The effect of ageing on the metabolism of the infective larvae of Strongyloides ratti Sandground, 1925

The effect of physical factors on the rate of respiration of the infective larvae of Strongyloides ratti Sandground, 1925

Dense larval suspensions have a higher Qo2 than dilute ones, probably due to an oxygen debt acquired during preliminary washings. Ammonia (0·1M) did not affect the respiratory rate of the infective larvae of S. ratti. Mechanical agitation of larvae reduced their rate of respiration.

The partial pressure: respiration curve of the infective larvae was sigmoidal, that of larval homogenates was a rectangular hyperbola. At low partial pressures of oxygen the respiratory rate depends to a certain extent on the rate of change of the partial pressure.

In 100% oxygen the respiratory rate of the larvae is at first stimulated and then falls to its initial level. On returning to air after 100% oxygen, the respiratory rate is at first depressed and then recovers.

The infective larvae of S. ratti develop an oxygen debt when kept under anaerobic conditions. During the recovery period, which lasts for about 1 h, the Qo2 may increase by up to 100%.

The respiration of the infective larvae increases as the temperature is increased. When larvae are maintained at 37 °C there is a gradual decrease in their rate of respiration and this change is apparently irreversible.

The rate of respiration of the larvae is slightly inhibited at low pH values and slightly stimulated at high pH values.

Moderate levels of carbon dioxide (5%) have no effect on the respiratory rate of the infective larvae of S. ratti, high levels of carbon dioxide (10–20%), have a definite narcotic effect on the larvae.

The respiration of the infective larvae is unaffected by osmotic pressures up to an equivalent of 1% sodium chloride. Above this level the respiratory rate is at first stimulated then decreases.

This work was carried out during the tenure of a Medical Research Council Scholarship.

The effect of long term storage on the lipid reserves and fatty acid composition of cysts and hatched juveniles of Globodera rostochiensis G. pallida

The lipid composition of three batches of single generation cysts of Globodera rostochiensis, stored dry at 4 degreesC for 1, 7 and 13 years, comprised 81%, 74% and 53% neutral lipids, 14%, 18% and 27% non-acidic phospholipids and 5%, 8% and 20% free fatty acids, respectively. Lipids in eggs from two batches of G. pallida cysts, stored for 3 and 7 years, comprised 80% and 67% neutral lipids, 15% and 23% non-acidic phospholipids and 5% and 10% free fatty acids, respectively. All batches contained the same fatty acids which were dominated by C18:1, C20:1 and C20:4. The fatty acid profiles of hatched J2 of G. rostochiensis from two batches, stored for 1 and 9 years, differed only in their free fatty acid fractions. Thus, while it is not possible to determine the age of cysts by their fatty acid profile, it may be possible to use the relative amounts of the main lipid classes as an indicator of age. Four batches of hatched J2 of G. pallida were investigated, with sample A hatched during the second week in potato root diffusate, B during week 3, C during week 4 and D during weeks 5 and 6 and stored for 3.5 days (on average) after hatching. Total lipid content was 27.2%, 31.5%, 18.5% and 6.3% of the dry weight for A, B, C and D, respectively. In the neutral lipid fraction of D an increase in C18:1 and to a lesser extent C18:2 was observed. In the free fatty acid fraction of sample D, the percentages of C18:1, C18:2 and C18:3 were greater but the percentages of C20:3 and C20:4 were smaller compared with sample C. Fresh early hatched J2 of G. rostochiensis were compared with later hatched and stored (for 13 days on average) individuals for their lipid content and fatty acid composition. The lipid content was 26.1% and 11.4% in fresh and stored J2, respectively. Total lipid consisted of 77% and 70% neutral lipid, 18% and 26% non-acidic phospholipid and 6% and 4% free fatty acid in fresh and stored J2, respectively. In the neutral lipid fraction of stored J2 C18:1, C16:0 and C18:0 increased, whereas C20:4, C20:1 and C20:3 decreased. Therefore, both neutral lipid and free fatty acid fractions showed changes in their fatty acid profiles after long delayed hatching and/or storage in both PCN species.

