Sodium Absorption Rate Research Articles

Effect of Secretin and Caerulein on the Absorption of Water, Electrolytes and Glucose from the Jejunum of Dogs

The effects of secretin and caerulein on the absorption of water, sodium, potassium and glucose from the jejunum of dogs were investigated. Intravenous infusion of 1 clinical unit (CU; 82 pmol/kg/h) of secretin inhibited jejunal absorption of water, sodium and glucose compared to control period. Adding an intravenous infusion of 0.4 micrograms (300 pmol)/kg/h of caerulein to the infusion of secretin, the jejunal absorption rates of water, sodium and glucose were restored to control values. Intravenous infusions of 0.2 and 0.4 micrograms/kg/h of caerulein induced no significant difference in the absorption compared to control. Thus it seems that secretin inhibits the absorption of water, sodium and glucose from the jejunum of dogs and caerulein, added to secretin, reverses the effect of secretin.

Aldosterone Metabolism and Transepithelial Potential Difference in Normal and Cystic Fibrosis Subjects

The transepithelial potential difference (PD) is raised across cystic fibrosis (CF) respiratory epithelia. This raised voltage reflects active sodium absorption across a relatively chloride impermeable membrane. Because relatively little is known about the regulation of the rate of sodium absorption across mammalian airways, we assessed the possible contribution of aldosterone to the PD in normal and CF respiratory epithelia. Aldosterone excretion in five CF patients was 12.2 +/- 0.9 micrograms/24 h, a mean value not different from normal control subjects (13.6 +/- 1.5 micrograms/24 h, n = 5). Despite similar aldosterone excretion rates, nasal PD was more than 2-fold greater in the CF patients (-53.6 +/- 6.4 mV) than normal subjects (-21.3 +/- 1.4 mV). The effect of an aldosterone antagonist, spironolactone, on aldosterone excretion and nasal and rectal PD was evaluated in four CF patients and five normal subjects. During spironolactone administration, aldosterone excretion increased (2- to 4-fold) and rectal PD decreased in both groups. However, nasal PD was unchanged in each group (CF = -52.1 +/- 4.3 mV pre, -53.6 +/- 1.4 mV during; normal = -21.2 +/- 3.1 mV pre, -21.6 +/- 3.2 mV during). We conclude that neither increased aldosterone secretion rates nor organ sensitivity to aldosterone can account for the abnormally raised PD that characterizes the respiratory epithelium of subjects with CF.

Oral hydration solutions: Experimental optimization of water and sodium absorption

Eight solutions of potential efficacy for hydration orally, which differed in composition, osmolality, and pH, were tested in an in vivo perfusion system on rat jejunum to assess the rate of water and sodium absorption or secretion. Optimal results were obtained with a preparation of the type recommended by the World Health Organization, containing 60 mEq/L sodium and 111 mM glucose; there was a maximum influx of both water and sodium, which may be ideal for rehydration. It appeared that the critical factor was the molar relationship between glucose and sodium at a 2:1 ratio. Sodium absorption was inversely correlated with glucose concentration in the perfusates. Osmolality and pH may also have a role in the regulation of fluxes across the mucosa. Citrate at concentrations up to 30 mEq/L did not interfere with water absorption. The data presented may thus contribute to a better rationale for the use of orally administered hydration solutions and guidelines for the preparation of more effective ready-to-use solutions.

