2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD)-induced decrease in the fluidity of rat liver membranes.

1. 2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCCD)-induced lipid peroxidation has previously been demonstrated by assessing the hepatic content of thiobarbituric acid reactive substances (TBARS) as well as the NADPH-dependent microsomal formation of TBARS as well as the NADPH-dependent microsomal formation of TBARS using malondialdehyde as the standard. 2. Changes in membrane fluidity as a result of lipid peroxidation may occur. Therefore the dose- and time-dependent effects of TCDD on lipid peroxidation in mitochondrial, microsomal, and plasma membranes, and changes in membrane fluidity in these subcellular fractions, were examined. Animals were treated with either 50 or 100 micrograms TCDD/kg orally, and killed 3, 6, or 9 days post-treatment. 3. Time-dependent increases occurred in TBARS content and formation following TCDD administration for all three membranes. Similar results were observed after 50 and 100 micrograms TCDD/kg. 4. Following TCDD administration, fluorescence polarization measurements as determined by the fluorescence polarization (r) and anisotropy parameter (a.p.) values demonstrated significant decreases in membrane fluidity in all membrane fractions, indicative of membrane structural alterations. 5. Excellent inverse correlations between lipid peroxidation and membrane fluidity were observed. Thus, decreased membrane fluidity and increased membrane damage may contribute to the toxic manifestations of TCDD as a consequence of an oxidative stress.

Suppression of diamine oxidase activity enhances postresection ileal proliferation in the rat.

To assess the influence of diamine oxidase activity on the adaptive process of the small bowel after resection, we administered aminoguanidine, a potent diamine oxidase inhibitor, to rats for 10 days after either small bowel transection (n = 5) or 80% jejunoileal resection (n = 7). Five or more additional animals from each group received saline as controls. Ileal mucosal homogenates from the resection group receiving aminoguanidine, when compared with those from resection controls, showed no diamine oxidase activity with increased putrescine content and ornithine decarboxylase activity. Mucosal proliferation, as measured by mucosal mass, protein content, and deoxyribonucleic acid content, was greater in the resected animals receiving aminoguanidine when compared with that of resection controls. Sucrase activity per gram of mucosa was almost identical in both resection groups. These results show that the suppression of diamine oxidase during the postresection adaptive period results in enhanced mucosal proliferation with no effect on mucosal functional differentiation. Diamine oxidase may play a regulatory role in adaptive intestinal proliferation.

Effects of dietary linoleic acid on mucosal adaptation after small bowel resection.

We have shown that dietary long-chain triglycerides and 16,16-dimethyl prostaglandin E2 enhance and aspirin impairs postresection mucosal adaptation in rats. The present studies examined the hypothesis that supplemental linoleic acid (LA) above the minimum requirement may enhance postresection mucosal adaptation through altered prostaglandin (PG) synthesis. Forty male Sprague-Dawley rats (105 +/- 5 g) were fed purified diet containing either 5% LA or 4% palmitic acid and 1% LA. After 2 weeks, 12 rats from each dietary group underwent 70% proximal jejunoileal resection and the remainder were sham-operated. Dietary regimens were continued for an additional 13 days. Mucosal fatty acid analysis of 1% LA group revealed a ratio of 20:3 n-9/20:4 n-6 lower than 0.2, indicating normal essential fatty acid status. Mucosal protein per centimeter bowel was higher in the 5% LA group compared to the 1% group, but mucosal DNA, maltase, and ex vivo PG synthesis were not affected. These results indicate that LA stimulates postresection mucosal hypertrophy, which does not appear to be related to PG synthesis.

Morphological and functional effects of 16,16-dimethyl-prostaglandin-E2 on mucosal adaptation after massive distal small bowel resection in the rat.

The ability of 16,16-dimethyl-prostaglandin-E2 (PGE) to augment mucosal adaptation 14 days after a 70% distal small bowel resection in the rat was evaluated. In resected (R) and sham operated (S) animals, subcutaneous PGE 75 mg/kg, 2 X/day, induced significant (p less than 0.05) increases in mucosal protein, DNA, and disaccharidase concentrations per centimetre of bowel. The respective per cent increases in the residual proximal small intestine compared with their respective untreated controls were: protein, R = 60%, S = 66%; DNA, R = 69%, S = 29%; maltase, R = 57%, S = 5%. The uptake of leucine by intestinal rings was significantly higher (50%) in the PGE treated group at a concentration of 2 mmol/l of substrate, while the uptake of glucose was similar in all groups. The drug appears to be an effective agent in stimulating morphological and functional adaptation after massive distal small bowel resection.

