Differential effects of prophylactic, concurrent and therapeutic lactoferrin treatment on LPS-induced inflammatory responses in mice.

Mice injected with endotoxin develop endotoxaemia and endotoxin-induced death, accompanied by the oxidative burst and overproduction of inflammatory mediators. Lactoferrin, an iron binding protein, provides a natural feedback mechanism to control the development of such metabolic imbalance and protects against deleterious effects of endotoxin. We investigated the effects of intraperitoneal administration of human lactoferrin on lipopolysaccharide (LPS)-induced release of tumour necrosis factor alpha (TNF-alpha), interleukin 6 (IL-6), interleukin 10 (IL-10) and nitric oxide (NO) in vivo. Lactoferrin was administered as a prophylactic, concurrent or therapeutic event relative to endotoxic shock by intravenous injection of LPS. Inflammatory mediators were measured in serum at 2, 6 and 18 h post-shock induction. Administration of lactoferrin 1 h before LPS resulted in a rather uniform inhibition of all mediators; TNF by 82%, IL-6 by 43%, IL-10 by 47% at 2 h following LPS injection,and reduction in NO (80%) at 6 h post-shock. Prophylactic administration of lactoferrin at 18 h prior to LPS injection resulted in similar decreases in TNF-alpha (95%) and in NO (62%), but no statistical reduction in IL-6 or IL-10. Similarly, when lactoferrin was administered as a therapeutic post-induction of endotoxic shock, significant reductions were apparent in TNF-alpha and NO in serum, but no significant effect was seen on IL-6 and IL-10. These results suggest that the mechanism of action for lactoferrin contains a component for differential regulation of cellular immune responses during in vivo models of sepsis.

Organ sites of lipopolysaccharide-induced nitric oxide production in the anesthetized rat.

The objective of this research was to determine the amount and timing of nitric oxide (NO, nitrogen monoxide) gas produced by the lungs, intestinal mucosa, and organ surfaces facing the peritoneal cavity after iv injection of a bacterial toxin, lipopolysaccharide (LPS). Some of the deleterious effects of LPS on organ function have been attributed to NO or strong oxidants formed locally from NO. Medical-grade air was used as an inspiratory air source (50 strokes/min x 3 ml/stroke) or was pumped through the ileal lumen or peritoneal cavity (20 strokes/min x 3 ml/stroke). The air was collected at intervals of 15-30 min for 3 h after LPS and analyzed for authentic NO gas by chemiluminescence. LPS (5 mg/kg) or saline was injected iv. Sodium nitroprusside (SNP) was injected to determine the appearance of its NO released into the perfused compartments. Blood pressure, plasma nitrate plus nitrite (NO(x)), and total plasma leukocytes were measured as other manifestations of LPS effects. NO began to increase in the pulmonary expired air 90 min after LPS and continued to increase for the remainder of the experiment. The final pulmonary post-LPS [NO] was about 20-fold greater than the [NO] before LPS. LPS had no effect on intraluminal or intraperitoneal [NO]. The saline injection had no effect on [NO] in any compartment. SNP injection increased NO entry into all three air-perfused compartments. Thus, NO from an exogenous tissue source was not prevented from being detected. Blood pressure was decreased by LPS only during the pulmonary perfusion. There were no significant effects of LPS on leukocytes or plasma NO(x). LPS decreased blood pressure and leukocytes and increased plasma NO(x) when air perfusion was not done. It was concluded that different organs can produce LPS-induced NO at markedly different rates and times. However, some aspect of the experimental technique of air perfusion could alter the effects of LPS.

Temporal expression of tumor necrosis factor-alpha and nitric oxide synthase 2 in rat small intestine after endotoxin.

Temporal changes in tumor necrosis factor-alpha (TNF-alpha) and nitric oxide synthase 2 (NOS 2) were evaluated in segments of duodenum, jejunum, and ileum removed from male Sprague-Dawley rats 30, 60, 120, 180, and 240 min after lipopolysaccharide (LPS), 5 mg/kg, intraperitoneally. Plasma was assayed for TNF-alpha and for nitrate/nitrite (NOx). Intestinal and plasma TNF-alpha were elevated by 60 min after LPS and were back to control levels by 180 min. For control rats, NOS 2 was detected in the ileum, but not in the duodenum or the jejunum. In rats treated with LPS, NOS 2 was detected in all areas of the intestine at 120 min and was greatest at 240 min. Plasma NOx was elevated at 120 min and continued to increase to 240 min. The time course of changes in intestinal TNF-alpha and NOS 2 were similar to those reported for other tissues and suggest that the early and late actions of the LPS on the intestine may involve both mediators.

