing the conditions in downstream peritubular capillaries, this time favoring augmented APR (i.e., high intracapillary oncotic pressure), again leading to nearly perfect glomerulotubular balance.

Influence of peritubular protein on solute absorption in the rabbit proximal tubule. A specific effect on NaCl transport

The effect of removal of peritubular protein on the reabsorption of various solutes and water was examined in isolated rabbit proximal convoluted tubules (PCT) perfused in vitro. In 22 PCT perfused with ultrafiltrate (UF) and bathed in serum, volume absorption (Jv) was 1.44 nl/mm per min and potential difference (PD) was -3.6 mV. When these same PCT were bathed in a protein-free UF, Jv was reduced 38% without a change in PD. Simultaneous measurements of total CO2 net flux (JTCO2) and glucose efflux (JG) showed that less than 2% of the decrease in JV could be accounted for by a reduction in JTCO2 and JG, suggesting that removal of peritubular protein inhibited sodium chloride transport (JNaCl). Therefore, in eight additional PCT, JNaCl was measured, in addition to PD, Jv, JG, and JTCO2. In these PCT, the decrease in total solute transport induced by removal of bath protein was 201.7 +/- 37.5 posmol/mm per min. JG decreased slightly (9.1 +/- 3.9 posmol/mm per min); NaHCO3 transport did not change (9.2 +/- 6.6 posmol/mm per min); but JNaCl decreased markedly (160.6 +/- 35.7 posmol/mm per min). 80% of the decrease in Jv could be accounted for by a decrease in JNaCl. In 13 additional PCT perfused with simple NaCl solutions, a comparable decrease in Jv and JNaCl was observed when peritubular protein was removed without an increase in TCO2 backleak. In summary, removal of peritubular protein reduced Jv and JNacl, but did not significantly alter PD, JG, JTCO2, or TCO2 backleak. The failure to inhibit JG and JTCO2, known sodium-coupled transport processes, indicates that protein removal does not primarily affect the Na-K ATPase pump system. Furthermore, since PD and TCO2 backleak were not influenced, it is unlikely that protein removal increased the permeability of the paracellular pathway. We conclude that protein removal specifically inhibits active transcellular or passive paracellular NaCl transport.

Water and electrolyte movement and mucosal morphology in the jejunum of patients with portal hypertension

Intestinal secretion and intercullular space dilatation can be induced in animal models by acute elevation of intravascular volume or portal pressure. We examined whether patients with increased portal venous pressure might represent a clinical counterpart to these animal models. Portal venous pressure, determined by hepatic wedge pressure measurement, was elevated to 10-55 mmHg (mean 29 mmHg) in 8 patients with chronic liver disease without diarrhea. Intestinal transport studies utilizing a steady-state perfusion technique revealed normal absorption of a plasmalike electrolyte solution. A solution dsigned to unmask intestinal secretion demonstrated no difference from control subjects in the movement of water, electrolytes, or protein into the intestional lumen. There was no correlation of absorption of secretion with hepatic wedge pressure. Jejunal biopsy revealed a significant increase in dilatation of intercellular spaces in patients compared to controls; this increase was not correlated with hepatic wedge pressure, but was significantly inversely correlated to plasma renin and aldosterone concentration. We conclude that patients with chronic liver disease and portal hypertension absorb water and electrolytes normally, but have mild morphologic alterations in the intestinal mucosa, possibly related to intravascular volume status.

Intestinal filtration as a consequence of increased mucosal hydraulic permeability. A new concept for laxative action

Two mechanisms have been proposed to explain the secretory action of laxative compounds in the intestine: 1. increase of the intracellular amount of cyclic adenosine monophosphate due to stimulation of the adenylate cyclase system and 2. inhibition of intestinal transfer processes, in particular the Na,K-ATPase activated sodium absorption. In a set of in vivo and in vitro experiments in rat colon it could be demonstrated that dihydroxy bile acids (deoxycholate) and diphenolic laxatives (oxyphenisatin) enhance the hydraulic permeability of the mucosal tissue. The permeability changes take place--and there is good experimental evidence--at the zonulae occludentes which bind the epithelial cells together at their luminal borders. Due to laxative action the hydraulic permeability of the colonic mucosa increases to such an extent that according to the Starling forces the normal subepithelial hydrostatic pressure is a sufficient driving force to reverse net sodium, chloride, and water absorption into net secretion. A new concept of "intestinal filtration as a consequence of increased mucosal hydraulic permeability" is proposed to explain the laxative action of deoxycholate and oxyphenisatin in the colon. The question whether inhibition of Na,K-ATPase activity, cyclic AMP-mediated secretion or increased hydraulic permeability of the colonic mucosa are causatively linked to and quantitatively meaningful in intestinal secretion remains open.

