14C-polyethylene Glycol Research Articles

Testicular capillary permeability: the movement of luteinizing hormone from the vascular to the interstitial compartment.

It has previously been shown in several species that pulses of luteinizing hormone (LH) in peripheral serum are followed within 10-20 minutes by pulses of testosterone. Whether or not LH pulses directly stimulate Leydig cells to produce the testosterone pulses would depend on the vascular permeability of LH within that physiologically relevant time. In the present experiments, the capillary permeability of the testicular microvasculature was characterized in adult rats, and the relative permeability to LH was determined. Adult male rats were prepared for in vivo micropuncture and testes were infused with 3H-water, 14C-urea, 14C-polyethylene glycol (PEG), and 3H-dextran directly into the testicular surface artery. Testicular interstitial fluid (TIF) and testicular venous plasma were collected at 5 minutes, 10 minutes, and 15 minutes after initiation of isotope infusion. Data were recorded as isotope concentration in TIF as a proportion of the isotope concentration in testicular venous plasma collected at the same time period. 3H-water movement into the TIF from blood was rapid reaching 50% of serum values within 15 minutes. 14C-PEG and 3H-dextran were largely excluded from the TIF, typically not exceeding 5-10% of serum concentrations. In subsequent experiments, 125I-LH was infused using the same protocol. 125I-LH concentrations in TIF were 3.6 +/- 2.0% of plasma concentrations 10 minutes after initiation of infusion. Preceding the 125I-LH infusion experiments with 5-day hypophysectomy or with LH pulses delivered either 10 minutes or 4 hours prior to the initiation of infusion did not alter the capillary permeability of 125I-LH. These data demonstrate the restricted availability of LH to the TIF. This implies that Leydig cells are not exposed to LH pulses through the TIF and raises the question whether LH pulses directly stimulate testosterone pulses.

Ion and Luminal Marker Concentrations in the Gut of Saline-Acclimated Ducks

Concentrations of Na+, K+, and C1in digestive tract fluid were measured in eight saline-acclimated domestic Pekin ducks, Anas platyrhynchos, and the concentration of nonabsorbable luminal marker 14C-polyethylene glycol ('4C-PEG, orally loaded in 180 mM NaC1) was measured in five of these birds. The birds were sacrificed and the gut was ligated into sections. All sections were hyponatremic to plasma; [C1-] in the proventriculus and ventriculus were equal to and higher than plasma [C1-], respectively, and elsewhere [C1-] was less than plasma [C1-]. The [Na+]/[K+] ratio (1.5 or less) was lower than that of birds without salt glands (2-3, Hurwitz et al. 1970). The initial 10-fold dilution of ['4CPEG] in the duodenum and subsequent 80-fold increase in ['4C-PEG] in the ileum are consistent with secretion into the duodenum and net absorption of Na+ and water in the ileum. Rectal (and cecal) ['4C-PEG] was 5-fold lower than ileal ['4C-PEG], a decrease presumably due to retropulsion of urine into the rectal-cecal complex. These observations suggest sodium-replete ducks continue to reflux urine into the hindgut where NaC1 and water uptake have been shown to occur (Skadhauge et al. 1984) and offer indirect evidence that hindgut NaCl reabsorption and extrarenal NaCl secretion may be linked.

Luminal adrenergic agents modulate ileal transport: Discrimination between α1 and α2 receptors

