Review article: the therapy of constipation

Constipation is a common symptom that may be idiopathic or due to various identifiable disease processes. Laxatives are agents that add bulk to intestinal contents, that retain water within the bowel lumen by virtue of osmotic effects, or that stimulate intestinal secretion or motility, thereby increasing the frequency and ease of defecation. Drugs which improve constipation by stimulating gastrointestinal motility by direct actions on the enteric nervous system are under development. Other modalities used to treat constipation include biofeedback and surgery. Laxatives and lavage solutions are also used for colon preparation and evacuation of the bowels after toxic ingestions.

Constipation and fecal incontinence in the elderly

Although constipation and fecal incontinence are common symptoms in the elderly, relatively little research has been done to differentiate physiologic changes in rectoanal function resulting from aging and pathologic changes resulting from diseases occurring as patients age. Certain physiologic changes occur in many older patients and may predispose them to the development of constipation or fecal incontinence. These symptoms need the same thoughtful evaluation and management in the elderly as in younger patients. Results of therapy often can be good, leading to alleviation of suffering and the ability to lead a fuller life.

Diarrhea

Diarrhea is a common symptom of many conditions, and making an accurate diagnosis can be daunting. Research efforts have expanded the differential diagnosis of chronic diarrhea and have provided improved methods for the evaluation and management of patients with diarrheal diseases. This article discusses some of these trends and presents the emerging consensus regarding appropriate pathways of caring for patients with diarrheal diseases.

Microscopic colitis syndrome: lymphocytic colitis and collagenous colitis

Microscopic colitis is a syndrome consisting of chronic watery diarrhea, a normal or near-normal gross appearance of the colonic lining, and a specific histological picture described as either lymphocytic colitis or collagenous colitis. Since its initial descriptions a quarter of a century ago, microscopic colitis has become a frequent diagnosis in patients with chronic diarrhea. Understanding of the cause and pathogenesis of microscopic colitis remain incomplete, but potentially important clues have been discovered that shed light on predisposing factors. In particular, specific HLA-DQ genotypes may be permissive for the development of microscopic colitis, and suggest a linkage to the pathogenesis of celiac sprue. Although the differential diagnosis of chronic watery diarrhea is broad, the diagnosis of microscopic colitis is straightforward, involving endoscopic inspection of the colonic mucosa and proper pathologic interpretation of biopsy specimens. As the limitations of drugs ordinarily used for other forms of inflammatory bowel disease are being recognized, new approaches, such as the use of bismuth subsalicylate, are being evaluated. The prognosis of patients with microscopic colitis syndrome remains good, and symptomatic improvement can be expected in most patients.

Secretory diarrhea

Diarrhea, defined as loose stools, occurs when the intestine does not complete absorption of electrolytes and water from luminal contents. This can happen when a nonabsorbable, osmotically active substance is ingested ("osmotic diarrhea") or when electrolyte absorption is impaired ("secretory diarrhea"). Most cases of acute and chronic diarrhea are due to the latter mechanism. Secretory diarrhea can result from bacterial toxins, reduced absorptive surface area caused by disease or resection, luminal secretagogues (such as bile acids or laxatives), circulating secretagogues (such as various hormones, drugs, and poisons), and medical problems that compromise regulation of intestinal function. Evaluation of patients with secretory diarrhea must be tailored to find the likely causes of this problem. Specific and nonspecific treatment can be valuable.

AGA technical review on the evaluation and management of chronic diarrhea

This literature review and the recommendations therein were prepared for the American Gastroenterological Association Clinical Practice and Practice Economics Committee. The paper was approved by the committee on September 27, 1998.

Clinical pharmacology and use of laxatives and lavage solutions

Laxatives and lavage solutions are used in the treatment of constipation and toxic ingestion and also for preparation of the colon before endoscopic or surgical procedures. Several different categories of agents are available for use. These include bulking agents, osmotic agents, secretagogues and agents with direct effects on epithelial nerve or smooth muscle cells, and lubricating agents. Each category has different pharmacologic effects, side effects, and clinical indications. This review summarizes current information about these agents.

A comparison of stool characteristics from normal and constipated people

In people with constipation, it is not known if decreased frequency of defecation is associated with abnormalities in the weight or in the consistency of stools or if the weight or the consistency of stools correlates with the severity of various discomforts associated with bowel movements. In neither normal nor constipated subjects has the consistency of stools been carefully correlated with their relative contents of water and solids. Our aim was to gain insight into these questions. Twenty subjects with idiopathic chronic constipation and 20 age- and sex-matched control subjects were recruited by advertisement. Stools were collected for one week. After each bowel movement, the subject's perception of various discomforts associated with the bowel movement were recorded. The stools were then analyzed. The results and conclusions were as follows: (1) Stool weight per bowel movement was similar in the two groups but stool weight per week was markedly reduced in constipated subjects. (2) Reduced stool weight per week in constipated subjects was due to a nearly proportional reduction in stool water and stool solids output. (3) Using data from both groups, there was a curvilinear correlation between percent insoluble stool solids and stool hardness, as measured by a texture analyzer; hardness increased only slightly as percent insoluble solids increased between 7 and 20%, but hardness increased dramatically when percent insoluble solids exceeded 25%. (4) Only 6% of stools from constipated subjects (2 of 34) had abnormally high values for percent stool solids and physical hardness. (5) In subjects with constipation, the severity of various discomforts associated with bowel movements (such as straining) correlated poorly with the weight or the hardness of stool that was produced by the bowel movement.

Glucose-stimulated sodium transport by the human intestine during experimental cholera

BACKGROUND & AIMS

Net sodium absorption from oral rehydration solution is increased by both glucose-sodium cotransport and solvent drag. The aim of this study was to measure the relative importance of glucose-sodium cotransport and solvent drag in the stimulation of net sodium absorption by oral rehydration solution.

