Indulging Curiosity: Preliminary Evidence of an Anxiolytic-like Effect of Castor Oil and Ricinoleic Acid

In the process of validating the elevated zero maze, a common test of anxiety-like behavior, in our laboratory, we demonstrated an anxiolytic-like effect of castor oil and its primary component, ricinoleic acid. We tested the effects of vehicle and chlordiazepoxide in male mice in the elevated zero maze following a 30-min pretreatment time. Chlordiazepoxide is a United States Food and Drug Administration-approved drug that was previously shown to exert anxiolytic-like effects in both the elevated zero maze and elevated plus maze. Chlordiazepoxide was administered at doses of 5 or 10 mg/kg. We used 5% polyoxyl 35 castor oil (Kolliphor® EL) and saline as treatment vehicles and found that the effect of chlordiazepoxide on open zone occupancy and open zone entries was blunted when 5% Kolliphor was used as the vehicle. These tests demonstrated that chlordiazepoxide increased open zone occupancy and entries in the elevated zero maze more effectively when saline was used as the treatment vehicle and that Kolliphor dampened the anxiolytic-like effect of chlordiazepoxide when it was used as the treatment vehicle. Notably, 5% Kolliphor alone slightly increased baseline open zone occupancy and entries. Given that Kolliphor is a derivative of castor oil, we next tested the effect of 5% castor oil and 5% ricinoleic acid, which is a major component of castor oil. We found that both castor oil and ricinoleic acid increased open zone occupancy but not entries compared with saline. Altogether, our findings demonstrate that Kolliphor, castor oil, and ricinoleic acid may exert anxiolytic-like effects in male mice in the elevated zero maze. This potential anxiolytic-like effect of castor oil is consistent with its well-established beneficial effects, including anti-inflammatory, antioxidant, antifungal, and pain-relieving properties.

Synthesis and Biological Evaluation of Four New Ricinoleic Acid-Derived 1-O-alkylglycerols

A series of novel substituted 1-O-alkylglycerols (AKGs) containing methoxy (8), gem-difluoro (9), azide (10) and hydroxy (11) group at 12 position in the alkyl chain were synthesized from commercially available ricinoleic acid (12). The structures of these new synthesized AKGs were established by NMR experiments as well as from the HRMS and elementary analysis data. The antimicrobial activities of the studied AKGs 8-11 were evaluated, respectively, and all compounds exhibited antimicrobial activity to different extents alone and also when combined with some commonly used antibiotics (gentamicin, tetracycline, ciprofloxacin and ampicillin). AKG 11 was viewed as a lead compound for this series as it exhibited significantly higher antimicrobial activity than compounds 8-10.

PAF formation by human gastrointestinal mucosa/submucosa in-vitro: release by ricinoleic acid, and inhibition by 5-aminosalicylic acid

Human isolated gastrointestinal mucosa/submucosa incubated with ricinoleic acid (12·5–100 μg mL−1) or the calcium ionophore A23187 (10 μg mL−1) released platelet-activating factor (PAF) as determined by a scintillation proximity assay after extraction and purification. 5-Aminosalicylic acid (25–100 μg mL−1) inhibited PAF release by ricinoleic acid in a concentration-dependent manner, and 50 μg mL−1 reduced the effect of A23187. We suggest that PAF may play a role in the taxation and mucosal damage by ricinoleic acid released from castor oil.

Growth temperatures and various concentrations of ricinoleic acid affect fatty acid composition in two strains of Hansenula polymorpha

The fatty acid composition of two strains (wild-type and M2 mutant cells of Hansenula polymorpha strain CBS 1976) were studied at different growth temperatures and various concentrations of ricinoleic acid. Two strains of yeast cultured on YEPD medium containing 1, 2, 3 and 8 mM of ricinoleic acid at 25, 30, 37 and 45 degrees C. Lipids were extracted from the yeast culture and the fatty acids esterified with BF3-MeOH. Gas chromatography analysis of total lipids showed that C16:1 (delta7), which has been synthesized in low concentration by WT strain, was found to increase in the M2 mutant. The biotransformation of C16:1 (delta7) found in M2 indicated the presence of dehydroxylation and beta-oxidation systems. An increase in the growth temperature from 25 to 45 degrees C resulted in a decrease in the total unsaturated fatty acids of C16:1, C18:1, C18:2 and C18:3 from 44.0 to 22.1% and 65.0 to 49.3% of the total fatty acids in M2 and wild-type strains, respectively. The differential production of unsaturated fatty acids, especially C16:1, indicated that regulation of unsaturated fatty acid levels, is an important control point in membrane composition in the adaptation of H. polymorpha M2 to diet and temperature.

Toxicology and pharmacology of sodium ricinoleate

Ricinoleic acid constitutes approximately 90% of the fatty acid content of castor oil. Castor oil is known for its purgative effects and can be used to induce labor. Both castor oil and ricinoleic acid are approved for use in food. The mechanistic basis for purgative actions likely includes the membrane-disruptive effects of detergent-like molecules, such as sodium ricinoleate (a 'soap'). These effects have been shown to be dose-related and to exhibit a threshold below which no laxative response was evident, in both animals and in humans. Castor oil was not toxic in subchronic feeding studies in rodents at doses ranging up to 10-20% of the diet. Sodium ricinoleate, as a surfactant, demonstrates predictable skin and mucus membrane irritant effects, and may induce a Type IV dermal sensitization response in those previously sensitized to it. However, food-grade castor oil and sodium ricinoleate are prepared in such a manner as to be free of the castor bean constituents that have been proven to be the source of reported Type I immediate hypersensitivity responses. Feeding studies with castor oil in rodents provide a basis for a no observable adverse effect level (NOAEL) estimate of 7,500 mg/kg/day and 5,000 mg/kg/day in mice and rats, respectively (). Applying an uncertainty factor of 100 to the lesser of these NOAELs, one can thus estimate an acceptable daily intake (ADI) in man to be 50 mg/kg, or 3,000 mg of castor oil per day in an average 60 kg person. As ricinoleic acid constitutes approximately 90% of castor oil, applying this calculation to the 3,000 mg/day estimated ADI in humans for castor oil (given the rapid hydrolysis of castor oil glyceride in the gastrointestinal tract), the acceptable daily intake of ricinoleic acid may be as high as 2,400 mg/person.

