Intraduodenal infusion of lysophosphatidylcholine restores the intestinal absorption of vitamins A and E in rats fed a low-zinc diet

Our previous work has shown that the lymphatic absorptions of lipids and lipid-soluble vitamins, retinol and alpha-tocopherol (alphaTP), are lowered markedly in rats fed a low-zinc (LZ) diet in parallel with lower lymphatic phospholipid outputs. Phosphatidylcholine (PC), when infused enterally, restored the absorptions of fat and retinol, but further lowered the absorption of alphaTP in rats fed the LZ diet. This study was conducted to determine whether a luminal infusion of lysophosphatidylcholine, a product of PC hydrolysis by pancreatic phospholipase A2 (PLA2), would simultaneously restore the absorptions of retinol and alphaTP in LZ rats. Rats were trained to consume two meals per day and were divided into two groups. One group was fed an AIN-93G diet containing a LZ (3.0 mg Zn/kg), and the other was fed the same diet, but containing adequate zinc (AZ; 30.0 mg Zn/kg) for 6 weeks. Rats with lymph cannula were infused at 3.0 ml/hr for 8 hr with a lipid emulsion containing retinol, alphaTP, and 14C-labeled triolein (14C-oleic acid) with or without 1-oleoyl-2-hydroxy phosphatidylcholine (lysoPC) in 24 ml of PBS (pH 6.5). When the lipid emulsion without lysoPC was infused, the absorptions of retinol and alphaTP were significantly lower in LZ rats (retinol, 13.2+/-1.5 nmol; alphaTP, 430.6+/-66.8 nmol) than in AZ rats (retinol, 18.2+/-1.0 nmol; alphaTP, 543.8+/-58.9 nmol). The lower absorptions of the vitamins in LZ rats occurred in parallel with a significant decrease in 14C-oleic acid absorption. When the emulsion containing lysoPC was infused, however, absorptions of the vitamins (retinol, 18.4+/-3.0 nmol; alphaTP, 777.2+/-92.1 nmol) in LZ rats were restored completely to the control levels (retinol, 20.4+/-2.8 nmol; alphaTP, 756.3+/-136.1 nmol). The results suggest that the luminal hydrolysis of PC to lysoPC by PLA2 may be impaired in LZ rats, resulting in impaired absorption of fat and the fat-soluble vitamins.     

Feeding of a low-zinc diet lowers the tissue concentrations of alpha-tocopherol in adult rats

Previous work has shown that a low dietary intake of zinc for a short duration significantly lowers the lymphatic absorption of α-tocopherol (αTP) in adult male rats. The present study investigated whether the nutritional status of zinc is critical in maintaining the tissue levels of the vitamin. One group of rats was fed an AIN-93G diet containing 3 mg zinc/kg (low zinc, LZ) and the other was fed the same diet but containing 30 mg zinc/kg (adequate zinc, AZ). Food intakes between groups were matched by feeding two meals per day. At 6 wk, the body weights (356±8 g) of LZ rats reached 98% those (362±10 g) of AZ rats. Feeding of the LZ diet for 6 wk significantly lowered the concentrations of both αTP and zinc in the liver, kidney, heart, testis, and brain. No consistent relationships between αTP and zinc concentrations were observed in other tissues such as spleen, lung, gastrocnemius muscle, and retroperitoneal fat tissues. The concentrations of αTP in the liver, testis, brain, spleen, heart, and kidney were significantly correlated with the tissue concentrations of zinc. The LZ diet slightly but significantly increased the total lipid contents (mg/g) of liver, kidney, heart, and spleen. However, the tissue levels of phospholipid (μmol/100 mg lipid) in the heart, lung, testis, and spleen were decreased significantly in LZ rats. These findings indicate that low zinc intake results in a pronounced decrease in the animal’s αTP status under the conditions of matched food intakes, body weights, and feeding patterns. The lower tissue levels of αTP may explain in part the compromised antioxidant defense system and increased susceptibility to oxidative damage observed in zinc deficiency.     