METHODS

Total intestinal perfusion was used in normal subjects with and without intrajejunal cholera toxin using three test solutions containing 100 mmol/L sodium and either 100 mmol/L mannitol (control), 100 mmol/L glucose, or no additional solute (hypotonic solution). The increase in sodium absorption greater than control with hypotonic solution represented sodium absorption stimulated by solvent drag; the further increase in sodium absorption induced by glucose, greater than that noted with the hypotonic solution, represented sodium absorption stimulated by cotransport.

RESULTS

Without cholera toxin, solvent drag and cotransport promoted sodium absorption at rates of 62 and 33 mmol/h, respectively. With cholera toxin, solvent drag and cotransport promoted sodium absorption at rates of 44 and 71 mmol/h, respectively.

CONCLUSIONS

Net sodium absorption caused by cotransport increased more than twofold after exposure of the intestine to cholera toxin (P < 0.003). This could be mediated by increased cotransport, a change in the stoichiometry of cotransport, or an increase in chloride permeability.

Validation of polyethylene glycol 3350 as a poorly absorbable marker for intestinal perfusion studies

Polyethylene glycol (PEG) has been used as a poorly absorbable marker in intestinal perfusion studies, but there is controversy about the absorbability of PEG, particularly when glucose-sodium cotransport is occurring. Total intestinal perfusion studies were done in five normal humans using three solutions containing 1 g/liter PEG 3350 and designed to produce low rates of water absorption, high rates of water absorption, or high rates of glucose-sodium cotransport. Water absorption rates were calculated by traditional nonabsorbable marker equations and by a novel balance technique in which absorption was taken as the difference between the volumes of solution infused and recovered during steady-state conditions. Effluent PEG recovery was 99 +/- 4%, 109 +/- 2%, and 104 +/- 6% of the amount infused with each solution. Water absorption rates measured by use of PEG concentrations were similar to those calculated by the balance technique (r = 0.99). The complete recovery of PEG confirms the poor absorbability of PEG 3350, and the excellent agreement between techniques validates PEG as a poorly absorbed marker, even when glucose-sodium cotransport is occurring.

Upper gastrointestinal motility disorders and respiratory symptoms

The association between upper gastrointestinal (GI) motility disorders and respiratory problems is reviewed. Upper GI motility disorders, such as gastroesophageal reflux disease, gastroparesis, and achalasia, have been associated with respiratory problems, including aspiration, airway obstruction, asthma, bronchospasm, chronic cough, and laryngitis. These associations, which had been based solely on clinical observation, have recently been supported by physiologic studies and treatment trials. The association of reflux disease with asthma has the most support. Up to 80% of persons with asthma have evidence of pathologic gastroesophageal reflux, and in several studies antireflux therapy with prokinetic agents, antisecretory drugs, or fundoplication surgery has been found to reduce asthma symptoms and the need for medication in some patients. Reflux has also been associated with chronic cough and laryngitis, and antireflux therapy can reduce respiratory symptoms. Gastroesophageal reflux, gastroparesis, and achalasia are all associated with aspiration. In addition, in rare instances, the megaesophagus associated with achalasia can produce mechanical airway obstruction. Effective therapy for these GI motility disorders can eliminate complicating respiratory problems.

Determinants of decreased fecal consistency in patients with diarrhea

BACKGROUND/AIMS

Loose stools are a common and troublesome feature in diarrhea. The purpose of this study was to investigate factors that determine different degrees of stool looseness in diarrhea.

METHODS

Fecal consistency was measured visually. Stools were analyzed for content of water and solids. Water-holding capacity of insoluble solids was measured in vitro.

RESULTS

Formed stools from normal subjects had a near constant ratio of water to solids despite a sevenfold variation in daily stool weight. In diarrhea, loose consistency was correlated directly with percent fecal water. For any level of percent water, steatorrhea stools were looser than nonsteatorrhea stools. Ingestion of psyllium reduced stool looseness without changing the percent water. Both the effect of fat and psyllium could be explained by consideration of the ratio of fecal water to water-holding capacity of insoluble solids.

CONCLUSIONS

(1) The normal intestine delivers stools that differ widely in quantity but maintains percent fecal water within a narrow range. (2) Stool looseness in diarrhea is determined by the ratio of fecal water to water-holding capacity of insoluble solids. (3) In patients with diarrhea with normal stool weight, loose stools are due to low output of insoluble solids without the concomitant reduction in water output that occurs in normal subjects when insoluble solids are low.

Review article: anti-diarrhoeal pharmacology and therapeutics

Anti-diarrhoeal drugs reduce the symptoms of diarrhoea (loose stool consistency, frequency of defecation and excessive stool weight) by effects on intestinal transit, mucosal transport or luminal contents. Opiates and opioids are the most useful antidiarrhoeal agents. Opiates have major effects on intestinal transit; pro-absorptive and anti-secretory effects are less well documented, but may be important for some of these drugs. Alpha-adrenergic agonists, somatostatin analogues and several other agents have had limited clinical use; these drugs may modify mucosal transport in addition to slowing transit. Adsorbents, bismuth and stool texture modifiers are used frequently by the public, but their efficacy is largely unproven. Oral rehydration solutions have had the greatest impact in saving lives and continue to be improved. Many new approaches to the treatment of diarrhoea are yet to be exploited.