JEJUNAL MUCOSAL FUNCTION DURING INFUSION OF Na-DEOXYCHOLATE (DC) INTO THE MESENTERIC ARTERY IN SITU IN DOGS

Studying 16 children (9 mos. to 3 yrs.), with protracted diarrhea and malnutrition, we found that unconjugated bile salts (UBS), were not clearly elevated in the jejunal luminal contents, whereas UBS in their serum was high (DC 14.7±8.3 uM), and not detectable in sera of healthy controls. We, therefore, studied the effects of DC in the circulation on the jejunal mucosal handling of water, sodium, glucose, and glycine. We perfused in situ the lumen of a 30 cm segment of proximal jejunum in dogs, using phenol red as a non-absorbable marker. The supplying mesenteric arterial branch was infused with DC solutions in normal saline, calculated to reach tissue level at successive concentrations of 0, 7.5, 15, 30, and 60 uM. For each concentration of DC infused a 30-minute equilibration period was allowed and, thereafter, four 15-minute aliquots of effluent perfusate were collected. Results: The addition of DC to the arterial supply of the jejunal segment was associated with a significant decrease in the absorption rates of water, sodium, glucose, and glycine; the magnitude of this effect correlated with the concentrations of DC employed. Mucosal activity of Na+ -K+ -ATPase was practically abolished by infusion of DC at 30 uM. No structural abnormalities of the mucosa were seen on light microscopy. Our experiments indicate that UBS (e.g. DC), in the circulation are detrimental to small intestinal mucosal function, and may, thus, contribute to the perpetuation of diarrheal disease.

Sodium absorption with bacterial fatty acids and bile salts in the proximal and distal colon as a guide to colonic resection.

Rates of sodium absorption in the presence of bacterial fatty acids and bile salts are unknown along the length of the colon. Such information may guide resection of colon with a view to leaving colon most optimal for ion absorption. Absorption of sodium and permeability of the colonic mucosa to 51Cr EDTA was measured in the proximal (PC) and distal colon (DC) instilled with NaCl (120 mM), n-butyrate (40 mM) and chenodeoxycholic acid (1 or 2 mM) in varying combinations. Sodium absorption in the PC was 123.6 +/- 19 (nmoles/min/cm2)(n = 7) with saline alone and was doubled (P less than .001) when 40 mM n-butyrate replaced chloride anions. Sodium absorption in the DC with saline alone was 106.9 +/- 18 without significant alteration by addition of n-butyrate. CDC (1 mM) diminished sodium absorption in the PC and DC. Diminished sodium absorption induced by bile salts was significantly reversed by n-butyrate in the PC but not DC. Permeability of 51Cr EDTA was greatest with 2 mM CDC in the distal colon. Mucosal function--sodium absorption with SCFAs, permeability changes, and protection by bacterial fatty acids from sodium losses due to bile salts--was superior in the PC compared with DC. Our results suggest that it may be preferable to preserve the proximal rather than distal colon in operations of the colon to secure optimal absorption of sodium.

A comparative study of electrolyte absorption from the caecum and colon of Oryctolagus cuniculus—II. Sodium and potassium

1. 1. The movements of sodium and potassium across the wall of large intestine in anaesthetized rabbits have been studied. 2. 2. At colonic level the relationship between the sodium absorption rate and its intraluminal concentration depends on the initial conditions. 3. 3. In caecum or colon, sodium absorption occurs from intraluminal levels lower than the plasma ones. 4. 4. At colonic level, potassium is secreted for concentrations similar to the plasma ones.

Anion effects on fluid absorption from rat jejunum perfused in vivo.

Perfusion of rat jejunal segments in vivo with an isotonic, HCO3-free SO4-Ringer solution resulted in low rates of net sodium (JNanet) and water absorption. When the perfusion fluid was changed to one containing 25 mM Na2SO3, JNanet increased from 4.7 +/- 1.2 to 11.6 +/- 1.5 (SE) mumol X cm-1 X h-1 (P less than 0.001). This increased absorption was accompanied by comparable increases in chloride and water absorption, occurred without a detectable change in potential difference across the perfused segment, and was readily reversed on reinstitution of perfusion with SO4-Ringer. Perfusion with SO3-Ringer had no effect on electrolyte absorption from terminal segments of rat ileum. Addition of L-phenylalanine stimulated absorption from SO4-Ringer perfusate but not from SO3-Ringer perfusate. Addition of 25 mM NaHCO3 to SO4-Ringer perfusate caused parallel increases in JNanet and JHCO3net; when 25 mM NaHCO3 was added to SO4-Ringer perfusate that also contained 25 mM NaSCN, the same increase in JHCO3net occurred but was not associated with any increase in JNanet. These results indicate a potent effect of SO2-3 and HCO-3 to stimulate JNanet from rat jejunum but not from ileum. These anion effects on intestinal transport in vivo resemble their effects on ATPase activity of brush-border fractions from small intestine in vitro and raise the possibility that these effects on ion transport could be mediated through the changes in brush-border ATPase activity, which are brought about by exposure to these anions, although other explanations are also possible.

