Adaptation of intestinal glucose transport in rats with diabetes mellitus occurs independent of hyperphagia

Chronic diabetes enhances intestinal absorption of glucose and induces hyperphagia. We examined the enhanced intestinal absorption of glucose in ad libitum-fed rats with streptozocin-induced diabetes mellitus and compared these results with those obtained from pair-fed diabetic animals. Maximal transport capacity (Vmax) and carrier affinity (K0.5) were determined by measuring jejunal and ileal short circuit current (Isc) responses to varying concentrations of 3-O-methyl-D-glucopyranose and D-glucose. Pair-fed diabetic animals maintained the same body weight as animals fed ad libitum, although ad libitum-fed diabetic rats had an increased oral chow intake. Age-matched control rats maintained a constant jejunal and ileal Vmax and K0.5 throughout the study. Diabetic rats fed ad libitum demonstrated an enhanced Vmax and K0.5 in both jejunum and ileum. Pair feeding diabetic animals further enhanced jejunal Vmax while lowering jejunal K0.5 levels. In contrast, pair feeding diabetic animals delayed and blunted changes in ileal Vmax and prevented changes in ileal K0.5. In conclusion, signals other than those of hyperphagia regulate kinetic changes in glucose absorption during diabetes mellitus. Furthermore, these changes have differing effects on jejunum and ileum.

Feeding rats a diet enriched with saturated fatty acids prevents the inhibitory effects of acute and chronic ethanol exposure on the in vitro uptake of hexoses and lipids

Chow-fed rats were given 15% ethanol in their drinking water for 4 weeks, and then for the next 2 weeks of ethanol exposure they were fed isocaloric semisynthetic diets enriched in either saturated (S) or polyunsaturated (P, linoleic acid) fats. Food intake was lower in ethanol-fed (ETH) than in control (C) rats, but the average body weight gain was similar in ETH and C fed S or P. Intestinal dry weight and the percentage of the intestinal wall comprised of mucosa were more than 2-fold higher in ETH than C fed P, whereas these values were 50% lower in ETH than C fed S. The in vitro jejunal uptake of glucose and galactose was higher in ETH than C fed S, whereas the converse was true when feeding P. These effects were due to differences in the values of the maximal transport rate (Vmax), the Michaelis constant (Km), and the contribution of passive permeation. The relative permeability of the intestine to lipids was unchanged by giving ethanol or by feeding S or P, but the individual rates of uptake of most medium- and long-chain fatty acids and cholesterol were lower in ETH fed P as compared with S. In a second series of studies the acute effect of ethanol exposure was examined: animals were fed S or P for 2 weeks and the intestine was then removed: when 5% ethanol was added directly to the test solutions, there was lower in vitro jejunal and ileal uptake of glucose and higher jejunal uptake of 18:2 when rats were previously fed P, but not in those fed S. In summary; (1) feeding an isocaloric polyunsaturated fatty acid diet has a trophic effect on the intestinal mucosa of animals chronically drinking ethanol; and (2) feeding rats a diet enriched with saturated fatty acids prevents the inhibitory effects of acute and chronic ethanol exposure on the in vitro jejunal uptake of glucose, galactose and lipids observed in animals fed a polyunsaturated diet. Thus, the effect of chronic consumption of ethanol on the active and passive jejunal uptake of nutrients is influenced by the type of lipids in the animal's diet.

Lovastatin prevents the impairment of endothelium dependent relaxation and inhibits accumulation of cholesterol in the aorta in experimental atherosclerosis in rabbits

STUDY OBJECTIVE

The aim was to determine the effect of the HMG CoA reductase inhibitor, lovastatin, on the loss of endothelium dependent relaxation and the accumulation of cholesterol in the aorta produced by feeding a diet enriched with cholesterol.

DESIGN

The study was conducted in two stages. In stage 1, New Zealand white rabbits were randomised into four groups. Group 1 (n = 15) was fed standard rabbit diet for 6 weeks. Groups 2 (n = 15), 3 (n = 12), and 4 (n = 12) were fed standard rabbit diet supplemented with 2% cholesterol for 2 weeks followed by standard rabbit diet only for the next 4 weeks. In addition, lovastatin (4 mg.kg-1.d-1) was given for the entire 6 weeks in group 3 and for the first 2 weeks only in group 4. In stage 2 a second group of animals was fed a diet supplemented with 0.5% cholesterol for 2 weeks in order to match the serum cholesterol levels in groups 3 and 4 of stage 1.