Low zinc intake decreases the lymphatic output of retinol in rats infused intraduodenally with beta-carotene

Previously, we have shown that the lymphatic absorption of retinol is significantly decreased in rats fed a low zinc diet. This study was conducted to determine whether the absorption of beta-carotene also is altered in zinc-deficient male rats. The absorption of beta-carotene was estimated by determining the amount of retinol appearing in the mesenteric lymph during intraduodenal infusion of beta-carotene. One group of rats was fed the AIN-93G diet but low in zinc (LZ; 3 mg/kg) and the other was fed the same diet adequate in zinc (AZ; 30 mg/kg). The LZ and AZ rats were trained to meal feed equal amounts of the diets twice daily. At 6 weeks, each rat with lymph cannula was infused via an intraduodenal catheter at 3 ml/h for 8 h with a lipid emulsion containing 65.0 nM beta-carotene, 565.1 microM triolein, 27.8 kBq 14C-triolein (14C-OA), 72 mg albumin, and 396 microM Na-taurocholate in 24 ml PBS (pH 6.7). The lymphatic output of retinol over the 8-h period was significantly lower in LZ rats than in AZ rats. The absorption of 14C-OA also was significantly lower in LZ rats. No significant differences were observed between groups in intestinal beta-carotene 15,15'-dioxygenase, retinal reductase, and retinal oxidase activities. The findings demonstrate that low zinc intake or marginal zinc deficiency significantly lowers the absorption of beta-carotene as estimated by lymphatic retinol output. The results also indicate that the decrease in retinol output in LZ rats is not linked to defects in beta-carotene cleavage and subsequent conversion of retinal to retinol in the intestinal mucosa. This study suggests that zinc status is an important factor determining the intestinal absorption of beta-carotene and hence the nutritional status of vitamin A.     

Estradiol replacement in ovariectomized rats increases the hepatic concentration and biliary secretion of alpha-tocopherol and polyunsaturated fatty acids

Previously, we showed that estradiol replacement in ovariectomized rats produced prominent increases in serum and liver alpha-tocopherol (alphaTP). The present study was conducted to examine whether the estrogen-induced increase in the liver concentrations of alphaTP affects its biliary secretion and the fatty acid compositions of hepatic and biliary lipids. Ten ovariectomized rats were assigned to two groups: five rats were implanted subcutaneously with time-release estradiol pellets (OXE; 25 microg/day/rat) and five with placebo (OXP). Twice daily rats were pair-fed a modified AIN-93G diet containing soybean oil. At 5 weeks, bile was collected via a bile cannula hourly for 8 hours during duodenal infusion of a lipid emulsion (565 micromol triolein and 396 micromol Na-taurocholate/24 mL phosphate buffered saline, pH 6.45) at 3.0 mL/hr. During the 8-hour period, no difference was noted in the hourly rate of bile flow (0.95 mL/hr in OXE rats vs. 0.99 mL/hr in OXP rats). The biliary output of alphaTP for 8 hours was higher in OXE rats (51.6 +/- 3.6 nmol) than OXP rats (31.7 +/- 2.9 nmol). Likewise, the liver concentration of alphaTP was higher in OXE rats (81.9 +/- 3.5 nmol/g liver) than in OXP rats (53.3 +/- 7.4 nmol/g liver). The biliary secretion of phospholipids (PL) for 8 hours was significantly (P < 0.05) higher in OXE rats (55.1 +/- 4.9 micromol) than in OXP rats (42.3 +/- 4.7 micromol). Among the PL fatty acids, the outputs of 20:4 and 22:6n-3 were increased most markedly by estradiol replacement. The total outputs of 22:6n-3 for 8 hours in OXE and OXP rats were 2.95 +/- 0.20 micromol and 1.37 +/- 0.23 micromol, respectively. In the liver, the concentrations of PL 22:5n-3 and 22:6n-3 were elevated significantly in OXE rats. The present results suggest that estradiol may protect hepatic PL and membranes against oxidative damage by improving the liver status of alphaTP.     

Green tea catechins inhibit pancreatic phospholipase A(2) and intestinal absorption of lipids in ovariectomized rats

