Harold P. Schedl

Effect of Insulin and Oral Glutathione on Glutathione Levels and Superoxide Dismutase Activities in Organs of Rats With Streptozocin-Induced Diabetes

The effect of insulin or glutathione treatment on glutathione content of liver and jejunal mucosa and on superoxide dismutase (SOD) activity of liver, kidney, and erythrocytes was investigated in pair-fed animals with streptozocin (STZ)-induced diabetes. Diabetes lowered hepatic glutathione concentration, but glutathione concentration of the jejunal mucosa was not affected. Insulin, but not oral glutathione, restored hepatic glutathione concentration to normal levels. Diabetes depressed activity of the cytosolic form of SOD in liver, kidney, and erythrocyte. Treatment of diabetic rats with oral glutathione or intramuscular insulin increased cytosolic SOD activity of renal cortex and liver (but not erythrocytes) to control levels. These results suggest a link between glutathione metabolism and cytosolic SOD activity in diabetes.

Effects of carbohydrate type and concentration and solution osmolality on water absorption

We studied intestinal absorption of solutions containing either one (glucose, Glu, or maltodextrin, Mal) or two (fructose, Fru, and Glu or sucrose, Suc) transportable carbohydrate (CHO) substrates using segmental perfusion technique in eight healthy male subjects. These CHO were either free or directly transportable monosaccharides (Glu, Fru), bound as the disaccharide (sucrose, Suc), or as oligomers (maltodextrins, Mal). [CHO] was varied from 6% to 8% (120-444 mmol.1(-1)). All solutions contained low [Na+] (15-19 mEq) and [K+] (3-4 mEq). Solutions osmolalities varied from 165 to 477 mOsm.kg(-1). Osmolalities in the test segment ranged from 268 to 314 mOsm.kg(-1). The regression line of osmolality with water absorption differed for single as compared with multiple substrate solutions. The significantly different intercepts of these two regression lines suggest that solutions with multiple substrates produce greater water absorption at a given osmolality than those with one. Comparing all solutions, test segment solute flux (partial r = 0.69) was more important than mean osmolality (partial r = 0.32). In conclusion, solutions with multiple substrates stimulate several different solute absorption mechanisms yielding greater water absorption than solutions with only one substrate.

Total Recovery Studies of Nonabsorbable Indicators in the Rat Small Intestine

Summary Polyethylene glycol, phenol red, polyethylene glycol- 14 C, inulin-carboxyl- 14 C, and mannitol-1- 14 C were compared as nonabsorbable indicators in the rat small intestine. The indicator solution was perfused through the lumen of the in situ intestine. The indicator content of collected perfusion solution and luminal washings was used to calculate total recovery. Mean total recoveries for all indicators were more than 95 % except for tracer mannitol-1- 14 C. When carrier mannitol was added, recovery of mannitol-1- 14 C was satisfactory. Even the indicators polyethylene glycol and phenol red were only 97 to 98 % recovered. Total indicator recoveries from serum and urine could not explain the 2 to 3 % loss of indicator. If recovery data are a valid measure of indicator absorption, indicators underestimate net water absorption by 2 to 3 %. The radioactively labeled indicators are analyzed readily and should prove to be increasingly useful.

The small intestinal basic electrical rhythm (slow wave) frequency gradient in normal men and in patients with a variety of diseases

Summary We used an intraluminal salt-bridge electrode to record the small intestinal slow wave or basic electrical rhythm (BER) at many levels of the intestine. We found a descending BER frequency gradient in 12 normal subjects and in 13 patients with a variety of diseases. The descending gradient was stepwise in some normal subjects but linear in others. The data from normal subjects have bfeen pooled to establish a range of normal values. The mean frequency at the ligament of Treitz was 11.80 cycles per min (sd 0.32); at 225 to 239 cm below the incisor teeth it was 9.39 cycles per min (sd 0.18). Abnormal gradients were found in patients with hyperthyroidism and hypothyroidism, and in a patient with hyperparathyroidism, gastric hypersecretion, and diarrhea. The form and magnitude of this gradient may be important determinants of small intestinal motor function.

Calcium and sodium transport and vitamin D metabolism in the spontaneously hypertensive rat.

Serum ionized calcium levels are lower and immunoreactive parathyroid hormone levels are higher in the spontaneously hypertensive (SH) rat than in the normotensive Wistar-Kyoto (WKy) control. We postulated that there is either a defect in the regulation of vitamin D metabolism by parathyroid hormone or that the gut target organ for vitamin D in the SH rat is unresponsive. To test these hypotheses we measured serum concentrations of vitamin D metabolites and intestinal transport of calcium and sodium. Compared with that of WKy controls, in vitro calcium transport by duodenal sacs of the SH rat was decreased (P less than 0.001) at 5 wk, before the development of hypertension, and at 12 wk, after hypertension was well established. When measured in vivo in the most proximal 20 cm of small intestine, maximum velocity (Vmax) for calcium transport was decreased (P less than 0.05) and net absorption of sodium and water was increased (P less than 0.05) in SH rats as compared with WKy rats. Vmax for calcium transport was also decreased (P less than 0.05) in the most distal 20 cm of small intestine of SH rats, but net sodium and water transport were the same in SH and WKy rats. At 12 wk, serum concentration of 1,25-dihydroxycholecalciferol [1,25-(OH)2D3] was the same in both SH and WKy groups, but its precursor, 25-hydroxycholecalciferol, was increased (P less than 0.05) in the SH rat. We conclude that in the SH rat: (a) the concentration of 1,25-(OH)2D3 is inappropriately low in relation to the elevated immunoreactive parathyroid hormone and the depressed calcium absorption, suggesting a defect in the regulation of vitamin D metabolism; and (b) the depressed calcium absorption, in the setting of normal concentrations of [1,25-(OH)2D3], demonstrates unresponsiveness of the gut to vitamin D and may explain in part the low serum ionized calcium found in earlier studies. The presence of these abnormalities before we found a significant difference in blood pressure suggests that they may be causal, not secondary, to the hypertension.

