Role of calcium ion in Schistosoma mansoni cercarial tail loss induced by unsaturated fatty acids.

Linoleate (C18: 2) and oleate (C18: 1), but not stearate (C18: 0), induced tail removal in cercariae. Linoleate stimulated tail loss more strongly than oleate did. Tail loss induced by linoleate was significantly suppressed by incubating cercariae with ethyleneglycol-bis-(beta-aminoethyl ether) N,N,N',N'-tetraacetic acid (EGTA). Preincubation of cercariae with EGTA for 5 min caused further inhibition of the tail loss. Calcium ionophore A23187 (A23187) increased the cercarial tail-loss rate. When A23187 was combined with linoleate at 0.03 mM, an additive effect on tail loss appeared, whereas the ionophore in combination with linoleate at 0.3 mM had no such effect. EGTA almost completely abolished cercarial tail loss induced by linoleate at both 0.03 and 0.3 mM in the presence and absence of A23187. Linoleate at 3 mM provoked cercarial tail loss even in the presence of EGTA, although the effect of oleate at 3 mM disappeared. Under these conditions, the effect of linoleate was synergistically enhanced by the combination with A23187. A similar, but not significant, synergism took place in cercariae stimulated by oleate. These findings suggest that unsaturated fatty acids enhance calcium influx into cercariae, resulting in triggering tail loss, and, furthermore, that the fatty acids have other potentiating effects on cercarial tail loss. Protein kinases play an insignificant role in fatty acid-induced cercarial tail loss, because a protein kinase C inhibitor, 1-(5-isoquinolinylsulfonyl)-2-methylpiperazine (H-7), and an inhibitor of various protein kinases, staurosporine, had little or no effect on cercarial tail loss induced by linoleate at 3 mM.

Penetration of Schistosoma mansoni cercariae into a living skin equivalent.

We evaluated the use of a living skin equivalent (LSE) as a suitable membrane for Schistosoma mansoni cercarial penetration. LSE is a living artificial skin composed of a dermal layer containing human dermal fibroblasts embedded in a collagen lattice and an epidermal layer consisting of differentiated human keratinocytes. The keratinocytes differentiate into a stratum corneumlike layer, whereas the dermal-epidermal junction forms a layer similar, but not identical to, the basement membrane. We exposed LSE to 50 cercariae for 0, 3, 6, 20, and 30 hr at 37 C, and the percentage of penetration was evaluated by counting cercariae remaining on the LSE surface. No cercarial penetration was observed in the first 15 min of exposure; however, penetration was detected at all other times. Maximum penetration rates were observed at 20 hr (80%). In other experiments LSE was pretreated topically with 0 or 4 micrograms/cm2 linoleic acid, then exposed to between 800 and 1,000 cercariae for 18-20 hr at 37 C. LSE pretreated with linoleate had significantly higher penetration rates than untreated membranes (81% +/- 2.51% vs. 65.9% +/- 6.97%, P = 0.03). Increasing linoleate concentrations from 10 to 40 micrograms/cm2 gradually decreased the ability of cercariae to penetrate the membrane. Some LSE membranes also were processed for light microscopy, and we present photomicrographs showing schistosomulae within the epidermal and dermal layers of the LSE. We conclude that despite the time it takes for cercariae to penetrate LSE, these membranes may allow investigators to examine, in vitro, host-parasite interactions at the level of the skin.

Cytokine and eicosanoid regulation by Schistosoma mansoniduring LSE penetration.