Reduced mucosal prostaglandin synthesis after massive small bowel resection.

Exogenous 16,16-di-methyl-prostaglandin (PG) E2 administration augments mucosal hyperplasia after massive small bowel resection in the rat. We, therefore, evaluated the ability of aspirin to inhibit mucosal PG synthesis in the small intestine and further evaluated the effects of reduced PG synthesis on mucosal adaptation after a 70% jejunoileal resection in male Sprague-Dawley rats. Sixteen of 27 resected and 8 of 16 sham-operated rats were given aspirin 20 mg/kg body wt subcutaneously every 8 h for 12 days; the remainder were given vehicle only. Although mucosal PGE2, PGF2 alpha, and thromboxane B2 synthesis were all reduced by aspirin administration to 20-40% of the control values, mucosal adaptation in resected animals as measured by mucosal weight, DNA, protein, and maltase levels was only inhibited in the distal ileum. Aspirin did not affect these values in the duodenum, the upper jejunum, and the midileum. This study provides evidence for some involvement of endogenous PGs in regulation of the mucosal adaptation process in the distal ileum after massive small bowel resection in the rat. However, lack of inhibition more proximally suggests that factors other than PGs are more important.

Essential fatty acid deficiency and postresection mucosal adaptation in the rat.

The effect of short-term (biochemical) and long-term (clinical) essential fatty acid (EFA) deficiency on mucosal adaptation was studied in a surgical model of short bowel syndrome. Rats fed an EFA-deficient diet for 4 wk had biochemical evidence of EFA deficiency (hepatic and red blood cell triene to tetraene ratios greater than 0.4). Resected animals (70% proximal jejunoileal resection) receiving an EFA-deficient diet had a significantly impaired intestinal mucosal hyperplasia response in all remaining small bowel segments compared with resected controls. The effect of refeeding a control diet to clinically EFA-deficient resected rats was also evaluated. Short-term refeeding (2 wk) of a control diet resulted in a significant return toward normal tissue triene to tetraene ratios. Concomitantly, refed animals had significantly greater mucosal adaptation in the remaining duodenal/jejunal segment compared with resected animals maintained on an EFA-deficient diet postoperatively. These experiments underscore the dynamic nature of tissue EFA status and the importance of fatty acids in the normal compensatory mechanisms of mucosal adaptation after resection.

Effects of cytochalasin B on the synthesis and secretion of plasma proteins by developing rat liver.

Antimicrotubular drugs such as colchicine impair plasma protein secretion markedly less from developing liver than from mature tissue, suggesting the reduced participation of microtubules in hepatic protein secretion during liver development. In order to evaluate the possible contribution of microfilaments to protein export by immature liver, we incubated slices prepared from adult and gestation day 19 fetal rat liver for up to 4 h with the antimicrofilamentous agent cytochalasin B and with colchicine in various concentrations. In adult tissue, cytochalasin B did not reduce either the synthesis or secretion of [14C]leucine-labeled proteins and albumin. Cytochalasin B decreased apparent albumin synthesis by fetal liver, but otherwise, its effects on [14C]leucine incorporation did not differ from those observed in the adult. In contrast with leucine, the uptake of [3H]glucosamine into both adult and fetal liver was reduced by cytochalasin B. When this reduced uptake was normalized to that in corresponding control incubations, [3H]glucosamine incorporation into glycoproteins was markedly diminished in fetal slices, but was unaffected in the adult. Despite this age-dependent difference, cytochalasin B only minimally affected glycoprotein secretion in each group. Cytochalasin B never modified the antisecretory effects of colchicine. These results suggest that during early development, liver protein synthesis is more sensitive to toxic effects of cytochalasin B than during adulthood. However, microfilaments are not required for plasma protein export at either time.

Augmentation of postresection mucosal hyperplasia by plerocercoid growth factor (PGF). Analog of human growth hormone.