This study was conducted to examine whether the inhibition of intestinal lipid absorption by green tea is associated with the inhibitory effect of its catechins on pancreatic phospholipase A(2) (PLA(2)). PLA(2) activity was assayed by using 1,2-dioleoylphosphatidylcholine (DOPC), porcine pancreatic PLA(2) and catechins at varying concentrations (0.075-1.80 micromol/L). The amount of 1-oleoyl-2-hydroxyphosphatidylcholine liberated was determined by HPLC. The percentage of inhibition of PLA(2) by catechins at 0.6 micromol increased in the order of (-)-epicatechin (23.3%), (+)-catechin (CAT; 24.8%), (-)-epigallocatechin (25.7%), (-)-epicatechin gallate (39.7%) and (-)-epigallocatechin gallate (EGCG; 64.9%). In an in vivo study, ovariectomized rats with lymph cannula were infused intraduodenally for 8 h with a triolein emulsion containing [dioleoyl-1-(14)C]-phosphatidylcholine, DOPC, alpha-tocopherol (alphaTOH) and retinol (ROH) without (CAT0) or with CAT or EGCG. The lymphatic total (14)C-radioactivity was significantly lowered by EGCG (45.5+/-4.9% dose) compared with CAT (56.2+/-5.2% dose) and CAT0 (64.7+/-2.0% dose). The (14)C-radioactivity remaining in the small intestinal lumen and cecum was higher in EGCG (24.1% dose) than in CAT (9.5% dose) and CAT0 rats (9.0% dose). Significantly less (14)C radioactivity was incorporated into lymph triacylglycerol and cholesteryl ester in EGCG rats. The absorption of alphaTOH, used as a marker of extremely hydrophobic lipids, was significantly lower in EGCG (7.8+/-1.7 micromol) than in CAT (14.4+/-2.8 micromol) and CAT0 rats (16.8+/-2.1 micromol). The absorption of ROH was unaffected, whereas oleic acid output was lower in EGCG rats. The results show that EGCG inhibits the intestinal absorption of lipids, which is in part associated with its inhibition of phosphatidylcholine hydrolysis. Data suggest that EGCG may inhibit the absorption of other highly lipophilic organic compounds.     

Green tea extract markedly lowers the lymphatic absorption and increases the biliary secretion of 14C-benzo[a]pyrene in rats

Previously, we have shown that green tea extract (GTE) lowers the intestinal absorption of lipids and lipophilic compounds in rats. This study was conducted to investigate whether GTE inhibits the intestinal absorption and biliary secretion of benzo[a]pyrene (BaP), an extremely lipophilic potent carcinogen, present in foods as a contaminant. Male rats with lymph or bile duct cannula were infused at 3.0 ml/h for 8 h via a duodenal catheter with lipid emulsion containing (14)C-BaP with or without GTE in PBS buffer. Lymph and bile were collected hourly for 8 h. The (14)C-radioactivities in lymph, bile and intestine were determined and expressed as % dose infused. Results showed that GTE drastically lowered the lymphatic absorption of (14)C-BaP (7.6±3.2% in GTE-infused vs. 14.4±2.7% dose/8 h in control rats), with a significantly higher amount of (14)C-radioactivity present in the small intestinal lumen and cecum in rats infused with GTE. GTE also markedly increased the hourly rate (3.9±0.1% dose/h in GTE-infused vs. 3.0±0.1% dose/h in control rats) and the total biliary secretion of (14)C-BaP (31.5±0.8% dose/8 h in GTE-infused vs. 24.3±0.4% dose/8 h in control rats). The findings provide first direct evidence that GTE has a profound inhibitory effect on the intestinal absorption of BaP and promotes the excretion of absorbed BaP via the biliary route. Further studies are warranted to investigate whether green tea could be recommended as a dietary means of ameliorating the toxicity and carcinogenic effect of BaP.     

Administration of phosphatidylcholine-cholesterol liposomes partially reconstitutes fat absorption in chronically bile-diverted rats

BACKGROUND AND AIMS: Intestinal bile deficiency in cholestatic patients leads to fat malabsorption. We addressed the potency of model bile, bile salts and phosphatidylcholine (PC)-cholesterol (CH) liposomes to reconstitute fat absorption in permanently bile-diverted (BD) rats. METHODS: The plasma appearance of 13C-labeled palmitic acid (13C-16:0) and linoleic acid (13C-18:2) was determined after their enteral administration to BD or to control rats with an intact enterohepatic circulation (EHC) (13C-16:0 and 13C-18:2 dissolved in 25% olive oil-75% medium chain triacylglycerol oil mixture). BD rats were intraduodenally infused with buffer, model bile [consisting of 60 mM taurocholate (TC), 8 mM PC and 1 mM CH], buffer with TC, buffer with PC and CH liposomes, or buffer with lyso-PC and CH. RESULTS: Plasma concentrations of 13C-16:0 and 13C-18:2 were consistently three- to eightfold higher in control rats than those in buffer-infused BD rats (P < 0.01). ID administration of either model bile or TC to BD rats restored plasma appearance of 13C-fatty acids at least to concentrations observed in control rats. Administration of PC + CH liposomes to BD rats partially reconstituted the plasma appearance of 13C-16:0, but did not affect that of 13C-18:2. Compared with control rats, the area under the curve (AUC) of plasma 13C-16:0 concentrations was 13.0 +/- 6.9% in buffer-infused rats and 40.9 +/- 3.1% in liposome-infused rats (P < 0.005). CONCLUSIONS: Enteral administration of PC + CH liposomes to BD rats partially corrects the absorption of palmitic acid. Present data suggest that administration of PC + CH liposomes could enhance fat absorption in clinical conditions of cholestasis in which bile salt supplemention is contraindicated.     