Water and NaCl absorption by the intestine of the tilapiaSarotherodon mossambicus adapted to fresh water or seawater and the possible role of prolactin and cortisol

Rates of intestinal water, sodium and chloride absorption in tilapia, adapted to fresh water (FW) and seawater (SW), were measured in vitro, using noneverted sacs made from the anterior, middle and posterior intestinal regions. The anterior intestine from SW fish showed considerably less water, sodium and chloride absorption compared with that seen in FW fish. The middle intestine showed either minimal absorption or some secretion in both FW and SW. In the posterior intestine, water absorption was only limitedly affected by SW-adaptation, but sodium and chloride absorption rates were significantly lower in SW fish. Reductions in water absorption were already evident in the anterior intestine 24 h after transfer to 1/3 SW but reached lower levels 3 to 5 days following transfer to 100% SW. Thus, the anterior intestine of tilapia responds to increased environmental salinity by decreasing uptake of ions, whereas the posterior intestine maintains similar water absorption in both FW and SW, although ion absorption is lower in SW.

Effects of varying mucosal medium on electrical parameters of the isolated lower intestine (Coprodeum) of the hen

1. 1. Isolated epithelium of hen coprodeum was subjected to mucosal solutions with hyperosmotic potassium-ammonium-phosphate concentrations similar to the composition of ureteral urine of dehydrated birds. 2. 2. Only small effects of these physiological challenges were encountered on net sodium absorption rate (short-circuit current) or epithelial resistance. 3. 3. The coprodeum is thus very resistant to the urine stored in the organ.

Maximal capacity for fluid absorption in human bowel.

The intestinal handling of fluid has been studied in ten healthy volunteers while an isotonic saline solution (NaCl 140 mM, KC1 5 mM) was perfused into the stomach at rates of 5, 10, 15, and 20 ml/min. Polyethylene glycol 4000 (PEG-4000), as a nonabsorbable marker, was infused into the second portion of duodenum, and the intestinal contents were sampled continuously at a steady rate at 25, 50, 155, and 180 cm distally. Radiological assessment showed that the proximal sampling point was located at the angle of Treitz when the distal site was usually in the terminal ileum. Stools were collected for the following 12 hr. Volumes sampled from each site were used as a correction for volumes calculated at each distal site. The absorption rates of water (0.035 ml), sodium (4.72 muEq), and potassium ((0.18 183 muEq) per minute and per centimeter of bowel were constant along the small intestine and were independent of the perfusion rate. Stools only appeared when terminal ileal input to the colon was above 6 ml/min. When this occurred, the net absorption of water by the colon was 2.7 +/- 0.3 ml/min whatever the rate fluid entered the colon. A significant positive correlation was observed between ileal outputs and volume of stools.

Prolactin effects on ion transport across cultured mouse mammary epithelium.