Cercarial penetration, in low to moderate numbers, does not cause a normal skin inflammatory response; therefore, the authors sought to determine whether cercariae can down-regulate keratinocyte activation and thus the secretion of pro-inflammatory cytokines and eicosanoids. Human living skin equivalent (LSE, Organogenesis) consisting of dermal, epidermal and stratum corneum-like layers was used as the skin substrate. The surface of the LSE membrane was exposed to 100 ng IFNgamma or ~850 cercariae for 18 h. Incubation media and tissue was then assayed for IL-1alpha, IL-6, IL-8, TNFalpha, 5-HETE, 12-HETE, PGF(2), LTB(4), and LTC(4) via RIA and Western Blots. TNFalpha was not detected. Secreted IL-1alpha levels were (mean +/- S.E.M. (n)): Control, 1.03 ng +/- 0.15 (11); IFNgamma 1.90 ng +/- 0.48 (5); cercariae, 1.79 ng +/- 0.22 (22). In spite of this increase, cercariae down-regulated IL-8 (cercariae 11.13 +/- 1.70 ng vs. IFNgamma = 16.47 +/- 0.29 ng, p = 0.04) and LTB(4) (cercariae = 98.86 +/- 19.65 pg/0.1 ml vs. IFNgamma = 193.42 +/- 44.21 pg/0.1 ml p = 0.02). No changes were seen in IL-6, 12-HETE, 5-HETE, and PGE(2) levels. It is concluded that cercarial penetration causes a release of IL-1alpha consistent with skin trauma; however, schistosomulae may regulate the production of chemotactic (neutrophils, macrophages, T-cells, etc.) and activation factors such as IL-8 and LTB(4).

Influence of a menhaden oil diet on cercarial penetration of Schistosoma mansoni.

The ability of a menhaden oil (MO) diet to influence cercarial penetration into mouse tail skin was evaluated. Male CD-1 mice 4-6 wk old (15.2 g average weight) were fed a 0, 10%, or 20% MO-supplemented diet for 2 wk. After this time mice were infected with either 65 +/- 3 or 145 +/- 3 [35S]methionine/cysteine-labeled cercariae for 1 hr by tail immersion. Twenty-four hours and 7 days later groups of mice were killed and their tail skin removed and autoradiographed. At 24 hr postinfection, mice fed a 20% MO diet had significantly higher cercarial penetration than controls and 10% MO diets (56% +/- 5.2 vs. 44% +/- 2.9, P = 0.02, 1-tailed t-test). After 7 days mice fed a 20% MO diet retained more radioactive foci than controls or 10% MO diets (21% +/- 2.0 vs. 15% +/- 1.3, P = 0.01, 1-tailed t-test).

Schistosoma mansoni: the role of calcium in the stimulation of cercarial proteinase release.

We investigated the role of calcium mobilization in the induction of proteinase release from cercarial preacetabular glands. Proteinase release was measured by the ability of cercariae to break down a 3H-labeled proline extracellular fibroblast matrix and calcium influx was measured using 45Ca2+. The role of calcium in the activation of cercarial proteinase was examined by investigating the effects of calcium addition and removal on linoleate-induced matrix degradation, the ability of various calcium modulators (Verapamil, fendiline, nifedipine, SK-525A, BAY K-8644, Ryanodine, and SK-7171A) to stimulate or inhibit linoleate-induced proteinase release, the ability of calcium modulators directly to induce cercarial proteinase release, and the ability of various stimulants of proteinase release to induce calcium influx or efflux from cercariae. The results of these studies indicate that proteinase release is dependent on external calcium concentration, voltage-operated channels are either nonexistent in cercariae or have a minimal role in overall calcium influx, and that activation of Ca2+ influx can be caused by both free fatty acids and calcium modulators by a hypothesized receptor-operated channel. Although calcium uptake is important in cercarial proteinase release, it is not the only factor involved. Calcium uptake alone does not guarantee that proteinase will be secreted. On the other hand, if Ca2+ influx does not occur, proteinase will not be secreted.

Radiolabeling of Necator americanus third stage larvae with 75Se-methionine.

Third stage larvae of Necator americanus were radiolabeled with 75Se-methionine by two methods. Larvae labeled in aqueous cultures contained 188 and 25 cpm per sheathed and ex-sheathed larva, respectively. Larvae labeled in coproculture incorporated 25 and 18 cpm per sheathed and ex-sheathed larva, respectively. All of the label was decayed in 5 days from larvae labeled in aqueous cultures, whereas appreciable amounts of radioactivity were still detectable at day 7 of chase period in coproculture labeled larvae.