Proabsorptive effect of gum arabic in isotonic solutions orally administered to rats: effect on zinc and other solutes

We have previously shown that the addition of gum arabic (GA) to oral rehydration solution (ORS) enhances water and electrolyte absorption during jejunal perfusion in rats under anesthesia. This study investigates whether GA by oral administration could be equally effective in rats. Isotonic solutions containing 25 g/L GA (AG), or without GA (A0) were administered via oral tube to lightly anesthetized adult female rats. Similar experiments were conducted with hypertonic solutions containing no GA (B0), or either 10 (B10) or 50 g/L GA (B50). Blood concentrations of sodium, glucose, glutamate, zinc, and tritiated water were determined at 0, 15, 30, 60, 90, 120, and 180 minutes, and results between treatments were compared. Administration of the isotonic, GA-containing solution (AG) resulted in a higher blood zinc level than with the isotonic GA-free solution (A0) from 15 minutes throughout 180 minutes. Blood zinc at 15 minutes (means +/- SEM) was as follows: for A0: 69.3 +/- 2.0, for AG: 83.4 +/- 3.5 nmol/L, P=0.002. At 180 minutes, A0: 52.6 +/- 1.8; AG: 68.1 +/- 4.6 nmol/L, P=0.004. The corresponding areas under the curve (AUC) were as follows: for A0: 10,737 +/- 214; for AG: 13,919 +/- 765 nmol x min/L, P<0.001). Glucose, glutamate, sodium, and tritiated water body distribution presented no differences in blood concentrations. For sodium and tritiated water body distribution, there was a significant time effect (P<0.0001). In hypertonic solutions, blood zinc levels declined over time, possibly due to their osmotic, counter-absorptive action, thus obscuring possible opposite effects of GA. GA appears to be an effective enhancer of zinc absorption when orally administered in isotonic solutions to laboratory animals. This proabsorptive capacity could be attributed to some of the physicochemical and biochemical properties of GA and suggest possible applications of GA in liquid formulas and solid food preparations.     

A new method for the study of chylomicron kinetics in vivo

Our understanding of the metabolism of chylomicrons, the lipoprotein that transports dietary fat from the intestine to peripheral tissues, is incomplete. The present studies were conducted to determine whether a labeled intravenous lipid emulsion could be used to estimate chylomicron triglyceride (TG) rate of appearance (R(a)) and thereby quantify the rate of intestinal fat absorption. After an overnight fast, healthy volunteers (n = 6) sipped a (3)H-labeled drink over 6.5 h at a rate of 175 mg fat. kg(-1). h(-1). Beginning at hour 5, an HPLC-purified, (14)C-labeled lipid emulsion was infused intravenously for 90 min. During the study, plasma total and chylomicron TG concentrations increased from 100 +/- 21 to 237 +/- 40 mg/dl and from undetectable to steady-state levels of 35 +/- 13 mg/dl, respectively. After a minor correction for VLDL contamination, tracer-determined chylomicron TG R(a) was 175 +/- 30 mg. kg(-1). h(-1), equal to the presumed ingestion rate. In summary, a radiolabeled intravenous lipid emulsion is able to accurately estimate chylomicron TG R(a) and therefore can be used to measure in vivo fat absorption rates.     

