Effects of 5-hydroxytryptamine (serotonin) on the incorporation of 32P-inorganic phosphate into phospholipids in Hymenolepis diminuta (Cestoda)

5-Hydroxytryptamine (5-HT) (1,2 and 5 mM) significantly stimulated the incorporation of radioactive inorganic phosphate (32Pi) into phosphatidylinositol, phosphatidylethanolamine, phosphatidic acid and also total phospholipid fraction of Hymenolepis diminuta after one hour of incubation. Such effect was both time and concentration dependent. In the presence of 5-HT early labelling of phosphatidylinositol was observed. Also, the percentage stimulation by 5-HT was the highest in this fraction under all experimental conditions. The inorganic, organic, total and phosphatidylcholine-bound phosphate of H. diminuta incubated with 5-HT were not significantly different from those of the control under all incubation conditions. Results reported herein suggest that messenger molecules that are derived from phosphoinositides may be involved in the stimulatory mechanism of 5-HT in H. diminuta.     

Effects of galactose, mannitol, glucose and alpha-methyl-D-glucoside on the incorporation of 32P-inorganic phosphate into phospholipids in Hymenolepis diminuta (Cestoda)

In the presence of glucose and galactose, the incorporation of radioactive inorganic phosphate (32Pi) into phosphatidylcholine of Hymenolepis diminuta was significantly lowered as compared to the control, whereas other phospholipids remained unaffected. alpha-methyl-D-glucoside, however, significantly lowered the amount of 32Pi incorporated into phosphatidylcholine, phosphatidylinositol, phosphatidylethanolamine and phosphatidic acid. Mannitol did not have any effect on the incorporation of 32Pi into the phospholipids of H. diminuta. The effect of glucose and alpha-methylglucoside on phospholipid metabolism was both time and concentration dependent. The inorganic, organic, total and phosphatidylcholine-bound phosphate of H. diminuta in the presence of various substrates were not significantly different from the control values under all incubation conditions. The results indicate that the observations made in the presence of external glucose, galactose and alpha-methylglucoside were due to their physical interaction with the transport mechanism in the tegumental membrane of H. diminuta and also their being subsequently metabolized in the cases of the former two hexoses.     

Trypsin adsorption by Hymenolepis diminuta (Cestoda)

Significant amounts of radioactivity were associated with Hymenolepis diminuta following incubation in 3H-trypsin. Autoradiography of worms incubated in 3H-trypsin for 30 min demonstrated that all radioactivity was associated with the worm's surface (tegument). The amount of 3H-trypsin adsorbed by the worms was not sufficient to account for the inactivation of this enzyme in the presence of intact worms. Unlabeled trypsin and poly-L-glutamate (but not poly-L-lysine) inhibited adsorption of 3H-trypsin, but were without effect on trypsin inactivation by H. diminuta. Therefore, trypsin was adsorbed by intact H. diminuta, but the process of adsorption apparently did not play any role in inactivation of the enzyme.     

Monoamine oxidase in adult Hymenolepis diminuta (Cestoda).

A membrane-bound monoamine oxidase (EC 1.4.3.4) was demonstrated in homogenates of Hymenolepis diminuta. The enzyme oxidized a variety of biologically active amines (in decreasing order: dopamine, adrenaline, noradrenaline, tryptamine, tyramine, octopamine), there was, however, no activity with 5-hydroxytryptamine or benzylamine. No diamine oxidase (EC 1.4.3.6.) could be detected in H. diminuta (using histamine, cadaverine or putrescine as substrates). The monoamine oxidase from H. diminuta was not inhibited by azide, hydroxylamine or semicarbazide, but was inhibited by cupferron, alpha-alpha dipyridyl and iodoacetamide, and by the specific monoamine oxidase inhibitors pargyline, nialamide and iproniazid. Several anthelmintics were also found to be inhibitors of monoamine oxidase. The possible roles of monoamine oxidase in H. diminuta are discussed.     