Schistosoma mansoni: experimental chemoprophylaxis in mice using oral anti-penetration agents.

The ability to prevent schistosomiasis by using an oral chemoprophylactic agent, which acts by preventing cercarial penetration, has been unexplored. We initially examined the effect of praziquantel (PZQ) as such an agent and found that it was moderately effective in blocking cercarial penetration, but that this effect was dependent on the vehicle used to administer the drug. ICR mice were given a total of 200 mg/kg PZQ per os over an 8-hr period in a divided dose of 50 mg/kg/2 hr. At time periods ranging from 0 to 92 hr after the last dose, mice were exposed to approximately 75 75Se-labeled cercariae via the tail. Twenty-four hours later, mice were sacrificed, their tails were removed and subjected to autoradiography, and the percentage of penetration was calculated. Cremophor El, 50% PEG 200, 50% propylene glycol, vegetable oil, and cod liver oil were used as PZQ vehicles. When Cremophor El (ethoxylated castor oil) was used to administer PZQ, a 93% reduction in cercarial penetration was seen at 0 hr and a 98%+ reduction rate was seen from 4 to 24 hr postexposure. However, Cremophor El alone had an essentially equivalent effect on cercarial penetration from 8 to 92 hr after administration. These unexpected results led us to investigate both castor oil and ricinoleic acid (castor oil is 87% ricinoleate as triglyceride) as oral anti-penetration agents. Mice were given the lipids orally by gavage for 7 days. On Day 8, each group of 12 mice was exposed to approximately 75 75Se-radiolabeled cercariae. Castor oil gave protection rate ranging from 90 to almost 100% at an optimal concentration of 0.3 ml/day x 3 or 7 days (approximately 9.8 g/kg/day). These observations suggest that chemoprophylaxis may be possible by dietary supplementation with lipids having anti-penetration activity or by molecules that resemble these lipids.

A simple method for the collection of Necator americanus larvae.

A simple method for the collection of third-stage larvae of Necator americanus has been described. This technique provides repeated recovery of very clean larvae from cultures in moderate numbers.

Schistosoma mansoni: analysis of cercarial transformation methods.

Four methods of transforming cercariae to schistosomulae in vitro in ELAC buffer (pH 7.2, 37 C, 0-6 hr incubation) were compared in relation to biochemical and ultrastructural characteristics. The transformation methods used were chemical (3 mM linoleate), mechanical (centrifuge/vortex), mechanical/chemical, and heat (incubation at 37 C). Ultrastructural characteristics examined were based on the presence or absence of glycocalyx, heptalaminate membrane, cyton granules, and nuclear condition. Two EM fixation methods were used. Biochemical parameters assayed were loss of water tolerance (uptake of trypan blue dye), eicosanoid biosynthesis (PGE, LTB4, and 5-HETE), protein synthesis (leucine uptake), RNA synthesis (uracil and orotic acid uptake), and DNA synthesis (thymidine uptake). EM characteristics were remarkably similar for all transformation methods except heat incubation, with transformed cercariae evidencing the characteristics of schistosomulae (cyton granule migration, absence of glycocalyx and heptalaminate membrane); however, euchromatic nuclei could not be demonstrated using in vivo or in vitro transformation methods. Despite the ultrastructural similarities between transformation methods, biochemical data demonstrated that the resultant organisms were quite different. The chemical transformation method gave the highest rate of loss of water tolerance and eicosanoid production. RNA and protein synthesis were not correlated to ultrastructural changes and were highest in those organisms undergoing mechanical transformation methods, significantly higher than in those cercariae transformed by the chemical method. DNA synthesis was not demonstrated using any transformation method, although thymidine uptake did occur. Our data indicate substantial biochemical differences exist between morphologically similar organisms. Thus, experiments using any type of artificially transformed schistosomule must be interpreted with caution until additional biochemical and physiological studies on cercarial transformation are undertaken.