Monohydroxylation and esterification as determinants of the effects of cis- and trans-9-octadecenoic acids on the permeation of hydrocortisone and 5-fluorouracil across hairless mouse skin in vitro

The effects of cis-9-octadecenoic acid (oleic acid) and of a group of chemically related cis- (ricinoleic acid) and trans- (ricinelaidic acid) 12-monohydroxylated derivatives and their corresponding ethyl and methyl esters on the skin permeation of model hydrophobic (hydrocortisone, log K=1.61) and hydrophilic (5-fluorouracil, log K=-0.89) drugs was investigated in vitro using excised hairless mouse skin. Drug solutions were prepared in propylene glycol, with and without the addition of a fatty acid to a level of 5%. Whereas the addition of oleic acid markedly enhanced the transdermal flux of both drugs relative to a sample in propylene glycol alone (hydrocortisone approximately 1800-fold; 5-fluorouracil approximately 330-fold), that of a cis- or trans-12-monohydroxylated analog of oleic acid resulted in only a small increase (1.4-2.7-fold for hydrocortisone; 4.4-6.6-fold for 5-fluorouracil). On the other hand, the methyl and ethyl esters of cis- and trans-12-hydroxy-9-octadecenoic acid exerted a much greater enhancing effect (327-720-fold for hydrocortisone, 42-74-fold for 5-fluorouracil) than the corresponding parent fatty acids. Furthermore, whereas the ethyl esters were found to have a greater effect on the skin permeation of hydrocortisone than the methyl esters, the reverse was true with regards to 5-fluorouracil. Additionally, the esters of trans-12-hydroxy-9-octadecenoic acid promoted permeation to an extent comparable to that achieved with their cis-counterparts.

Antinociceptive activity of ricinoleic acid, a capsaicin-like compound devoid of pungent properties

The antinociceptive effect of ricinoleic acid ([R-(Z)]-12-hydroxy-9-octadecenoic acid) in comparison with capsaicin (trans-8-methyl-N-vanillyl-6-nonenamide) has been investigated in several "in vivo" tests. Acute topical application of capsaicin, but not ricinoleic acid, produced by itself an hyperalgesic effect detected as a decrease in paw withdrawal latency in response to a painful (heat) stimulus in mice. Capsaicin, but not ricinoleic acid at any dose tested, showed an irritant effect in the wiping test in guinea pig conjunctiva after local application and in the paw licking test in mice after intradermal injection. Whereas acute application of ricinoleic acid or capsaicin decreased paw withdrawal latency to heat in the presence of a pre-existing inflammation (injection of carrageenan in the mouse paw), the repeated local treatment for 8 days with either compounds markedly increased paw withdrawal latency. In a chronic model of inflammation (complete Freund's adjuvant arthritis in mice), the repeated topical and intradermal treatments with both ricinoleic acid and capsaicin increased paw withdrawal latency to heat, the antinociceptive effect of ricinoleic acid being more persistent than that of capsaicin. Antinociceptive effect of 8 days of treatment with ricinoleic acid and capsaicin was observed in acetic acid-induced writhing in mice, capsaicin-induced foot licking in mice and capsaicin-induced wiping movements in guinea pig conjunctiva. A decrease of substance P tissue levels in the mouse paw was found after repeated treatment with ricinoleic acid. In conclusion, ricinoleic acid seems to be a new antinociceptive agent lacking the pungent and acute hyperalgesic properties of capsaicin.

Fatty acids enhanced tubermycin production by Pseudomonas strain 2HS

A new microbial isolate, Pseudomonas 2HS, produced trace amounts of a greenish-yellow pigment when grown aerobically in a 1% yeast extract medium at 30 degrees C and shaken at 250 rpm for 5 days. In contrast, cells produced more greenish-yellow pigment (2.16 mg/15 ml culture) when grown in the presence of 0.5% 12-hydroxyoctadecanoic acid (w/v). The greenish-yellow pigment was identified as phenazine-1-carboxylic acid (tubermycin B), and the Pseudomonas 2HS was identified as P. aeruginosa 2HS. This is the first report that 12-hydroxyoctadecanoic, ricinoleic and other fatty acids can enhance the production of phenazine-1-carboxylic acid by a Pseudomonas species.

[Effects of castor oil-diet on the synthesis of prostaglandin E2 in pregnant rats]

OBJECTIVE

To determine effects of castor oil-diet on the synthesis of prostaglandin E2(PGE2) and explore the mechanism of labor induced by castor oil-diet in pregnant rats.

METHODS

Pregnant rats were gavaged castor oil-diet in 18 and 19 days of gestation. At the time of death, blood of portal and peripheral veins, intestinal mucosa, amnion, amniotic cells and placenta were collected, and the tissues were cultured in the presence of ricinoleic acid or indomethacin. The concentrations of PGE2 in the media or blood were measured by RIA methods.

RESULTS

The PGE2 levels in the portal vein increased, while the PGE2 levels in peripheral blood had no changes significantly, the PGE2 levels in the tissues of the intestinal mucosa, placenta, amnion and amniotic cells were increased significantly; Ricinoleic acid stimulated the synthesis of PGE2 in the above tissues in vitro, which had the positive correlations with the dose of ricinoleic acid and its lasting time. Indomethacin inhibited the synthesis of PGE2 in-vitro.

CONCLUSION

The increased synthesis of PGE2 in the intrauterine tissues is a key of the initiation of labor induced by castor oil-diet, and ricinoleic acid in castor oil-diet might be the active component which induced the initiator of labor.

Differentiation of Malassezia species: selectivity of cremophor EL, castor oil and ricinoleic acid for M. furfur

In recent years, the genus Malassezia has been reclassified based on molecular data. In addition to M. furfur, M. pachydermatis and M. sympodialis, four new species, M. globosa, M. obtusa, M. restricta and M. slooffiiae, have been described. However, apart from their lipid dependence, little is known about the metabolism and nutritional requirements of all the seven species. Further to recent studies, 10 hydrophilic emulsifiers (HLB > 10) were examined in an agar diffusion test to determine their growth-promoting effect on reference strains of the different Malassezia species. Polyethylene glycol (PEG) 7 glyceryl monoalcanoate (Cetiol HE). PEG-glyceryl stearate (Tagat S2) and macrogol-50 stearate (Myrj 53) were metabolized by all strains, while PEG-35 castor oil (Cremophor EL) was metabolized only by M. furfur. The latter observation is due to a different metabolism of castor oil and its main component, ricinoleic acid (12-hydroxy oleic acid), which may also give an insight into the pathogenesis of diseases that are associated with Malassezia spp. As hydroxy fatty acids are important in maintaining the epidermal structure and function, their metabolism specifically by M. furfur might clarify some clinical aspects of pityriasis versicolor. Apart from this speculation, use of Cremophor EL, with splitting of esculin as an additional key character, improves the distinction of the species M. furfur, M. slooffiae and M. sympodialis.