Transport of lipid and apolipoproteins A-I and A-IV in intestinal lymph of the rat

Intestinal lipid absorption is associated with marked increases in the synthesis and secretion of apolipoprotein A-IV (apoA-IV) by the small intestine. Whether the increased intestinal apoA-IV synthesis and secretion results from increased fat uptake, increased cellular triglyceride (TG) content, or increased secretion of TG-rich lipoproteins by the enterocytes is unknown. Previous work from this laboratory has shown that a hydrophobic surfactant, Pluronic L-81 (L-81), is a potent inhibitor of intestinal formation of chylomicrons (CM), without reducing fat uptake or re-synthesis to TG. Furthermore, this inhibition can be reversed quickly by the cessation of L-81 infusion. Thus L-81 offers a unique opportunity to study the relationship between lymphatic TG, apoA-I and A-IV secretion. In this study, we studied the lymphatic transport of TG, apoA-I, and apoA-IV during both the inhibitory phase (L-81 infused together with lipid) and the subsequent unblocking phase (saline infusion). Two groups of lymph fistula rats were used, the control and the experimental rats. In the experimental rats, a phosphate-buffered taurocholate-stabilized emulsion containing 40 mumol [3H]triolein, 7.8 mumol of phosphatidylcholine, and 1 mg L-81 per 3 ml was infused at 3 ml/h for 8 h. This was then replaced by glucose-saline infusion for an additional 12 h. The control rats received the same lipid emulsion as the experimental rats, but without L-81 added, for 8 h. Lymph lipid was determined both by radioactivity and by glyceride-glycerol determination, and the apoA-I and apoA-IV concentrations were determined by rocket electroimmunophoresis assay. L-81 inhibited the rise in lymphatic lipid and apoA-IV output in the experimental rats after the beginning of lipid + L-81 infusion. Upon cessation of L-81 infusion, the mucosal lipid accumulated as a result of L-81 treatment was rapidly cleared into lymph as CM. This was associated with a marked increase in apoA-IV output; the maximal output was about 3 times that of the fasting level. There was a time lag of 4-5 h between the peak lymph lipid output and the peak lymph apoA-IV output during the unblocking phase in the experimental rats. There was also a comparable time lag between the maximal lipid and apoA-IV outputs in the control animals. Incorporation studies using [3H]leucine showed that apoA-IV synthesis was not stimulated during lipid + L-81 infusion, perhaps explaining the lack of increase in lymphatic A-IV secretion.(ABSTRACT TRUNCATED AT 400 WORDS)     

GLP-1 reduces intestinal lymph flow, triglyceride absorption, and apolipoprotein production in rats

Glucagon-like peptide 1 (GLP-1) is a gastrointestinal hormone secreted in response to meal ingestion by enteroendocrine L cells located predominantly in the lower small intestine and large intestine. GLP-1 inhibits the secretion and motility of the upper gut and has been suggested to play a role in the "ileal brake." In this study, we investigated the effect of recombinant GLP-1-(7-36) amide (rGLP-1) on lipid absorption in the small intestine in intestinal lymph duct-cannulated rats. In addition, the effects of rGLP-1 on intestinal production of apolipoprotein (apo) B and apo A-IV, two apolipoproteins closely related to lipid absorption, were evaluated. rGLP-1 was infused through the jugular vein, and lipids were infused simultaneously through a duodenal cannula. Our results showed that infusion of rGLP-1 at 20 pmol.kg(-1).min(-1) caused a dramatic and prompt decrease in lymph flow from 2.22 +/- 0.15 (SE) ml/h at baseline (n = 6) to 1.24 +/- 0.06 ml/h at 2 h (P < 0.001). In contrast, a significant increase in lymph flow was observed in the saline (control) group: 2.19 +/- 0.20 and 3.48 +/- 0.09 ml/h at baseline and at 6 h of lipid infusion, respectively (P < 0.001). rGLP-1 also inhibited intestinal triolein absorption (P < 0.05) and lymphatic apo B and apo A-IV output (P < 0.05) but did not affect cholesterol absorption. In conclusion, rGLP-1 dramatically decreases intestinal lymph flow and reduces triglyceride absorption and apo B and apo A-IV production. These findings suggest a novel role for GLP-1 in lipid absorption.     

Investigation of excretion and absorption of different zinc salts in puppies.

The effects of dietary zinc on zinc absorption and excretion were evaluated with six 12-week-old beagles. The dogs were fed a commercial dry food later supplemented with 2 and 4mg/kg of body weight per day of either zinc sulphate, zinc acetate or zinc oxide. The concentrations of zinc in the urine and faeces of all treatment groups were increased depending on the type of zinc salts and the dosage in the diet (P < 0.05). The apparent absorption of zinc salts ranged from 0.20 to 0.36. The zinc salt supplements at both dosages did not affect the digestibility of crude protein, fat and fibre. The zinc concentration in plasma varied with the type of zinc salt and with the dosage. The mean concentrations ranged from 61+/- 1.46 microg to 73 +/- 1.57 microg/dl in the unsupplemented groups, whereas it was 115 +/- 2.33 microg/dl in the group supplemented with zinc acetate at the highest dosage.     