EXPERIMENTAL MATERIAL

Aortic tissue was removed for measurement of cholesterol content, endothelium dependent relaxation (to acetylcholine), contractile responses (to noradrenaline), relaxant responses (to sodium nitrite), and sudan staining. Serum was obtained for measurement of cholesterol and triglyceride concentrations.

MEASUREMENTS AND MAIN RESULTS

In stage 1, at the end of 2 weeks, the serum cholesterol was significantly lower in groups 3 and 4 than in group 2. At 6 weeks, endothelium dependent relaxation to acetylcholine (-6.0 log mol.litre-1) was impaired in group 2 compared to the other groups: group 1 78.5(SEM 5.0); group 2 43.5(7.8)%; group 3 79.4(4.6)%; group 4 84.7(3.4)%. The relaxant response to sodium nitrite was not impaired in group 2. Further, the aortic tissue cholesterol concentration in group 2 was significantly greater than that in group 1, at 355(65) v 105(10) nmol.mg-1 protein. In groups 3 and 4, the aortic cholesterol concentrations were significantly lower than those in group 2, at 74(4) and 94(17) nmol.mg-1 protein respectively. In stage 2, the serum cholesterol values were matched to those in groups 3 and 4 of stage 1. In these animals, after a further 4 weeks the aortic cholesterol was significantly greater than in group 3.

CONCLUSIONS

Lovastatin attenuates the accumulation of cholesterol and preserves endothelium dependent relaxation in this model of experimental atherosclerosis. It is likely that the latter is a secondary phenomenon.

Effect of dietary fat on diabetes-induced changes in liver microsomal fatty acid composition and glucose-6-phosphatase activity in rats

Experimental diabetes may manifest itself in a defect in liver microsomal fatty acid desaturation and increased activity of glucose-6-phosphatase (G-6-Pase). The present study was designed to determine whether these changes could be normalized by a change in the dietary fat consumed. Control and streptozotocin-induced diabetic rats were fed nutritionally adequate diets which varied in fatty acid composition. Fatty acid analysis of liver microsomal phospholipids revealed that non-diabetic control animals fed saturated fat (beef tallow) or a diet high in omega 3 fatty acids (fish oil) exhibited a significantly higher level of 18:2 omega 6 and a lower level of 20:4 omega 6 in the phosphatidylcholine and phosphatidylethanolamine fractions compared with diabetic animals. Control and diabetic animals fed the high linoleic acid diet had similar levels of 18:2 omega 6 in the microsomal phosphatidylcholine and phosphatidylserine fractions. Microsomal G-6-Pase activity was higher in diabetic than in control animals. Activity of G-6-Pase was lower in microsomes of control animals fed the soybean oil or the fish oil diet, but was not significantly reduced in diabetic animals fed high polyunsaturated fats. Blood glucose levels were similar in control groups fed the different diets, but the plasma hemoglobin Alc level was lower in diabetic animals fed the soybean oil diet. Cholesterol and triglyceride levels were lower in diabetic animals fed the fish oil-based diet. The results suggest that dietary fat manipulation has the potential to change at least some of the abnormalities in the microsomal membrane in experimental diabetes.

Lipid composition and peroxide levels of mucosal cells in the rat large intestine in relation to dietary fat

To examine whether dietary fat alters membrane lipid composition and peroxidation of polyunsaturated fatty acids in "non-proliferative" and "proliferative" cells in the large intestine, Sprague-Dawley rats were fed diets providing a polyunsaturated-to-saturated fatty acid ratio of 1.2 or 0.3 at a high or low level of fat intake for a 25-day period. Cell populations were isolated and the effect of dietary fat on membrane polyunsaturated fatty acid content and peroxide levels was determined. Neither fat level nor fatty acid composition of diet influenced total cholesterol, total phospholipids, and percentage of phospholipid classes in membrane phospholipids. Feeding the high fat and/or high polyunsaturated-to-saturated fatty acid ratio diet increased polyunsaturated fatty acid content of mucosal cell phospholipids. Increase in polyunsaturated fatty acid content was paralleled by a decrease in the monounsaturated fatty acid content of mucosal cell phospholipids. Membrane content of total saturated fatty acids was not significantly affected by diet. Variation in phospholipid fatty acid composition between "non-proliferative" and "proliferative" cells was observed. Lipid peroxide levels in mucosal cell lipid fractions were altered by dietary fat treatment. Animals fed high fat diets, compared to groups fed low fat diets, exhibited higher membrane peroxide levels when results are expressed as nmol/mg protein. Higher peroxide levels were observed in mucosal cells for rats fed high polyunsaturated-to-saturated fatty acid ratio diets when results were expressed per nmol of phospholipid. It is concluded that changes in fat level and fatty acid composition of the diet alters the mucosal cell membrane lipid composition in the rat large intestine and influences susceptibility of mucosal cell lipid to peroxidation. Further research is required to delineate which dietary factors--fat level, polyunsaturated-to-saturated fatty acid ratio, or both--have a primary influence on the degree of lipid peroxidation.