Fatty acid accumulation in the yeast Sporidiobolus salmonicolor during batch production of gamma-decalactone

This paper provides new information about the metabolism of various fatty acids and gamma-decalactone production by yeast. An analysis of the fatty acid composition of the yeast Sporidiobolus salmonicolor during batch production of lactone with ricinoleic acid methyl ester as a precursor showed an accumulation of the gamma-decalactone precursor inside the cells. Electron microscopy of the yeasts showed the presence of large internal inclusions leading to membrane and organelle lysis and, consequently, death of the yeast. S. salmonicolor cultivated with methyl oleate did not produce gamma-decalactone and is viable during the whole culture. Analysis of the long chain fatty acid fraction showed incorporation of methyl oleate.

Metabolism of ricinoleate by Neurospora crassa

Neurospora crassa is a potential expression system for evaluating fatty-acid-modifying genes from plants producing uncommon fatty acids. One such gene encodes the hydroxylase that converts oleate to ricinoleate, a fatty acid with important industrial uses. To develop this expression system, it is critical to evaluate the metabolism and physiological effects of the expected novel fatty acid(s). We therefore examined effects of ricinoleate on lipid biosynthesis and growth of N. crassa. Ricinoleate inhibited growth and reduced levels of phospholipids and 2-hydroxy fatty acids in glycolipids, but led to increased lipid accumulation on a mass basis. To evaluate incorporation and metabolism of ricinoleate, we followed the fate 14 microM-3mM [1-14C]ricinoleate. The fate of the [14C]ricinoleate was concentration-dependent. At higher concentrations, ricinoleate was principally incorporated into triacylglycerols. At lower concentrations, ricinoleate was principally metabolized to other compounds. Thus, N. crassa transformants expressing the hydroxylase gene can be detected if the level of hydroxylase expression allows both growth and ricinoleate accumulation.

Therapeutic modalities for mechanical cleansing of the colon

Mechanical cleansing of the colon is an accepted standard of practice prior to colon surgery, and endoscopic and radiographic procedures. Cleansing the bowel prior to these procedures increases the accuracy of the diagnostic procedures and decreases the morbidity and mortality following surgery, where fecal contamination is a concern. Mechanical cleansing agents are sometimes used for acute constipation, but because of the extent and harshness of the evacuation they induce, and because of their adverse effects, they are not used for long-term management of constipation. Dosages vary among products, procedures, and individuals. Manufacturer guidelines should be consulted for proper dosing and administration.

The direct effect of injectable cyclosporine and its vehicle, cremophor, on endothelial vascular cell adhesion molecule-1 expression. Ricinoleic acid inhibits coronary artery endothelial activation

As in humans, rabbit coronary artery endothelium basally expresses vascular cell adhesion molecule-1 (VCAM-1). Treatment with parenteral cyclosporine (CsA) to prevent graft rejection in rabbits receiving heterotopic heart transplantation reduced VCAM-1 expression in coronary arteries not only in transplanted, but also in native rabbit hearts. To explore the mechanism of this effect, we co-incubated cultured human saphenous vein endothelial cells for 24 hr with CsA or its vehicle (containing polyoxyethylated castor oil, or Cremophor, and ethanol), at concentrations compatible with those achievable in plasma during administration of parenteral preparations of CsA. Cells were then stimulated with TNF alpha or IL-4 to induce VCAM-1 expression, assessed by a cell-surface enzyme immunoassay. Both CsA and vehicle inhibited IL-4-stimulated VCAM-1 expression in a dose-dependent manner (from [OD mU, mean +/- SEM] 230 +/- 5 to 165 +/- 3 for CsA 50 ng/ml, and to 181 +/- 6 for the corresponding vehicle concentration; P < 0.05 for both comparisons). To investigate whether this vehicle effect also occurs in vivo, we treated 9 New Zealand White rabbits with saline (n = 3), CsA (10 mg/kg/day, n = 3), or vehicle at corresponding doses (n = 3) for 6 weeks. Profiles of coronary arteries (> or = 48 for each group) were semiquantitatively scored (0-5) for VCAM-1 in immunostained heart cross-sections. Administration of both CsA and vehicle significantly reduced VCAM-1 expression compared with saline. Two vehicle components, ethanol and ricinoleic acid, were further evaluated directly on endothelial cells in vitro. While ethanol was ineffective, the monounsaturated fatty acid ricinoleic acid inhibited IL-4-stimulated VCAM-1 expression in a dose-dependent manner (IC50 between 10 and 100 microM). Thus, a fatty acid component of CsA vehicle exerts direct endothelial effects, potentially limiting arterial leukocyte recruitment during parenteral CsA treatment. This observation reveals a novel mechanism for CsA as an inhibitor of leukocyte-endothelial interactions, and furnishes a new potential rationale for the therapeutic action of unsaturated fatty acids in graft coronary disease.

Essential fatty acids are antagonists of the leukotriene B4 receptor

A series of essential fatty acids and fatty acid derivatives were evaluated for their ability to inhibit [3H] leukotriene B4 (LTB4) binding to pig neutrophil membranes. The fatty acids varied in chain length, extent of unsaturation, position of unsaturation, and isomerization. Generally, fatty acids with two or more unsaturated sites and chain lengths of 18-22 were potent inhibitors of [3H]LTB4 binding; both n-3 and n-6 fatty acids were inhibitory. The most potent compounds tested were homogammalinolenic acid and ricinelaidic acid which gave Ki values of 1 microM and 2 microM in the binding assay. Ricinelaidic acid was also tested for its ability to inhibit LTB4-mediated chemotaxis (IC50 = 10 microM) and LTB4-induced calcium fluxes (IC50 = 7 microM) in isolated human neutrophils. Ricinelaidic acid did not show agonist activity in these assays. In an in vivo model of LTB4-induced bronchoconstriction, ricinelaidic acid and homogammalinolenic acid gave 46% and 53% inhibition, respectively, at a 1 mg/kg i.v. dose. These results indicate that essential fatty acids are LTB4 receptor antagonists, which may account in part for their reported anti-inflammatory activities.