Hymenolepis diminuta (Cestoda): uptake of cycloleucine by metacestodes

Cycloleucine uptake by metacestodes of H. diminuta of various ages was investigated. Absorption occurs by active mediated transport, mean Kt = 0.28 mM. Vmax values are age-related, and can be correlated to developmental changes. Cycloleucine uptake in the metacestode is very similar to that in the adult worm and the implications of this are discussed.     

Biochemical effects of thiabendazole and cambendazole on Hymenolepis diminuta (Cestoda) in vivo

An investigation of the chemotherapeutic and biochemical effects of two benzimidazole anthelmintics, thiabendazole (TBZ) and cambendazole (CBZ), on Hymenolepis diminuta in experimentally infected rats is reported. Thiabendazole was active against H. diminuta at a relatively high dosage. A single oral dose of TBZ at 250 mg/kg body weight on day 15 of infection eliminated 100% of the tapeworms as determined at necropsy 5 days after treatment. The chemotherapeutic actions of TBZ on H. diminuta were accompanied by marked changes in worm weight and chemical composition. Tapeworms recovered from rats that had received a therapeutically effective dose of TBZ 24 hr earlier were significantly smaller and contained much less glycogen (as a percent of the wet weight) than worms from unmedicated controls. Protein concentrations increased in TBZ-treated worms and at a rate sufficient to offset the decline in glycogen concentration. Glycogen/protein ratios in TBZ-treated worms were significantly lower than the corresponding control values. Cambendazole proved to be five times more potent than TBZ against H. diminuta and produced the same basic changes in worm weight and chemical composition within 18 hr of treatment of the host. Administration of a single oral dose of TBZ or CBZ to the host produced in H. diminuta another change, the onset of which coincided with, or preceded, the gross alterations in worm weight and chemical composition. That change, observed in in vitro studies carried out 14 hr after treatment, revealed that tapeworms from drug-treated rats absorbed and metabolized much smaller quantities of exogenous glucose than did the controls, and the ability of the worm to accumulate glucose against a concentration difference was significantly depressed.     

Hymenolepis diminuta: membrane transport of glucose and beta-methylglucoside

Absorption kinetics of [¹⁴C]glucose and [β-methyl-¹⁴C]glucoside in Hymenolepis diminuta are reported. β-Methylglucoside (βMG) is a pure competitive inhibitor of [¹⁴C]glucose transport and has kinetic parameters, V_max and K_t, for transport similar to those reported for glucose. While absorbed ¹⁴C-βMG is not metabolized, transport of this glucose analog retains the general characteristics which have been established for glucose transport including: (1) Na⁺ dependence, (2) inhibition by K⁺, (3) sensitivity to phlorizin and various hexoses, (4) transport against an apparent concentration gradient, and (5) increase in worm water during accumulation. It is concluded that glucose and βMG are transported by the same system. The value of using βMG to study the mechanism of hexose transport and accumulation in H. diminuta is suggested.     

Effects of L-thyroxine on incorporation of (32)P into phospholipids of freshwater eels

The effects of L-thyroxine on phospholipid biosynthesis, via (32)P incorporation, were studied in gill, kidney, liver and muscle tissue of eels acclimatized at 11 degrees C. L-thyroxine treatment had no effect on tissue content of lipid, inorganic and organic acid-soluble phosphorus. Only an increase of the specific radioactivities of lipid, inorganic and organic acid-soluble phosphorus was observed in the muscle. Percentage distribution of (32)P among classes of phospholipid were significantly altered in liver and muscle, without change in phospholipid composition. A specific effect of L-thyroxine on (32)P incorporation into phosphatidic acid in muscle and liver has been shown. As expected by the higher specific radioactivity of muscle inorganic and organic acid-soluble phosphorus, the increased incorporation of (32)P into phosphatidic acid probably results from a higher specific radioactivity of muscle ATP phosphorus.