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J R Sauer

Publications and source records attributed to J R Sauer.

At least 37 records · Page 2Linked to original sources
PubMed1996

Alteration of arachidonate levels in tick salivary glands by dietary modification of host blood lipids.

Tick saliva contains prostaglandins of the 2-series, believed to facilitate bloodmeal acquisition. Because ticks cannot synthesize the prostaglandin precursor, arachidonic acid, investigations were undertaken to study the uptake, incorporation, and distribution of arachidonic acid in the salivary glands of the lone star tick in vitro and in vivo. Uptake of [3H]arachidonate by isolated salivary glands was reduced in the presence of low concentrations of arachidonic or eicosapentaenoic acids, but much higher, non-physiological concentrations of oleic and linoleic acids were required to inhibit [3H]arachidonate uptake. The incorporation of [3H]arachidonate into triglycerides increased at high concentrations of arachidonic or eicosapentaenoic acid, but not at any concentration of oleic or linoleic acid. Eicosatetraynoic acid greatly inhibited [3H]arachidonic acid. Guinea pigs fed hydrogenated coconut oil, safflower/primrose oil, or fish oil exhibited altered blood lipids; notably increased levels of eicosapentaenoic acid when fed fish oil. Salivary gland lipids in ticks fed on these hosts were also altered. Ticks parasitizing fish oil-fed guinea pigs contained high levels of eicosapentaenoic acid with a 30% reduction in arachidonate levels. The results demonstrated that eicosapentaenoic acid in the host diet had profound effects on arachidonate assimilation by tick salivary glands, which could lead to altered prostaglandin content in tick saliva.

Animals↗
PubMed1996

Tick salivary prostaglandins: Presence, origin and significance.

Prostaglandins (PGs) are oxygenated metabolites of polyunsaturated fatty acids, most notably arachidonic acid, that act as 'local hormones', regulating a plethora of physiological processes in mammals and other vertebrates. For a long time, PGs were reported only in higher vertebrates, but more recently they have been reported in lower organisms such as bacteria, yeasts and protozoa, and much information is now available on PGs in insects. Prostaglandins are increasingly reported to exist at the host-parasite interface and are thought to aid the parasite by modulating the inflammatory and immune response. Ticks secrete saliva containing extremely high concentrations of PGs into the host, and in this article Alan Bowman, Jack Dillwith and John Sauer provide a synopsis of the information, to date, on the presence, synthesis and proposed roles for these tick salivary PGs.

Journal Article↗
PubMed1996

Dietary modification of host blood lipids affect reproduction in the lone star tick, Amblyomma americanum(L.).

The feeding and reproductive performance of female lone star ticks (Amblyomma americanum (L.)) infesting guinea pigs on diets containing 15% fish oil (FO) or safflower oil (SO) were investigated. Replete ticks fed on FO-fed guinea pigs weighed approximately 30% less than those on the SO-fed guinea pigs. The lower engorged weight resulted in a similar decrease in the mass and number of eggs laid and number of larvae hatching. No effect of host dietary treatment was observed upon the reproductive efficiency index, egg weight, or hatchability. Guinea pig blood on the FO-diet contained high levels of eicosapentaenoic acid, which has previously been shown to inhibit the accumulation of arachidonic acid in the tick salivary gland. It is suggested that the ticks on the FO-fed guinea pigs have impaired production and secretion of dienoic prostaglandins in the saliva resulting in poorer feeding performance, possibly by altering the amount of host blood present in the feeding lesion.

Adipose Tissue↗
PubMed1995

Regulation of free arachidonic acid levels in isolated salivary glands from the lone star tick: a role for dopamine.

An important regulatory step for prostaglandin synthesis is the availability of the precursor, free arachidonic acid (AA). In isolated salivary glands of the lone star tick, Amblyomma americanum (L.), the level of free AA appears to depend on higher phospholipase A2 (PLA2) activity rather than decreased rates of re-esterification by lysophosphatide acyl transferase (LAT). This conclusion is supported by experiments where inhibition of LAT with merthiolate was without effect, while the calcium ionophore A23187, a PLA2 stimulant, increased levels of free AA. The PLA2 activity in A. americanum was reduced by the substrate analog, PLA2 inhibitor, oleyloxyethyl phosphorylcholine in a dose-dependent manner, but was insensitive to the other mammalian PLA2 inhibitors mepacrine (20 microM), aristolochic acid (45 microM), and dexamethasone (50 microM). No substrate preference was observed for the functional group of the phospholipid, with phosphatidylcholine and phosphatidylethanolamine being equal sources of AA in A23187-stimulated glands. Compared to phospholipids containing other fatty acids, only arachidonyl-phospholipid (arachidonyl-PL) was significantly hydrolyzed by PLA2 activity in A23187-stimulated glands. Dopamine was as effective as A23187 as a stimulant of PLA2 activity in isolated glands, but this effect was abolished in the presence of the calcium channel blocking agent verapamil. It is concluded that free AA levels in tick salivary glands are increased through activation of a Type IV-like PLA2 following an increase of intracellular calcium caused by the opening of voltage-dependent calcium channels due to dopamine stimulation.