Volume flows across gallbladder epithelium induced by small hydrostatic and osmotic gradients

The hydraulic conductivity of rabbit gallbladder epithelium has been studied using a continuous volumetric method based on capacitance measurements. The time resolution for measuring osmotic flows is in the range of seconds. Volume flows have been induced by osmotic gradients between 0 and 100 mosmol. In this range the flow-force relation is linear and the Pf value is 9.3 X 10(-3) cm/sec. After correction for solute polarization effects, the Pf value amounts to 0.05 cm/sec. The observed flow is constant between 5 sec up to 20 min after a sudden increase in the osmolarity of the mucosal solution. The wet weight of the gallbladder tissue decreases by 22% and increases by 30% during osmotic flows from mucosa to serosa, respectively. Volume flows induced by hydrostatic pressure gradients on the mucosal surface are linearly related to the driving forces between 0 and 40 mbar. The Pf value is 0.15 cm/sec. The volume flows are constant between 2 sec and 15 min after pressure application. The flow-force relation for pressure gradients on the serosal surface is markedly nonlinear for gradients greater than 5 mbar. Below 5 mbar the Pf value is 4.5 cm/sec. From electrical measurements, e.g., resistance and streaming potentials, and from flux studies with inulin and polyethylene glycol 4000, it is concluded that hydrostatic and osmotic gradients are not comparable when they are applied to gallbladder epithelium. They induce volume flows across different pathways, e.g., osmosis predominantly across the cellular route and pressure filtration predominantly across paracellular routes.

A mathematical model of proximal tubule absorption

A previous model of the mechanisms of flow through epithelia was modified and extended to include hydrostatic and osmotic pressures in the cells and in the peritubular capillaries. The differential equations for flow and concentration in each region of the proximal tubule were derived. The equations were solved numerically by a finite difference method. The principal conclusions are: (i) Cell NaCl concentration remains essentially isotonic over the pressure variations considered; (ii) channel NaCl concentration varies only a few mosmol from isotonicity, and the hydrostatic and osmotic pressure differences across the cell wall are of the same order of magnitude; (iii) both reabsorbate osmolality and pressure-induced flow are relatively insensitive to the geometry of the system; (iv) a strong equilibrating mechanism exists in the sensitivity of the reabsorbate osmolality to luminal osmolality; this mechanism is far more significant than any other parameter change.

Anomalous calcium secretion in rat ileum: role of paracellular pathway

The mechanism of apparent calcium secretion by unstripped rat ileum in vitro has been investigated using mannitol and polyethylene glycol (mol wt 900) as markers for extracellular transepithelial flux. In the absence of electrochemical gradients between the mucosal and serosal bathing media in a modified Ussing chamber, net fluxes of both mannitol and polyethylene glycol were observed from serosa to mucosa in the presence of 11 mM D-glucose. Mucosal-to-serosal calcium flux reveals a significant cellular component, but serosal-to-mucosal calcium permeability is a linear function of mannitol permeability, suggesting an exclusively extracellular route. For the mucosal-to-serosal fluxes, inhibition of calcium flux by 1 mM N-ethylmaleimide results in a calcium-to-mannitol permeability ratio indistinguishable from that measured for serosal-to-mucosal flux. This evidence suggests that the apparent calcium secretion observed at 10 mM medium calcium is not the result of a cellular secretory mechanism. It is proposed that a hydrostatic driving force generated internal to the tissue but external to the cells results in net calcium secretion at calcium conentrations that saturate the cellular absorptive mechanism.

Paracellular permeability of extracellular space markers across rat jejunum in vitro. Indication of a transepithelial fluid circuit