Diagnostic value of fasting plasma peptide concentrations in patients with chronic diarrhea

To evaluate the utility of screening for multiple gastrointestinal peptides in the evaluation of patients with chronic diarrhea, we studied 193 patients referred for evaluation of chronic diarrhea and eight patients with known peptide-secreting tumors as a reference group. Fasting plasma samples were assayed for motilin, neurotensin, pancreatic polypeptide, somatostatin, substance P, vasoactive intestinal polypeptide, gastrin-releasing peptide, and calcitonin during a protocol evaluation for causes of chronic diarrhea. Although none of the referred patients were found to have tumors, abnormal levels of one or more peptides were found in 86 of 193 patients (45%). Abnormal plasma peptide levels were sometimes as high in these patients as in patients with known peptide-secreting tumors and would have led to mistaken diagnoses of tumors much more often than they would have led to correct diagnoses. The positive predictive value of elevation of any assayed peptide was < 2% at realistic prevalence rates for peptide-secreting tumors; the negative predictive value of a series of normal results was > 99%, but much of this was due to the rarity of these tumors. Patients with chronic diarrhea should not be screened routinely with a panel of plasma peptide assays in an effort to detect tumors; instead, peptide levels should be ordered selectively. Elevated fasting concentrations of the plasma peptides measured in this study are most likely epiphenomena due to diarrhea and should not be the sole basis for invasive diagnostic or surgical management of these patients.

The self-limited nature of chronic idiopathic diarrhea

BACKGROUND

Little is known about the clinical presentation and natural history of previously healthy patients in whom chronic idiopathic diarrhea develops.

METHODS

We reviewed the case records of 152 patients with chronic diarrhea who had no history of gastrointestinal surgery and who were evaluated in detail as part of a chronic-diarrhea protocol from 1985 to 1990. Patients were considered to have chronic idiopathic diarrhea if they had persistently loose stools for more than four weeks, no systemic illness, and no identifiable cause of diarrhea.

RESULTS

Seventeen patients (10 men and 7 women) ranging in age from 33 to 72 years met the criteria for chronic idiopathic diarrhea. Each patient had a history of a relatively abrupt onset of symptoms, often soon after returning home from a trip, starting two to seven months before evaluation. Their diarrhea did not occur during a local outbreak of diarrhea, and other family members did not become ill. Stool frequency ranged from 5 to 25 movements per day, stool weights ranged from 417 to 1480 g per day, and fecal electrolyte and osmolality values were consistent with a diagnosis of secretory diarrhea. The results of biopsies of the small intestine and colon were normal, as were small-bowel roentgenograms. Extensive studies for infectious causes of diarrhea were negative, and no patient responded to antibiotic therapy. In every patient the diarrhea stopped without specific therapy after 7 to 31 months (mean, 15) and did not recur during a follow-up period averaging 38 months.

CONCLUSIONS

Sporadic idiopathic chronic diarrhea is a recognizable syndrome that can last many months, but is self-limited.

Subepithelial collagen table thickness in colon specimens from patients with microscopic colitis and collagenous colitis

Microscopic colitis and collagenous colitis are similar conditions that are differentiated by the presence or absence of subepithelial collagen table thickening. To better understand the relationship between these two disorders and the role of collagen table thickening in the pathogenesis of diarrhea, colonic mucosal biopsy specimens from 24 patients with microscopic or collagenous colitis and 9 control subjects were analyzed using a computer-assisted morphometric method to evaluate the average thickness of the subepithelial collagen table. The collagen table thickness in colitis patients taken together formed a multimodal rather than a unimodal distribution. There was no tendency for collagen table thickening to increase with age or with duration of symptoms. In general, the types and distribution of inflammatory cells were similar in patients with normal and thickened collagen tables. Stool weight correlated with lamina propria cellularity but not with collagen table thickening. The multimodal distribution of collagen table thickening and the lack of correlation with age, duration of symptoms, or inflammation suggest that microscopic colitis and collagenous colitis are discrete conditions, although the inflammatory changes in the two conditions are similar. Moreover, because stool weight correlates with lamina propria cellularity but not with collagen table thickening, diarrhea probably is caused by the inflammatory changes and not by collagen table thickening per se.

Treatment of severe steatorrhea with ox bile in an ileectomy patient with residual colon

Patients with ileectomy can present with severe steatorrhea due to bile acid depletion. While exogenous bile acid would seem to be ideal therapy for this condition, it is not often used because it is thought that the bile acid would be malabsorbed and would enter the colon, producing a secretory diarrhea. This report describes a patient who had an ileectomy and partial right colon resection for Crohn's disease and then developed severe steatorrhea due to bile acid malabsorption. Although steatorrhea was reduced from 134 to 9 g/24 hr with chronic ingestion of ox bile extract, stool weight did not increase with ox bile (stool weight 669 g/24 hr before therapy and 507 g/24 hr after therapy). In this patient, oral bile acid supplementation reduced fat excretion markedly, but did not aggravate diarrhea, even though the colon was still present. This result may have been due to impaired solubility of bile acid in fecal fluid due to an acid pH or to binding of bile acid with particles of solid stool. Ingestion of ox bile extract does not necessarily increase stool weight in patients with defective fat absorption due to bile acid malabsorption and can be tried with caution in an effort to diminish steatorrhea.

Carbohydrate malabsorption. Its measurement and its contribution to diarrhea

The major purpose of this research was to gain insight into the effect of carbohydrate malabsorption on fecal water output. To do this we measured daily fecal output of total carbohydrate, reducing sugars, and organic acids (a product of bacterial fermentation). Normal subjects were studied in their native state and when diarrhea was induced by mechanisms that did and did not involve carbohydrate malabsorption. Patients with malabsorption syndrome were also studied. We concluded that: (a) Excretion of carbohydrate and its breakdown products can be expressed as a single number by converting organic acids to their monosaccharide equivalents. (b) Diarrhea per se causes only a trivial increase in fecal carbohydrate excretion. (c) The molar output of osmotic moieties in feces due to unabsorbed carbohydrate can be determined by adding fecal reducing sugars to organic acids and their obligated cations. This expression parallels almost exactly the effect of increasing doses of lactulose (a nonabsorbable sugar) on fecal water output; one excreted millimole obligates 3.5 g of stool water. This relationship can be used to predict the effect of carbohydrate malabsorption on stool water output in patients with diarrhea. (d) 12 of 19 patients with malabsorption syndrome due to various diseases had excessive fecal excretion of carbohydrate and its breakdown products; of the diseases that cause malabsorption syndrome, combined small and large bowel resection is most likely to result in excessive fecal excretion of carbohydrate and monosaccharide equivalents. In 6 of these 19 patients carbohydrate malabsorption appeared to be the major cause of diarrhea.