Upper limit for intestinal absorption of a dilute glucose solution in men at rest.

We studied gastric and intestinal function by gastric intubation/intestinal perfusion in six healthy male volunteers to evaluate optimal use of a 6% glucose-electrolyte (GES) solution. Gastric volume, residual volume, emptying rate, and secretion were measured for an initial 763 +/- 19 ml gastric load of GES and at the beginning and end of four additional gastric loads (2.2 ml.kg-1; approximately 180 ml) given at 10-min intervals. The relatively high gastric (713 +/- 58 ml) and residual (507 +/- 26 ml) volumes maintained a high gastric emptying rate (19.5 +/- 1.4 ml.min-1). Composition of the GES emptied into the duodenum was also measured in this first experiment. In a second experiment, this modified solution was infused (triple lumen tube) into the duodenum at a rate equal to gastric emptying rate, or at 38 or 77% greater rates. Absorption of water (11.3-12.9 ml.h-1.cm-1) and glucose 4.3-5.6 mmol.h-1.cm-1) were similar at all perfusion rates during the second experiment. We conclude that duodenojejunal segmental absorption rates of water and glucose produced by a rapid, sustained gastric emptying rate cannot be increased by delivering a greater load of glucose and water by intestinal perfusion.

Absorption of l-methionine from the human small intestine

Absorption of L-methionine was measured in all parts of the human small intestine using transintestinal intubation and perfusion. In four normal subjects, adsorption was higher in the proximal than in the distal intestine. In two patients with nontropical sprue in relapse, there was a proximal zone of low absorption with higher absorption distally. In all parts of the small intestine, absorption showed rate-limiting kinetics as methionine concentration was increased. In normal subjects, the proximal K(m) (Michaelis constant) was more than 3 times higher than the distal, which suggests a difference in transport mechanisms between the two segments.

Intestinal Adaptation to Dietary Calcium Restriction: In Vivo Cecal and Colonic Calcium Transport in The Rat

Small intestinal calcium transport adapts to dietary calcium restriction, but conservation of calcium by the ileum is incomplete. To examine the role of large intestine in calcium homeostasis, weight-matched growing rats were placed on semisynthetic diets containing 1.2 or 0.02% calcium. After 3 to 4 weeks, net calcium movements in cecum and colon (large bowel excluding cecum and distal rectum) were studied in vivo by perfusing a 0.4, 0.8, or 3.4 mM calcium solution. In animals taking 1.2% calcium, the cecum absorbed calcium actively at 0.8 mM; the colon showed net secretion except at 3.4 mM. In calcium-restricted animals, the cecum absorbed at all concentrations; the colon reduced secretion at 0.4 mM, converted to net absorption at 0.8 mM, and greatly increased net absorption at 3.4 mM. These observations suggest that the large intestine may have a role in calcium homeostasis, particularly when dietary calcium is restricted.

Nonabsorbed Indicators: A Comparison of Phenol Red and Inulin-14C and Effects of Perfusion Technique

Nonabsorbed indicators should be completely recoverable from the intestinal lumen and have an intraluminal distribution pattern identical to the unabsorbed residue of the substance(s) whose transport is being studied. Since small amounts of all nonabsorbed indicators are lost, an error is introduced when indicators are used in transport studies. We examined this error with phenol red and inulin-carboxyl-14C in the small intestine of the rat using two common techniques: (1) single pass perfusion, in which a relatively large volume and amount of indicator traversed the lumen once; and (2) recirculation, in which a relatively small volume and amount of indicator was repeatedly passed through the lumen. We found no difference between techniques in the absolute rate of loss of indicator. However, when a smaller quantity of indicator was recirculated, the percentage loss of indicator was significantly greater. Since indicator concentration is used to calculate net water flux, any loss of indicator causes spuriously low final concentrations (spuriously high estimates of secretion). The greater percentage loss of indicator with recirculation doubled this error. Moreover, the indicators differed significantly: more phenol red was lost than inulin, and about 20% more was washed from the mucusal surface (adsorption). Thus, experimental design as well as the behavior of individual indicators significantly influence the results of transport studies.

Cortisol absorption in man.

Summary Absorption of cortisol from Ringers solution in the normal human small gut was characterized by a distally decreasing gradient. This defines a membrane gradient in terms of this lipophilic-hydrophilic molecule. Glucose in the Ringers increased cortisol absorption uniformly throughout the small gut, but the gradient was maintained. It is hypothesized that this is a specific metabolic effect of high glucose concentration on mucosal cells throughout the small gut. It was concentration dependent, and was detected in the earliest measurements we could make, continued throughout glucose perfusion, and persisted for about 2 hours after glucose was stopped. Net water absorption from the gut was higher with glucose-Ringers than with Ringers and showed a gradient. The glucoseinduced increase in water absorption was chiefly in the upper small gut ( In patients with small gut malabsorption, cortisol and net water absorption rates were reduced, and in some cases their gradients were reversed.