1. The characteristics of [51Cr]EDTA, [3H]methoxyinulin ([3H]MI), [14C]polyethylene glycol-4000 ([14C]PEG), and [3H]mannitol as markers of the extracellular space (e.c.s.) of isolated mucosa from the rat small intestine have been examined. 2. Unidirectional transmural fluxes across the rat jejunum of [3H]MI, [14C]PEG and [3H]mannitol have been measured in the absence of glucose or in the presence of 28 mM glucose. 3. Assuming that [14C]PEG does not enter the cells, [51Cr]EDTA and [3H]mannitol seem to have access to approximately 50 and 90% of the intracellular water respectively. 4. The commercially availabel [3H]MI had access to a space which exceeded th [14C]PEG space by 10%. Upon purification by gel filtration the high molecular weight fraction of the [3H]MI provided estimates of the e.c.s. identical with the estimates obtained with [14C]PEG. 5. For all the markers used the e.c.s. estimates remained constant between the 40th and 80th min of incubation. 6. In the absence of glucose the transepithelial net fluxes of each of the different markers were zero. In the presence of 28 mM glucose the serosato-mucosa fluxes of all markers were dramatically increased. The ratio between the serosa-to-mucosa and the mucosa-to-serosa fluxes increased in the order [3H]mannitol greater than [3H]MI greater than [14C]PEG. 7. The effect of glucose on the flux ratio of the marker substances suggests that glucose-induced net water transport to the serosa side of the gut wall represents the difference between a transcellular net water transport to the serosal side and a significant paracellular net water transport through the lateral intercellular spaces to the mucosal solution.

Symposium on diarrhea. 1. Definition and mechanisms of diarrhea

Diarrhea, an increase in frequency of evacuation and in water content of the stool, is the result of three categories of mechanism--solute malabsorption, secretion of fluid and motility disturbance. Before diarrhea is considered an abnormal condition, any alteration in stool frequency and content must be related to an individual person's normal bowel habit and to norms for the population, but more than three bowel movements or the passage of liquid stools exceeding 300 g daily should, in general, be considered abnormal. A useful way of understanding the mechanism of diarrhea is to become familiar with the normal functions of the bowel in regard to water and electrolyte absorption and motility, and then to relate these functions to solute malabsorption, fluid secretion and motility disturbance.

Influence of hydrostatic pressure gradients on net transfer of sodium and water across isolated rat colonic mucosa

1. The dependence of net transfer of water and sodium on hydrostatic pressure gradients from the serosal to the mucosal side was investigated in everted sacs of the stripped mucosa of the rat colon. 2. In the range of 3-20 cm H2O both, net sodium and water transfer were linearly dependent on hydrostatic pressure. The hydraulic permeability coefficient was 1.1 ml per gram dry weight, hour and cm H2O. At a pressure gradient of 5.8 cm H2O the net movement of water from the mucosal to the serosal side ceased. Above this pressure a net movement in the opposite direction occurs. Sodium net movement from the mucosal to the serosal side ceased at 11 cm H2O. The fluid, which appears-driven by higher values of hydrostatic pressure-on the mucosal side, is hypotonic. 3. Oxyphenisation increases the hydraulic permeability of the colonic epithelium. The fluid, which appears--driven by the hydrostatic pressure gradient--on the mucosal side, is isotonic.

Interactions of intestinal lymph flow and secretion

The relationship between lymph flow and intestinal secretion was studied in an isolated, vascularly perfused cat ileal preparation in which secretion was caused by three different means: 1) plasma dilution from a constant infusion of Tyrode solution (2.5 ml/min per kg), 2) elevation of intestinal venous pressure to 30 mmHg, and 3) exposure to cholera toxin. In the plasma-dilution group, lymph flow attained a peak value of 38 times control at 60-90 min following the onset of the infusion, after which time lymph flow progressively decreased. Concomitant to the rapid decrease in lymph flow was a rapid increase in intestinal secretion (filtration secretion). A similar pattern, i.e., a rapid increase in lymph flow followed by a progressive decrease in lymph flow and concomitant increase in filtration secretion, was observed in the venous hypertension group; however, peak lymph flow (20 X control) was observed within 10 min of the pertubation. No correlation between the onset of intestinal secretion and a decline in lymph flow was observed in the cholera toxin group.

Effect of parathyroid hormone and volume expansion on jejunal calcium, sodium, and water transport in the rat

The effects of PTH on jejunal calcium, sodium, and water transport were studied in the rat in situ. In TPTx rats, as well as in normal rats, bovine PTH induced a decrease in net calcium, sodium, and water absorption. Additionally, lumen-to-plasma calcium flux was found decreased in both groups. Stimulation of endogenous PTH secretion by calcium-poor hyperoncotic albumin resulted in a similar decrease in net calcium, sodium, and water absorption. It is suggested that PTH has a direct inhibitory effect on jejunal calcium, sodium, and water absorption.