Time- and surgery-dependent effects of lipopolysaccharide on gut, cardiovascular and nitric oxide functions.

Lipopolysaccharide (LPS) is considered a major effector of hypotension in septic shock, partly through increasing nitric oxide (NO) formation. LPS-activation of leukocytes that express cytokines which induce NO synthase (iNOS) has also been considered an important contributor to shock. However, LPS, cytokines, and NO are not necessarily associated with hypotensive shock. We investigated whether the timing of LPS injection after initial surgery could influence responses to LPS. E. coli LPS (17 mg/kg 0111:B4 and 026:B6 serotypes) was injected 15 or 120 min after tracheal and femoral cannulation in the anesthetized rat. LPS caused hypotension for 2 h when injected 15 min (early injection) after initial surgery. LPS decreased blood pressure for only 15 min when injected 2 h (late injection) after initial surgery. Plasma NO was increased and leukocytes were decreased after both the early and late LPS injection. Blood pressure responded the same when a second surgery (ileal cannulation and luminal perfusion) followed the early or preceded the late LPS injection. Ileal NO secretion increased and effective mucosal blood flow decreased when LPS followed gut surgery, but these did not change when gut surgery followed LPS. Plasma NO was increased and leukocytes were decreased when LPS followed gut surgery, but these did not change when gut surgery followed LPS. Ileal water absorption was not affected by LPS. These observations suggest that a desensitization to the hypotensive effect of LPS develops with time after an initial trauma. An additional gut trauma does not change the blood pressure response, but does have effects on leukocyte sequestration and NO synthesis. NO synthesis alone could not explain the effects on blood pressure.

Modulation of hemorrhagic shock by intestinal mucosal NG-nitro-L-arginine and L-arginine in the anesthetized rat.

Maintaining intestinal function protects against shock of various origins. Nitric oxide (NO) can protect tissues. The present research examined whether the presence of 50 microM NG-nitro-L-arginine (NOLARG), a nitric oxide synthase (NOS) inhibitor, or L-arginine (LARG), the substrate of NOS, in the jejunal lumen of the anesthetized rat could affect the progress of hemorrhagic shock. The jejunal lumen was perfused with saline containing 14C-inulin and 3H2O to measure net H2O absorption and absorptive site blood flow (ASBF). Luminal NOx (NO3- +NO2-) secretion into the gut effluent and blood pressure (BP) were also measured. The animals were bled to and maintained at 40 mmHg for 60 min and then reinfused. Survival time was significantly decreased in luminally-perfused NOLARG animals, but was significantly increased in LARG perfused animals. Most deaths occurred during the hemorrhage periods. Animals perfused with LARG through the ileal lumen required significantly less blood to be reinfused to maintain blood pressure during the hemorrhage periods. There were not significant differences in BP among surviving animals. Net H2O absorption and ASBF were significantly decreased only in NOLARG-perfused animals in the period just before and after reinfusion. There were no significant differences in luminal NOx secretion among the groups. Thus, intestinal mucosal NOS substrates or antagonists modulate the progress of hemorrhagic shock, but the mechanism was not defined in these experiments.

Splenic sympathetic response to endotoxin is blunted in the fetal alcohol-exposed rat: role of nitric oxide.

This study was designed to test the hypothesis that nitric oxide (NO) mediates the blunted splenic sympathetic response to lipopolysaccharide (endotoxin) that occurs in young rats exposed to alcohol in utero (FAE). The subjects, 26-29-day-old rats, were progeny of pregnant dams fed an alcohol diet (35% of the calories were derived from ethanol) or their control and pair-fed (PFC) cohorts. We examined the effects of lipopolysaccharide (LPS) (0.5 mg/kg, i.p.) on splenic norepinephrine (NE) turnover, an index of sympathetic neural activity, splenic inducible NO synthase (iNOS) protein immunoreactivity, and NO metabolites nitrite/nitrate concentrations in plasma. In response to LPS, splenic NE turnover was increased by more than twofold in the PFC groups, but the increase did not occur in their FAE cohorts. The blockade of NOS with L-NAME (30 mg/kg, i.p.) reversed this difference. In both the PFC and FAE rats, basal levels of splenic iNOS protein immunoreactivity were equally barely detected and plasma NO metabolite levels were relatively low (25 microM in both groups). In response to LPS, however, iNOS protein displayed a marked increase in the PFC group and an even greater increase (by close to threefold) in the FAE rats. LPS also substantially increased plasma NO metabolite levels by close to eightfold in the control groups, but by 15-fold in their FAE cohorts compared to the basal levels. These findings support the hypothesis that in the FAE rat, an augmented NO formation accounts for the blunted sympathetic response to endotoxin.