Luminal α-adrenergic agonists alter ileal water, ion, and glucose transport by a local mechanism. This study tested the hypothesis that luminal adrenergic agents modulate ileal transport selectively, via specific α 1 and α 2 receptors. Absorption studies (n = 72) were performed on dogs with 25-cm ileal Thiry-Vella fistulas (TVF). Perfusion with ( 14C) polyethylene glycol was used to calculate absorption of water, ions, and glucose from the TVF. Experiments included four 1-hour periods. Agonists used were phenylephrine ( α 1), clonidine ( α 2), and norepinephrine ( α 1 > α 2 and β). Antagonists used were terazosin ( α 1) and yohimbine ( α 2)- Phenylephrine and norepinephrine caused significant increases in water and ion absorption (p < 0.05). Clonidine caused significant decreases in water, ion, and glucose absorption (p < 0.05). Terazosin and yohimbine had no effect alone. Terazosin prevented the proabsorptive effect of phenylephrine and norepinephrine, and yohimbine blocked the prosecretory effect of clonidine. Yohimbine significantly increased the norepinephrine-induced proabsorptive effect. Luminal α-adrenergic agents selectively modulate ileal transport. Alpha 1-receptor activation causes a proabsorptive response, whereas α 2-receptor activation causes a prosecretory response. The combination of a luminally administered mixed and β-adrenergic agonist (norepinephrine) with α 2 receptor blockade (yohimbine) may prove useful in pathologic secretory states such as intestinal transplants, diabetic diarrhea, or diarrhea-associated endocrinopathies.

Exposure of the duodenum to high concentrations of hydrochloric acid. Effects on mucosal permeability, alkaline secretion, and blood flow.

Proximal duodenum was perfused with HCl for 5 min and the effects on blood-to-lumen clearance of 51Cr-EDTA (ED-Cl), morphology, luminal alkalinization, and blood flow determined in anesthetized rats. The rate of alkalinization was determined by back titration and blood flow assessed by laser Doppler flowmetry or by ultrasonic transit time flowmetry. Perfusion of duodenum with 30, 50 or 100 mM HCl for 5 min increased ED-Cl in a concentration-dependent manner and induced a small increase in alkalinization but had no effect on blood flow. At 55 min after cessation of perfusion with 100 mM HCl ED-Cl was 2.2-fold higher than control whereas the ED-Cl values in animals perfused with 30 or 50 mM HCl were not different from pre-acid control values. 100 mM HCl also induced an increase in 14C-mannitol and 14C-polyethylene glycol 4000 clearance, suggesting that HCl does indeed increase mucosal permeability. The 100 mM HCl-induced rise in mucosal permeability most probably reflects disturbance of mucosal integrity because three of five animals exhibited villous tip damage. The increases in ED-Cl in response to 100 mM HCl were the same in control rats as in rats with the renal pedicles ligated, indicating that the acid susceptibility is not affected by acute functional nephrectomy.

Motor activity and transit in the autonomically denervated jejunum

The role of extrinsic (autonomic) innervation in postprandial contractile activity of the small intestine is unknown. Using a canine model, we investigated the effects of complete extrinsic denervation on the parameters of fasting and postprandial jejunal contractions and their relationship to intestinal transit. Individual contractions were recorded using strain gauge transducers. Spatial and temporal parameters of contractions were analyzed by computer methods. Bolus injection of 14C-polyethylene glycol was used to calculate intestinal transit rates. Statistical comparisons of control and denervated animals were made by nonparametric tests. Extrinsic denervation did not abolish fasting or fed motor activity, but the following effects were observed: (1) the frequency of migrating motor complexes (MMCs) increased; (2) the onset of fed motor activity was delayed, and the duration of fed activity was shortened; (3) frequency, mean amplitude, and mean area of postprandial contractions were decreased; (4) fewer contractions propagated distally, and mean propagation distance was shortened; and (5) intestinal transit was slower for solids, but not for liquids. In the small intestine, extrinsic nerves modulate motor activity, which is under primary control of the intrinsic (enteric) nervous system.

Postprandial biliary and pancreatic secretion during profound inhibition of gastric secretion in humans.