Direct vasoconstrictor effects of sandimmune (cyclosporine A) are mediated by its vehicle cremophor EL: inhibition by the thromboxane A2/prostaglandin endoperoxide receptor antagonist ifetroban

The use of cyclosporine A (CsA), a cyclic polypeptidic immunosuppressive agent, is associated with a number of cardiovascular problems. This study assessed the effects of CsA and its vehicle, cremophor EL (cremophor), on force development in isolated vascular tissue. CsA evoked a concentration-dependent increase in force (EC50 = 2.5 +/- 0.8 micrograms/ml) in the rabbit jugular vein. Cremophor alone also produced a concentration-dependent increase in force (EC50 = 39.5 +/- 10.9 micrograms/ml) that matched the CsA/cremophor response at equivalent cremophor concentrations. The cremophor-induced vasoconstriction was inhibited by the structurally distinct thromboxane A2 receptor antagonists ifetroban and glyburide, but not by indomethacin (10 microM). Ricinoleic acid also produced vasoconstriction (EC50 = 0.24 +/- 0.04 microgram/ml) that was sensitive to inhibition by ifetroban but not by indomethacin. CsA dissolved directly in ethanol produced a small increase in force that was indistinguishable from that evoked by ethanol alone. Cremophor (EC50 = 1.5 +/- 0.5 mg/ml) and ricinoleic acid (EC50 = 4.7 +/- 0.7 microgram/ml) also evoked force development in the rabbit aorta, responses that were antagonized by ifetroban. Thus, force development evoked by CsA in the rabbit jugular vein appears to be mediated primarily by its vehicle, cremophor. It is hypothesized that cremophor, by virtue of its ricinoleic acid component, evoked force development by acting as a weak thromboxane A2 agonist.

Differential modulation of brain benzodiazepine receptor subtypes by ricinelaidic acid in vitro

The C-18 hydroxy fatty acids ricinelaidic acid and ricinoleic acid diminish the oleic acid-stimulated agonist benzodiazepine binding in the rat brain in vitro. The oleic acid-induced enhancement of [3H]diazepam binding was completely abolished in membranes from the cerebellum, but only partially decreased in membranes from the hippocampus, cortex and the whole brain from 7-day-old rat pups. Related hydroxy fatty acids as well as hydroxy fatty acid esters had no effect on the oleic acid-stimulated diazepam receptor binding.

Alteration of colonic absorption by long-chain unsaturated fatty acids. Influence of hydroxylation and degree of unsaturation

Unabsorbed dietary unsaturated fatty acids may cause diarrhea in patients with steatorrhea, but their ability to cause colonic fluid secretion is not known. The present study investigated the effect of several dietary long-chain unsaturated fatty acids on colonic absorption and morphology in the rat colon in vivo. The fatty acids tested induced concentration-dependent net water secretion. The ability of these fatty acids to induce net water secretion varied as follows: linolenic acid (18:3) > linoleic acid (18:2), ricinoleic acid (18:1 OH) > oleic acid (18:1), palmitoleic acid (16:1). Net absorption of sodium and chloride were decreased in fatty acid perfusions. Mucosal activity of sodium potassium adenosine triphosphate and adenyl cyclase were not significantly altered by fatty acids. Epithelial cell damage was noted and correlated with the ability of the fatty acid to induce fluid secretion. Unsaturated fatty acids induce epithelial cell damage and fluid secretion in the colon, their effect being related to the degree of unsaturation.

Inhibitors of nitric oxide synthase enhance rat ileum contractions induced by ricinoleic acid in vitro

The effects of NG-nitro-L-arginine methyl ester (L-NAME) and NG-monomethyl-L-arginine (L-NMMA), inhibitors of nitric oxide (NO) synthase, were studied on ricinoleic acid-evoked contractions in rat isolated ileum. Ricinoleic acid (10(-5) to 10(-4) M) caused a concentration-dependent contraction. Addition of L-NAME (30-300 microM) or L-NMMA (30-300 microM) to the Tyrode's solution increased in a concentration-dependent fashion the amplitude of the ricinoleic acid-evoked responses. L-Arginine (900 microM), a natural substrate of NO synthase, but not D-arginine (900 microM), counteracted the effect of L-NAME (300 microM). The potentiating effect of L-NAME was also prevented by sodium nitroprusside (0.1-1 microM), a generator of NO. These results provide evidence that endogenous NO may modulate the contraction of rat ileum induced by ricinoleic acid. As the contraction induced by ricinoleic acid is not blocked by tetrodotoxin (0.6 and 6.0 microM) the contractile effect of ricinoleic acid results mainly from a direct action on the smooth muscle.

[Comparative effects of ricinoleic acid and senna on orocecal and oroanal transit time in healthy subjects. Application of the salacylazosulfapyridine method]

The appearance in plasma of sulphapyridine after oral administration of salicylazosulphapyridine (Salazopyrin) was shown to be useful for measuring the orocecal transit time in normal subjects. The purpose of this study was to use this method in diarrhea with accelerated intestinal transit time. A two-step study was performed in 12 healthy volunteers: a) under resting conditions; b) 2 weeks later with ricinoleic acid 40 ml (n = 6) or senna 19 mg (X-Prep = 1.2 g; n = 6) administration. In each step, Salazopyrin (2 g) and 20 radiopaque markers were ingested with a 200 kcal meal (Polydiet TCM = 200 ml). The following parameters were determined: a) plasmatic level of sulphapyridine (spectrophotometry) at 30 min intervals during 12 h; b) 2-day stool frequency and weight; c) oro-anal transit time (passage of the first marker and half of the markers in stools). In one subject, no sulphapyridine level was detected after administration of ricinoleic acid. With senna, 2 day stool frequency and weight increased by 80 and 131 percent respectively: orocecal transit time decreased from 6.1 +/- 1.3 to 4.8 +/- 1.2 h (m +/- SD; P less than 0.01) and oro-anal transit time (first marker) decreased from 31.8 +/- 9.6 to 20.7 +/- 8.9 (P less than 0.05). With ricinoleic acid, 2 day stool frequency and weight increased by 212 and 350 percent respectively; orocecal transit time decreased from 5.8 +/- 1.8 to 2.2 +/- 0.7 (P less than 0.01) and oroanal transit time (first marker) decreased from 25.3 +/- 7.1 to 8.0 +/- 6.8 h (P less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Correlation of the efficiency of fatty acid derivatives in suppressing Plasmodium falciparum growth in culture with their inhibitory effect on acyl-CoA synthetase activity

The intraerythrocytic malaria parasite depends on the surrounding medium for a supply of phospholipid precursors. Efficient inhibition (IC50 7-90 microM) of Plasmodium falciparum growth in vitro was achieved using modified fatty acids. The fatty acid analogues most effective in suppressing P. falciparum growth in culture were also the most active inhibitors of acyl-CoA synthetase from the monkey parasite P. knowlesi.