Hypotension during septic shock does not correlate with plasma levels of nitric oxide metabolites in the conscious rat.

Hypotension following administration of lipopolysaccharide may be due to excessive production of the potent vasodilator nitric oxide brought about by induction of nitric oxide synthase. The purpose of this study was to determine in conscious, fasted rats what role nitric oxide played in lipopolysaccharide-induced hypotension. When examined by Western immunoblot analysis, inducible nitric oxide synthase immunoreactivity was detected in the aorta at 3 hours and increased over time following administration of intraperitoneal lipopolysaccharide (20 mg/kg). When compared with saline-treated control rats, significant hypotension was observed at 2, 4, and 6 hours following lipopolysaccharide treatment. Blood pressure at 2 hours did not differ significantly from that at 6 hours. Using the Griess reaction to quantify plasma levels of nitrates and nitrites as an index of systemic nitric oxide production, an augmentation in the formation of these nitric oxide metabolites was demonstrated at 4 and 6 hours but not at 2 hours. Subcutaneous administration of the nitric oxide synthase inhibitor NG-nitro-L-arginine methyl ester (5 mg/kg) prevented lipopolysaccharide-induced hypotension, an effect reversed by subcutaneous L-arginine but not D-arginine (350 mg/kg). However, nitric oxide synthase inhibition did not attenuate the ability of lipopolysaccharide to increase plasma nitrate/nitrite levels. These data indicate that lipopolysaccharide-induced production of nitric oxide metabolites does not correlate with lipopolysaccharide-induced hypotension.

Influence of the Ward colon tumor on the host response to endotoxin.

Cachexia and a decreased immune function are negative prognostic factors for cancer patients. While the decreased immunity results in a greater susceptibility to bacterial infection, the response of the host to the resulting infection is not clear. The experiments reported here were designed to evaluate the toxicity of endotoxin to rats with a transplantable Ward colon tumor (WCT) and to evaluate the mechanism of the observed increase in lethal toxicity. The lethal toxicity of endotoxin (lipopolysaccharide, LPS) at 5 mg/kg, i.p. was evaluated in the first of two experiments. Rats received LPS and were observed for morbidity and weight loss for a period of 11 days. A second experiment was done to evaluate the effect of LPS on the plasma nitrate/nitrite concentrations and plasma indicators of host tissue dysfunction. LPS was administered as previously described but blood and tissues were collected 5 h after LPS administration. LPS resulted in the death of 1 of 12 nontumor-bearing (NTB) rats and a transient weight loss in the survivors. This same dose of LPS, however, resulted in death for 10 of 12 WCT rats with tumor burdens less than 4% of body weight. The response of WCT rats 5 h after LPS was then compared with that of age-matched NTB rats. Plasma albumin concentrations were not affected by LPS in NTB rats but were significantly decreased in WCT rats. Peripheral blood gases were not consistently affected by LPS in either group. Peripheral blood white cell counts, except monocytes, were significantly decreased by LPS in both groups. Monocyte counts in peripheral blood were further reduced in WCT rats compared with NTB rats receiving LPS. The presence of the WCT significantly enhanced the LPS-associated increase in spleen weight. Liver weights were lower in LPS rats but there was no effect of the presence of WCT. The LPS-associated increase in plasma nitrate/nitrite concentration was enhanced by the WCT. The plasma arginine and citrulline concentrations were altered in a manner consistent with an increase in nitric oxide synthesis. An increase in plasma ornithine concentration suggests an increase in arginine metabolism by arginase. The plasma concentration of alanine aminotransferase was significantly elevated when WCT rats received LPS, suggesting enhanced hepatic dysfunction. The plasma blood urea nitrogen concentration was elevated by LPS to a greater extent in the WCT rats than in the NTB controls, indicating increased renal dysfunction. These results demonstrate that the Ward colon tumor increases the host lethal response to the endotoxin, a toxic product of bacterial infections. The mechanisms of lethality may include an increased nitric oxide synthesis in WCT rats and enhanced liver and renal toxicity.