Schistosoma mansoni: correlations between mouse strain, skin eicosanoid production, and cercarial skin penetration.

We have previously reported that cercarial penetration is highly correlated with cercarial production of leukotrienes (LT's) and hydroxyeicosatetraenoic acids (HETE's). Because skin also produces various eicosanoids, we undertook an investigation of skin eicosanoids in various strains of mice and 1 strain of rat in order to ascertain if skin eicosanoids could be correlated to cercarial penetration. SENCAR, ICR, NMRI, A/J, C3H/HeJ, C57Bl/6, ASEBIC, and BALB/c mouse strains were used in this study as well as the SD-Rat strain. The ability of cercariae to penetrate skin was strain specific. A/J and SENCAR mice had the highest penetration rates (approximately 98%), whereas the SD-Rat strain had the lowest (43%). These penetration rates we linearly correlated with tail skin HETE production at 10 min (R = 0.826), whereas HETE production at 60 min had a parabola-shaped relationship (R = 0.793). The primary infection of mice with Schistosoma mansoni cercariae may therefore be directly correlated with both the skin's innate ability to synthesize HETE, as well as with cercarial eicosanoid production, especially HETE levels. However, we believe that skin eicosanoid production is just one of many factors affecting cercarial skin penetration. Other factors discussed are: skin surface fatty acid levels, cercarial eicosanoid production, epidermal vs. dermal eicosanoid production, and the immunocompetence of the host.

Schistosoma mansoni: a comparison of secreted vs nonsecreted eicosanoids in developing schistosomulae and adults.

We have determined that developing schistosomulae and adults of Schistosoma mansoni synthesize a wide range of eicosanoids when stimulated with linoleic acid, an essential fatty acid. Developing schistosomulae secrete 64%, while adults secrete over 80% of synthesized eicosanoids. On a per milligram soluble protein basis, eicosanoid secretion is ordered as follows: adult females greater than adult males much much greater than developing schistosomulae. Together one mature adult worm pair secreted approximately 4.36 micrograms prostaglandin E, 3.41 micrograms leukotriene B4, and 15.13 micrograms 5-hydroxyeicosatetraenoic acid (HETE) as determined by radioimmunoassay (RIA). High-performance liquid chromatography (HPLC) results have determined that 15-HETE is the major HETE species secreted by adults and developing schistosomulae. The immunosuppressant roles of 15-HETE, PGE, and LTB4 are discussed in relation to a possible mechanism for S. mansoni to evade the host immune system. Adults and schistosomules of S. mansoni have evolved rather sophisticated mechanisms for evading the host immune response. These include both host antigen acquisition and antigen shedding. In addition, young schistosomes have an as yet unidentified intrinsic defense mechanism against the host immune system. We postulate that part of the defense mechanism in schistosomules and adults may involve secretion of immunosuppressant eicosanoid species.

Schistosoma mansoni: pH dependence of cercarial eicosanoid production, penetration, and transformation.

The pH dependence of Schistosoma mansoni cercarial penetration and transformation was determined using a gelatin:agar matrix, containing 3mM linoleate, as a penetration substrate. Penetration was largely unaffected by pH, approaching 100% over the pH range of 5.4 to 8.2, while transformation had an optimum pH range between 6.2 and 7.4. Within this pH range, between 74 and 89% of cercariae lost their tails. Outside this range, transformation decreased to 0% above pH 7.8 and dropped to 57% at pH 5.4. Esculetin, a lipoxygenase inhibitor, also incorporated into the agar:gelatin plates at a concentration of 1 mM, had little effect on cercarial penetration, except between pH 6.5 and 6.65, where penetration rates fell to 50% at pH 6.63. Transformation, however, was inhibited by esculetin, except between pH 6.5 and 6.8, where transformation was statistically equivalent to controls (P = 0.064, two-tailed Student's t test). Cercarial eicosanoid production measured at pH 6.55 and 7.2 in the presence and absence of 1 mM esculetin has led to the tentative identification of a 5-lipoxygenase product associated with cercarial penetration: LTB4 or 6-trans LTB4, a breakdown product of LTB4. We discuss the importance of pH control in cercarial experiments as well as the possible modulatory role skin pH (surface, epidermal, and dermal) may have in regulating cercarial eicosanoid production.