Feeding diets containing 2% cheno- or urso-deoxycholic acid or cholestyramine to rats for two weeks alters intestinal morphology and bile acid absorption

This study was undertaken to examine the effect of supplementing chow for 2 weeks with 2% cheno- (CDC) or ursodeoxycholic (UDC) acid or cholestyramine (CHOL) on the intestinal morphology and in vitro uptake of bile acids in adult rats. Food intake was higher in UDC and CHOL as compared with animals fed chow or CDC, or in animals pair-fed a chow-restricted diet (CRD). Body weight gain was lower in CDC and CRD but was unchanged by feeding UDC or CHOL. Jejunal mucosal surface area was similar in the five groups, although the ileal mucosal surface area was lower in UDC than in the other animals. Feeding UDC reduced the ileal uptake of cholic acid (C), taurocholic acid (TC), and glycocholic acid (GC). Feeding CDC had no effect on bile acid uptake except when compared with animals fed a chow-restricted diet. Feeding CHOL reduced the active ileal uptake of C, had no effect on the uptake of TC or GC or CDC, and was associated with increased uptake of stearic, linoleic, and linolenic acids. These effects were likely related to a direct effect of changes in the luminal bile acids rather than due to an indirect effect of the reduced food intake, since the ileal uptake of CDC and GC was greater in animals fed CDC than in those fed a chow-restricted diet with comparable weight gain. Thus, 2 weeks of feeding bile acids or bile acid binding agents may alter the form and function of the rat intestine, and as well may lead to changes in food intake and body weight gain.

Effect of nisoldipine on atherosclerosis in the cholesterol fed rabbit: endothelium dependent relaxation and aortic cholesterol content

STUDY OBJECTIVE

The aim was to determine the effect of the calcium channel blocker nisoldipine on the loss of endothelium dependent relaxation and the accumulation of cholesterol in the aorta produced by feeding a diet enriched with cholesterol.

DESIGN

12 week old New Zealand white rabbits were assigned randomly to four groups with the following dietary and drug regimens: group A--standard diet + 2.5% cholesterol (n = 45); group B--standard diet + nisoldipine (n = 9); group C--standard diet + nisoldipine + 2.5% cholesterol (n = 9); group D--standard diet (n = 9). After 3 weeks the cholesterol supplements were stopped and all animals were given the standard rabbit diet. The animals in groups B and C were given nisoldipine (1 mg.kg-1.d-1) by mouth for the entire 7 week period.

EXPERIMENTAL MATERIAL

Aortic tissue was removed for measurement of cholesterol content, endothelium dependent relaxation to acetylcholine, contractile responses to noradrenaline, relaxant responses to sodium nitrite, and sudan staining. Serum was obtained for measurement of cholesterol and triglyceride concentration.

MEASUREMENTS AND MAIN RESULTS

At 7 weeks, endothelium dependent relaxation to acetylcholine was impaired in group A compared to group D, while that in group C was not. Aortic tissue cholesterol content in group A was significantly greater than in groups B, C, and D. At 15 weeks, ie, 12 weeks after reversal of the diet, endothelium dependent relaxation had recovered in the animals in group A. There was a significant reduction in the aortic cholesterol content at this stage. In two subgroups of A (groups A2 and A4) which were given nisoldipine immediately after and 4 weeks after cessation of cholesterol feeding respectively, the drug was found to have no influence upon restoration of endothelium dependent relaxation. However, the drug appeared to promote the retention of cholesterol within the aorta after cessation of cholesterol feeding.