Differential inhibition of thromboxane B2 and leukotriene B4 biosynthesis by two naturally occurring acetylenic fatty acids

The seed oil of the plant Ixiolaena brevicompta is a rich source of crepenynic acid (octadec-cis-9-en-12-ynoic acid), which has been linked with extensive sheep mortalities in Western New South Wales and Queensland, Australia. A number of acetylenic fatty acids have been found to interfere with lipid and fatty acid metabolism and inhibit cyclooxygenase and lipoxygenase enzymes in a variety of tissues. We have investigated the effects of crepenynic acid and ximenynic acid (octadec-trans-11-en-9-ynoic acid) on leukotriene B4 and thromboxane B2 production in rat peritoneal leukocytes and compare them with non-acetylenic compounds linoleic and ricinoleic acids. In concentrations ranging from 10 to 100 microM linoleic acid and ricinoleic acid had only minimal effects on leukotriene B4 and thromboxane B2 production in ionophore-stimulated cells. Ximenynic acid gave dose-dependent inhibition of leukotriene B4, thromboxane B2 and 6-ketoprostaglandin F1 alpha production. Ximenynic acid appears to be a more effective inhibitor of leukotriene B4 than crepenynic acid with an IC50 of 60 microM compared to 85 microM. On the other hand, crepenynic acid is a much more effective inhibitor of the cyclooxygenase products, having an IC50 for thromboxane B2 of less than 10 microM. Both acetylenic fatty acids inhibited phospholipase activity in these cells by 40-50% at a concentration of 100 microM but had no inhibitory effect at 10 microM. These results indicate that crepenynic acid and ximenynic acid differentially inhibit the cyclooxygenase and lipoxygenase products of stimulated leukocytes, and that at high doses of these fatty acids the effect on these products may be partially due to inhibition of phospholipase A2.

Short-chain fatty acids stimulate motility of the canine ileum

Based on earlier observations that colonic contents stimulated ileal motility in the dog, our hypothesis is that the ileum would respond to physiological amounts of short-chain fatty acids (SCFA). Four dogs had isolated ileocolonic loops constructed surgically and boluses of test solutions (15 ml) were instilled into the distal ileum through a small catheter. Intraluminal pressure catheters were used to record motility. Concentrations of SCFA (also called volatile fatty acids) comparable to those found in dog stool (108 mM; 66% acetic, 24% propionic, and 10% butyric acids) regularly stimulated motility with a dose-related effect. The response was not due to the pH of the SCFA solutions and was independent of the pH at which SCFA were instilled. Ricinoleic acid (4 mM) also stimulated motility, as did chenodeoxycholic acid; the bile acid was active only at supraphysiological concentrations (approximately 7.6 mM). Instillates that simulated the composition of ileal chyme in malabsorptive states were without effect. The results suggest that the ileum can "sense" the presence of colonic contents in the lumen and that SCFA are the responsible mechanisms. Stimulation of ileal motility by SCFA could be a response to coloileal reflux.

Ricinoleic acid and loperamide have opposite motor effects in the small and large intestine of the cat

The actions of laxatives and antidiarrheal agents in the gut are incompletely understood. Therefore, the effects of Na ricinoleate 10(-4)-10(-2) g/kg b. w. and of loperamide 10(-4) g/kg b. w. on myoelectric activity and marker propulsion were studied in the small and large intestine of 7 unanesthetized cats. Intraduodenal application of ricinoleate briefly increased and then decreased spike activity in the small intestine; marker transit was delayed (92 +/- 18 min vs. 55 +/- 14 min in controls). Ricinoleate also initiated spike complexes of 10-215 sec duration. Transit from the right to the left colon was sometimes accelerated and sometimes delayed. The number of uncoupled slow waves was increased to 278% of control. Loperamide accelerated small intestinal transit to 17 +/- 6 min and markedly delayed it in the colon. At the same time it caused a strong and prolonged rise in colonic spike activity. When ricinoleate and loperamide were given together, their effects almost compensated for each other. The resulting net effect was similar to the data in the control experiments. It is concluded that laxatives and antidiarrheal agents alter not only transit, but also myoelectric activity in the small and large intestine. The effects are largely in opposite direction. Loperamide may, therefore, antagonize motor effects of ricinoleate in the gut.

Eicosanoid formation by mammalian intestine. Effects of some intestinal secretagogues

Intestinal tissues of man, rat, mouse, guinea-pig and rabbit were preincubated with laxatives, homogenised, and incubated with [14C]arachidonic acid. After extraction into chloroform, the eicosanoids were separated by thin layer chromatography. Metabolism of [14C]arachidonic acid into prostaglandins (PGs), and the lipoxygenase products LTB4 and 5-HETE, was stimulated by ricinoleic acid (100 micrograms/ml) or phenolphthalein (100 micrograms/ml), and to a lesser extent by picosulphate (125 micrograms/ml) and sulfosuccinate (200 micrograms/ml). Mannitol (500 micrograms/ml) had no effect. Indomethacin (1 microgram/ml) inhibited the stimulation of PG formation. The dual pathway inhibitor BW755C (1 microgram/ml) reduced the formation of prostaglandins, LTB4 and 5-HETE. In some experiments on rat colon, prostanoids were separated from lipoxygenase products, characterised by their chromatographic mobility and quantitated (relative amounts PGE2 greater than PGF2 alpha greater than TXB2 greater than PGD2). Their formation was enhanced by ricinoleic acid (100 micrograms/ml) and inhibited by either indomethacin or BW 755C (1 microgram/ml). The present results indicate that mammalian isolated gut tissue can convert [14C]arachidonic acid into both cyclo-oxygenase and lipoxygenase products, and support the suggestion that eicosanoids may participate in the laxative effect of some secretagogues.

Use of calcium depletion and chlorpromazine to study calcium dependence of secretory detergent action in the colon

The role of Ca2+ in the in situ secretory response of rat colon and pig ileum was studied by chelation depletion of Ca2+ and by treatment with chlorpromazine. The effect of depleting lumenal Ca2+ by chelation and the effect of intraperitoneal administration of chlorpromazine were determined relative to colonic permeability and net fluid flux measured across the rat colon or pig ileum. Replacement of Ca2+ in the perfusate by 1.0 mM ethyleneglycol-(bis-beta-ethylaminoether) (EGTA) did not produce significant changes in the net absorptive fluid flux measured in the control state or in the net secretory fluid flux caused by secretory detergent agents. The concentration of EGTA used in the perfusate did not alter mucosal permeability. Nonsecretory bile acids or A23187 had no effect on net colonic fluid flux or on colonic permeability to mannitol in the rat. The known correlation between net fluid flux and increased colonic permeability to polar molecules has been confirmed for the secretory detergent compounds. Chlorpromazine pretreatment caused a partial reversal of net secretory fluid fluxes induced by deoxycholate and high concentrations (6.0 mM) of ricinolate and dioctyl sulfosuccinate without significantly altering mucosal permeability to mannitol. We conclude that depletion of lumenal Ca2+ is not an effective method for determining the possible Ca2+ dependence of these intestinal secretory events. The antisecretory actions of chlorpromazine may provide some indirect evidence for Ca2+ involvement in the secretory effects of the detergent class of laxative compounds. Permeability may be essential for secretion caused by these agents, but the driving force would appear to be provided by the active transfer of electrolytes from the blood to the lumen of the colon.