Schistosoma mansoni: production of cercarial eicosanoids as correlates of penetration and transformation.

A method was developed, using a 0.25% agar matrix, to incorporate varying concentrations of linoleate and correlate cercarial transformation and eicosanoid production in vitro. Schistosoma mansoni cercariae were stimulated to penetrate over a wide range of linoleate concentrations; however, the transformation process occurred over a narrow range. Approximately 25% of cercariae penetrated the agar matrix in controls (no linoleate) and 0.003 mM linoleate. Penetration rates rose gradually until, at linoleate concentrations of 0.3 mM or greater, penetration approached 100%. The transformation process did not begin until the linoleate concentration in agar reached 2.0 mM (3.8%), and achieved maximum (91%) at 3.0 mM. A concentration of 9.0 mM linoleate gave 100% penetration and transformation rates, but penetration was superficial and cercariae were not viable. Cercarial eicosanoid production was concentration-related. Various eicosanoid classes were associated with cercarial penetration and transformation. Penetration rates were correlated with increasing leukotriene (LT, R = 0.9541) and hydroxyeicosatetraenoic acid (HETE, R = 0.8363) levels, while transformation rates correlated with increasing prostaglandin levels (R = 0.9225). Correlating eicosanoid production with penetration and transformation rates strengthened the hypothesis that successful cercarial penetration and transformation are dependent on both skin essential fatty acid levels and resulting cercarial eicosanoid production.

Nutrition and somatomedin. XIV. Altered levels of somatomedins and somatomedin inhibitors in rats with streptozotocin-induced diabetes.

Diabetes is associated with poor growth despite elevated levels of growth hormone (GH). Skeletal GH effects are mediated by somatomedins; in diabetes, somatomedins measured by radioassay are normal, yet somatomedin activity measured by bioassay is low. Since bioassay measurements reflect the presence of both somatomedins and somatomedin inhibitors, we asked if diabetes might be associated with discordant regulation of these circulating factors. Graded severity of diabetes was induced in rats by injection of streptozotocin at 37, 73, 146, and 293 mg/kg. After two days, metabolic derangement varied from normal serum beta-hydroxybutyrate with slight increase in glucose and minimal weight loss at 37 mg/kg streptozotocin to beta-hydroxybutyrate 10.6 mmol/L, glucose 447 mg/dL, and 33 g weight loss at 293 mg/kg streptozotocin. After fractionation of serum on Sephacryl S-300 pH 7.0, somatomedins and somatomedin inhibitors were measured by rat cartilage bioassay. Somatomedins (Kav 0.25 to 0.50) were comparable to control levels despite beta-hydroxybutyrate 2 mmol/L, glucose 534 mg/dL, and weight loss 11 g at 73 mg/kg streptozotocin and fell only at higher streptozotocin dosage. In contrast, somatomedin inhibitors (Kav 0.62 to 0.88) began to rise at 37 mg/kg streptozotocin and increased with higher dosage. Levels of somatomedins were correlated weakly only with beta-hydroxybutyrate (r = 0.48, P less than 0.05), while somatomedin inhibitors were correlated significantly with all indices, particularly beta-hydroxybutyrate (r = 0.78, P less than 0.0001). The early rise in somatomedin inhibitors but late fall in somatomedins could explain low somatomedin activity (and poor growth) despite normal levels of somatomedins measured by radioassay; measurement of somatomedin inhibitors may provide an index of growth potential in diabetes mellitus.

Schistosoma mansoni: cercarial eicosanoid production and penetration response inhibited by esculetin and ibuprofen.