CONCLUSIONS

Nisoldipine protects against the accumulation of cholesterol and loss of endothelium dependent relaxation in the aorta of rabbits fed a diet supplemented with 2.5% cholesterol for three weeks. Administration of the drug after the lesions are established in the aorta also appears to retard the removal of cholesterol from the aorta.

Fish oil-enriched diet is mucosal protective against acetic acid-induced colitis in rats

Products of arachidonic acid metabolism are elevated in patients with inflammatory bowel disease and this elevation is correlated with disease activity. Eicosapentaenoic acid competes with arachidonic acid and alters eicosanoid biosynthesis. In this experiment, the possibility that eicosapentaenoic acid could be used in the treatment of inflammatory bowel disease was investigated by determining the effect of 6 weeks of a fish oil-supplemented diet, enriched in eicosapentaenoic acid, on colonic and ileal morphology, histology, and in vivo fluid absorption in rats with 4% acetic acid-induced colitis. The results of an eicosapentaenoic acid-enriched diet were compared with results of saturated and polyunsaturated fatty acid-enriched diets. In rats with misoprostol pretreated acetic acid-induced colitis, an eicosapentaenoic acid-enriched diet reversed net colonic fluid secretion to absorption and prevented macroscopic and histologic injury, compared with saturated and poly-unsaturated fatty acid-enriched diets, which did not. The fish oil mucosal protective effect occurred in the presence of a 30-fold enhancement of PGE2 synthesis. In rats with non-misoprostol pretreated acetic acid-induced colitis, an eicosapentaenoic acid-enriched diet returned ileal fluid absorption to control levels, as compared with saturated and polyunsaturated fatty acid-enriched diets, which did not. In conclusion, a fish oil (eicosapentaenoic acid)-enriched diet, but not a saturated- or a polyunsaturated-enriched diet, protected colonic and ileal net fluid absorption in an experimental model of inflammatory bowel disease.

Isocaloric modification of dietary lipids influences intestinal brush border membrane composition in diabetic rats

Variations in the dietary fatty acid composition and cholesterol content are associated with alterations in the intestinal uptake of hexoses and lipids in control and diabetic rats. Changes in the composition of the brush membrane (BBM) lipids may provide a possible mechanism for the observed alterations in transport properties. Accordingly, control and streptozotocin diabetic animals were fed one of four isocaloric semisynthetic diets for two weeks: beef tallow with low cholesterol, beef tallow with high cholesterol, fish oil with low cholesterol or fish oil with high cholesterol. BBM were prepared and assessed for marker enzyme activity and lipid composition. Fish oil feeding was associated with a reduction in total phospholipid content in control and diabetic jejunal and ileal BBM; this fall in total phospholipids was due to a reduction in BBM sphingomyelin. Cholesterol supplementation increased control jejunal BBM sucrase activity in animals fed beef tallow but reduced sucrase activity in animals fed fish oil. In fish oil fed diabetic animals, jejunal and ileal BBM alkaline phosphatase activity was increased with cholesterol supplementation. The elevation in BBM total phospholipids (phosphatidylethanolamine) associated with diabetes in beef tallow fed animals was not observed in the jejunal BBM of animals fed fish oil or in the ileal BBM of animals fed fish oil with high cholesterol. Thus, (a) feeding an omega-3 polyunsaturated fatty acid diet (fish oil) reduced total phospholipid content in BBM of control and diabetic animals, primarily due to a reduction in sphingomyelin; and (b) feeding an omega-3 polyunsaturated fatty acid diet or dietary cholesterol supplementation alter the activity of BBM enzymes. These results suggest that variations in dietary fat composition and the associated changes in BBM composition and enzyme activity contribute to altered intestinal function in diabetes.