Intestinal zinc transport: influence of streptozotocin-induced diabetes, insulin and arachidonic acid

The influence of arachidonic acid (AA) on the zinc flux rates of jejunal segments, isolated from streptozotocin-induced diabetic rats injected with saline or with insulin, was investigated using an Ussing chamber technique. Although the zinc flux rates from mucosa-to-serosa (Jms) of normal rats were inhibited by addition of 5 microM AA to the jejunal segment bathing medium (46.4 +/- 5.0 vs 32.6 +/- 4.3 nmol/hr/cm2), AA had no effect on the Jms of diabetic rats either with or without insulin treatment. Induction of diabetes also significantly reduced Jms (46.4 +/- 5.0 vs 22.1 +/- 4.9 nmol/hr/cm2), but 3 day insulin treatment (NPH 8 U/Kg/day subcutaneously) did not reverse this effect (29.2 +/- 5.1 nmol/hr/cm2). Addition of AA to the serosal side did not significantly alter the zinc flux rate from serosa-to-mucosa (Jsm) in either control, diabetic or diabetic rats treated with insulin. The net zinc absorption rate (Jnet) of jejunal segments was decreased in diabetic rats compared to controls (13.2 +/- 3.0 vs -0.7 +/- 2.1 nmol/hr/cm2), but normalization of blood glucose with 3 day insulin treatment did not increase Jnet. Addition of AA was associated with a tendency to increase zinc uptake capacity. This change reached statistical significance in insulin treated diabetic rats. Short-circuit current (Isc) for diabetic rats was increased compared to controls but addition of AA to the mucosal side bathing medium decreased Isc in all groups. The results indicate that the zinc flux rate in the small intestine of streptozotocin-induced diabetic rats is decreased, that zinc uptake capacity of the small intestine does not directly reflect the zinc flux rate across the small intestine, and that AA or one of its metabolites may play a significant role in the control of the zinc flux across the intestinal epithelium.     

Inhibitory action of gemfibrozil on cholesterol absorption in rat intestine

This study was designed to determine whether gemfibrozil inhibits intestinal lipid absorption. Male Sprague-Dawley rats received an oral dose of 30 mg gemfibrozil/kg body weight for 14 days. Mesenteric lymph cannulation was performed, and a lipid infusion containing 40 micromol/h (35.4 mg/h) of radiolabeled triolein and 2.74 micromol/h (1.06 mg/h) of radiolabeled cholesterol with the addition of 1 mg/h of gemfibrozil was infused intraduodenally at a rate of 3 ml/h for 8 h. The lymph was collected, and the radioactivity levels of the lumen and gut mucosa were measured after the infusion. Lymph cholesterol transport was depressed in gemfibrozil-treated rats, in terms of mass measurements as well as radioactivity in a lesser degree. More radioactive cholesterol remained in the proximal portion of the intestinal lumen and mucosa in the treated rats than in the control rats. More radioactive triglycerides also remained in the proximal intestinal lumen of treated rats, although no difference in lymphatic triglyceride transport was observed between the groups. A significant portion of the radioactive cholesterol remained in the lumen in the gemfibrozil-treated rats. Gemfibrozil increased biliary cholesterol excretion. Thus, this study shows that gemfibrozil inhibits cholesterol absorption in rat intestine.     

Impaired lymphatic cerebrospinal fluid absorption in a rat model of kaolin-induced communicating hydrocephalus