Cercariae of Schistosoma mansoni produce a wide variety of eicosanoids when stimulated by 3.3 mM linoleate. High-performance liquid chromatography indicated that 10(-5) M esculetin dramatically decreased eicosanoid production by cercariae. Ibuprofen (10(-4) M) also decreased eicosanoid production, but to a lesser extent. These results were confirmed by radioimmunoassay using time-dose curves for esculetin and time curves for ibuprofen. The results reported here indicated that, for cercariae, ibuprofen was neither a specific cyclo-oxygenase inhibitor, as has been reported for platelet and endothelial cells, nor was esculetin a specific inhibitor of lipoxygenase, as has been reported for platelets and mastocytoma cells. Rather, both drugs inhibited cyclo-oxygenase and lipoxygenase enzyme systems. Further, the data indicated that two forms of cyclo-oxygenase exist in cercariae (isozymes?), one initiating the conversion of gamma-dihomolinolenate into the 1-series prostaglandins and another acting on arachidonate forming the 2-series prostaglandins. The cyclo-oxygenase acting on arachidonate has a greater sensitivity to both ibuprofen and esculetin than the enzyme acting on gamma-dihomolinolenate. Cercarial lipoxygenases also varied greatly in their sensitivity to ibuprofen.

Schistosoma mansoni: eicosanoid production by cercariae.

Cercariae of Schistosoma mansoni are stimulated to penetrate skin by certain free fatty acids. The cercariae have an active arachidonate cascade, presumably using host skin essential fatty acids as cascade precursors. Exposing cercariae to 3.3 mM linoleate for 1, 10, and 60 min resulted in production of a wide variety of eicosanoids. Using high-performance liquid chromatography, eicosanoids coeluting with prostaglandin E2, D2, and A2, leukotriene B4, and 5-hydroxyeicosatetraenoic acid standards were identified, as well as unidentified peak positions. Radioimmunoassay confirmed the presence of immunoreactive prostaglandin E1, and E2, and 5- and 15-hydroxyeicosatetraenoic acids in cercarial extracts. No eicosanoid production occurred when cercariae were exposed to 3.3 mM oleate and 1 or 330 microM linoleate. Both high-performance liquid chromatography and radioimmunoassay data indicated that cercariae regulate the production of eicosanoids through time. It is postulated that arachidonate metabolism and subsequent eicosanoid production are required for successful cercarial penetration.

Nutrition and somatomedin--XII. Fractionation of somatomedins and somatomedin inhibitors in normal and diabetic rats.

Bioassayable somatomedins and somatomedin inhibitors were examined after chromatographic separation, using serum from normal rats (enriched in somatomedins) and diabetic rats (enriched in somatomedin inhibitors). At neutral pH, gel filtration on Sephacryl S-300 revealed somatomedins at mol. wt approximately 140,000 (presumably carrier-bound) and inhibitors at mol. wts approximately 250,000, approximately 24,000 and approximately 1,000. At acid pH, gel filtration on Sephadex G-50 revealed somatomedins at mol. wt approximately 8,000 (presumably carrier-free) and a single inhibitor at mol. wt approximately 21,000. Ion exchange chromatography revealed that the inhibitor(s) may be more acidic than the somatomedins, but only low quantities of somatomedins were recovered. Sephadex G-50 fractionation was applied to pathophysiologic models in rats: 3 days of fasting were associated with a 62% fall in somatomedins and a 159% rise in inhibitors; 2 days of diabetes were associated with a 60% fall in somatomedins and a 344% rise in inhibitors. Since chromatography on Sephadex G-50 at pH 2.4 appears to provide adequate separation of somatomedins and somatomedin inhibitors with good estimated recovery of biological activity, this simple approach may be a probe useful in examining the regulation of somatomedins and somatomedin inhibitors in vivo.

Somatomedin inhibitor in uremia.