Effects of saline loading on jejunal absorption of calcium, sodium, and water, and on parathyroid hormone secretion in the rat

To investigate whether intestinal calcium absorption parallels that of sodium following extra-cellular fluid volume expansion, the effects of saline loading on intestinal transport of calcium, sodium and water were studied in rats by perfusing jejunal loops in situ. After calcium-free saline infusion net calcium absorption was reversed similar to that of sodium and water and net secretion occurred. Concurrently, blood-to-lumen (b-l) calcium flux, measured using 45Ca, increased significantly (P less than 0.001). Following expansion with calcium-containing Ringer a similar reversal of net calcium, sodium and water flux was also observed. Again the b-l calicum flux increased but to a significantly lesser extent (P less than 0.05). Plasma ionized calcium remained unchanged after calcium-rich Ringer loading, but decreased significantly (P less than 0.001) when calcium was omitted from the solution. Plasma immunoreactive parathyroid hormone unchanged after expansion with the calcium containing solution but increased following calcum-free infusion. It is concluded that after extracellular fluid volume expansion: 1. net jejunal calcium absorption is decreased; 2. the decrease parallels that of sodium and water; 3. b-l calcium transport is enhanced to a greater degree of calcium-free Rnger infusion than by a calcium-rich solution. This difference could be the result of increased parathyroid hormone secretion.

Bidirectional sodium ion movements via the paracellular and transcellular routes across short-circuited rabbit ileum

1. It has been confirmed that the agent 2,3,6-triaminopyrimidine decreases Na+ conductance in the paracellular pathway of rabbit ileum. 2. Triaminopyrimidine has been used as a means of measuring transcellular bidirectional Na+ flux, and also, of assessing the contribution of the paracellular pathway to transepithlial Na+ flux. 3. Reduction of Ringer [Na+] to 25 mM or incubation with 0.1 mM ouabain reduces paracellular Na+ permeability. This effect may be due to lateral space collapse. Ringer galactose increases serosa to mucosa Na+ flux by a stimulating reflux through the tight junctions. A proportion of net Na+ flux in control tissues is due to asymmetry generated in the paracellular pathway. It is likely that this passive asymmetry results from an osmotic pressure gradient across the tight-junction. 4. Measurement of the tissue isotope specific activity ratio together with bidirectional transcellular Na+ fluxes allows calculation of the four unidirectional fluxes across the mucosal and serosal boundaries. Values obtained for Na+ entry (J12) and exit (J21) across the mucosal boundary are 7.97 alnd 7.13 mumol-cm(-2)-h(-1) respectively. Entry flux (J12) is a saturable function of Ringer [Na+]. The calculated Km is 295 mM and the V is 17.6 mumul-cm(-2)-h(-1). Na+ entry flux is insensitive to ouabain (0.1 mM). Ouabain results in elevation of exit (J21) flux of Na+ across the brush border. D-Galactose causes a saturable increase in Na+ flux (J12) across the mucosal boundary; the Km for this relationship is 1.2 mM and the V 2.17 mumol-cm(-2)-h(-1). The stoichiometry between sugar and Na+ entry is applixmately 1:1. In contrast to the effect of galactose on entry flux, no change in Na+ efflux across the mucosal boundary is observed when Ringer [galactose] is raised. This finding is dissonant with the prediction of the Na+ -gradient hypothesis. The calculated values of exit (J23) and entry (J32) Na+ fluxes across the serosal border are 16.74 and 15.90 mumol-cm(-2)-h(-1). 0.1 mM ouabain markedly reduces both these unidirectional fluxes. This result is consistent with a serosal location of the Na+-pump. Serosal Na+ exit flux J23 increases as a hyperbolic function of Ringer [galactose]. A small galactose-dependent decrease in entry (J32) is also observed. 0.1 mM ouabain abolishes these galactose-dependent changes. 5. The present findings together with those in the previous paper are discussed in relation to the convective-diffusion model for sugar transport.

Renal control of intestinal sodium and water transport in the dog

The influence of an intravenous infusion of saline on the absorption of water and sodium by the jejunum has been investigated in dogs previously submitted to sodium-rich or poor diets. While the net intestinal transport was reduced in sodium-loaded animals, no response was observed in the sodium-deprived dogs, despite identical changes in arterial pressure, intravascular volume and blood dilution indexes. The intestinal response of sodium-deprived dogs became positive after transplanting to their neck vessels the kidneys removed from sodium-loaded animals, thus demonstrating that the presence in the blood of a humoral message of renal origin is required to permit the inhibition of net transport. The difference of the responses depended on the variations of the mucosa-to-serosa unidirectional flux. The net potassium transport did not change significantly. The experimental conditions made unlikely an interference of mineralocorticosteroids, angiotensin or antidiuretic hormone. The present results suggest that the kidney might modulate sodium transport in the jejunum, and perhaps elsewhere in the body, by the way of an additional endocrine function.