This study assessed the effect of profound inhibition of gastric secretion by an H2 antagonist on postprandial gastric emptying of acid and chyme, and on bile acid and pancreatic enzyme secretion under physiological conditions in humans. Six subjects were studied before and while they were given famotidine (40 mg). This study combined a continuous intestinal perfusion technique using 14C-polyethylene glycol (14C-PEG) as duodenal recovery marker, with intermittent sampling of gastric content using PEG 4000 as meal marker. During the three hour study, the area under the curve for gastric acid output decreased from mean (SEM) 88.9 (7.6) mmol for those not receiving treatment, to 21.2 (2.7) mmol for subjects receiving famotidine (p < 0.01). The corresponding values for the rate of acid delivery into the duodenum decreased from 65.2 (11.9) to 16.6 (2.9) mmol (p < 0.05), and those for the rate of gastric emptying of chyme remained unchanged for the group receiving no treatment and during famotidine (1040 (200) v 985 (160) ml respectively, NS). Duodenal bile acid and trypsin output remained unchanged (area under the curve, 457 (128) v 373 (86) umol/kg and 5022 (565) v 5058 (400) IU/kg respectively, NS) receiving no treatment and during famotidine. It is concluded that profound inhibition of postprandial gastric acid secretion by anti-secretory drugs is not accompanied by changes in biliary and pancreatic secretion, mainly because the gastric emptying of chyme is unaffected.

Effects of serotonin on rat ileocolonic transit and fluid transfer in vivo: possible mechanisms of action.

The aim was to investigate the action of serotonin (5HT) on function of the ileocolonic junction (ICJ) in vivo. In anaesthetised rats, models were developed to study the effects of intra-aortic (ia) serotonin on ileocolonic and colonic transit, and the effects on transit of a number of 5HT receptor antagonists. In the first series of experiments, a bolus of saline labelled with 99mTc DTPA was instilled 20 cm proximal to the ICJ and transit was assessed three hours later by the geometric centre of the spread of isotope. In the second series, similar techniques were used on the postcaecal colon and transit assessed two hours later. In the third series of experiments, the effects of ia 5HT on ileal net fluid flux was evaluated by standard perfusion experiments with 14C polyethylene glycol (PEG) 4000 as a non-absorbable marker in rat plasma-like electrolyte solution. Compared with ia saline, 5HT accelerated ICJ transit significantly (p < 0.05). This acceleration was comparable with the effect of ia bethanechol. The effects of 5HT on ICJ transit were inhibited by the intraperitoneal (ip) infusion of atropine, the 5HT receptor antagonists, methysergide, ketanserin, zacopride, and the 5HT4 agonist, SC53116. Methysergide, zacopride, and SC53116 given with ia 5HT slowed ICJ transit to rates below those of ia saline alone. When these same agents were given together with ia saline, the ICJ transit was not significantly altered. Serotonin, at the dose that accelerated ICJ transit, did not significantly alter colonic transit or ileal fluid transport. In conclusion, 5HT is a potent pharmacological stimulant of transit across the rat ICJ in vivo; the action of 5HT is mediated partly through muscarinic neurones and several 5HT receptor subtypes.

Influence of gastric acidity on fluoride absorption in rats.

The rate of F absorption from the stomach is pH-dependent, with greater absorption at low pH. Since the rate of absorption is also strongly influenced by the rapidity of gastric emptying, we have compared the relative importance of gastric acidity and gastric emptying in overall F absorption. Male rats (350 g, n = 85) were pre-treated with cimetidine (to inhibit gastric acid secretion) or pentagastrin (to stimulate gastric acid secretion) or were untreated controls, and given 50 micrograms F by stomach intubation. The pH of the F-containing solution was varied in the cimetidine-pre-treated group (pH 1.5, 5.5, 8.5), and was 5.5 for the control and pentagastrin-pre-treated groups. Gastric emptying was measured by addition of 14C polyethylene glycol to the F solution as an unabsorbed marker of fluid movement. F absorption was measured after 10, 20, and 40 min. The rate of gastric emptying was unaffected by pre-treatment or pH of the intubating solution. Initially, F absorption was greatest at low pH. After 40 min, absorption was comparable in all groups, averaging approximately 70% of the initial dose. The extent of absorption from the stomach was inversely related to pH, but increased absorption from the small intestine compensated for the low gastric absorption at high pH.