Dietary omega-3 fatty acids partially correct the enhanced in vivo uptake of glucose in diabetic rats

This study was undertaken to determine the effects of feeding isocaloric semisynthetic diets high in saturated fatty acids from beef tallow (BT) or high in polyunsaturated fatty acids from fish oil (FO), on the clinical control and the in vivo uptake of varying concentrations of D-glucose into perfused jejunal and ileal loops of intestine of rats with streptozotocin diabetes. Jejunal and ileal weights were greater in diabetic than in control rats fed BT or FO, but the percentage of the intestinal wall comprised of mucosa was lower, resulting in a similar mass of mucosa in diabetic and in control animals. Feeding FO increased the jejunal unstirred water layer (UWL) resistance in control rats but decreased ileal UWL in diabetic animals; UWL was lower in diabetic than in control rats fed FO but was similar in those fed BT. The passive permeability coefficient (Pd) of the intestine for L-glucose was greater in diabetic than in control rats fed BT but not in those fed FO; Pd was higher in control rats fed FO than BT. The maximal transport rate (Vmax) and Michaelis constant (Km) of jejunal D-glucose uptake were lower in control rats fed FO than BT. Jejunal Vmax was lower in diabetic than control rats fed BT, yet was higher for those fed FO. The ileal Vmax for D-glucose uptake was greater in diabetic than in control animals fed BT or FO.(ABSTRACT TRUNCATED AT 250 WORDS)

Long-term effects of manipulations of dietary omega-3 fatty acids on clinical control and in vitro uptake of glucose and lipids in diabetic rats

The intestinal absorption of nutrients is increased in diabetic rats fed chow, yet short-term (two week) studies have demonstrated reduced and near-normal intestinal nutrient absorption in diabetic rats fed a diet high in polyunsaturated fatty acids. In this study we undertook to establish the effect of 10 weeks' feeding of isocaloric semisynthetic diets with high or low ratios of saturated (S)-to-omega-3 polyunsaturated (P) fatty acids ("fish oil") when given to streptozotocin diabetic rats. The fasting plasma glucose concentration was approximately 10% lower in diabetic rats fed P as compared with S, although the oral and intravenous glucose tolerance tests and the time-course of the oral and intravenous glucose-stimulated immunoreactive insulin levels were similar in P and S, as also were the levels of the hemoglobin A1C. The fasting plasma triglyceride concentrations were similar in P and S, but the fasting plasma cholesterol concentrations were approximately 20% lower in diabetic rats fed P as compared with S. Feeding P to diabetic animals was associated with a heavier intestine, which was comprised of a greater proportion of mucosal than submucosal tissue. The enhanced jejunal uptake of fatty acids 18:0 (stearic) and 18:2 (linoleic) as well as cholesterol observed in diabetic as compared with non-diabetic animals fed S was not observed in those fed P. The enhanced uptake of glucose in diabetic rats was also influenced by diet, with a lower rate for jejunal and ileal uptake of glucose in diabetic rats fed P than in those fed S.(ABSTRACT TRUNCATED AT 250 WORDS)

Dietary fat saturation alters diabetic rat brush border membrane phospholipid fatty acid composition

Alteration in dietary fatty acid composition produces changes in brush border membrane (BBM) fatty acid composition and changes in nutrient transport. Feeding a highly polyunsaturated fatty acid diet (P) reduces glucose uptake in diabetic rats to near control levels, whereas feeding a highly saturated fatty acid diet (S) enhances glucose uptake. Female Wistar rats were placed onto either a P or S diet for 5 weeks, injected with streptozotocin and continued on their respective diets for an additional 3 weeks. BBM were isolated, purified and extracted for analysis of fatty acyl constituents of phosphatidylcholine (PC) and phosphatidylethanolamine (PE). In jejunal and ileal BBM PC and PE, feeding S was associated with a decrease in total omega 6 fatty acids (18:2 omega 6), and an increase in the ratio of monounsaturated/saturated fatty acids as compared with animals fed P. In jejunal BBM PC and PE, the ratio of 18:2 omega 6/20:4 omega 6 was reduced in animals fed S as compared with those fed P. Diabetes was associated with fewer changes in BBM fatty acid composition in animals fed P as compared with those fed S. Feeding P to diabetic animals prevents the changes in BBM fatty acid composition observed when animals are fed S. Alterations in BBM lipid composition may be related to the enhanced permeability to glucose in animals fed S, while the similarity of BBM fatty acid composition in diabetic and control animals fed P may be related to the similar glucose uptake. The mechanisms controlling BBM lipid composition require further investigation, and may be important for the development of nutritional strategies for the control of diabetes.