Involvement of the enteric nervous system in the intestinal secretion induced by sodium deoxycholate and sodium ricinoleate

Rat small intestine was continuously perfused for up to 3 h with two different concentrations of sodium deoxycholate (4 and 8 mM) or with sodium ricinoleate (6 mM). The 4-mM bile salt solution produced a secretion that developed to a maximal rate within 3 h, whereas the maximal rate was reached within 1 h with the 8-mM bile salt solution. Hexamethonium, a ganglionic blocker, and lidocaine, a local anesthetic, always reduced the net fluid secretion to approximately zero irrespective of the rate of bile-salt-induced secretion, the concentration of the bile salt, or the perfusion time. Fluid secretion induced by sodium ricinoleate was, like the bile-salt-induced secretion, markedly inhibited by hexamethonium and lidocaine but not by atropine. It is concluded that the rate of secretion induced by the bile salt is related to the monomer concentration of free bile salt molecules in close proximity to or within the intestinal epithelium. The intestinal fluid secretion is mainly due to stimulation of an active secretory process via an activation of enteric nerves. Sodium ricinoleate evokes secretion via similar nervous reflex mechanisms.

The role of calcium in eicosanoid production induced by ricinoleic acid or the calcium ionophore A23187

Rat isolated intestine incubated in Krebs solution converted exogenous [14C]-arachidonic acid into products that chromatographed with prostaglandins, leukotriene B4 and 5-hydroxy-eicosatetraenoic acid. Accumulation of these products was increased by the laxative ricinoleic acid (0.34 mM) or the calcium ionophore A23187 (7.6 microM). In the presence of the calcium antagonists TMB-8 (0.43 microM) or verapamil (0.2 microM) the mean effects of ricinoleic acid or the calcium ionophore were smaller. Stimulation of arachidonic acid metabolism by ricinoleic acid therefore seems likely to involve a calcium-dependent mechanism.

Evidence for size and charge permselectivity of rat ascending colon. Effects of ricinoleate and bile salts on oxalic acid and neutral sugar transport

We have measured unidirectional transmural fluxes of oxalate and neutral sugars across rat ascending colon in vitro, under short-circuit conditions, to characterize permeability barriers selective for size and charge. Ionic oxalate appears to be transported preferentially to sodium oxalate. Mucosal addition of taurocholate (1 mM), deoxycholate (1 mM), or ricinoleate (1 mM) increased bidirectional oxalate fluxes, and the ricinoleate effects were independent of medium calcium. Bidirectional fluxes of uncharged sugar molecules fell sharply at molecular weights above 76 (molecular radius above 3 A), and oxalate transport was retarded relative to that of uncharged molecules of similar size, suggesting that there is both size and charge permselectivity. Ricinoleate increased fluxes of all neutral molecules tested but changed neither the exclusion limits nor the cation selectivity of the epithelium. Bile salts and ricinoleate increase oxalate transport, probably by making more channels available, but do not alter size and charge selectivity.

Influence of ricinoleic acid on the contractions elicited by PGE2 on the guinea-pig ileum

The effect of ricinoleic acid on prostaglandin E2 (PGE2)-evoked contractions was studied on guinea-pig isolated ileum. Addition of ricinoleic acid (10 micrograms ml-1) to the organ bath increased the amplitude of the PGE2-evoked responses. Ricinoleic acid (10 micrograms ml-1) also sensitized the guinea-pig isolated ileum to acetylcholine and histamine. The effect of the ricinoleic acid was greatly reduced by indomethacin either in-vivo (10 mg ml-1) or in-vitro (2 micrograms ml-1).

The effects of deoxycholic and ricinoleic acid on the isolated circular muscle of the cat colon are modified by leucine-enkephalin

The mechanism of the diarrheogenic effect of bile acids and fatty acids is incompletely understood. In order to study their effects on motility we tested sodium deoxycholate and sodium ricinoleate in their actions on the spontaneous mechanical and myoelectrical activity of the isolated circular muscle of the cat colon in a perfusion apparatus. Sodium deoxycholate activated the muscle in concentrations from 10(-9) to 10(-5) M. ED50 was 6.3 X 10(-9) M, ED100 10(-6) M. Sodium ricinoleate similarly stimulated muscle contractions. ED50 was 2.3 X 10(-7) M, ED100 5.1 X 10(-6) M. Both agents increased the occurrence of oscillating potentials in the myoelectrical records. Oscillations probably correspond to the migrating electrical complexes in diarrhea. The addition of leucine-enkephalin augmented primarily the number of brief spike potentials which may correspond to segmenting contractions. Thus, bile acids and fatty acids cause profound changes in colonic motility which by themselves may promote diarrhea. The endogenous opiate leucine-enkephalin could possibly counteract these effects.

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.

Effects of various secretagogues and human carcinoid serum on lymph flow in the cat ileum

Previous studies from our laboratory indicate that the lymph flow response of the cat ileum to net volume secretion is dependent upon the mechanism involved in the secretory process, i.e, active secretion (cholera toxin) decreases lymph flow while passive fluid secretion (increased portal pressure, plasma dilution) is associated with a rise in lymph flow. In the present study, we examined the effects of ricinoleic acid, vasoactive intestinal polypeptide, theophylline, histamine, and human carcinoid serum on lymph flow in autoperfused segments of cat ileum. Local intraarterial infusion of theophylline, vasoactive intestinal polypeptide, or human carcinoid serum caused lymph flow to decrease. However, intraluminal placement of ricinoleic acid or intraarterial infusion of histamine produced significant increases in lymph flow. The results indicate that the fluid secretion associated with vasoactive intestinal polypeptide, theophylline, and carcinoid serum are consistent with an active process while ricinoleic acid and histamine secretions are associated with a passive component.

Ricinoleate and deoxycholate are calcium ionophores in jejunal brush border vesicles

The intestinal secretagogues ricinoleate and deoxycholate have been tested for a capacity to form complexes with Ca2+ ions and to affect the passive equilibration of Ca2+ ions across the jejunal brush border membrane. Both of these agents formed butanol-soluble Ca2+ complexes in a model phase distribution system. They also promote the passive uptake and efflux of Ca2+ across brush border vesicles in a concentration-dependent manner. The levels of ricinoleate and deoxycholate that increase the rate of transvesicular Ca2+ movement are in the 100 to 300 microM range. Concentrations as high as 1.0 mM had no significant detergent effects in vesicles as measured by release of entrapped sorbitol. The kinetics of Ca2+ uptake and efflux are similar in brush border vesicles treated with A23187, ricinoleate, or deoxycholate. The influx rates observed in this study were high enough to cause the collapse of a Ca2+ gradient, which had been generated by Ca--Mg ATPase enzyme activity in the brush border membrane. Ricinoleate did not affect Ca--Mg ATPase activity at concentrations used in this study, but deoxycholate was inhibitory, indicating two potential modes for elevation of intracellular Ca2+ content by deoxycholate. When compared with the effects of the Ca2+ ionophore, A23187, it appears that both ricinoleate and deoxycholate could have significant intestinal secretory activity due to this Ca2+ ionophore property. It is also noteworthy that, at least in this model system, potential secretory effects are expressed at concentrations significantly below levels that have been associated with detergent effects or altered epithelial morphology.