Small Bowel Origin and Calorie Dependence of a Signal for Meal-induced Jejunal Absorption

The ingestion of a meal stimulates the absorption of water and electrolytes from the small intestine independent of the cephalic or gastric phases of digestion. This study tested two hypotheses: (1) the jejunum is the origin of a postmeal proabsorptive signal and (2) the magnitude of the proabsorptive response is dependent on the caloric content of the meal stimulus. Twenty-five-centimeter proximal canine jejunal Thiry-Vella fistulas and feeding jejunostomies were constructed under general anesthesia. Jejunal absorption studies (n = 50) were performed by luminal perfusion of the Thiry-Vella fistula with 14C-polyethylene glycol (PEG) to calculate fluxes of water and electrolytes. Five groups were studied: (1) CONTROL: no meal, (2) 240 kcal oral meal, (3) 480 kcal oral meal, (4) 240 kcal jejunal meal, and (5) 480 kcal jejunal meal. Independent of the route of delivery (i.e., oral vs. jejunal), each meal stimulus significantly increased jejunal water and electrolyte absorption (p < 0.05). The magnitude of the proabsorptive response increased significantly as the calories delivered increased (p < 0.05). These data support the hypothesis that a proabsorptive signal responsible for meal-induced jejunal absorption originates from, or distal to the jejunum and suggest that intestinal chemoreceptors or osmoreceptors participate in the generation of the proabsorptive signal.

Regional gastrointestinal absorption of the beta-blocker pafenolol in the rat and intestinal transit rate determined by movement of 14C-polyethylene glycol (PEG) 4000.

The gastrointestinal absorption characteristics of pafenolol following oral administration as a solution in man and rat has previously been found to be a double-peak phenomenon and exhibited dose-dependent bioavailability, despite negligible presystemic metabolism. In both man and rat the first peak appeared approximately 0.5-1 hr postdose and the second, more pronounced peak 3-4 hr postdose. In rat more than 90% of the available dose was absorbed during the second peak. In the present study we investigated the absorption of a solution of pafenolol in rats after intrajejunal and intraileal administration. The resulting blood concentration-time profile of pafenolol exhibited one peak only; the extent of absorption was similar to that observed when the same dose was given orally. The small intestinal transit time of the 14C-PEG 4000 solution was found to be more than 3 hr. The transit rate was higher in the proximal part of the small intestine compared to the more distal part, where the transit of the solution was staggered. In conclusion, the results of the intestinal transit time investigation and the administrations of pafenolol at different levels of the alimentary tract indicate that pafenolol is a drug with a specific absorption site located in the ileocolonic region.

Meal-induced jejunal absorption requires intact neural pathways

A signal for meal-induced absorption originates from the small intestine and is transmitted to a luminally excluded segment of the proximal jejunum (Thiry-Vella [TV] fistula). Using intraluminal topical anesthesia with oxethazaine, this study assessed the role of intestinal neural pathways in basal and postprandial jejunal water and electrolyte absorption. Studies (n = 45) were performed on dogs with 25-cm proximal jejunal TV fistulae and feeding jejunostomies, using luminal perfusion with 14C-polyethylene glycol. The animals were randomized into five study groups: (1) jejunostomy oxethazaine alone, (2) jejunostomy water and jejunal meal, (3) jejunostomy oxethazaine and jejunal meal, (4) TV fistula water and jejunal meal, and (5) TV fistula oxethazaine and jejunal meal. The jejunal meal significantly increased TV fistula absorption, whereas oxethazaine significantly reduced basal absorption when administered via the TV fistula and postprandial absorption when administered via the jejunostomy (p < 0.05). TV fistula oxethazaine did not diminish the magnitude of postprandial absorption. We conclude that intact intestinal neurotransmission is necessary for maintenance of the normal basal absorptive state of the proximal jejunum and for the generation of a normal meal-stimulated proabsorptive signal from the small intestine. A nonneural mechanism appears to be of predominant importance in transmitting the proabsorptive signal from the intact gastrointestinal tract to the TV fistula.