Alterations in dietary fatty acid composition alter rat brush border membrane phospholipid fatty acid composition

Female Wistar rats were fed for 8 weeks a high polyunsaturated fatty acid diet (P) enriched with 18:2w6 and 18:3w3, or a high saturated fatty acid diet (S) enriched with 16:0, 18:0 and 18:1w9. There was a similar jejunal BBM fatty acid profile in phosphatidylcholine (PC) and phosphatidylethanolamine (PE) composition in animals fed P. However, feeding S altered the fatty acid composition of BBM phospholipids: for PC, feeding S increased total monounsaturated fatty acids (e.g. 18:1(9)) and reduced total polyunsaturated fatty acids, especially the total w6 fatty acids. For PE, feeding S increased only the total monounsaturated fatty acids. The ratio of monounsaturated/saturated fatty acids was increased for PC and PE. Fatty acid changes were more pronounced in the jejunal than ileal BBM. It is concluded that alterations in dietary fatty acid saturation: (a) influences intestinal BBM phospholipid fatty acid composition; (b) these changes are quantitatively and qualitatively different for PC and PE; and (c) changes are greater in the proximal than in the distal intestine. It is proposed that the previously reported diet-associated changes in active and passive intestinal transport are due at least in part to these alterations in the fatty acid composition in brush border membrane phospholipids.

Diet fat composition alters membrane phospholipid composition, insulin binding, and glucose metabolism in adipocytes from control and diabetic animals

The present study was designed to determine if diet fat-induced alteration in the fatty acid composition of the adipocyte plasma membrane alters insulin binding and the insulin responsiveness of glucose metabolism in control and diabetic states. Normal (control) and diabetic (streptozotocin-induced) rats were fed high fat semipurified diets providing a high or low polyunsaturated to saturated fatty acid (P/S) ratio. Feeding a high P/S diet increased the polyunsaturated fatty acid content of major membrane phospholipids of the adipocyte plasma membrane from both normal and diabetic animals. The diabetic state was associated with an elevated content of linoleic acid and a reduced level of arachidonic acid consistent with reduced delta 6-desaturation. Feeding the high P/S diet to diabetic animals increased membrane linoleic acid content and prevented the decrease observed in the arachidonic acid of membrane phospholipids. The high P/S diet was associated with increased insulin binding in nondiabetic animals but did not change the amount of insulin bound by cells from diabetic animals. Significantly (p less than 0.05) increased rates of insulin-stimulated glucose transport and lipogenesis (glucose incorporation into lipids) were observed in control animals fed the high as compared to the low P/S diet. The rates of insulin-stimulated glucose transport, oxidation, and lipogenesis were lower (p less than 0.05) for cells from diabetic as compared to control animals. However, feeding a high P/S diet significantly improved rates for all three of these functions (p less than 0.05). It is concluded that diet-induced alterations in membrane composition may provide a mechanism for improving the cellular response to insulin in cells from diabetic animals.

A model for demonstration of reversal of impairment of endothelium-dependent relaxation in the cholesterol-fed rabbit

This investigation was undertaken to determine whether it was possible to restore endothelium-dependent relaxation (EDR) in the cholesterol-fed rabbit model of atherosclerosis following discontinuation of the cholesterol. New Zealand white rabbits, approximately 8 weeks of age, were randomized into (i) control group (9 animals fed a standard rabbit diet) and (ii) experimental group (27 animals: fed the same diet supplemented with 2.5% cholesterol). The experimental animals were restored to the standard diet after 3 weeks. EDR to acetylcholine (-9.0 to -5.0 log mol/L) was examined in the experimental animals at 3, 7, and 15 weeks after commencement of the study (n = 9 at each stage) and the nine control animals examined after 7 weeks. At the end of 7 weeks, EDR to acetylcholine (-6.0 log mol/L) was significantly (p less than 0.05) impaired in the experimental group (34.3 +/- 3.8%) compared with that in the control group (79.8 +/- 3.0%). The loss of EDR was not apparent in the experimental group at 3 weeks (relaxation: 81.7 +/- 4.7%). At the end of 15 weeks, the EDR was significantly restored in the experimental group (relaxation: 63.6 +/- 5.1%). These findings demonstrate that it is possible to reverse the loss of EDR that occurs with cholesterol feeding in the rabbit by limiting the period of exposure to a high cholesterol diet.