Differential effects of lumenal L-arginine and NG-nitro L-arginine on blood flow and water fluxes in rat ileum.

1. The role of endogenous mucosal nitric oxide (NO) in the local regulation of H2O absorption and blood flow in rat ileum was studied by perfusing L-arginine (L-Arg) (0.1-1.0 mM) and NG-nitro L-arginine (L-NOARG) (0.01-1.0 mM) through the lumen. D-Arginine (D-Arg) or L-Arg (1 mM), combined with L-NOARG, were used to determine if any of the measured intestinal effects of L-NOARG were exerted through NO formation. 2. Net and unidirectional H2O fluxes and effective mucosal blood flow were measured using 3H2O and [14C]-inulin in the perfusate. Mucosal NO formation was measured as the appearance of lumenal NO2-. 3. L-NOARG, beginning at a concentration of 0.1 mM, decreased net H2O absorption, but had only minor effects on unidirectional H2O fluxes or on blood flow. L-NOARG increased blood pressure, beginning at a concentration of 0.5 mM. 4. L-Arg had no significant effects on net H2O absorption or blood pressure, and only minor effects on unidirectional H2O fluxes and blood flow. 5. NO appearance in the lumen was marginally decreased by 1.0 mM L-NOARG, but not increased by L-Arg. 6. Mucosal blood flow resistance paralleled systemic blood pressure suggesting that vascular effects on the mucosa were exerted only after L-NOARG had reached the general circulation. 7. Lumenal L-Arg reversed the effects of lumenal L-NOARG on net H2O absorption and blood pressure, but D-Arg did not. 8. It was concluded that there is tonic NO production by the rat intestinal mucosa that promotes H20 absorption, but does not affect blood flow resistance. Mucosal NO production was not related to the observed effects on mucosal function.

Crystals in pulmonary cytologic preparations in association with aspiration of barium. A case report.

Crystals were found in a pulmonary cytologic preparation in association with the aspiration of barium. This type of event has not been described previously, although rare occurrences of crystals in pulmonary cytology specimens in association with Aspergillus infection and other situations have been reported. We recommend that patients suspected of aspiration be given no oral substances for at least 12 hours before bronchoscopy.

Villous motility and unstirred water layers in canine intestine.

The possibility that villous motility reduces the mucosal unstirred water layer by mechanical stirring was examined. The frequency of contraction of villi was measured by using videomicroscopic techniques while a segment of anesthetized canine jejunum or ileum with its nerve and blood supply intact was maintained in a sealed chamber through which Tyrode solution was perfused. Radioisotopically labeled inulin, H2O, and butyric and lauric acid were used to measure net and/or unidirectional fluxes from the chamber. The unidirectional absorptive transport of H2O and butyric acid but not lauric acid by jejunal segments was significantly correlated with flow through the chamber. Plasma volume expansion increased villous motility but decreased the absorption of H2O and lauric acid. Absorption of butyric acid from the ileum was little different than from the jejunum although the degree of villous motility was less and net water absorption was greater from the ileum. Absorption of butyric acid into dead tissue indicated that passive diffusion into the tissue accounted for between 7 and 25%, depending on flow rate, of the absorption in intact tissue and that nonspecific binding was low. It was concluded that villous motility did not stir the unstirred water layers and was not directly associated with altered transport.

Binding and solubility of oleic acid to laboratory materials: a possible artifact.

The possibility that significant amounts of fatty acids were dissolved in or bound to the surfaces of common laboratory materials was examined. The uptake or adsorption of radioisotopically labeled oleic acid and cholic acid by plastic tubing of Tygon, Teflon, and polyethylene, and Pyrex, and borosilicate glass, and steel was measured. 3H-oleic acid and 14C-cholic acid were used in the presence of different concentrations of unlabeled oleic acid, cholic acid, and/or bovine serum albumin. Concentrations, composition, pH, and perfusion rates were varied. Relatively large amounts (10-95%) of oleic acid (25 microM) were lost by dissolving in plastic and adsorption to glass or metal. The degree of losses decreased in the presence of compounds in the perfusion solution which could bind or dissolve oleic acid. In contrast, cholic acid was not lost to plastic, glass or metal. The magnitude of and influence of perfusion rate, composition, pH, and sequence of perfusion solutions on oleic acid losses were sufficiently large that the results of certain studies, such as those of unstirred water layers of albumin - stimulated fatty acid uptake by hepatocytes may need to be reexamined.