The effect of capsaicin on gallbladder fluid absorption

The role of the enteric nervous system of the gallbladder on mucosal water absorption was evaluated by intraluminal administration of capsaicin, a selective stimulant of afferent nerve endings. It has been postulated that the neural responses of the gallbladder are peptidergic and mediated by prostanoids. Anesthetized cats underwent gallbladder perfusion with a physiological buffer solution containing 14C polyethylene glycol as a nonabsorbable tracer to quantitate mucosal water absorption. Capsaicin was added to the perfusate and administered intraluminally at a rate of 5 mg/kg-1/hr-1 for 2 hr. One experiment on five cats was performed when capsaicin was administered and five control experiments were performed when only vehicle was added to the perfusate. Five experiments were performed when indomethacin was administered intravenously (5 mg/kg-1/hr-1) and buffer solution alone was used to perfuse the gallbladder, and five experiments were performed when capsaicin was added to the perfusate and indomethacin was administered intravenously. Additional experiments were performed when lidocaine was added to the perfusate and when lidocaine and capsaicin were administered simultaneously. Gallbladder absorption and perfusate and tissue prostaglandin E and 6 keto prostaglandin F1 alpha concentrations were evaluated. To determine whether capsaicin induced gallbladder inflammation, tissue myeloperoxidase concentrations were measured. Control feline gallbladders absorbed approximately 0.6 ml/hr. Indomethacin alone significantly decreased gallbladder absorption. Capsaicin administration increased gallbladder absorption to approximately 1.6 ml/hr, and this increase was significantly inhibited by indomethacin. (ABSTRACT TRUNCATED AT 250 WORDS)

Intestinal permeability to polyethylene glycol 4000 and porcine albumin in piglets infected with transmissible gastroenteritis virus

The intestinal permeability of specific pathogen free piglets has been studied by measuring the concentration of 14C in the blood after oral administration of 14C polyethylene glycol (14C PEG, MW = 4000) and the concentration of 131I in the faeces after intraperitoneal administration of 131I porcine albumin (131I PA, MW = 68,000). The tests were performed one day before and up to two days after the piglets were infected with transmissible gastroenteritis (TGE) virus. Jejunal biopsies were taken from two piglets before the experimental infection, from two piglets 12 h after the experimental infection and from five piglets at the end of the experiment, 46 h after infection. Blood samples were taken six-hourly and faecal samples several times. Some piglets vomited before diarrhoea and loss of appetite started at 14 h after infection; the packed cell volume decreased before but increased after infection. Morphological examination showed hyperregenerative villous atrophy at 46 h after infection. There was no increase in the permeation of 14C PEG but there was a significant increase in the flux of 131I PA from the blood to the gut lumen.

Almitrine bismesylate disposition in the human digestive tract.

The absorption of almitrine from the upper gastrointestinal tract has been evaluated in 6 healthy volunteers by an intubation technique. Almitrine bismesylate dissolved in malic acid was introduced into the stomach after homogenization with a meal containing the marker 14C-polyethylene glycol (PEG) 4000. Unlabeled PEG 4000 was infused into the second part of duodenum throughout the experiment. Samples of the luminal content were collected every 15 min for four hours from the stomach and at the ligament of Treitz. Blood was also collected. Almitrine was neither absorbed from nor metabolized in the stomach. About 37% of the quantity of drug emptied from the stomach was absorbed from the duodenum. Almitrine was detected in plasma 50 min after ingestion of the meal and its plasma concentration-time profile reflected the cumulative gastric emptying rate. The metabolite tetrahydroxy almitrine was found in intestinal samples as soon as unchanged drug was detected in plasma. The intraluminal rate of formation of the metabolite increased with time. The results suggest hepatic metabolism of almitrine followed by rapid excretion of the metabolite in the bile.

Gastric and intestinal absorption of oxprenolol in humans.