Comparison of endogenous and radiolabeled bile acid excretion in patients with idiopathic chronic diarrhea

Fecal recovery of radioactivity after ingestion of a bolus of radiolabeled bile acid is abnormally high in most patients with idiopathic chronic diarrhea. To evaluate the significance of this malabsorption, concurrent fecal excretion of both exogenous radiolabeled bile acid and endogenous (unlabeled) bile acid were measured in patients with idiopathic chronic diarrhea. Subjects received a 2.5-microCi oral dose of taurocholic acid labeled with 14C in the 24th position of the steroid moiety. Endogenous bile acid excretion was measured by a hydroxysteroid dehydrogenase assay on a concurrent 72-h stool collection. Both radiolabeled and endogenous bile acid excretion were abnormally high in most patients with chronic diarrhea compared with normal subjects, even when equivoluminous diarrhea was induced in normal subjects by ingestion of osmotically active solutions. The correlation between radiolabeled and endogenous bile acid excretion was good. However, neither radiolabeled nor endogenous bile acid excretion was as abnormal as is typically seen in patients with ileal resection, and none of these diarrhea patients responded to treatment with cholestyramine with stool weights less than 200 g. These results suggest (a) that this radiolabeled bile acid excretion test accurately reflects excess endogenous bile acid excretion; (b) that excess endogenous bile acid excretion is not caused by diarrhea per se; (c) that spontaneously occurring idiopathic chronic diarrhea is often associated with increased endogenous bile acid excretion; and (d) that bile acid malabsorption is not likely to be the primary cause of diarrhea in most of these patients.

Studies of osmotic diarrhea induced in normal subjects by ingestion of polyethylene glycol and lactulose

The purpose of these studies was to gain insight into the pathophysiology of pure osmotic diarrhea and the osmotic diarrhea caused by carbohydrate malabsorption. Diarrhea was induced in normal volunteers by ingestion of polyethylene glycol (PEG), which is nonabsorbable, not metabolized by colonic bacteria, and carries no electrical charge. In PEG-induced diarrhea, (a) stool weight was directly correlated with the total mass of PEG ingested; (b) PEG contributed 40-60% of the osmolality of the fecal fluid, the remainder being contributed by other solutes either of dietary, endogenous, or bacterial origin; and (c) fecal sodium, potassium, and chloride were avidly conserved by the intestine, in spite of stool water losses exceeding 1,200 g/d. Diarrhea was also induced in normal subjects by ingestion of lactulose, a disaccharide that is not absorbed by the small intestine but is metabolized by colonic bacteria. In lactulose-induced diarrhea, (a) a maximum of approximate 80 g/d of lactulose was metabolized by colonic bacteria to noncarbohydrate moieties such as organic acids; (b) the organic acids were partially absorbed in the colon; (c) unabsorbed organic acids obligated the accumulation of inorganic cations (Na greater than Ca greater than K greater than Mg) in the diarrheal fluid; (d) diarrhea associated with low doses of lactulose was mainly due to unabsorbed organic acids and associated cations, whereas with larger doses of lactulose unmetabolized carbohydrates also played a major role; and (e) the net effect of bacterial metabolism of lactulose and partial absorption of organic acids on stool water output was done dependent. With low or moderate doses of lactulose, stool water losses were reduced by as much as 600 g/d (compared with equimolar osmotic loads of PEG); with large dose, the increment in osmotically active solutes within the lumen exceeded the increment of the ingested osmotic load, and the severity of diarrhea was augmented.

Effect of the time of administration of calcium acetate on phosphorus binding

Phosphorus binders are given to patients with renal failure to increase gastrointestinal excretion of phosphorus. To determine the relative importance of the binding of dietary as compared with endogenous phosphorus and to determine the optimal dose schedule, we gave either 4.4 g of calcium acetate (25 mmol of calcium) or a placebo to six normal subjects on each of seven different schedules in a randomized sequence. The net gastrointestinal balance of phosphorus and calcium was determined by a one-day lavage technique. After a meal containing approximately 12 mmol of phosphorus, the mean phosphorus absorption (+/- SE) measured 9.17 +/- 0.36 mmol (78 percent) with placebo but decreased to 3.81 +/- 0.58 mmol (31 percent) when calcium acetate was given immediately before the meal (representing binding of 5.36 +/- 0.77 mmol of phosphorus). Similar binding was observed when calcium acetate was given immediately after the meal and when half the dose was given before and half after the meal. In contrast, when calcium acetate was given two hours after the meal or while the subject was fasting, phosphorus binding was reduced to 2.00 +/- 0.52 mmol and 1.81 +/- 0.84 mmol, respectively. Calcium absorption from calcium acetate averaged 21 +/- 1 percent when the binder was given with a meal; absorption from calcium acetate averaged 40 +/- 4 percent when the binder was given while the subject was fasting. We conclude that calcium acetate increases fecal excretion of phosphorus by binding both dietary and endogenous phosphorus, but the binding of dietary phosphorus is quantitatively much more important. For the most efficient phosphorus binding, calcium (and presumably other phosphorus-binding cations) should be given with meals.