Postresection villus hyperplasia is a major compensatory mechanism in the short-bowel patient. Substances capable of augmenting postresection mucosal hyperplasia could have therapeutic implications. Human growth hormone (hGH) and human growth hormone releasing factor (hGHRF) stimulate growth of the gastrointestinal tract; however, the diabetogenic actions of growth hormone limit its usefulness in clinical practice. Plerocercoid larvae of the tapeworm Spirometra mansonoides produce an analog of hGH void of diabetogenic side effects. We assessed effects of plerocercoid growth factor (PGF) on mucosal adaptation following 70% proximal jejunoileal resection in young rats. Mucosal weight, DNA, protein, and total sucrase activity per centimeter of bowel were increased in resected PGF-treated animals compared to resected controls. We conclude PGF augments intrinsic postresection mucosal hyperplasia following extensive intestinal resection.

Augmentation of mucosal adaptation following massive small-bowel resection by 16,16-dimethyl-prostaglandin E2 in the rat.

Survival following massive resection of the small intestine is often possible due to substantial hyperplasia of the mucosal surface in the remaining small intestine. While nutrients provide the major stimulus for hyperplasia in the clinical setting, the availability of drugs to augment this process would have obvious therapeutic implications. We evaluated the ability of 16,16-dimethyl-prostaglandin E2 (PGE2 to augment mucosal hyperplasia following massive small bowel resection in the rat. Three groups of 7 Sprague-Dawley rats, 160 g body weight, were subjected to 70% jejunoileal resection. One group was given 150 micrograms/kg of 16,16-dimethyl-PGE2 intragastrically twice daily, a second group 75 micrograms/kg subcutaneously, and a third group was untreated. After 17 days, segmental evaluation of mucosal mass in the remaining small intestine was determined by measuring mucosal protein, DNA, and disaccharidase levels. A significantly greater increase in mucosal mass was developed in the duodenum proximal to the anastomosis in both treatment groups, but neither the proximal nor distal ileum demonstrated significantly more adaptation. Histological examination in the duodenum confirmed the presence of a greater adaptive response in both the intragastrically and subcutaneously treated animals. 16,16-dimethyl-PGE2 appears to augment mucosal adaptation following massive small bowel resection in the rat, primarily in the very proximal small intestine.

Effect of zinc deficiency on mucosal hyperplasia following 70% bowel resection.

We evaluated the effect of zinc deficiency on the development of mucosal hyperplasia in male Sprague-Dawley rats following 70% small-bowel resection: 20 underwent 70% jejunoileal resection, another 20 were sham operated. Half of each group were made zinc deficient by force-feeding technique. Operations were then performed, and feedings were continued for another 9 days. While mucosal weight did not differ between zinc-deficient and zinc-replete animals, whether or not they underwent resection, mucosal protein and DNA levels were decreased in both resected and sham-operated, zinc-deficient animals. Functional indices were also affected. Maltase activities were decreased in zinc-deficient animals in the midileum. Mucosal zinc-dependent enzymes, alkaline phosphatase and leucine aminopeptidase, were likewise depressed in zinc-deficient animals. Findings suggest that zinc deficiency in short-bowel syndrome will likely impair mucosal hyperplasia.

Effect of pure zinc deficiency on glucose tolerance and insulin and glucagon levels.

The effect of zinc deficiency on glucose tolerance was investigated using intragastric force feeding to obviate decreased food intake and altered eating patterns. Three groups of weanling male Sprague-Dawley rats were fed a purified zinc-deficient diet: zinc-deficient, ad libitum-fed animals (ZDA) were offered powdered zinc-deficient diet; zinc-replete, force-fed controls (ZRF) were tube fed a diet blended with water containing 25 ppm of zinc; zinc-deficient, force-fed animals (ZDF) were similarly tube fed the zinc-deficient diet. The ZRF and ZDF groups received a diet of identical amount based on the intake of ad libitum-fed, zinc-replete rats. After 8 days of feeding, the ZDF group had impaired glucose tolerance curves, yet blood insulin and glucagon levels were normal. The ZDA group had normal glucose tolerance with low insulin levels compared with the ZRF group. The islet cell morphology among the three dietary groups were similar. These results suggest that the glucose intolerance observed in ZDF rats is not due to altered blood insulin and glucagon levels but rather to peripheral resistance to insulin action.

Effects of isolated zinc deficiency on the composition of skeletal muscle, liver and bone during growth in rats.