The gastrointestinal absorption of the beta blocker oxprenolol was investigated in four healthy subjects by an intubation technique. Oxprenolol was introduced into the stomach, dissolved in a homogenized meal containing the marker 14C-polyethylene glycol (PEG) 4000. Unlabeled PEG 4000 was perfused during the whole experiment into the duodenum at the ampulla of Vater. Samples of luminal contents were collected at regular intervals over four hours in the stomach, at the angle of Treitz, and 30 cm below this point. Blood was also collected. Oxprenolol was not absorbed in the stomach. About 80% of the drug emptied from the stomach was absorbed in the duodenum, and 80% of that released from the duodenum was absorbed in a 30-cm segment of the jejunum. The amounts absorbed in these two intestinal segments were directly proportional to the amounts delivered. The areas under the plasma concentration-time curves were not related to the amounts absorbed. A single dose of oxprenolol taken with an homogenized meal did not modify the gastric emptying and secretory response.

The effect of β-glucanase on the utilization of starch and nitrogen by broiler chickens fed on barley of low- or high-viscosity

Day-old broiler chickens of mixed sex were randomly distributed over 4 groups of 15 birds. The groups received diets containing either a high- or a low-viscosity barley and with and without β-glucanase in the diet. The high- and low-viscosity barleys were harvested from the same crop at different stages of ripeness; early-yellow and combine ripeness, respectively. At 19 days old, the chickens were killed and sections of the gastro-intestinal tract were taken. The digesta from each section were analyzed for dry matter, starch, mixed-linked β-glucans, nitrogen and 14C-polyethylene glycol. Supplementation with β-glucanase increased mean values for weight gain and improved feed conversion. The dry matter content of the small intestine digesta was lower in chickens receiving the high-viscosity barley. Supplementation with β-glucanase increased the dry matter content of the small intestine digesta. Starch and nitrogen digestibility in the small intestine, calculated relative to 14C-polyethylene glycol content, was improved by β-glucanase supplementation. The β-glucans were better degraded in the diets supplemented with β-glucanase.

Paracellular water uptake and molecular sieving by the foot epithelium of terrestrial slugs

A paracellular pathway in the foot epithelium of Lehmannia valentiana can be opened by dehydrating the slug. Movement of water from a wet pad through the opened pathway into the haemolymph of this terrestrial slug is rapid. The sieving properties of this paracellular pathway have been determined using the reference isotope 3HOH and various 14C-labelled solutes. Paracellular uptake of 14C-insulin (Fig. 1) and 3HOH (Fig. 2) is initial rate for at least 3 min. If the wet pad contains 1,000 cpm of 14C per ml of 3HOH, slugs absorb only about 400 cpm of 14C with each ml of 3HOH absorbed representing a sieving ratio of 0.4 for insulin. The sieving ratio of 14C-inulin does not change when the concentration is increased from 0.1 to 2.5 mmol/l. Moreover, the sieving ratio of 14C-inulin was not affected significantly by the nature of the labelling, i.e., 14C-carboxyl vs 14C-methoxy. Sieving ratios for 14C-mannitol (182 Da), 14C-polyethylene glycol (4,000 Da), and 14C-inulin (5,250 Da) were 0.92, 0.63, and 0.39, respectively (Table 1), indicating that sieving is dependent on molecular size. 14C-Dextran (70,000 Da) and blue dextran (200,000 Da) were excluded from the paracellular pathway (Fig. 4). The effective pore size of the paracellular pathway was estimated using the relationships between sieving ratio and molecular weight of 3HOH and the various solutes that can pass through the pathway. The extrapolated pore size is equivalent to that of a sieve having a molecular weight cutoff of about 10,000 Da (Fig 3).