Loss of absorptive capacity for sodium chloride as a cause of diarrhea following partial ileal and right colon resection

Previous studies have emphasized the role of bile acid and fat malabsorption as the cause of the diarrhea that may follow ileal and right colon resection; unabsorbed bile acids and fat are believed to reduce sodium chloride and water absorption in the remaining colon. In this paper we report studies in eight patients with severe postresection diarrhea, in search of a more basic defect in sodium chloride absorption, ie, a loss of sodium chloride absorptive capacity as a direct consequence of resection of sodium chloride absorption sites. First, we determined whether or not diarrhea persisted during a 48-hr fast; in all patients diarrhea and large fecal electrolyte losses continued during a fast. Second, we measured sodium chloride and water absorption rates during total gut perfusion with a balanced electrolyte solution; compared to normal controls, the patients absorbed 23-31% less water, sodium, and chloride. In three patients who could be studied further, the absorptive defect was markedly accentuated when the perfusing solution was such that sodium chloride absorption had to take place against a concentration gradient. These observations indicate that postresection diarrhea patients have a reduced capacity to absorb sodium chloride, particularly when there is a concentration gradient between lumen and plasma. Although all of these patients had malabsorption of radiolabeled taurocholic acid, there was only a modest and statistically insignificant reduction in daily stool weight during treatment with large doses of cholestyramine, suggesting that bile acid malabsorption was not responsible for a major part of their diarrhea.(ABSTRACT TRUNCATED AT 250 WORDS)

Reduction of dietary phosphorus absorption by phosphorus binders. A theoretical, in vitro, and in vivo study

Antacids used to decrease phosphorus absorption in patients with renal failure may be toxic. To find more efficient or less toxic binders, a three-part study was conducted. First, theoretical calculations showed that phosphorus binding occurs in the following order of avidity: Al3+ greater than H+ greater than Ca2+ greater than Mg2+. In the presence of acid (as in the stomach), aluminum can therefore bind phosphorus better than calcium or magnesium. Second, in vitro studies showed that the time required to reach equilibrium varied from 10 min to 3 wk among different compounds, depending upon solubility in acid and neutral solutions. Third, the relative order of effectiveness of binders in vivo was accurately predicted from theoretical and in vitro results; specifically, calcium acetate and aluminum carbonate gel were superior to calcium carbonate or calcium citrate in inhibiting dietary phosphorus absorption in normal subjects. We concluded that: (a) inhibition of phosphorus absorption by binders involves a complex interplay between chemical reactions and ion transport processes in the stomach and small intestine; (b) theoretical and in vitro studies can identify potentially better in vivo phosphorus binders; and (c) calcium acetate, not previously used for medical purposes, is approximately as efficient as aluminum carbonate gel and more efficient as a phosphorus binder than other currently used calcium salts.

Calcium absorption: effect of meal and glucose polymer

Various nonelectrolyte meal components such as glucose and lysine enhance gastrointestinal calcium absorption under experimental conditions. The effect of a mixed meal on Ca absorption from Ca supplements is unknown. The effect of glucose polymer on Ca absorption when ingested with food also is unknown. Using a single-day method, we measured net Ca absorption from Ca carbonate when ingested in fasting state, with a steak and potatoes meal, and with the meal and 50 g glucose polymer. Eight healthy human subjects were studied after a 500-mg elemental Ca dose. Mean net Ca absorption was 195 +/- 18 mg (4.87 +/- 0.45 mmol) fasting, 213 +/- 21 mg (5.31 +/- 0.52 mmol) with a meal, and 179 +/- 16 mg (4.47 +/- 0.40 mmol) with a meal plus glucose polymer. The differences are not statistically significant. In normal people Ca absorption from Ca carbonate was not significantly enhanced by a meal or by 50 g glucose polymer ingested with food.

Effect of amiloride on sodium transport in the proximal, distal, and entire human colon in vivo

In vitro studies under short-circuited conditions suggest that amiloride, a diuretic agent which is thought to block apical membrane sodium entry, has significant effects on sodium absorption by the human colon. To evaluate this in vivo, we studied the effect of amiloride applied in concentrations of 10(-5) and 10(-4) M on sodium transport and potential difference (PD) in human colon during steady-state perfusion. Net sodium absorption was reduced 25% by amiloride and chloride absorption by 15%; potassium and bicarbonate secretion rates were enhanced. In other studies the colon was divided into a proximal and distal test segment by endoscopic introduction of a collection channel to the descending colon-sigmoid junction. Comparison of tritiated water absorption by the two segments indicated that the distal segment comprised approximately 20% of the total colon surface area. However, the distal test segment only accounted for 5-7% of total sodium, chloride, or water absorption; in contrast, 17-20% of total potassium or bicarbonate secretion occurred there. In the proximal test segment, amiloride reduced net sodium absorption by almost one third from 21.0 to 14.4 mmol/hr (P less than 0.02) but had no significant effect on PD. In the distal test segment, amiloride produced a 25% reduction in mean sodium absorption from 1.2 to 0.9 mmol/hr, but this reduction was not statistically significant; however, potential difference was significantly reduced by 33% (P less than 0.02). These results suggest that most sodium absorption in normal human colon in vivo is mediated by transport processes which are insensitive to these doses of amiloride.(ABSTRACT TRUNCATED AT 250 WORDS)