We investigated the effects of zinc deficiency on body composition by using intragastric force-feeding to obviate decreased food intake and altered eating patterns. Weanling male Sprague-Dawley rats were fed a purified zinc-deficient diet: the ad libitum-fed control group (AL; eight rats) was given powdered diet and water containing 25 ppm zinc; the zinc-replete group (ZN; nine rats) was force-fed a diet blended with water containing zinc in an amount of equal caloric intake to the AL group and allowed access to water containing zinc. The zinc intake of ZN rats was approximately twice that of AL rats based on water intake. The zinc-deficient group (ZD; 13 rats) was fed similarly to the ZN group except deionized water was used for diet preparation and drinking water. After 8 d, body and muscle weight were lower in the ZD group than in the ZN group. Femur weights were similar in the two groups. Serum, liver and femur zinc concentrations were 85, 22 and 42% lower, respectively, in the ZD group than in the ZN group. Serum glucose, relative liver weight, liver glycogen and liver lipids were higher, but muscle and liver DNA were lower in the ZD group than in control groups.

Effects of short-term isolated zinc deficiency on intestinal growth and activities of several brush border enzymes in weaning rats.

To determine whether zinc has a specific role on intestinal growth and function, three groups of male weanling Sprague-Dawley rats were fed a semipurified zinc-deficient diet: ad libitum fed group received powdered diet and water containing 25 ppm of zinc; force fed (ZN, ZD) groups were fed identical amounts of diet to the ad libitum fed group by intragastric infusion three times per day. The diets were aqueous suspensions made with either deionized water (ZD) or water containing 25 ppm of zinc (ZN), and additional drinking water with (ZN) or without zinc (ZD) was offered ad libitum. Rats were sacrificed after 8 days of feeding. The ZD group showed growth arrest, perioral and periorbital dermal lesions, and abdominal distention within 8 days of feeding. Mucosal DNA, protein, sucrase, maltase, lactase, leucine aminopeptidase, and alkaline phosphatase were significantly decreased in the ZD group, whereas intestinal length, weight, and mucosal weight were unaltered. These results suggest that short-term isolated zinc deficiency impairs growth, digestion, and absorption in the rat small intestine, even in the absence of associated protein calorie malnutrition.

Effect of intestinal location on growth and function of neomucosa.

Growing intestinal neomucosa in patched intestinal defects has been investigated as a means of permanently increasing the absorptive capacity in the short bowel syndrome. Several factors, including luminal contents, appear to affect the growth and function of the neomucosa. The purpose of this study was to compare function and rate of growth of neomucosa in patched defects of the jejunum and ileum. In both the jejunum and ileum of 11 New Zealand white male rabbits 2 X 5-cm patched intestinal defects were created using the serosal surface of adjacent colon. The animals were sacrificed at 4 weeks (n = 6) and 8 weeks (n = 5) after operation. Grossly there was more complete coverage of the defect by neomucosa in the ileum at both 4 and 8 weeks (99.1 +/- 1.1% vs 92.6 +/- 6.3% overall P less than 0.005). Villous height of the ileal neomucosa was similar to normal mucosa at 8 weeks (209 +/- 21 vs 244 +/- 18 m) but was significantly less in the jejunum (209 +/- 16 vs 273 +/- 16 m, P less than 0.005). Glucose uptake by neomucosa was greater in the ileum than the jejunum (3.34 +/- .84 vs 2.39 +/- .46 nmole/min/mg, P less than 0.05) but was similar to normal mucosa at both sites. Disaccharidase activity (lactase, sucrase, and maltase) was similar in both jejunum and ileum but was significantly less in ileal neomucosa than in normal mucosa (P less than 0.005).(ABSTRACT TRUNCATED AT 250 WORDS)

Carcinogenicity of diallylnitrosamine following intragastric administration to Syrian hamsters.

Single and multiple intragastric doses of diallylnitrosamine [(DAN) CAS: 16338-97-9] administered to Syrian golden hamsters induced tumors, primarily of the respiratory tract, in which the nasal cavity epithelium was the preferred site. When compared to the effect of DAN after subcutaneous administration at equal doses, the incidence of respiratory tract tumors was lower but that of hepatic tumors was higher, suggesting partial metabolism of DAN in the liver. Comparative metabolic and mutagenesis studies in BD IX rats (which reportedly are refractory to the carcinogenic effects of DAN), in Wistar rats, and in Syrian hamsters showed that a greater proportion of orally administered DAN was exhaled by both rat strains (12-19%) than by hamsters (2-4%). The activity of the microsomal fraction of the hamster liver for metabolizing DAN to allyl alcohol was about 10 times higher than that in rats, whereas no significant species differences were found with the cytosolic fraction. Pretreatment of animals with phenobarbital (PB) or pregnenolone-16 alpha-carbonitrile (PCN) did not influence either microsomal or cytosolic enzyme activities in hamsters, whereas about a tenfold increase in enzyme activities was seen after pretreatment with PB in both rat strains and following PCN in Wistar rats. Moreover, in bacterial mutagenesis assays, hamster liver microsomes were twice as active as those in BD IX rats. The results are discussed in relation to the carcinogenicity of DAN in rats and hamsters.