Prolactin is a known osmoregulatory hormone in lower vertebrates, and recent evidence indicates that this hormone modulates ionic concentrations in milk. In an ultrastructurally and biochemically differentiated primary cell culture system in which mouse mammary epithelium is maintained on floating collagen gels, prolactin causes an increase in short-circuit current (Isc) of monolayers of cells derived from midpregnant (24.6 to 48.0 microA . cm-2) and lactating (10.4 to 16.1 microA . cm-2) glands. Transepithelial potential differences (basal side ground) average about -12 mV and are similar to those seen in vivo. Prelactating mammary epithelial cell cultures have transepithelial resistances ranging from 374 omega . cm2 (prolactin present) to 507 omega . cm2 (prolactin absent), and lactating cell cultures have resistances averaging almost 1,000 omega . cm2. Prolactin effects require at most one day of culture maintenance in prolactin-containing medium, and the effects are not due to known contamination of prolactin preparations with arginine vasopressin or growth hormone. Medium concentrations of prolactin as low as 1 ng/ml can elicit these effects. In prelactating cell cultures not treated with prolactin, the Isc is equal to the rate of sodium absorption. Prolactin increases sodium absorption fourfold but increases Isc only twofold. Clearly, prolactin induces other active transport; neither potassium nor chloride movements can account for this additional transport. Resistance values, current-voltage plots, and permeability coefficients indicate that in vitro mammary epithelium is a moderately "tight" tissue. Comparisons with intact glands indicate that in vitro mammary epithelium closely resembles its in vivo counterpart. Floating collagen gel cultures appear suitable for elucidating transport properties in cellularly heterogeneous and structurally complex mammalian tissues.

Reduction of lead toxicity on the kidney and the small intestinal mucosa by kaolin and pectin in the diet

The possibility that chemically inert intestinal adsorbents, such as koalin and pectin, may reduce the toxic effects of oral lead poisoning on growth, renal function, and active transport capacity of the jejunum was tested in rats. Seventy-gram rats were fed for 6 weeks diets containing 0.65% of lead (basic) carbonate, with or without a mixture of 4% kaolin and 1% pectin. Corresponding control groups fed cellulose instead of the lead salt were also followed. During the last week of the experiment, quantitative measurements of urinary lead, glucose, and amino nitrogen were carried out, and small intestinal absorptive capacity was determined by an in vivo perfusion technique. The inclusion of kaolin and pectin in the diets prevented growth stunting caused by lead. It also resulted in a greater weight gain in control rats (means ± SEM: 318.8 ± 5.4 g versus 296.5 ± 6.0 g, P < 0.02). However, these additives did not alter lead absorption and urinary excretion of lead, nor did it reduce glycosuria and aminoaciduria in heavy metal poisoning. In the lead-exposed rats, transport capacity for glucose was normalized by kaolin and pectin fed in the diet. These substances also produced a general enhancement of glucose transport capacity in control rats, concomitant with a Vmax increase from 0.285 to 0.388 in animals fed lead-containing diets, and from 0.307 to 0.482 mmoles/min × cm in the lead-free groups. There was no change in the Kt affinity constant for glucose (range between 41 and 56 mM), regardless of the kind of diet. Comparable effects were observed for the intestinal absorption rates of sodium, , l-tryptophan, and glycine. No changes were observed in the transport capacity for l-phenylalanine, l-leucine, and α-aminoisobutyric acid by feedings of kaolin and pectin. Ingestion of these substances reduced l-tyrosine absorption. Intake of lead resulted in an elevation of gamma glutamyl-transpeptidase in the small intestinal mucosa. Kaolin and pectin had no specific effect on this enzyme. These findings indicate that two widely used intestinal adsorbents, kaolin and pectin, do not prevent the absorption of lead when fed simultaneously with high doses of the heavy metal. However, they act at the level of the small intestinal mucosa enhancing the absorptive capacity for glucose and certain amino acids, and allowing the rats a normal weight gain despite systemic lead poisoning.

Villous tissue osmolality and intestinal transport of water and electrolytes.

The villous tissue hyperosmolality created by the intestinal countercurrent multiplier has been proposed to be of importance for fluid transport across the intestinal epithelium in vivo. This study was performed to test this hypothesis. Net transport of fluid and electrolytes (sodium, potassium and chloride), as well as unidirectional fluxes of water and sodium were determined in the small intestine of the cat. The villous osmolality was altered by varying the composition of sodium and glucose in the isotonic solutions perfusing the intestinal lumen. Net transport of fluid was correlated to tissue osmolality mainly due to an increase of the unidirectional flux of water from lumen to tissue with augmented tissue osmolality. The results are thus consistent with the view that the intestinal countercurrent multiplier is of essential importance for net water transport. A correlation was found between net water and net sodium intestinal transport. A similar correlation was also demonstrated between net sodium and net chloride absorption rates in the jejunum while in the ileum net loss of sodium into the intestinal lumen was not accompanied by any corresponding loss of chloride ions. This observation suggests the presence of a sodium independent transport mechanism for chloride in the ilium but not in the jejunum.