Osmotic effects of polyethylene glycol

Polyethylene glycol (PEG) has been used to increase the osmotic pressure of fluids used to cleanse the gastrointestinal tract. However, little is known about its osmotic activity. To investigate this activity systematically, solutions of PEG of differing molecular weights were made and subjected to measurement of osmolality by both freezing point depression and vapor pressure osmometry. Measured osmolality was increasingly greater than predicted from average molecular weight as PEG concentration increased. Measurement of sodium activity in NaCl/PEG solutions by means of an ion-selective electrode suggested that the higher than expected osmolality could be due in part to interactions that, in effect, sequestered water from the solution. Osmolality was consistently greater by freezing point osmometry than by vapor pressure osmometry. To determine which osmometry method reflected biologically relevant osmolality, normal subjects underwent steady-state total gut perfusion with an electrolyte solution containing 105 g/L of PEG 3350. This produced rectal effluent that was hypertonic by freezing point osmometry but isotonic by vapor pressure osmometry. Assuming that luminal fluid reaches osmotic equilibrium with plasma during total gut perfusion, this result suggests that the vapor pressure osmometer accurately reflects the biologically relevant osmolality of intestinal contents. We conclude that PEG exerts more of an osmotic effect than would be predicted from its molecular weight. This phenomenon may reflect interactions between PEG and water molecules that alter the physical chemistry of the solution and sequester water from the solution.

Quantification of colonic lamina propria cells by means of a morphometric point-counting method

The lamina propria of colonic mucosa normally contains eosinophils, lymphocytes, plasma cells, and a few neutrophils. If the number of such cells is judged to be increased, colonic inflammation is said to be present. However, the number of cells present in normal mucosa has not been clearly established. Mild abnormalities are difficult to identify, yet might be associated with colonic dysfunction. We therefore developed a morphometric point-counting method to quantitatively analyze the areas occupied by different structures in the mucosa of the human colon. A computer was used to move a dot in a rectilinear pattern over the X400 magnified image of biopsy specimens obtained from throughout the colon by colonoscopy. The structure on which the dot landed was identified and tabulated by a pathologist. In preliminary studies, we established counting parameters that would yield the most representative results. Based on statistical analysis, it was decided to count 98 points in each of seven regions of six biopsy specimens, i.e., over 4000 points per subject. Results were expressed as percentages of counts landing on a given item, and represented the area of the biopsy specimen covered by that item. Using this method, we determined the range of normal in healthy volunteers. The sensitivity of this method was tested by studying patients with chronic diarrhea previously diagnosed as having or not having mild to moderate mucosal inflammation. In the patient group, colonic fluid absorption measured by a perfusion technique was directly correlated with epithelial cell counts and inversely correlated with lamina propria cellularity and with the counts of lamina propria neutrophils and plasma cells. We conclude that morphometric analysis of colon biopsy specimens can be used to quantitate histologic features of colonic mucosa and to accurately identify even mild abnormalities, and that it can be a useful clinical research tool.

Role of vitamin D-dependent and vitamin D-independent mechanisms in absorption of food calcium

We measured net calcium absorption and the calcium content of the digestive glands secretions in people with widely different serum concentrations of 1,25 dihydroxy vitamin D (hereafter referred to a 1,25-D). Patients with end stage renal disease on hemodialysis served as a model of human 1,25-D deficiency; they were also studied when they had abnormally high serum 1,25-D concentrations as a result of short periods of treatment with exogenous 1,25-D. Normal subjects were studied for comparison. The amount of calcium secreted into the duodenum by the digestive glands was found to be trivial compared to the calcium content of normal or even low calcium meals; therefore, values for net and true net calcium absorption differed only slightly. There was a linear correlation between true net calcium absorption and serum 1,25-D concentration. By extrapolating the short distance to a zero value for serum 1,25-D, D-independent true net calcium absorption was estimated. By subtracting D independent from true net calcium absorption, values for D-dependent absorption were obtained. For a given level of meal calcium intake, D-dependent calcium absorption was found to be directly proportional to serum 1,25-D concentration. At any given value for serum 1,25-D, absorption via the D-dependent mechanism was approximately the same with a low (120 mg) calcium meal as it was when meal calcium intake was increased to 300 mg. We interpret this to mean that the D-dependent mechanism is saturated or nearly saturated by low calcium meals. The D-independent absorption/secretion mechanism resulted in secretion (a loss of body calcium in the feces) when intake was low (120 mg per meal) and absorption when intake was normal. All of the increment in calcium absorption that occurs when low or normal calcium meals are supplemented with extra calcium is mediated by the D-independent mechanism.

Gastrointestinal absorption of calcium from milk and calcium salts

Whether ingested calcium is absorbed more efficiently from freely water-soluble calcium salts than from poorly soluble salts is unclear. It is also unknown whether calcium is absorbed better from dairy products than from calcium salts. Using a method by which the net absorption of calcium can be accurately measured after a single dose, we studied eight healthy fasting subjects after they took a 500-mg dose of calcium from each of five calcium salts with various degrees of water solubility and from milk. The order of administration of the agents given was randomly determined. The mean (+/- SEM) net calcium absorption, in decreasing order of the solubility of the salts, was 32 +/- 4 percent from calcium acetate, 32 +/- 4 percent from calcium lactate, 27 +/- 3 percent from calcium gluconate, 30 +/- 3 percent from calcium citrate, and 39 +/- 3 percent from calcium carbonate. The differences in absorption were not statistically significant according to analysis of variance. On the basis of in vitro solubility experiments in acid mediums, we hypothesize that acid dissolution in the gastrointestinal tract may be responsible for the similar absorption of calcium from salts with widely different water solubilities. Calcium absorption from whole milk (31 +/- 3 percent) was similar to absorption from calcium salts. We conclude that calcium absorption from carbonate, acetate, lactate, gluconate, and citrate salts of calcium, and from whole milk, is similar in fasting healthy young subjects. Further study will be required to determine whether the results would be different in older subjects, with a higher dose of calcium, or if the calcium was ingested with food.