Acid secretion and acid suppression in pathogenesis and healing of peptic ulcer disease

Numerous environmental and genetic factors have been implicated in the pathogenesis of peptic ulcer disease. Although the cause of this disorder has not been established, acid pepsin has been acknowledged at least as a permissive factor in its development. More important, inhibition of nocturnal or 24-hour intragastric acidity is predictably associated with ulcer healing. Famotidine 40 mg at bedtime maintains approximately one-third of pH readings at or above 3.5, reduces pepsin activity, and has no adverse effect on mean total serum gastric concentrations after one week of therapy. In addition, the effect of this dose of famotidine is comparable to ranitidine 300 mg at bedtime and predicts comparable rates of ulcer healing. Thus, monitoring of intragastric pH levels may be useful in identifying potent healers of peptic ulcer disease and in selecting optimal doses or timing of drug administration. Studies of famotidine using such measurements have suggested that this new H2-receptor antagonist is comparable to ranitidine in the healing of duodenal ulcers.

Alteration of the lipid composition of rat testicular plasma membranes by dietary (n-3) fatty acids changes the responsiveness of Leydig cells and testosterone synthesis

Experiments were conducted to assess whether changing dietary fat composition altered phospholipid composition of rat testicular plasma membranes in a manner that altered receptor-mediated action of luteinizing hormone (LH)/human chorionic gonadotropin (hCG). Weanling rats were fed diets that provided high or low cholesterol intakes and that were enriched with linseed oil, fish oil or beef tallow for 4 wk. Feeding diets high in (n-3) fatty acids decreased plasma and testicular plasma membrane 20:4(n-6) content. A marked reduction of the 22:5(n-6) content and an increase in the 22:6(n-3) content of testicular plasma membrane was found only in animals fed fish oil. A decrease in binding capacity of the gonadotropin (LH/hCG) receptor in the plasma membrane, with no change in receptor affinity, was observed for animals fed either linseed oil or fish oil diets. Dietary treatments that raised plasma membrane cholesterol content and the cholesterol to phospholipid ratio in the membrane were associated with increased binding capacity of the gonadotropin receptor. Feeding diets high in 18:3(n-3) vs. those high in fish oil altered receptor-mediated adenylate cyclase activity in a manner that depended on the level of dietary cholesterol. Feeding diets high in cholesterol or fish oil increased basal and LH-stimulated testosterone synthesis relative to that in animals fed the low cholesterol diet containing linseed oil. It is concluded that changing the fat composition of the diet alters the phospholipid composition of rat testicular plasma membranes and that this change in composition influences membrane-mediated unmasking of gonadotropin receptor-mediated action in testicular tissue.

The physiology of adaptation to small bowel resection in the pig: an integrated study of morphological and functional changes

This study examined the adaptive response to extensive small intestinal resection in the juvenile domestic pig. Control animals underwent an ileal transection with end-to-end anastomosis, whereas resected pigs had a resection of the mid-75% of the total small bowel length. Animals were followed for 16 weeks. Resected animals gained less weight than controls, with no significant difference in feed intake per unit animal weight. In vivo fat, protein, carbohydrate, and total energy absorption were reduced in resected animals. Resected pigs had increased in vitro passive ileal uptake of fatty acids, cholesterol, and L-glucose, but no change in active D-glucose uptake. Microscopic morphology was altered, with an increase in the size of villi, a decrease in villous density, and no net change in mucosal surface area per unit of serosal surface area. Gross bowel length and diameter increased proportionately more in the resected than the control groups. This study demonstrated that massive resection results in a significant change in nutritional status in the growing pig. Functional and morphological changes occur, demonstrating intestinal adaptation. These findings suggest that this model would be suitable for the study of therapeutic modalities for the short-bowel syndrome in humans.

Intestinal microsomes: polyunsaturated fatty acid metabolism and regulation of enterocyte transport properties

Recent evidence has suggested that transport of nutrients from the lumen to the interior of the gastrointestinal epithelium and exit of nutrients from the enterocyte to the circulation is governed by physicochemical properties of brush border and basolateral membranes, respectively. The main determinants of membrane properties are phospholipid, cholesterol, and fatty acyl chain composition (chain length and degree of unsaturation). Lipid synthesis occurs in enterocyte microsomes and the fine tuning of lipid composition is done at other subcellular sites by deacylation-reacylation or by changing the polar head group (e.g., by phosphatidylethanolamine methyltransferase). The present paper will focus on the mechanisms by which enterocyte membranes adapt functional properties in response to external stimuli. It is proposed that under the influence of internal or external stress, the enzymes of lipid metabolism in microsomes are modulated. These changes in lipid synthesis are reflected in other subcellular membranes, changing their physicochemical status and thus transport phenomena. One of the initial events appears to be alteration in desaturase enzyme activity. Our results suggest that desaturase activity and the fatty acyl profiles of the intestinal mucosal phospholipid rapidly respond to physiological conditions such as fasting and dietary fat treatment.