1-Acylglycerophosphocholine O-Acyltransferase↗
PubMed1995

Origin of arachidonic acid in the salivary glands of the lone star tick, Amblyomma, americanum.

The contribution of synthesis and dietary sequestration to the high arachidonate content of the lone star tick, Amblyomma americanum, salivary glands was investigated by assessing the salivary metabolites of various radiolabeled fatty acid substrates administered to partially fed females. A portion of each of the fatty acids studied was incorporated into the fatty acid moiety of the phospholipid fraction. [14C]acetate was metabolized only into myristic, palmitic, palmitoleic, steric, and oleic acids. [3H]oleic acid, [14C]linoleic acid, [14C]gamma-linolenic acid and [14C]eicosatrienoic acids were incorporated into salivary gland phospholipids but underwent little change including elongation and/or desaturation to arachidonate. Ingested [3H]arachidonic acid was readily taken up by the salivary gland and distributed among the lipid classes in a pattern markedly different from that of the other fatty acids tested. We conclude that ticks are unable to synthesize arachidonic acid for incorporation into the salivary glands, but rather sequester it from the host bloodmeal.

Animals↗
PubMed1995

Uptake, incorporation and redistribution of arachidonic acid in isolated salivary glands of the lone star tick.

The ability of isolated salivary glands from the lone star tick, Amblyomma americanum, to take up, incorporate and redistribute [3H]arachidonic acid was examined. Uptake of arachidonic acid was concentration dependent--a single salivary gland incorporated up to approximately 2.8 micrograms arachidonic acid in 60 min. Over 90% of the [3H]arachidonate entering the glands was esterified and found only in the phospholipid (approximately 80%) and triglyceride (approximately 10%). Essentially no radioactivity was associated with the diglyceride fraction and none with phosphatidic acid indicating de novo phospholipid synthesis was negligible. Phospholipid synthesis via acylation of lysophospholipids (the Lands pathway) was indicated by the rapidity of the synthesis (< 2 min) and the sensitivity to sulfhydryl-blocking agents. Within the phospholipids, [3H]arachidonate was incorporated only into phosphatidylcholine (PC) and phosphatidylethanolamine (PE). Initially [3H]arachidonate was incorporated primarily into PC, but as the incubation proceeded PE contained an increasing proportion of the label. The proportion of [3H]arachidonate incorporated into triglyceride increased at higher media concentrations of arachidonic acid. The roles of lysophosphatide acyltransferase, transacylase and diglycerol acyltransferase in the distribution of arachidonate in tick salivary glands are discussed.

1-Acylglycerophosphocholine O-Acyltransferase↗
PubMed1995

Biosynthesis of salivary prostaglandins in the lone star tick, Amblyomma americanum.

Dopamine-induced saliva from ticks fed [3H]arachidonic acid contained the radiolabelled prostaglandins E2, F2 alpha, D2, and B2, the latter probably derived from PGE2 owing to the alkalinity of tick saliva. Prostaglandin synthetase (PGS) activity in the salivary gland homogenate from the lone star tick, Amblyomma americanum, could not be detected by standard radiometric methodologies successfully employed for tissues from many animal species, including numerous arthropods. Modifications to the assay conditions had no effect. The presence of a PGS-inhibitor in the salivary glands was ruled out. It is postulated that the PGS in A. americanum salivary glands may be considerably different from that found in other animals, including vertebrate hosts.

Animals↗
PubMed1995

Prostaglandin biosynthesis and subcellular localization of prostaglandin H synthase activity in the lone star tick, Amblyomma americanum.