Positive intravenous secretin test in patients with achlorhydria-related hypergastrinemia

The intravenous secretin test is widely used to distinguish gastrinoma (Zollinger-Ellison syndrome) from other causes of fasting hypergastrinemia. We report 2 patients with fasting hypergastrinemia and a rise of greater than 200 pg/ml in serum gastrin concentration after intravenous injection of 2 CU/kg body wt of pure natural secretin. Both patients had pentagastrin-fast achlorhydria. Thus, the intravenous secretin test may be positive in patients with achlorhydria-related hypergastrinemia. Gastric acid secretion should be measured in hypergastrinemic patients before embarking on a secretin test.

Studies of the prevalence and significance of radiolabeled bile acid malabsorption in a group of patients with idiopathic chronic diarrhea

We studied radiolabeled fecal bile acid excretion in 11 normal subjects and 17 patients with idiopathic chronic diarrhea for three major purposes: to establish normal values for this test in the presence of increased stool volumes (induced in normal subjects by ingestion of poorly absorbable solutions); to test for bile acid malabsorption in the patients and to correlate this with an independent test of ileal function, the Schilling test; and to compare the results of the bile acid excretion test with the subsequent effect of a bile acid binding agent (cholestyramine) on stool weight. In normal subjects fecal excretion of the radiolabel was increased with increasing stool volumes. As a group, patients with idiopathic chronic diarrhea excreted radiolabeled bile acid more rapidly than normal subjects with induced diarrhea (t1/2 56 +/- 8 vs. 236 +/- 60 h, respectively, p less than 0.005). There was a statistically significant positive correlation between t1/2 of radiolabeled bile acid and Schilling test results in these patients. Although 14 of 17 patients absorbed labeled taurocholic acid less well than any of the normal subjects with comparable volumes of induced diarrhea, cholestyramine had no statistically significant effect on stool weight in the patient group, and in none of the patients was stool weight reduced to within the normal range. In summary, most patients with idiopathic chronic diarrhea have bile acid malabsorption (as measured by fecal excretion of labeled bile acid), but they do not respond to cholestyramine therapy with a significant reduction in stool weight. Although the significance of these findings was not clearly established, the most likely interpretation is that bile acid malabsorption is a manifestation of an underlying intestinal motility or absorptive defect rather than the primary cause of diarrhea.

Studies of the antidiarrheal action of clonidine. Effects on motility and intestinal absorption

Clonidine, an alpha 2-adrenergic agonist, has been reported to stimulate the rate of electrolyte absorption in vitro, to alter intestinal motility in vivo, and to have antidiarrheal effects in animals. Experiments were performed in 8 healthy volunteers in order to evaluate the antidiarrheal effect of clonidine in humans. When diarrhea was induced by intragastric infusion of 2700 ml of balanced electrolyte solution over 90 min, oral administration of 0.3 mg of clonidine reduced the volume of rectal effluent by 48% (from 1233 +/- 62 to 640 +/- 77 ml, p less than 0.001), a clear-cut antidiarrheal effect. Clonidine increased total gut volume significantly (from 987 +/- 91 to 1830 +/- 142 ml, p less than 0.001), suggesting that clonidine exerted its antidiarrheal effect by altering gut motility, i.e., increasing the capacity of the gut and slowing the transit of fluid through the intestine. In other experiments, the net absorption rate of the whole gut during steady state total gut perfusion was measured. The rate of absorption of fluid was transiently stimulated by clonidine by 15% (from 696 +/- 77 to 799 +/- 55 ml/h, p less than 0.02), indicating an additional effect on mucosal cell function. These studies indicate that in this experimental diarrhea model, clonidine has antidiarrheal properties that are due largely to effects on motility of the gut but that clonidine also modestly stimulates the net rate of absorption by intestinal mucosa.

Mechanism of the antidiarrheal effect of loperamide

To determine whether the antidiarrheal effect of loperamide is due to an effect on intestinal motor function or to an acceleration of the rate of absorption by the intestine (as has been suggested recently), we studied absorption during experimental diarrhea produced by the rapid intragastric infusion of electrolyte solution. In studies in which a 2700-ml bolus of electrolyte solution was infused into the stomach over 90 min, loperamide delayed the appearance of rectal effluent in each of 5 subjects and decreased the volume of rectal effluent from 1090 +/- 118 to 770 +/- 73 ml (p = 0.05). When intragastric infusion was continued for 5 h, producing steady-state total gut perfusion, the volume of effluent produced per unit time and the concentration of a nonabsorbable polyethylene glycol marker in rectal effluent was not different with or without loperamide, indicating that loperamide did not alter the rate of absorption by intestinal mucosal cells. Loperamide also had no effect during steady-state perfusion when absorption rates were reduced by intravenous infusion of vasoactive intestinal polypeptide. Loperamide did substantially increase the intraluminal volume of the total gut, from 985 +/- 131 to 1764 +/- 195 ml (p less than 0.02). These results suggest that loperamide exerts its antidiarrheal effect by a change in the motor function of the intestine, which results in increased capacitance of the gut and a delay in the passage of fluid through the intestine. This change in motor function, rather than a change in the rate of absorption by intestinal mucosal cells, is responsible for the antidiarrheal effect of loperamide in our experimental diarrhea model.

Disorders of gastrointestinal motility associated with diabetes mellitus

Gastrointestinal symptoms such as vomiting, constipation, diarrhea, and fecal incontinence occur frequently in patients with diabetes mellitus. In a survey of 136 diabetic outpatients, 76% had one or more gastrointestinal symptoms, the commonest symptom being constipation (found in 60%). In many cases these symptoms are thought to be due to abnormal gastrointestinal motility that, in turn, may be a manifestation of diabetic autonomic neuropathy involving the gastrointestinal tract. The pathophysiology of these gastrointestinal symptoms, clarified in recent studies, and the clinical features and treatment of these problems in diabetic patients are reviewed.