Steady-state content of glycolytic/tricarboxylic acid-cycle intermediates, adenine nucleotide pools and the cellular redox-status in the infective (L3) larvae of (homogonic) Strongyloides ratti

Infective (L3) larvae of Strongyloides ratti (homogonic strain) were freeze-clamped (-196 degrees C) and the steady-state content of the glycolytic, Krebs tricarboxylic acid (KTA)-cycle intermediates and adenine nucleotides analysed. Comparison of the mass-action ratios (MARs) of the glycolytic enzymes with their apparent equilibrium constants (K9eq) indicate that phosphoglucomutase, glucosephosphate isomerase, triosephosphate isomerase, phosphoglyceromutase and phosphopyruvate hydratase reactions were all at or near equilibrium, whilst hexokinase, phosphofructokinase and pyruvate kinase were displaced from equilibrium. The S. ratti aldolase and myokinase appear to be somewhat displaced from equilibrium and thus may have pseudoregulatory roles. The adenylate energy charge (AEC), ATP/ADP ratio and the available adenylate energy (AAE) indices were 0.9 +/- 0.04, 8.76 +/- 1.5 and 397 +/- 43, respectively. The free [NAD+]/[NADH+H+] ratio of the cytoplasmic compartment of S. ratti L3 larvae calculated employing the steady-state content of the oxidised and reduced substrates of lactate dehydrogenase (E.C. 1.1.1.27) and the combined glyceraldehyde 3-phosphate dehydrogenase (E.C. 1.2.1.12)/3-phosphoglycerate kinase (E.C. 2.7.2.3) system were ca. 523 and 1200, respectively. The free[NAD+]/[NADH+H+] ratio in the mitochondrial compartment of S. ratti L3 larvae calculated using the malate dehydrogenase (E.C. 1.1.1.37) equilibrium was found to be 1962:1. The data is discussed with respect to the predominantly aerobic nature of the energy metabolism of the L3 larvae.

Strongyloides ratti: mitochondrial enzyme activities of the classical electron transport pathway in the infective (L3) larvae

Submitochondrial particles prepared from S. ratti L3 larvae exhibited NADH-oxidase (NOX), NADH-ferricyanide reductase (NFR), NADH-cytochrome-c-reductase (NCR), succinate-cytochrome-c-reductase (SCR), and cytochrome-aa3-oxidase activities of 2.1 +/- 0.3, 8.9 +/- 1.3, 0.6 +/- 0.1., 1.0 +/- 0.2 and 1.2 +/- 0.3 nm min-1 mg protein-1 respectively, at 37 degrees C. The NCR and NOX activities were 39.3% and 23.5% of the NFR activity, suggesting the occurrence of a rate-limiting step or bifurcation of the respiratory electron transport (RET) pathway on the oxygen-side of RET-Complex I. The NCR activity was 50% that of cytochrome-aa3-oxidase activity which suggests partitioning of electron flow at the level of RET-Complex III and/or the quinone-function. Antimycin A and rotenone but not 2-thenoyl trifluoroacetone (TTFA) inhibited NCR activity, the EC50 values were 3.6 x 10(-6) M, 3.7 x 10(-7) M, respectively. SCR activity was inhibited by antimycin A (EC50 = 3.8 x 10(-6) M) and TTFA (EC50 = 2.8 x 10(-5) M) but not by rotenone. The results suggest that presence of classical and alternate RET-pathways in S. ratti L3 larvae.

The response of intact Strongyloides ratti infective (L3) larvae to substrates and inhibitors of respiratory electron transport

Live, intact third-stage larvae (L3s) of Strongyloides ratti in the absence of exogenous substrates consumed oxygen at a rate (E-QO2) of 181.8 +/- 12.4 ng atoms min-1 mg dry weight-1 at 35 degrees C. Respiratory electron transport (RET) Complex I inhibitor rotenone (2 microM) produced 33 +/- 6.5% inhibition of the E-QO2. Unusually the rotenone-induced inhibition was not relieved by 5 mM-succinate. The E-QO2 of intact L3s was refractory to RET Complex III inhibitor antimycin A at 2 microM; 4 microM-antimycin inhibited less than or equal to 10% of the E-QO2. The electron donor couple ascorbate/TMPD augmented the E-QO2 in the presence of rotenone (2 microM) and antimycin A (4 microM) by 110%. Azide (1 mM) stimulated the antimycin A refractory QO2 by 36.6 +/- 7.2% which was only partially inhibited by 1.0 mM-KCN (IC50 = 0.8 mM). The data suggest the presence of classical (CPW) and alternate (APW) electron transport pathways in S. ratti L3s.