Critical period programming of intestinal glucose transport via alterations in dietary fatty acid composition

Intestinal adaptation occurs in response to physiological or pathological processes that include resection, aging, diabetes, radiation, lactation, chronic alcohol feeding, and feeding diets of varying lipid, protein, or carbohydrate composition. The mechanisms involved in the adaptive response include alterations in morphology, cell kinetics, digestive enzyme activity, transport, membrane lipid composition, and enzymes involved in lipid metabolism. This discussion will review the effect of aging and alterations in dietary fatty acid composition on the small intestine. In addition, it may be possible to program the intestinal response to aging by feeding diets of differing fatty acid composition during the critical period of weaning. Alterations in the ratio of polyunsaturated to saturated fatty acids in the diet modifies the age-associated changes in the intestinal uptake of glucose. The changes occur rapidly, progressively, and irreversibly, suggesting that the intestinal uptake of glucose is subject to critical period programming. The mechanism by which diet may modify the ability of the intestine to up- or down-regulate glucose transport requires further investigation.

Interactions of saturated, n-6 and n-3 polyunsaturated fatty acids to modulate arachidonic acid metabolism

Anti-thrombotic effects of omega-3 (n-3) fatty acids are believed to be due to their ability to reduce arachidonic acid levels. Therefore, weanling rats were fed n-3 acids in the form of linseed oil (18:3n-3) or fish oil (containing 20:5n-3 and 22:6n-3) in diets containing high levels of either saturated fatty acids (hydrogenated beef tallow) or high levels of linoleic acid (safflower oil) for 4 weeks. The effect of diet on the rate-limiting enzyme of arachidonic acid biosynthesis (delta 6-desaturase) and on the lipid composition of hepatic microsomal membrane was determined. Both linseed oil- or fish oil-containing diets inhibited conversion of linoleic acid to gamma-linolenic acid. Inhibition was greater with fish oil than with linseed oil, only when fed with saturated fat. delta 6-Desaturase activity was not affected when n-3 fatty acids were fed with high levels of n-6 fatty acids. Arachidonic acid content of serum lipids and hepatic microsomal phospholipids was lower when n-3 fatty acids were fed in combination with beef tallow but not when fed with safflower oil. Similarly, n-3 fatty acids (18:3n-3, 20:5n-3, 22:5n-3, and 22:6n-3) accumulated to a greater extent when n-3 fatty acids were fed with beef tallow than with safflower oil. These observations indicate that the efficacy of n-3 fatty acids in reducing arachidonic acid level is dependent on the linoleic acid to saturated fatty acid ratio of the diet consumed.

Radiation and the small intestine. Future perspectives for preventive therapy

Radiotherapy continues to enjoy a prominent role in the treatment of certain human tumors. Unfortunately, the undesired effect of radiation upon normal intestinal tissue often limits its therapeutic potential. While there is abundant information on the effects of radiation on the morphology of the intestine and on the proliferative process which occurs in the intestinal crypts, there is a paucity of information on the early and late effects of sublethal doses of radiation upon the absorptive functions of the intestine. The intestinal epithelium has a rapid turnover rate and is highly radiosensitive. Radiotherapy for malignant human neoplasms is a relatively safe and effective form of treatment, but it may become limited by its undesired side effects upon the gastrointestinal tract. A variety of clinical tests have been suggested as potential indicators of impending intestinal damage, but there is little information on the time course of radiation damage and the associated impairment of intestinal function. Such basic information is essential to assess early functional changes and to thereby allow for the development of suitable clinical tests to allow for the prediction of impending intestinal damage. Provision of this information to the radiotherapist would permit alterations to the timing or dose schedules of radiotherapy and would allow continued treatment, while avoiding or reducing unwanted side effects. In recent years, there has been extensive research on radiation injury to small intestine. This article will review some of the progress in this field, and will focus on potential future therapy to prevent or treat radiation damage to the intestine. These agents include WR-2721, enprostil, vasopressin, defined-formula diets and alterations in the ratio of dietary polyunsaturated-saturated fatty acids.