Effects of hydroxylated derivatives of vitamin D3 and of aqueous extracts of Solanum malacoxylon on the absorption of calcium, phosphate, sodium, potassium and water from the jejunum of pigs.

The effects of hydroxylated derivatives of vitamin D3 and aqueous extracts of Solanum malacoxylon on the intestinal absorption of calcium, phosphate, sodium, potassium and water have been studied in unstressed vitamin D-replete pigs each of which was surgically prepared beforehand with a Thirty–Vella loop of jejunum. The addition, for six 1 h periods of perfusion, of 1,25-dihydroxycholecalciferol (1,25-(OH)2D3) or 1α-hydroxycholecalciferol at similar concentrations (3·6–3·75 pmol/ml) to the solution used to perfuse the intestinal loop caused a rapid increase in the absorption of calcium but increased the absorption of phosphate only after a delay of at least 12 h. The absorption of both calcium and phosphate reached a maximum on the day following the addition of the vitamin D derivative to the perfusate. The addition of 25-hydroxycholecalciferol (25-(OH)D3) at a concentration of 3·75 pmol/ml was without effect on absorption except for a small increase in the absorption of phosphate on the following day. However, at higher concentrations (&gt; 250 pmol 25-(OH)D3/ml) the absorptions of calcium and phosphate were both increased rapidly. 24,25-Dihydroxycholecalciferol was without effect on absorption at the concentration tested (3·6 pmol/ml). Aqueous extracts (1%) of the leaf of S. malacoxylon showed similar effects on absorption to those of 1,25-(OH)2D3. However, there was one point of difference; the absorption of phosphate was stimulated with a similar time course to that of calcium in contrast to its delayed response to 1,25-(OH)2D3. The absorption rates of water, sodium and potassium were not consistently affected by 1,25-(OH)2D3 or S. malacoxylon. However, the major effects of these derivatives were usually seen on the day following the day of addition to the perfusate. In contrast, 25-(OH)D3 at high concentrations had a marked effect on the absorption of water, sodium and potassium on the day of addition.

Rectal absorption of short chain fatty acids in the absence of chloride.

The absorption of short chain fatty acids by the human rectum in the absence of chloride has been studied using a dialysis bag technique. Absorption rates of sodium, water, and short chain fatty acids were unchanged on replacing chloride with sulphate. Final concentrations of bicarbonate were 35.4 +/- 3.4 mmol/l in the presence of chloride and 37.1 +/- 5.2 mmol/l in the absence of chloride. The rates of movement of bicarbonate into the dialysates were similar. If bicarbonate is secreted in exchange for chloride then it also appears to be secreted in exchange for absorbed short chain fatty acids.

Effect of aspirin on intestinal absorption of glucose, sodium, and water in man.

The effect of aspirin on small intestinal function in six healthy volunteers was examined using a segmental perfusion technique, with a test solution of 40 mM D-glucose, 140 mM NaCl, and 0-5% polyethylene glycol. Jejunal glucose, sodium, and water absorption rates were inhibited by 50% after oral administration of 2-6 g aspirin. Adenosine triphosphate (ATP) concentration was assayed in jejunal mucosal biopsies before and after aspirin. There was an almost 50% decrease in mucosal ATP levels after aspirin. This effect may be mediated through cellular injury and impairment of mitochondrial energy metabolism. These data suggest that aspirin may significantly alter small intestinal function. It appears possible that the inhibitory effect of aspirin on glucose absorption may account, at least in part, for the lower blood sugar levels observed with the use of the drug.