Biochemical changes during the development of the miracidium of Gigantocotyle explanatum

Analysis of various biochemical components during the development of the miracidium of G. explanatum showed marked changes, particularly in glycogen, protein and DNA levels. Though the total lipids remained more or less unchanged, alterations in the levels of cholesterol, triglycerides, free fatty acids, phospholipids and phospholipid fractions were also recorded. Such changes could be intrinsically programmed for the cellular differentiation and organogenesis in larval amphistomes.

Analysis of polyunsaturated fatty acid composition of Strongyloides ratti in relation to development

The effect of linolenic acid (C18:3 omega 3) on the development of Strongyloides ratti first-stage larvae (L1) in culture was studied. The fatty acid composition of S. ratti free-living generations was analyzed by gas chromatography. L1 had abundant linoleic acid (C18:2 omega 6) but its proportion decreased with development. On the contrary, eicosapentaenoic acid (C20:5 omega 3) and C20:4 omega 3 were prominent in the filariform larva (L3). Because C20:5 omega 3 is generally synthesized from C18:3 omega 3 via C20:4 omega 3, the high ratio of C20:5 omega 3/C18:3 omega 3 of L3 in all the free-living generations suggested that polyunsaturated fatty acid metabolism, particularly the omega-3 series, and eicosanoids produced had important roles in the development of S. ratti L1.

The effect of fatty acids on the developmental direction of Strongyloides ratti first-stage larvae

The effect of fatty acids was studied on the developmental direction of Strongyloides ratti first-stage larvae (L1). The proportion of third-stage infective larvae increased markedly when L1 were cultured in faeces with added fatty acids such as palmitic (C16), stearic (C18), oleic (C18:1) and linoleic (C18:2) acids. Unsaturated fatty acids were more effective than saturated ones. Moreover, the proportion of infective larvae increased with quantity of linoleic acid but the triacylglycerols of any fatty acid had no effect. These results suggest that these free fatty acids cause physiological changes that determine the developmental course of L1 of S. ratti in nature.

Estimation of the numbers and infectivity of Nippostrongylus larvae

Experimental investigations of the subcutaneous infection of third-stage larvae of Nippostrongylus brasiliensis reveal discrepancies between the actual and intended inoculum, and also variability between replicate inocula. Emphasis is thus placed on the importance of obtaining accurate estimates of the level of confidence associated with inoculum size. Under specified laboratory conditions, the retention of infectivity of N. brasiliensis larvae was found to be age-dependent, with a maximum of between 120 and 156 days. The motility of the larvae was not found to be indicative of their ability to complete migration and to become established in the small intestine of the host following subcutaneous inoculation.

Determinants of the longevity of third-stage infective larvae of Ancylostoma tubaeforme

The effects of some extrinsic factors on the lipid (energy) reserves and longevity of third-stage larvae of the cat hookworm Ancylostoma tubaeforme, were investigated under controlled laboratory conditions. In nonstressful microenvironmental conditions, larval longevity was directly related to the rate of utilisation of the lipid reserves. The effects of the various environmental stresses on longevity could also be explained largely on the basis of their deleterious effects on the lipid metabolism of the larvae.

Growth and respiration throughout the life-cycle of Nematospiroides dubius Baylis, 1926 (Nematoda: Heligmosomidae). The free-living stages

The growth of the three free-living stages of N. dubius was measured in terms of dry and fresh weight. Changes in body water content during moulting were demonstrated by variations in dry weight when expressed as a percentage of fresh weight. The respiration rate of the larvae increased until they became infective, after which time it decreased until five days later no oxygen consumption could be recorded. The inability of all larval stages to withstand anaerobic conditions indicated that their metabolism was essentially aerobic. The relationship between body size and metabolic rate was established for each stage and its significance in relation to the life-cycle discussed.

Activity, ageing and penetration of hookworm larvae

Lipid levels of infective larvae of Ancylostoma tubaeforme are reduced and their behavioural activity declines with age. We have measured behavioural activity using the percentage active, rate of activity, and the percentage of larvae able to penetrate a membrane. Neostigmine bromide, a cholinergic drug, increased larval activity in all tests. Larvae, stored at 4 and 10 °C and in hypertonic saline, were inactive but consumed lipid. When returned to isotonic saline at 26 °C, these larvae were no more active than those at 26 °C throughout. We found no evidence that such inactive larvae had entered a state of quiescence. All our results, and those of other workers, have been used to emphasize that larval ageing is related directly to decreased metabolic rates, and not primarily to lipid levels.