Effects of intraarterial, intravenous, and intraluminal neurotensin on canine ileal sodium and water absorption and blood flow.

Neurotensin is a regulatory peptide which is found primarily in the ileum and is secreted into the blood and lumen. The physiologic effects of neurotensin are uncertain but in certain pathologic states neurotensin increases to levels which can have effects on many organs. The effects of intravenous, intraarterial and intraluminal neurotensin (0.075-7.5 micrograms/min) on fed canine ileal sodium and water fluxes, potassium secretion, and blood flows were studied. Intravenous and intraarterial infusion of neurotensin increased net sodium, potassium, and water secretion, due to increased secretory fluxes, and increased hematocrits. Intraarterial neurotensin was not more effective than intravenous neurotensin except for stimulating potassium secretion. Neurotensin increased potassium secretion at 0.075 micrograms/min IA, increased sodium and water secretion at 0.75 micrograms/min IA and IV, and increased hematocrit at 7.5 micrograms/min IA and and IV. Total and absorptive site blood flows and arterial and venous pressures were not changed. Intraluminal neurotensin had no effects at any infusion rate. Neurotensin can increase potassium secretion at physiologic levels by a local effect and can increase sodium and water secretion at high physiological-pathological levels through a hormonal mechanism. The secretion is not dependent on cardiovascular changes.

Effects of oleic acid and bile salts on canine villous motility.

The effects on canine villous motility of mucosal Tyrodes solution containing oleic acid (10 mM) and/or either taurocholic or cholic acid (15 mM) in the presence or absence of IV atropine (1 mg/kg) was used to assess the neural mediation of the effects of luminal nutrients. Villous motility was measured over 12 min periods by in vivo videomicroscopy of segments of jejunum. Neither bile salt had effects alone but villous motility increased after oleic acid was added to taurocholate and decreased after oleic acid was added to cholate. Villous motility increased when taurocholate and oleic acid were present initially and returned to control levels when removed. Villous motility was not affected by cholate and oleic acid but villous motility decreased when they were removed from the Tyrodes solution. Atropine blocked the increase in villous motility caused by taurocholate and oleic acid. Bile salts can modify the effect of oleic acid on villous motility and a cholinergic step is involved in the stimulation of motility.

Neurohumoral control of villous motility.

A quantitative videomicroscopic method was used to examine neurohumoral control of villous motility. Intraduodenal instillation of saline, 0.4% hydrochloric acid, or acidified predigested food did not cause a significant change in villous contraction frequency in an isolated segment of jejunum. Villous motility in the jejunum of fed dogs, from which the chyme had been removed, was not greater than that in fasted dogs (2.9 +/- 0.3 vs. 3.4 +/- 0.5 contractions/min). Furthermore, acid extracts of the duodenal mucosa did not produce an increase in jejunal villous motility when injected intravenously. These data argue against the existence of a humoral stimulant of villous motility (villikinin). Vagotomy caused only a small (20%) and transient (10 min) decline in villous motility. Vagal stimulation at 5, 10, and 20 Hz caused villous motility to increase by 24 +/- 7, 23 +/- 9, and 32 +/- 10%, respectively. Atropine blocked the effects of vagal stimulation. Section of the periarterial (sympathetic) nerves did not alter villous contractile activity. Stimulation of the periarterial nerves at 5, 10, and 20 Hz caused villous contraction frequency to decline by 41 +/- 5, 45 +/- 5, and 38 +/- 10%, respectively. This inhibition appears to involve both alpha- and beta-adrenergic receptors and a reduction in blood flow. Neither atropine, alpha-blockade, nor beta-blockade produced a sustained alteration in basal contraction frequency.

Effects of atropine and tetrodotoxin on neurotensin-induced ileal sodium transport in the dog.

1. Neurotensin was infused intravenously, in the presence or absence of intravenous atropine or intraarterial tetrodotoxin, into dogs anaesthetized with sodium pentobarbitone. Net and unidirectional fluxes of sodium and blood flows in the ileum were measured. Arterial and mesenteric venous blood pressures, haematocrits and plasma total solids were also determined. 2. Neurotensin caused a transient increase in net sodium absorption which was not associated with significant changes in unidirectional fluxes. This was followed by prolonged net secretion which was associated with an increase in unidirectional sodium secretion and a smaller decrease in sodium absorption. Potassium secretion was also increased when net sodium secretion increased. 3. Neurotensin increased haematocrit and total solids and decreased arterial pressure at the same time that secretion occurred. 4. Atropine blocked all the cardiovascular effects of neurotensin and reduced its early effects on both absorption and secretion but not the later effects on secretion. Tetrodotoxin only blocked the increase in absorption but not the secretion or the cardiovascular effects. 5. It was concluded that there is a cholinergic step in the cardiovascular effects of neurotensin and that the early effects of neurotensin on secretion are due to active secretion supported by fluid leakage from the plasma. The later effects of neurotensin on secretion do not have a cholinergic step and are due primarily to an active secretion. The increased absorption is mediated partly through intrinsic nerves of the gut.