We report on prostaglandin (PG) biosynthesis in the lone star tick, Amblyomma americanum. In vitro preparations of whole female ticks and internal tissues were competent to biosynthesize four PGs: PGA2/PGB2, PGD2, PGE2, PGF2 alpha. PGA2/PGB2 was the major product under optimal conditions. PG biosynthesis by whole tick and internal tissues were sensitive to incubation conditions including, protein concentration, time, temperature, pH, and presence of a co-factor cocktail composed of reduced glutathione, hydroquinone, and hemoglobin. Under standard assay conditions, 2 mg/ml protein were incubated at pH 8.0 for 2 min at 32 degrees C. PG biosynthesis was inhibited by indomethacin, a potent cyclooxygenase inhibitor in mammalian systems. Internal tissue preparations were fractionated into cytosolic and microsomal preparations by ultracentrifugation. PG biosynthetic activity was detected in both fractions. The subcellular distribution of PG biosynthetic activity in ticks is similar to other invertebrates, but quite different from mammals, in which PG biosynthetic activity is almost exclusively localized in the microsomal fractions. PGH synthase-2 was detected in the microsomal fraction on western blot analysis. These results suggest that the lone star tick is competent to biosynthesize PGs. These compounds may contribute to the success of tick feeding ecology by attenuating the defense responses of vertebrate hosts during lengthy feeding periods.

Animals↗
PubMed1995

Tick salivary gland physiology.

The multifunctional, morphologically complex salivary glands are essential to the biological success of ticks and are intricately involved in the transmission of pathogens. They are innervated, and there is convincing evidence that dopamine is a neurotransmitter at the neuroeffector junction controlling fluid secretion. As feeding progresses, the rate of salivary fluid secretion increases greatly, enabling the ixodid tick to concentrate the bloodmeal by returning excess water and ions to the host. Saliva in feeding ticks is rich in bioactive components and exhibits a range of pharmacological properties. Factors identified in saliva or salivary glands include cement to help anchor the mouthparts to the host, various enzymes and inhibitors, histamine agonists and antagonists, prostaglandins, antihemostatic factors, and immuno-modulating factors. A secretion from the salivary glands allows ticks to absorb water from the air during the lengthy periods off their hosts. The physiology of this remarkable organ provides a striking example of strategies that have evolved to meet the challenge of a unique parasitic life style.

Animals↗
PubMed1994

Cell membrane receptors and regulation of cell function in ticks and blood-sucking insects.

Immunoglobulins cross the midgut epithelium and enter the haemolymph of many blood-feeding arthropods without losing their immunological properties. Antigens essential to the survival of the blood-sucking arthropods which may be affected by the small amounts of specific antibody that cross the gut epithelium include membrane receptors or other factors which regulate cell function. Membrane receptors implicated in transmembrane signalling in response to specific neural and endocrine factors fall into three major classes: (1) gated ion channels, (2) agonist-stimulated tyrosine kinases and (3) receptors that interact with GTP-binding (G) proteins. Examples of all three types have been found in insects and ticks. A dopamine receptor interacts with a G-protein essential for controlling fluid secretion by the salivary glands of ixodid ticks. Another receptor in the ixodid tick salivary gland binds a neuropeptide from the tick synganglion and stimulates turnover of plasma membrane phosphoinositides, but its mechanisms of transmembrane signalling and function remain elusive. Another large class of membrane receptors are those concerned with endocytosis. Examples of receptor-mediated endocytosis include incorporation of vitellogenin by developing oocytes in mosquitoes and ticks and uptake of lysed blood-meal components by digest cells of the tick gut. Many cell membrane receptors and possibly hormones could serve as targets for vaccines in blood-feeding insects and ticks. The major challenge is to identify and characterize essential internal receptors and cellular components that are accessible to and affected by specific antibodies that are introduced into the body of blood-feeding arthropods.

Animals↗
PubMed1994

Protein phosphatase 1 and 2A in tick salivary glands as assessed by responses to okadaic acid.