Selective induction of nasal cavity tumors in rats by diallylnitrosamine.

Weekly intragastric administration of 20, 40, and 80 mg/kg body weight diallylnitrosamine to BD IX rats selectively induced nasal and paranasal cavity tumors with incidences of 30%, 85%, and 65% in females and of 0%, 75%, and 80% in males, respectively. All tumors were carcinomas of the olfactory region, and 95% were invasive. Only a few papillomas in the anterior region were found simultaneously with the carcinomas.

Effect of high percentage medium-chain triglyceride diet on mucosal adaptation following massive bowel resection in rats.

Patients undergoing massive small bowel resection for a variety of conditions develop severe nutrient malabsorption which gradually improves through mucosal hyperplasia in the remaining small intestine. Following massive small bowel resection, patients are generally fed elemental diets, often containing high concentrations of medium-chain triglycerides. We evaluated the effect of high percentage medium-chain triglyceride feeding on mucosal adaptation following massive small bowel resection in rats. Twenty 150-g Sprague-Dawley rats were subjected to 60% jejunoileal resection. Another 20 animals received sham operations. One-half of each group were fed a diet containing 83% of the fat as medium-chain triglycerides, the remainder were fed a diet containing 40% medium-chain triglycerides. Animals were pair-fed for 2 wk and subsequently killed. The remaining bowel was removed and unidirectional glucose and leucine uptake were measured using isolated sacs. Mucosal wet weight, protein, and sucrase content were determined. Animals fed medium-chain triglycerides demonstrated decreased mucosal weight in the proximal bowel, decreased mucosal sucrase activity in the proximal bowel, and decreased mucosal leucine uptake in the distal bowel. While medium-chain triglycerides offer an advantage to patients with short bowel syndrome because they are easily absorbed, they may not stimulate the same degree of mucosal adaptation following resection as long-chain triglyceride feedings.

Effect of casein versus casein hydrolysate on mucosal adaptation following massive bowel resection in infant rats.

Little is known concerning the effects of elemental diets on bowel adaptation following massive resection. Fourteen of 28 Sprague-Dawley rats (40-45 g) were subjected to a 60% jejunoileal resection. Seven of the resected animals and seven sham-operated controls were then placed on a diet containing all protein in the form of casein hydrolysate. The remaining seven resected animals and seven sham-operated controls were placed on a comparable diet in which all the protein was casein. Each control animal was paired with a resected animal. After 2 weeks, unidirectional glucose and leucine transport was determined from intestinal sacs made from the proximal 3 cm and distal 3 cm of the remaining bowel. The midportion was used for the determination of mucosal weight and protein and sucrase content. When expressed as a percent increase over control values per centimeter of bowel, only sucrase levels were significantly elevated in the distal bowel in casein hydrolysate-versus casein-fed animals. The mucosal protein level, mucosal weight, and glucose uptake did not differ from control values when expressed as a percent change. Leucine uptake was significantly decreased in casein hydrolysate-fed animals when compared to that in casein-fed animals in both the proximal and distal bowel, again when expressed as a percent change from the control values. The administration of protein in the form of casein hydrolysate following massive bowel resection does not adversely affect mucosal hyperplasia occurring after resection but may have an adverse effect on the enhancement of amino acid absorption.

The formation of N-nitrosomethyl(2-oxopropyl)amine from N-nitrosobis(2-oxopropyl)amine in vivo.

After injection of N-nitrosobis(2-oxopropyl)amine (BOP) (10 mg/kg) to male Syrian golden hamsters there were there concentrations of BOP and many of its metabolites in the hamster pancreas compared with the liver and salivary gland. Also, a potential methylating metabolite of BOP, N-nitrosomethyl(2-oxopropyl)amine, was found in both tissues.