It has been assumed that the pathogenesis of hydrocephalus includes a cerebrospinal fluid (CSF) absorption deficit. Because a significant portion of CSF absorption occurs into extracranial lymphatics located in the olfactory turbinates, the purpose of this study was to determine whether CSF transport was compromised at this location in a kaolin-induced communicating (extraventricular) hydrocephalus model in rats. Under 1-3% halothane anesthesia, kaolin (n = 10) or saline (n = 9) was introduced into the basal cisterns of Sprague-Dawley rats, and the development of hydrocephalus was assessed 1 wk later using MRI. After injection of human serum albumin ((125)I-HSA) into a lateral ventricle, the tracer enrichment in the olfactory turbinates 30 min postinjection provided an estimate of CSF transport through the cribriform plate into nasal lymphatics. Lateral ventricular volumes in the kaolin group (0.073 +/- 0.014 ml) were significantly greater than those in the saline-injected animals (0.016 +/- 0.001 ml; P = 0.0014). The CSF tracer enrichment in the olfactory turbinates (expressed as percent injected/g tissue) in the kaolin rats averaged 0.99 +/- 0.39 and was significantly lower than that measured in the saline controls (5.86 +/- 0.32; P < 0.00001). The largest degree of ventriculomegaly was associated with the lowest levels of lymphatic CSF uptake with lateral ventricular expansion occurring only when almost all of the lymphatic CSF transport capacity had been compromised. We conclude that lymphatic CSF absorption is impaired in a kaolin-communicating hydrocephalus model and that the degree of this impediment may contribute to the severity of the induced disease.     

Soybean phosphatidylcholine-induced enhancement of lymphatic absorption of triglyceride depends on chylomicron formation in rats

We investigated whether chylomicron formation is involved in the dietary phosphatidylcholine (PC)-induced increase in triglyceride (TG) absorption using an inhibitor of chylomicron formation, pluronic L-81 (L-81). In rats, cannulas were implanted into the duodenum (exps. 1 and 2) and the mesenteric lymph duct (exp. 1), and an emulsified lipid solution containing the test lipids (soybean oil, SO or soybean oil plus phosphatidylcholine, LE) with or without L-81 was infused through a duodenal cannula at a rate 3 ml/h for 2 h, and followed by infusion of a glucose-NaCl solution for 2 h. Mesenteric lymph was collected for 4 h (exp. 1). In exp. 2, the mucosa and contents of the small intestine were collected at 20, 40, or 90 min after the start of duodenal infusion of the test lipid to evaluate accumulation of lipids incorporated into the mucosa in the rats without a lymph cannula. In exp. 1, lymphatic TG outputs rapidly increased with infusion of both test lipids without L-81, but L-81 abolished these increases. TG accumulated in the small intestinal mucosa with L-81 treatment in a time-dependent manner, but the levels of accumulation were similar between the SO and LE groups (exp. 2). There were no differences in the amounts of lipid remaining in the small intestinal lumen between the L-81-treated SO and LE groups. These results indicate that uptake of lipid into the mucosal cells was not increased by LE. We conclude that the formation of chylomicron is responsible for increases in the promotive effect of a high level of dietary PC on the lymphatic absorption of TG.     

The influence of citrate, maltolate and fluoride on the gastrointestinal absorption of aluminum at a drinking water-relevant concentration: A 26Al and 14C study

The objectives were to test the null hypotheses that (1) citrate, maltolate, and fluoride do not significantly influence oral Al bioavailability, C(max) or T(max) at an Al dose relevant to drinking water exposure; and (2) Al citrate and maltolate are absorbed intact from the gastrointestinal tract. Male Fisher rats were given 1ml of solution intra-gastrically containing 1 nCi (26)Al (65nmol total Al) as the Al(3+) ion, or as complexes with (14)C-citrate, (14)C-maltolate or fluoride, during concurrent (27)Al iv infusion. Blood was repeatedly collected for serum (26)Al, total Al and (14)C quantification. Absorption parameters were estimated using WinNonlin. Al bioavailability, C(max) and T(max) from the ion, citrate, maltolate, and fluoride were 0.29+/-0.11%, 0.61+/-0.31%, 0.50+/-0.25%, and 0.35+/-0.10%; 659+/-195, 1073+/-250, 881+/-356, and 880+/-295fg/ml; and 1.2+/-0.9, 1.0+/-1.1, 1.3+/-1.0, and 1.0+/-0.9h (X+/-SD) respectively. Serum (14)C was approximately 100 times higher than (26)Al. The results suggest a non-significant enhancement of oral Al bioavailability by citrate and maltolate, some Al complex dissociation in the GI tract, and less absorption of Al than citrate or maltolate. The presence of citrate, maltolate and fluoride, at a similar molar concentration to Al, would not be expected to greatly influence Al absorption from drinking water.     