Crude protein phosphatase activity was inhibited 80% by nanomolar okadaic acid (OA) in salivary glands of unfed ticks but only 40% in salivary glands of feeding ticks. An additional 40% of protein phosphatase was inhibited by micromolar OA in the salivary glands of feeding ticks but only 10% in salivary glands of unfed ticks. Cyclic AMP and OA alone or together increased the phosphorylation of multiple proteins in a plasma membrane-enriched 900 g supernatant fraction of tick salivary glands. Exogenous cyclic AMP stimulated increased incorporation of phosphate into proteins with approximate molecular weights of 109, 70, 64, 51, 48, 42 and 18.5 kDa. Micromolar OA in the absence of exogenous cyclic AMP stimulated increased incorporation of phosphate into proteins with apparent molecular weights of 109, 93, 74.5, 70, 51, 48, 42 and 18.5 kDa. Cyclic AMP and OA (10(-6) and 10(-9) M) stimulated significantly greater phosphorylation of an 18.5 kDa mol. wt protein above that observed in response to stimulation by OA (10(-6) and 10(-9) M) or exogenous cyclic AMP alone. Micromolar okadaic acid inhibited the amount and number of proteins but not volume of saliva secreted by whole ticks in response to stimulation by DA and theophylline. However, micromolar and nanomolar okadaic acid inhibited the ability of dopamine to stimulate fluid secretion by isolated salivary glands. Overall, the data support the existence of type 1 and 2A protein phosphatases in tick salivary glands and a role for protein phosphatases in modulating tick salivary secretion.

Animals↗
PubMed1994

Distribution of arachidonic acid among phospholipid subclasses of lone star tick salivary glands.

The subclass composition of choline- and ethanolamine-containing phospholipids was determined by analysis of acyl-linked fatty acids released by base hydrolysis of diradylglycerobenzoates formed from lone star tick salivary gland diacyl, alkylacyl and alkenylacyl phospholipids. The diacyl subclass comprises 87% of all choline-containing phospholipids, while th alkylacyl subclass comprises c. 9% and the alkenylacyl subclass c. 4%. The diacyl subclass comprises 72-77% of ethanolamine-containing phospholipids and about 14 and 13% of this subclass of phospholipid are alkylacyl and alkenylacyl lipids, respectively. Arachidonic acid (20:4) is the most abundant fatty acid (28% of all fatty acids) esterified in the alkylacyl form of phosphatidylcholine (PC) and it comprises 17% of the fatty acids in alkenylacyl-PC. The alkylacyl form of phosphatidylethanolamine (PE) is also rich in 20:4 (24%) while the alkenylacyl-PE subclass contains only 9% 20:4. Despite the relatively high amounts of 20:4 within the ether-linked phospholipids, the majority of the salivary gland 20:4 (> 83%) is found in the diacyl phospholipid subclass because of the preponderence of this subclass in tick salivary glands. Isolated salivary glands incorporated [3H]-20:4 primarily (> 98%) into the sn-2 position of diacyl PC > PE, with some incorporation into triglycerides. Continued incubation in the absence of labeled 20:4 demonstrated remodeling of [3H]-20:4 from PC into PE, and from the diacyl subclass to the alkylacyl subclass in the choline containing phospholipids.

Animals↗
PubMed1993

Analysis of lipids in the salivary glands of Amblyomma americanum (L.): detection of a high level of arachidonic acid.

Analysis of lipids in salivary glands of the lone star tick, Amblyomma americanum, demonstrated that arachidonic acid (20:4, n-6) comprises 8% of all fatty acids identified by gas chromatography. The occurrence of arachidonic acid and other C20 polyunsaturated fatty acids in tick salivary glands was confirmed by gas chromatography-mass spectrometry. Arachidonate is located entirely in the phospholipid fraction and is associated exclusively with phosphatidylcholine (PC) and phosphatidylethanolamine (PE). Salivary glands stored and frozen for several months had a similar lipid composition as freshly dissected salivary glands, with the exception of a small amount of free arachidonic acid and an increase in lysophosphatidylcholine. Incubation of salivary gland homogenates with snake venom phospholipase A2 showed that most saturated fatty acids are esterified in the sn-1 position of PC and PE, with the unsaturated fatty acids in the sn-2 position. Approximately 75% of arachidonic acid is in the sn-2 position of PC and PE, adding support to the hypothesis that arachidonic acid is released into the cytoplasm after activation of a phospholipase A2 for subsequent metabolism to prostaglandins and/or other eicosanoids.

Animals↗
PubMed1993

Detection of Anaplasma marginale (Rickettsiales: Anaplasmataceae) in secretagogue-induced oral secretions of Dermacentor andersoni (Acari: Ixodidae) with the polymerase chain reaction.