Experimental pancreatitis after surfactant exposure

The effects of pancreatic intraductal infusions of the surface active pancreatic ductogram enhancing agent, polyoxyethylene hydrogenated castor oil, were studied in the dog. Moderately high pressure retrograde infusions of 5 per cent polyoxyethylene hydrogenated castor oil into the main pancreatic duct resulted in pancreatitis-like changes significantly greater than those seen in the saline solution control group. These changes persisted despite buffering of the agent to physiologic pH and the elimination of nonphysiologically high pressure by direct ductal perfusion. Similar inflammatory changes were associated with ductal perfusion using oleic and, to a lesser degree, ricinoleic-fatty acids at concentrations of 10(-4) molar sufficient to account for the titratable acidity of 5 per cent polyoxyethylene hydrogenated castor oil. It is postulated that residual-free fatty acids may play some role in polyoxyethylene hydrogenated castor oil related toxicity. The surface active properties of the agent may also be involved. Caution and further research are recommended prior to widespread use of the agent in endoscopic retrograde pancreatography.

The effect of cathartics on prostaglandin synthesis by rat gastro-intestinal tract

Rats were dosed with the cathartics cascara, phenolphthalein, senna or ricinoleic acid with or without a 3 day pretreatment with indomethacin. Jejunum, proximal and distal ileum and colon were assayed for prostaglandin E (PGE) content by RIA. While indomethacin significantly reduced the PGE content of all tissue in all treatment groups it did not completely prevent the increase in PGE content induced by phenolphthalein, senna and ricinoleic acid. It is concluded that the contact cathartics increase PGE synthesis by the gastro-intestinal tract and this could in part explain their action. Ricinoleic acid did not appear to act as a PG precursor.

Relationship between intestinal volume secretion and oxygen uptake

The effects of net volume secretion on blood flow, oxygen extraction, and oxygen extraction, and oxygen uptake were analyzed in autoperfused segments of cat ileum. Intestinal secretion was induced by local intraarterial infusion of glucagon, histamine, theophylline, prostaglandin E1, or vasoactive intestinal peptide, and, by intraluminal placement of cholera toxin or ricinoleic acid. Net volume secretion rates were determined using a volume recovery method. Intestinal oxygen uptake was increased by all secretagogues. The increases oxygen uptake by the screening intestine resulted from an increased blood flow or oxygen extraction or both. Significant positive correlations between intestinal oxygen uptake and secretion rate were acquired only during cholera toxin, theophylline, and prostaglandin E1, secretion. The results indicate that the metabolic work incurred in the small bowel during secretory states greatly exceeds that reported for the absorptive state.

Effects of intestinal secretagogues and distension on small bowel myoelectric activity in fasted and fed conscious dogs

1. Defined jejunal segments were perfused with solutions of bile salts and of ricinoleic acid during fasting and after feeding in two groups of conscious dogs, one with the segment in continuity, and the other with a Thirty-Vella loop. Myoelectric activity was recorded from chronically implanted electrodes on the jejunal segment and also from the proximal and distal in situ bowel.2. The results in both groups were identical. During fasting, migrating complexes were present in the segment, but were replaced by intermittent spike activity during chenodeoxycholate without and with ricinoleic acid perfusion. After food, when migrating complexes were replaced by intermittent spike activity, none of the solutions produced any consistent effect.3. In fasted animals, low levels of distension (15 mmHg) interrupted the migrating complexes in the segment and induced intermittent spike activity which was similar to that seen with the secretagogues. The migrating complexes in the main bowel continued during distension. In fed animals, spike activity increased in the segment during distension at 25 mmHg and decreased in the main bowel. In both groups, distension of the segment to pressures between 37.5 and 50 mmHg abolished spike activity both in the distended segment and the main bowel in fasted and fed states, and, in fasted dogs, migrating complexes were also abolished.4. These results demonstrate that the inhibitory intestino-intestinal reflex is mediated through extrinsic nerves and does not require an intact myenteric plexus, whereas the altered myoelectric activity induced by secretagogues is a local effect and does not spread to adjacent bowel through either intrinsic or extrinsic neural pathways. It seems likely that the local motor effect of secretagogues is a result of net secretion, producing distension to pressures below the threshold required to activate the intestino-intestinal reflex.

Ricinoleic acid causes secretion in autotransplanted (extrinsically denervated) canine jejunum

To examine the role of extrinsic nerves and hormones in intestinal secretion of fluid, we studied the effect of ricinoleic acid on absorption by isolated, autotransplanted jejunal loops in four dogs. Compared to perfusion with control solution, the addition of ricinoleic acid caused reversible secretion of water and electrolytes and inhibition of glucose absorption, as previously described in the innervated intestine. In contrast, oral castor oil caused diarrhea but had no effect on absorption from the denervated loop. Thus, the secretory action of ricinoleic acid is maintained without the influence of extrinsic nerves; in addition, further support is added to the proposal that hormones do not mediate secretion in this model. These findings support a local mechanism for the secretion induced by ricinoleic acid.

Increased cell loss in the human jejunum induced by laxatives (ricinoleic acid, dioctyl sodium sulphosuccinate, magnesium sulphate, bile salts)

Two conjugated bile salts (10 mmol/l sodium glycocholate, 10 mmol/l sodium taurodeoxycholate) and three laxatives (30 mmol/l magnesium sulphate, 10 mmol/l ricinoleic acid, 2 mmol/l dioctyl sodium sulphosuccinate) were tested on seven subjects with no intestinal lesions in 14 experiments by intestinal perfusion of the jejunum. A 25 cm segment was studied. Each solution was perfused at the rate of 10 ml/min. Water and electrolyte fluxes, losses of deoxyribonucleic acid (DNA), and intestinal cell enzyme activity were measured in the fluids collected. All the laxatives and bile salts tested (except sodium glycocholate) induced water and electrolyte secretion, a rise in intraluminal DNA loss, and enzyme activity. It was possible to establish a significant correlation (p less than 0.001) between the amounts of water fluxes and DNA loss under the effect of dioctyl sodium sulphosuccinate and ricinoleic acid.