Hydrolysis of micellar phosphatidylcholine accelerates cholesterol absorption in rats and Caco-2 cells

Lymphatic recovery of cholesterol infused into the duodenum as bile salt micelles containing phosphatidylcholine (PC) was accelerated by the co-administration of phospholipase A2 in bile and pancreatic juice diverted rats. Previously we observed that cholesterol esterase, which has the ability to hydrolyze PC, caused the same effect under a similar experimental condition (Ikeda et al., Biochim. Biophys. Acta, 1571, 34-44 (2002)). Accelerated cholesterol absorption was also observed when a part of micellar PC was replaced by lysophosphatidylcholine (LysoPC) and oleic acid. Phospholipase A2 facilitated the incorporation of micellar cholesterol into Caco-2 cells in a dose-dependent manner. There was a highly negative correlation between the incorporation of cholesterol into Caco-2 cells and the content of micellar PC remaining in the culture medium. The release of cholesterol as a monomer from bile salt micelles was enhanced when a part of micellar PC was replaced with LysoPC and oleic acid. These results strongly suggest that the release of monomer cholesterol from bile salt micelles is accelerated by hydrolysis of PC in bile salt micelles and hence that cholesterol absorption is enhanced.     

Activation of rat intestinal mucosal mast cells by fat absorption

Previous studies have linked certain types of gut mucosal immune cells with fat intake. We determined whether fat absorption activates intestinal mucosal mast cells (MMC), a key component of the gut mucosal immune system. Conscious intestinal lymph fistula rats were used. The mesenteric lymph ducts were cannulated, and the intraduodenal (i.d.) tubes were installed for the infusion of Liposyn II 20% (an intralipid emulsion). Lymphatic concentrations of histamine, rat MMC protease II (RMCPII), a specific marker of rat intestinal MMC degranulation, and prostaglandin D(2) (PGD(2)) were measured by ELISA. Intestinal MMC degranulation was visualized by immunofluorescent microscopy of jejunum sections taken at 1 h after Liposyn II gavage. Intraduodenal bolus infusion of Liposyn II 20% (4.4 kcal/3 ml) induced approximately a onefold increase in lymphatic histamine and PGD(2), ～20-fold increase in lymphatic RMCPII, but only onefold increase in peripheral serum RMCPII concentrations. Release of RMCPII into lymph increased dose dependently with the amount of lipid fed. In addition, i.d. infusion of long-chain triacylglycerol trilinolein (C18:2 n-6, the major composite in Liposyn II) significantly increased the lymphatic RMCPII concentration, whereas medium-chain triacylglycerol tricaprylin (C8:0) did not alter lymph RMCPII secretion. Immunohistochemistry image revealed the degranulation of MMC into lamina propria after lipid feeding. These novel findings indicate that intestinal MMC are activated and degranulate to release MMC mediators to the circulation during fat absorption. This action of fatty acid is dose and chain length dependent.     

A mutual inhibitory effect on absorption of sphingomyelin and cholesterol

Several studies have shown that there is a strong physical interaction between cholesterol and sphingomyelin (SM). The critical factor is thought to be the high degree of saturation in the very long acyl chains of SM. In this study we examined the effects of SM on cholesterol absorption in the rat and compared them with those of phosphatidylcholine (PC). Cholesterol absorption was studied by use of the dual-isotope plasma ratio method. We also studied the effect of sterols on the fecal excretion of undigested SM and its metabolites after a single oral meal of (3)H-dihydrosphingosine-labeled SM. When cholesterol was given dissolved in soybean oil, without addition of SM or other phospholipids, absorption was 68 +/- 12% in the rat intestine. As a general feature the absorption was less efficient from the cholesterol/phospholipid dispersions. In dispersions with cholesterol and SM, the lowest cholesterol absorption (9 +/- 2%) was seen with a cholesterol:SM molar ratio of 1:1. With dispersions of cholesterol and different PC substrates the absorption of cholesterol was lower with saturated PC (16 +/- 8%) than with soybean-PC (22 +/- 4%) or dioleoyl PC (23 +/- 8%). Uptake of SM in the rat intestine was reduced by sterols. For example, percentage recovery of (3)H radioactivity in fecal lipids was 38 +/- 8% when SM was given with cholesterol and 16 +/- 3% without any sterol. One third of the radioactivity in feces was present as ceramide. Sitostanol had the same effect on uptake of SM as cholesterol. This study shows that when rats are fed mixtures of SM and cholesterol the intestinal uptake of both lipids is decreased. By feeding mixtures of SM and sterols the exposure of the colon to ceramide can be increased.