The polymerase chain reaction (PCR) was used to detect Anaplasma marginale in secretagogue-induced oral secretions of male and female Dermacentor andersoni Stiles exposed as nymphs or adults by feeding on infected calves. A 409-bp DNA fragment derived from the A. marginale (Florida isolate) msp1 beta gene was amplified with oligonucleotide primers BAP-2 (5'-GTATGGCACGTAGTCTTGGGATCA-3') and AL34S (5'-CAGCAGCAGCAAGACCTTCA-3'). The target DNA was amplified in oral secretions of female ticks exposed to A. marginale as adults and stimulated to secrete by injection of dopamine. Conversely, A. marginale was detected in saliva from prefed female ticks exposed as nymphs only after stimulation with a combination of dopamine, gamma-aminobutyric acid, pilocarpine, and theophylline. Saliva from ticks exposed as nymphs and stimulated with ergot alkaloids did not contain the A. marginale target DNA. Saliva collected after 11 d of feeding from dopamine-stimulated male ticks contained A. marginale DNA. The results indicate that A. marginale is present in tick saliva and suggest that the parasite can be transmitted to cattle via saliva of feeding ixodid ticks. The variable appearance of A. marginale in saliva, regardless of the method used to induce salivation, suggests that transmission of A. marginale may be affected by the physiological state of the tick.

Anaplasma↗
PubMed1993

Changes in lipids of the salivary glands of the lone star tick, Amblyomma americanum, during feeding.

The lipid composition of salivary glands from male and female lone star ticks, Amblyomma americanum, was investigated at progressive stages of tick feeding. The amounts of fatty acids from both phospholipid and neutral lipid fractions increased dramatically during the initial stage of feeding and peaked in partially fed females weighing 100-250 mg. Percentage compositions of myristic (14:0) and palmitic acid (16:0) decreased, but stearic (18:0), oleic (18:1), linoleic (18:2), and arachidonic acid (20:4) increased during tick feeding. Arachidonic acid, the precursor to eicosanoids including the 2-series of prostaglandins, increased from 1.3% of all fatty acids in salivary glands from unfed female ticks to 8.2% in salivary glands from fully engorged female ticks. Arachidonic acid was found in the triglyceride fraction of unfed and fed virgin females but only in phosphatidylcholine and phosphatidylethanolamine from salivary glands of other fed female ticks. Comparisons between fed and unfed male ticks and fed/virgin, fed/mated, and unfed females demonstrate that feeding is necessary for accumulation of arachidonic acid in salivary gland phospholipids.

Animals↗
PubMed1992

Amblyomma americanum (L.): protein kinase C-independent fluid secretion by isolated salivary glands.

Protein kinase C activity was partially purified from tick salivary glands by fast protein liquid chromatography anion-exchange chromatography. Enzyme activity was stimulated by Ca2+, phosphatidylserine, and diacylglycerol with the highest activity observed in the presence of all three modulators. Enzyme activity was inhibited by a synthetic pseudosubstrate peptide with an amino acid sequence resembling the protein kinase C substrate phosphorylation site. The protein kinase C activator, 1-oleoyl-2-acetyl-sn-glycerol (OAG), when added to whole in vitro salivary glands previously prelabeled with 32P, stimulated the phosphorylation of salivary gland proteins. Activators of protein kinase C (phorbol ester or OAG) did not stimulate fluid secretion by isolated tick salivary glands. OAG and phorbol ester had only minimal affects on the ability of dopamine to stimulate secretion by isolated salivary glands and dopamine's ability to increase salivary gland cyclic AMP.

Amino Acid Sequence↗
PubMed1992

Oral secretion elicited by effectors of signal transduction pathways in the salivary glands of Amblyomma americanum (Acari: Ixodidae).

The abilities of various effectors of signal pathways in tick salivary glands to stimulate oral secretions in partially fed Amblyomma americanum (L.) female ticks were compared. Pilocarpine stimulated secretion the most rapidly following tick stimulation, but its effectiveness declined with time and subsequent injections. Secretion rates induced by dopamine and theophylline increased with time of collection and additional injections and were as effective as pilocarpine after 60 min. Activators of protein kinase C, phorbol 12-myristate 13-acetate (PMA), and 1-oleoyl-2-acetyl-sn-glycerol inhibited dopamine, and theophylline stimulated secretion. gamma-amino-butyric acid either by itself or in combination with other drugs had no effect on volume of oral secretions. Peptides were visible in the oral secretion stimulated by the various drugs after separation and staining in SDS-polyacrylamide gels. More peptides were present in the oral secretion obtained from the smallest partially fed (slow feeding) ticks. In some ticks, proteins were observed in oral secretions obtained from the same tick at one collection time but not another in response to the same pharmacological agent.

Animals↗