Changes in stability of isocitrate dehydrogenase (NADP+) during germination of castor bean seeds

In crude extract of castor bean endosperm, isocitrate dehydrogenase (NADP+) (EC 1.1.1.42) was stable at 57 degrees C at the beginning of seed germination as well as in maturing and dry seeds. The enzyme gradually became less thermostable as germination proceeded and became unstable after 4 days. Extract from 5-day-old endosperm reduced the thermostability of the thermostable enzyme. The destabilizing factor accumulated in the endosperm as germination progressed and was identified as ricinoleate. Ricinoleate destabilized the purified enzyme which was stabilized by isocitrate and Mg2+, but ricinoleate did not affect the activity of NADP+-isocitrate dehydrogenase itself. Stearate, oleate, palmitate and myristate were similar to ricinoleate in their effect on the thermostability of the enzyme. The thermolabile enzyme in the crude extract of 5-day-old endosperm was readily inactivated by trypsin and in low concentrations of buffer. The thermostable enzyme in the crude extract of 2-day-old endosperm was not affected by these treatments. The thermostable enzyme treated with ricinoleate showed the same instabilities as the thermolabile enzyme. The role of ricinoleate in the germinating castor bean endosperm is discussed.

Interaction of laxatives with enzymes of cyclic AMP metabolism from human colonic mucosa

The mechanism by which laxatives such as dioctyl sodium sulfosuccinate and ricinoleic acid evoke colonic fluid secretion has been suggested to involve mucosal cyclic AMP. Ricinoleic acid and dioctyl sodium sulfosuccinate were tested for their capacity to modulate the key enzymes of cAMP-metabolism--adenylate cyclase and cAMP-phosphodiesterase--in human colonic mucosa. Both laxatives were ineffective stimuli of human colonic adenylate cyclase. In contrast to ricinoleic acid, dioctyl sodium sulfosuccinate was a competitive inhibitor of soluble cAMP-phosphodiesterase activity. These experiments suggest that the cathartic properties of dioctyl sodium sulfosuccinate in human colonic mucosa might be mediated by cyclic AMP via inhibition of soluble phosphodiesterase activity.

Oxalate uptake by everted sacs of rat colon. Regional differences and the effects of pH and ricinoleic acid

Hyperoxaluria is a complication of disorders associated with steatorrhea. The colon is the presumed site of enhanced oxalate absorption in patients with steatorrhea. We performed studies of colonic mucosal oxalate uptake in everted sacs of rat colon to determine the kinetics of colonic oxalate transport and to evaluate the effect of both pH and ricinoleic acid, a hydroxy fatty acid, on colonic oxalate uptake. Our study demonstrated that oxalate is transported throughout the colon by passive diffusion. Tissue uptake increased linearly with increasing oxalate concentrations and was unaffected by metabolic inhibitors, oxygen deprivation, or temperature changes. There were pH-dependent regional differences of oxalate uptake both in the presence and absence of ricinoleic acid. In the absence of ricinoleic acid, the highest oxalate uptake occurred at the lower pH values (5.4 and 6.4). In the presence of ricinoleic acid oxalate uptake was enhanced at the higher pH values (7.4 and 8.4); a finding most likely related to decreased solubility of ricinoleic acid at pH 5.4 and 6.4. Intraluminal pH is an important determinant of colonic oxalate uptake in the presence and absence of ricinoleic acid.

Effect of ricinoleic acid and other laxatives on net water flux and prostaglandin E release by the rat colon

Ricinoleic acid, oleic acid, dioctyl sodium sulphosuccinate, deoxycholic acid, sennoside A + B and mannitol reduced or reversed water flux from lumen to blood in rat colon in situ. Stearinic acid was without any effect. Ricinoleic acid, oleic acid, dioctyl sodium sulphosuccinate, deoxycholic acid and sennoside A + B stimulated release of PGE-like material into the colonic lumen whereas the osmotic laxative mannitol and stearinic acid did not. Inhibition of PGE biosynthesis by pretreatment of the rats with indomethacin significantly reduced (but did not abolish) the effect of ricinoleic, oleic and deoxycholic acids on net water flux and PGE release. Indomethacin reduced the effect of dioctyl sodium sulphosuccinate and of sennoside A + B on PGE release but not their effect on the net water flux. The effect of mannitol was not influenced by indomethacin. The amount of PGE release in experiments with ricinoleic acid, oleic acid, stearinic acid and dioctyl sodium sulphosuccinate (with and without indomethacin) showed a good correlation (r = 0.99) with the change in net water flux. Deoxycholic acid, sennoside A + B and mannitol did not show this correlation. It is assumed that the action of non-osmotic laxatives is partially mediated by PGE, although other mechanisms also seem to be involved in their mode of action.

Mechanism of inhibition of alanine absorption by Na ricinoleate

The mechanism of inhibition of alanine absorption by Na ricinoleate has been examined in the rabbit intestine. This fatty acid in a concentration of 2--5 mM inhibits alanine absorption in vivo and in vitro. The inhibition is more evident in the jejunum than in the ileum. Strips of ileal mucosa treated with Na ricinoleate gain Na. Sodium ricinoleate inhibits alanine influx across rabbit ileum, even in the presence of a sodium gradient across these cells. The results suggest that the main action of Na ricinoleate is on the alanine-transport system at the brush-border membrane. The fatty acid may also inhibit amino acid absorption by increasing intestinal cell Na concentration, which results in a decreased Na gradient across the brush-border membrane.

Ricinoleic acid stimulation of active anion secretion in colonic mucosa of the rat

Perfusion of the colon with ricinoleic acid produces fluid and electrolyte accumulation. The mechanism of these changes in water and electrolyte movement is uknown. These studies were designed to determine whether ricinoleic acid effects active ion transport across isolated rat colonic mucosa. 0.5 mM Na ricinoleate produced significant increases in potential difference (3.8 +/- 0.5 mV) and short-circuit current (Isc) (99.2 +/- 10.1 muA/cm2). The increases in Isc produced by Na ricinoleate were inhibited by both removal of bicarbonate and chloride and by the presence of theophylline. The hydroxy fatty acid also resulted in a significant decrease in net Na absorption from 4.7 +/- 0.8 to 0.1 +/- 0.7 mueq/h cm2 and reversed net Cl transport from absorption (+ 4.5 +/- 0.9) to secretion (-2.2 +/- mueq/h cm2). In parallel studies 0.5 mM Na ricinoleate increased mucosal cyclic AMP content by 58%. The concentrations of Na ricinoleate required to produce detectable and maximal increases in both Isc and cyclic AMP were the same. These results provide evidence in support of the concept that hydroxy fatty acid-induced fluid and electrolyte accumulation is driven by an active ion secretory process.