Pathogenesis of fecal incontinence in diabetes mellitus: evidence for internal-anal-sphincter dysfunction

We studied 16 patients with diabetes and fecal incontinence. The onset of incontinence coincided with the onset of chronic diarrhea in most patients. Episodes of incontinence occurred when stools were frequent and loose; however, 24-hour stool weights were usually within normal limits. All patients had evidence of autonomic neuropathy, and one third had steatorrhea. Incontinent diabetics had a lower mean basal anal-sphincter pressure than 35 normal subjects (63 +/- 4 vs. 37 +/- 4 mm Hg; P less than 0.001), reflecting abnormal internal-anal-sphincter function. The increment in sphincter pressure with voluntary contraction (external-sphincter function) was not significantly different from normal. Incontinent diabetics also had impaired continence for a solid sphere and for rectally infused saline. In contrast, 14 diabetics without diarrhea or incontinence had normal sphincter pressures and normal results on tests of continence, even though 79 per cent had evidence of autonomic neuropathy and nearly half had steatorrhea. We conclude that incontinence in diabetic patients is related to abnormal internal-anal-sphincter function, and that as a group, diabetics without diarrhea do not have latent defects in continence.

Studies of the mechanism of the antidiarrheal effect of codeine

To determine whether the antidiarrheal action of opiate drugs in humans is due to enhanced intestinal absorption rates, as suggested by recent experiments in animals, or is due to altered intestinal motility, as traditionally thought, we studied the effect of therapeutic doses of codeine on experimental diarrhea and on the rate of intestinal absorption of water and electrolytes in normal human subjects. Our results show that codeine (30-60 mg i.m.) markedly reduced stool volume during experimental diarrhea induced by rapid intragastric infusion of a balanced electrolyte solution. There was, however, no evidence that codeine stimulated the rate of intestinal absorption in the gut as a whole or in any segment of the gastrointestinal tract, either in the basal state or when absorption rates were reduced by intravenous infusion of vasoactive intestinal polypeptide. We also measured segmental transit times to determine whether and where codeine delayed the passage of fluid through the intestine. Codeine caused a marked slowing of fluid movement through the jejunum, but had no effect on the movement of fluid through the ileum or colon. In other studies, we found that the opiate antagonist naloxone did not significantly affect water or electrolyte absorption rates in the jejunum or ileum. We conclude (a) that therapeutic doses of codeine increase net intestinal absorption (and thereby reduce stool volume) by increasing the contact time of luminal fluid with mucosal cells, not by increasing the rate of absorption by the mucosal cells; and (b) that endogenous opiates do not regulate intestinal absorption in humans.

Effect of sham feeding on gastric emptying

We studied the effect of vagal stimulation by sham feeding on gastric emptying in normal human subjects. When a saline test meal was infused into the stomach, simultaneous sham feeding did not alter the emptying of a nonabsorbable marker added to the meal or the volume of fluid emptied from the stomach. When a homogenized steak meal was infused, sham feeding caused a slight acceleration of emptying (47 +/- 2 vs. 53 +/- 2% marker recovered from the stomach 45 min after the meal, P less than 0.05). Gastric acid secretion in response to both meals was significantly augmented by sham feeding. Our results suggest that vagal stimulation by sham feeding has no effect on the emptying of isotonic saline and only a monor effect on gastric emptying of homogenized food in humans.

Distention-induced gastrin release: effects of luminal acidification and intravenous atropine

We evaluated whether gastric distention with saline test meals could release gastrin in healthy subjects and whether luminal acidification or atropine would modify this response. Distention with 700 ml saline adjusted to pH 5.0 led to a significant gastrin response (averaging 9 +/- 3 pg/ml above basal levels during the first 15 min after distention, P less than 0.02), whereas distention with 25 ml saline led to no gastrin release. Distention with 700 ml saline adjusted to pH 2.5 also led to a significant gastrin rise, which was nearly identical to that seen at pH 5.0. A small dose of atropine (2.3 micrograms/kg i.v.) significantly enhanced the gastrin response to 700-ml distention at pH 5.0 (average gastrin rise 20 +/- 3 pg/ml, P less than 0.02 vs. 700 ml without atropine). This enhancement of gastrin release by atropine was not due to changes in intragastric pH, because pH was held constant at 5.0 by in vivo intragastric titration. Enhancement was also not due to greater gastric distention after atropine, because gastric volumes after the 700-ml test meal were similar with or without atropine. Although atropine enhanced distention-induced gastrin release, atropine reduced acid secretion by more than 50% (P less than 0.05). Our findings indicate (a) that gastric distention releases significant amounts of gastrin in healthy subjects; (b) this gastrin response is resistant to inhibition by luminal acidification to pH 2.5 and (c) the gastrin response to distention is enhanced by atropine, suggesting that distention may also activate cholinergic pathways that inhibit gastrin release.

Fecal incontinence in chronic diarrhea. Report of a case with improvement after training with rectally infused saline

Patients with chronic diarrhea and fecal in continence are unable to retain as much rectally infused saline as patients without incontinence. We explored the effect of training such a patient to retain rectally infused saline. The patient was a 31-yr-old female with chronic diarrhea of obscure etiology who had daily episodes of fecal incontinence which markedly restricted her lifestyle. Training was accomplished by urging the patient to retain as much of a 25-min rectal infusion of 1500 ml saline as possible. After 10 training sessions, the patient increased her ability to hold rectally infused saline almost sevenfold. This increase was well maintained over 10 wk. In spite of continued diarrhea, the patient's incontinence did not recur after the first week of training, and she was able to resume a normal life. Anal sphincter pressure and a test of continence for a solid sphere did not change during or after training. This simple training technique has potential as a treatment for disabling fecal incontinence in patients with chronic diarrhea.