CONTRIBUTION OF PASSIVE PROXIMAL BILE SALT (BS) ABSORPTION TO ENTEROHEPATIC CIRCULATION (EHC) OF BS IN THE RAT

Although the active transport of BS across the terminal ileum has been well documented, analysis of previous studies shows that ileal active transport cannot account for total BS recovery (Am 3 Physiol 244:G507,1983). To evaluate passive BS absorption in the proximal small intestine, weanling male Sprague-Dawley rats (age 39±4 days; wt 146 ± 26 g - mean ± SD) were anesthetized, the common bile duct was cannulated and the jejunum (J) and ileum (I) were catheterized and isolated. 1 ml of taurocholate (TC) solution in concentrations ranging from 0.5 mM to 10 mM and containing 3H-TC and 14C-polyethylene glycol (PEG - non-absorbable marker) were injected into the J. Bile was collected for 90 min. post-injection and counted. J and I were then ligated (to prevent mixing), divided into 8 segments, homogenized, and counted. TC absorption from the intestine was determined using 14C-PEG as a reference substance. In all animals, >94% of the 14C-PEG marker was found in proximal J (segments 1-3). A linear correlation was found between the conc. of TC administered and the amount of TC recovered in bile (N=20, r=.91, p<.001). 8.4 ± 2.9 % of the dose was excreted in bile in 90 minutes. The rate of TC absorption was linearly related to TC conc. (N=13, r=.97, p< .001) and was non-saturable. These findings demonstrate that TC is avidly absorbed by a passive process at physiologic concentrations (8-10 mM) in the proximal small bowel of the rat. When calculated for the entire small bowel, passive absorption accounts for between 54 and 69% of total BS secretion and is the major mechanism of BS conservation. These findings suggest that rapid proximal BS absorption rather than fecal BS loss is the mechanism for decreased intraluminal BS concentration in the neonate.

EFFECT OF MATERNAL ANTIBODIES AND ENTERIC CHALLENGE WITH ANTIGEN ON THE UPTAKE OF BYSTANDER PROTEIN IN NEONATAL RABBITS

Antibodies, passively acquired from the mother, were previously shown to limit the circulation of antigen given enterically to newborn rabbits. In the present experiments, we tested the effect of passive immunization and enteric antigen challenge on uptake of bystander protein. Female rabbits were immunized with bovine gamma globulin (BGG). Litters from these animals were tested prior to suckling by the intragastric administration of bovine serum albumin (BSA) plus BGG (test) or ovalbumin (OVA) (control animals). Three hrs. later, serum from both groups was tested for immunoreactive BSA by radioimmunoassay. Test animals had significantly less serum iBSA than controls. In other experiments the same protocol was followed except for the addition of 14C-polyethylene glycol (14C-PEG). Three hrs. after challenge, the concentration of radioactivity in various segments of intestine was determined. There was less 14C-PEG in the small intestine of test compared to control animals. These findings suggest enteric antigen-antibody interaction in intact animals may limit contact of protein with the absorptive surface on the enterocyte and thus diminish uptake of bystander protein in the neonate.

Appearance of 14C-polyethylene glycol 4000 in intestinal venous blood: influence of osmolarity and laxatives, effect on net water flux determination.

In anaesthetized rats the appearance rate of 14C-polyethylene glycol 4000 (14C-PEG 4000) was measured in the intestinal venous blood after intraluminal administration into a jejunal, ileal, and colonic segment. The absorption rate was small, especially in the colon (0.5-4.2% within 60 min in an intestinal segment of about 300 mg wet tissue weight depending on the batch of 14C-PEG 4000). The absorbed PEG in the plasma consisted mainly of molecules with lower molecular weight than 4000 which were included in the commercial batches of 14C-PEG 4000. The appearance rate of 14C-PEG decreased with time after single dose but remained constant, when a 14C-PEG solution was perfused continuously through the intestinal lumen. A hypotonic solution increased and a hypertonic one decreased slightly the absorption of PEG in the jejunum and ileum but not in the colon. The influence of bisacodyl (100 mgl(-1)) and ricinoleate (10 mmol l(-1)) on the absorption of PEG was small or absent, while deoxycholate (5 mmol 1(-1)) raised the absorption rate considerably, predominantly of the high molecular weight fraction. If in intestinal absorption studies a batch of commercial 14C-PEG 4000 with a small low molecular weight fraction is used, the error in the determination of net water flux caused by the absorption of PEG can be neglected. The influence of osmolarity and laxatives is insignificant. Bile acids increase the intestinal permeability of PEG 4000, so that the net water flux determination can be biased considerably.