Villous motility: relationship to lymph flow and blood flow in the dog jejunum.

Villous contraction frequency, lymph flow, blood flow, and arteriovenous oxygen difference were measured in dog jejunum. Venous pressure elevation and plasma dilution were used to increase capillary fluid filtration. Both perturbations produced concomitant increases in villous contraction frequency and lymph flow. A highly significant correlation (r = 0.83, p less than 0.001) was obtained between villous contraction frequency and lymph flow. This finding, coupled with the observation that stimulation of net fluid absorption increases villous contraction frequency, suggests that villous motility is increased by a myogenic response elicited by increments in interstitial fluid pressure. In another series of experiments local arterial pressure was reduced in 20-mmHg steps from 120 to 20 mmHg. Although blood flow fell proportionately to arterial pressure, villous contraction frequency and oxygen uptake were maintained at a normal level when arterial pressure was between 120 and 60 mmHg. Villous motility and oxygen consumption fell progressively as arterial pressure was reduced below 60 mmHg. This observation indicates that ischemia does not alter villous contraction frequency unless blood flow is reduced below the level necessary to maintain normal tissue oxygenation.

Cardiovascular and flux relationships in canine ileum.

Blood flow and pressure in denerved ileum of anesthetized dogs were altered by occlusion of the mesenteric artery or vein or by infusion of intra-arterial sodium nitroprusside (0.015-1.5 mg/min). Unidirectional Na and H2O fluxes were measured and absorptive site blood flow was estimated from the clearance of tritiated H2O. Net Na and H2O absorptions were reduced by mesenteric venous or arterial occlusion. Net secretion occurred with mesenteric venous occlusion. Nitroprusside reduced net absorption only at an infusion rate of 0.15 mg/min. The absorptive Na and H2O fluxes were reduced by both mesenteric venous or arterial occlusion, with venous occlusion being more effective. Nitroprusside reduced the absorptive Na flux at an infusion rate of 0.15 mg/min but not the absorptive H2O flux. The secretory flux of Na was increased by mesenteric venous occlusion but reduced by arterial occlusion and not changed by nitroprusside infusion. The secretory H2O flux was decreased by moderate degrees of mesenteric venous occlusion but was unchanged at greater levels. Arterial occlusion decreased secretory H2O fluxes. Nitroprossude infusion increased secretory H2O fluxes at an infusion rate of 0.015 mg/min. The absorptive and secretory Na and H2O fluxes were significantly correlated with absorptive site blood flow plus estimated capillary pressure. Absorptive site blood flow was primarily responsible for changes in absorptive fluxes and estimated capillary pressure for changes in secretory fluxes. Absorptive site blood flow affected the secretory and absorptive fluxes of H2O more equally than the Na fluxes.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of atropine and guanethidine on canine intestinal absorption and blood flow.

The possibility of tonic autonomic control over intestinal Na and H2O absorption and whether the cardiovascular system was involved was tested by administration of atropine or guanethidine. 3H2O and 22Na in saline perfused through the lumen were used to calculate unidirectional fluxes and total and absorptive site blood flow in canine ileum. Both atropine and guanethidine had qualitatively similar effects on absorption and blood flow with atropine being quantitatively greater. Net Na and H2O absorption were not increased significantly but their absorptive and secretory unidirectional fluxes were increased significantly. Total blood flow was not affected but absorptive site blood flow was increased and resistance decreased. The absorptive site blood flow was correlated with the absorptive Na fluxes similarly in all groups. The secretory fluxes of Na and H2O were correlated with estimated capillary pressure when all three groups were considered together. It was concluded that there is tonic cholinergic control over intestinal absorption which is mediated, in part, through cardiovascular effects. The findings were consistent with tonic parasympathetic activity having primarily a direct effect on gut absorption and blood flow but tonic sympathetic activity primarily modulating the direct effects of other regulatory mechanisms.