In uremia, poor growth occurs despite normal to increased levels of insulin and GH. Since serum somatomedin levels measured by RIA and radioreceptor assay are normal in patients with renal failure, while serum somatomedin activity measured by bioassay is low but increased by dialysis, we asked if somatomedin activity could be decreased due to the presence of a low mol wt inhibitor(s). Serum was obtained from eight normal adults and eight uremic patients before hemodialysis treatment and was fractionated by gel filtration. Somatomedins and high mol wt inhibitors were separated on Sephadex G-50, pH 2.4, and high and low mol wt inhibitors were separated on Sephadex G-25, pH 7. Somatomedins were measured by stimulation of SO4 uptake by hypophysectomized rat costal cartilage in vitro, and inhibitor levels were determined by the blunting of stimulation produced by somatomedins in normal serum. Total biologically active somatomedin levels were comparable in uremic and normal sera. High mol wt somatomedin inhibitors (as found in malnutrition and diabetes) also were detected at similar levels in uremic and normal sera. In contrast, serum from uremic patients had increased levels of a low mol wt somatomedin inhibitor(s) [151 +/- 23% (mean +/- SEM) of serum stimulation inhibited vs. 47 +/- 9%; P less than 0.001]. Peak inhibitory activity was found at approximately 940 mol wt (range, 800-1100); an inhibitor of similar size was found in normal urine. Uremic serum fractions blunted cartilage sulfate uptake that was stimulated by whole serum, somatomedins (dissociated from serum carrier proteins), and insulin and lowered uridine and thymidine uptake that was stimulated by whole serum (all P less than 0.005). Lineweaver-Burk analysis indicated that somatomedin-inhibitor interactions on cartilage were noncompetitive, consistent with observations that direct exposure of cartilage to inhibitor decreased SO4 uptake to 30 +/- 3% below buffer levels (P less than 0.001). Despite these marked effects on cartilage, no alterations in basal or insulin-stimulated glucose oxidation occurred after addition of inhibitory serum fractions to adipose tissue incubations. Exposure of the inhibitor to proteolytic enzymes led to a significant decrease in inhibitory activity, indicating that the inhibitor may be a peptide. These studies suggest that decreased circulating somatomedin activity and impaired growth in uremia may reflect the accumulation of a circulating peptide inhibitor that would normally be cleared by the kidneys. Measurements of this factor may provide an index of growth potential in uremic children and help guide therapy of renal failure in both children and adults.

The role of essential fatty acids and prostaglandins in cercarial penetration (Schistosoma mansoni).

We used rat skin membranes to test the putative role of prostaglandins (PG) and essential fatty acids (EFA) in the penetration response of Schistosoma mansoni cercariae. To examine the effects of EFA on cercarial penetration an EFA-deficient rat model was used. Dams were fed an EFA-deficient diet during lactation and the pups were weaned to this diet. Cercarial penetration of EFA-deficient rat skin membranes was not reduced from control levels until 12 wk on the diet. At this time a decrease of 64.3% was observed. This decrease remained constant up to 16 wk, after which the study was terminated. Other normal rats were treated with 20 mg/kg ibuprofen, a PG inhibitor, to examine the role of PG in the penetration response. Treated rat skin contained a mean of 2 micrograms ibuprofen per 30 mm3 of skin (25-mm skin disc) at 1.5 hours post-injection. Skin from treated rats inhibited penetration by over 81%. These studies indicate that skin EFA and PG may have a critical role in the completeness of penetration by cercariae through the skin, although it is not clear whether cercarial or host PG are involved in the penetration response.

The role of prostaglandins in cercarial (Schistosoma mansoni) response to free fatty acids.

In examining the structure-activity relationship of a diverse group of chemicals reported to prevent cercarial penetration after topical application, we noticed a moiety that was common to free fatty acids and prostaglandins. Because unsaturated fatty acids have been reported to stimulate cercarial penetration, we hypothesized that cercarial stimulation by skin and fatty acids may invoke prostaglandin mechanisms in cercariae, skin, or both. Thus we compared the stimulation of cercariae by a series of essential and nonessential fatty acids and demonstrated an inhibition of this response by ibuprofen and aspirin, known cyclo-oxygenase inhibitors, and by 13-azaprostanoic acid, a potent antagonist of the thromboxane/endoperoxide receptor. These data led us to postulate a major role for prostaglandins in the cercarial penetration response.