Invasion of skin by larvae of the cat hookworm, Ancylostoma tubaeforme

A modification of the ‘floating raft’ method ofin vitropenetration study is described. This allows replication of results and additional conveniences in operation. Filter paper membranes have shown characteristics similar to those of skin and have been used for quantitative studies. A method of digesting penetrating larvae from skin has been used to reduce the variability inherent in whole skin. Neither chloroform soluble skin products nor gravity were found to have a significant effect on the number of larvae entering membranes. Exsheathment of larvae was not essential prior to penetration and no specific stimuli for exsheathment appear to be necessary. Scanning electron micrographs have shown that entry may be by either hair follicles or desquamations of the stratum corneum. No evidence of enzymic activity during the invasion process has been found so far and the results suggest that a mechanical rather than chemical system obtains.

Energy utilization of infective Ancylostoma tubaeforme larvae

It has been demonstrated that under prolonged experimental conditions lipid is utilized most quickly under optimal conditions of tonicity, gaseous exchange, pH and sensory stimulation. There is good evidence that activity may be an appreciable energy-consuming process. It has been deduced, however, that the low Reynold's number means viscous forces dominate locomotory energy consumption, and work done is proportional to the square of the velocity. Osmoregulation in hypotonic media and tolerance of hypertonic media do not require appreciable energy.

Locomotion is only possible in limited environmental conditions, and these may also be conditions of peak basal metabolism. Larvae are able to enter quiescence which is not energy-demanding, in poor conditions. Larvae can survive anaerobiasis, but finally die without reduction in lipid and cannot convert lipid to carbohydrate for anaerobic metabolism.

The help of Mrs Helen Foreman in staining the larvae and for statistical analyses, and of Mr J. M. Smith is greatly appreciated. I would like to thank Dr Elizabeth U. Canning for kindly providing the microdensitometer and Professor G. S. Nelson and Dr D. A. Denham for enabling us to establishA. tubaeformein our cats. The generous support of the British Medical Research Council is much appreciated.

Sensory basis of activity in Ancylostoma tubaeforme infective larvae

Upon stimulation, following a period of ambient conditions, infective A. tubaeforme larvae follow a committed characteristic pattern of activity, after being released by short-term mechanical or continuous photic stimulation. For the photic response this is stimulated by an increase in the intensity of stimulation, and for non-dark-adapted larvae a sudden fivefold increase in illumination is required, irrespective of previous stimulation.

Acetylcholine chloride, adenosine triphosphate, γ-amino butyric acid, histamine diphosphate, 5-hydroxytryptamine, neostigmine bromide, physostigmine (eserine), potassium hydroxide, succinyl choline chloride and d-tubocurarine chloride have been added to larvae and their subsequent postures and activity recorded. It is concluded that the typical activity pattern of larvae may be altered by the use of drugs which interfere with neuromuscular phenomena, and therefore the activity responses of infective A. tubaeforme are based on sensory and neurosecretory rather than energetic considerations.

We thank Mrs Helen Foreman for maintaining the larvae and the Medical Research Council of Great Britain for their generous support.

Observations on the effect of the rediae of Fasciola hepatica on the lipid composition of the hepatopancreas of Lymnaea truncatula

In the uninfected hepatopancreas of L. truncatula 7·0–11·0% of the dry weight is lipid. Of the total lipid 60% is neutral lipid and 40% is phospholipid. Free fatty acid is the major neutral lipid component; triglycerides, diglycerides, monoglycerides, sterols and esterified sterols are also present. The phospholipids identified were phosphatidyl choline, phosphatidyl ethanolamine, lyso-phosphatidyl choline and sphingomyelin. The fatty acids were analysed by gas chromatography. The major fatty acid is C16 (palmitic) and 60% of the total fatty acids are saturated.

In the hepatopancreas of L. truncatula infected with the rediae of F. hepatica, but with the rediae removed, 5·4–9·4% of the dry weight is lipid. Of this total lipid 73% is neutral lipid and 27% is phospholipid. All the fractions of neutral lipid, except the fatty acids are smaller than in the uninfected hepatopancreas. The fatty acids show an increase of 38%. The same phospholipids identified in the uninfected hepatopancreas are present, but all the fractions show a decrease in amount with the exception of the phosphatidyl choline fraction, which is present in approximately equal amounts in both the uninfected and the infected hepatopancreas. The major fatty acid is palmitic acid.