Effects of Synthetic Human Gastrin I on Movements of Water, Electrolytes, and Glucose Across the Human Small Intestine

The effect of graded doses (0.125, 0.500, 1.00 and 2.00 mug per kg per hr) of intravenous synthetic human gastrin I (SHG) on jejunal transport of water, electrolytes, and glucose from a glucose-saline solution (solution II) was studied in 12 healthy volunteers, using an intestinal perfusion technique with a proximal occluding balloon. SHG when infused at rates of 0.500 mug per kg per hr or greater significantly reduced water and electrolyte absorption; this effect was linearly related to the dose and reached 40 to 60% of basal absorption (and only 10% for glucose) with the highest dose; insorption of sodium and water were significantly decreased by SHG. In a further group of 9 subjects no effect of SHG (2 mug per kg per hr) was found on jejunal absorption from a mannitol-saline solution (solution I) and on ileal absorption from solutions I and II; in 5 additional subjects, SHG did not decrease jejunal transit time of intraluminal fluid. There was no increase in serum thyrocalcitonin during SHG infusion. It is proposed that SHG selectively depresses the glucose-stimulated sodium transport as suggested by the reduction of the rate of net sodium absorption per micromole of glucose absorbed during SHG infusion. Physiological and pathological implications of these findings are discussed, especially in the light of the circulating levels of immunoreactive gastrin achieved during SHG infusion.

Potassium Transport across the Distal Colon in Man

1. The mechanism of potassium transport across human distal colon was investigated in twenty-two individuals without evidence of bowel disease, by using a dialysis method in conjunction with measurements of the transepithelial potential difference (p.d.). 2. Whether potassium was absorbed or secreted depended on its initial concentration in the lumen. The potassium net flux was approximately zero when the luminal potassium concentration was between 30 and 50 mmol/l. 3. Potassium secretion rate was little affected by sodium absorption rate, or by the luminal sodium concentration or by the osmolality of the luminal solution. 4. Potassium secretion rate was increased by partial substitution of other cations for sodium, in the descending order Li greater than NH4 greater than Rb greater than Na. Potassium concentration increased on average to over 80 mmol/l when lithium was in the lumen. 5. The observed transepithelial p.d. was inadequate to account for the intraluminal potassium concentrations attained, the discrepancy being most marked when ammonium or lithium was in the lumen. It is suggested that some potassium is secreted by the epithelial cells and this component of the total potassium flux into the lumen is increased when rubidium, ammonium or lithium is substituted for sodium.

Effect of aldosterone on lithium permeability of rat colon mucosa.

The effect of aldosterone on the ionic composition of colonic epithelial cells and on lithium absorption rate was studied by experiments on rats in vivo. Aldosterone considerably increased the rate of sodium absorption without measurably altering the sodium and potassium content of the epithelium. Aldosterone did not alter the electrical resistance of the tissue. With lithium in the lumen, the net sodium fluxes in the colon were similar in normal and aldosterone-stimulated rats but the rate of diffusion of lithium across the epithelium was greater in the aldosterone-stimulated group. The amount of lithium accumulating in the epithelial layer was also considerably increased by aldosterone stimulation. Aldosterone appears to increase the permeability of the mucosal (luminal) barrier allowing increased entry of lithium into the colonic epithelial cells.

Ionic requirements of proximal tubular sodium transport. I. Bicarbonate and chloride.

Simultaneous perfusion of peritubular capillaries and proximal convoluted tubules was used to study the effect of varying transepithelial ionic gradients on ionic fluxes. Results show that net sodium influx and volume flux was one-third of normal when bicarbonate was absent, no chloride gradient existed, and glucose and amino acids were absent. Addition of bicarbonate to the luminal fluid did not restore the flux to normal, but peritubular bicarbonate did restore it. A chloride gradient imposed when no bicarbonate was present could only increase the fluxes slightly, but his flux was significant even after cyanide had poisoned transport. Reversing the chloride concentration gradient decreased the net sodium and volume fluxes whether bicarbonate was present or not. Glucose had no effect on fluxes, but substitution of Na by choline abolished them entirely. It is concluded that sodium is actively transported, that a chloride concentration gradient from lumen to plasma could account for up to 20% of net transport, and that peritubular bicarbonate is necessary for normal rates of sodium and fluid absorption.