Humoral serotonin and dopamine modulate the feeding in the snail, Helix pomatia.

We investigated the effect of elevated levels of humoral 5HT and DA on the feeding latency of Helix pomatia, 1 day, 3 days and 10 days following satiation, by injecting monoamines into the haemocoel. HPLC assay of monoamines showed that both 5HT and DA are present in pmol/ml concentrations in the haemolymph of both starved and non-starved animals. Elevated levels of 5HT and DA were most effective at decreasing the feeding latency 10 days following satiation when DA decreased the feeding latency in a concentration dependent manner between 10(-7) and 10(-5) M whereas 5HT levels decreased the feeding latency only at 10(-6) M but increased it at 10(-5) M. Immunocytochemistry revealed that both 5HT3 and D1 receptor-like immuno-reactivity are present in cell bodies located in the same areas of the buccal ganglia. Our observations suggest that both humoral DA and 5HT mutually modulate the activity of the feeding CPG through neurons which have these receptors.

Enzyme-linked immunosorbent assay for the determination of blood coagulation factor XIII A-subunit in plasma and in cell lysates.

A new one-step ELISA was developed for the determination of the concentration of blood coagulation factor XIII subunit A (FXIII-A) in plasma and in cell lysates. Monoclonal antibodies directed against different epitopes on FXIII-A were used for the assay. The capture antibody was biotinylated on its carbohydrate moiety and the detection antibody was labelled with horseradish peroxidase. The antigen-antibody reaction was carried out in the well of a streptavidin-coated microplate. Complex formation with FXIII subunit B (FXIII-B) and association to fibrinogen did not influence the accessibility of the antibodies to FXIII-A. The method could be performed within 2 h and demonstrated good reproducibility, recovery and sensitivity. Plasma samples could be assayed after storage at -20 degrees C for at least 6 months. However, in the case of platelet lysates freezing and rethawing resulted in a significant loss of FXIII-A. FXIII-A concentrations measured in the plasma samples of healthy individuals and patients correlated well with the concentrations of complexed plasma FXIII (A2B2) and with the results of FXIII activity measurements. A reference range of 46-82 fg/platelet was established for platelet FXIII-A.

A modified, optimized kinetic photometric assay for the determination of blood coagulation factor XIII activity in plasma.

BACKGROUND: Blood coagulation factor XIII (FXIII) is a zymogen that is transformed into an active transglutaminase by thrombin and Ca(2+). FXIII plays an essential role in fibrin stabilization and in the protection of fibrin from proteolytic degradation. No convenient method has been available for the measurement of FXIII activity in plasma. The aim of the present study was to improve and optimize a kinetic photometric FXIII assay originally developed in our laboratory. METHODS: In the assay, FXIII was activated by thrombin and Ca(2+). Fibrin polymerization was prevented by an inhibitory tetrapeptide. Glycine-ethyl ester and a glutamine residue of a synthetic dodecapeptide served as acyl acceptor and acyl donor transglutaminase substrates, respectively. The amount of ammonia released during the reaction was monitored using glutamate dehydrogenase and NADPH. RESULTS: The use of a new glutamine substrate and optimization of activator and substrate concentrations increased sensitivity. Substitution of NADPH for NADH and introduction of an appropriate blank eliminated systemic overestimation of FXIII activity. The recovery of FXIII was 96%, the assay was linear up to 470 U/L, the detection limit was 1 U/L, and the imprecision (CV) was <8% even at very low FXIII activities. A reference interval of 108-224 U/L (69-143%) was established. The results correlated well with results obtained by an immunoassay specific for plasma FXIII. CONCLUSIONS: The optimized FXIII assay is a simple, rapid method for the diagnosis of inherited or acquired FXIII deficiencies and increased FXIII concentrations. It can be easily adapted to clinical chemistry analyzers.

Effect of Val34Leu polymorphism on the activation of the coagulation factor XIII-A.

Coagulation factor XIII (FXIII) is a protransglutaminase involved in the last step of the coagulation cascade by stabilising the fibrin clot. Recently, a common variation (FXIII Val34Leu) has been associated with a decreased risk of myocardial infarction and deep venous thrombosis. Val34Leu is critically located near the thrombin activation site of FXIII-A. In this study we investigated its effects on the activation of FXIII. Both recombinant and platelet-derived FXIII Val34Leu variants were shown to be more susceptible to thrombin cleavage than the wild type FXIII. The rate of enzymatic activation of FXIII Val34Leu was found increased, however, the specific activity of fully activated wild type FXIII and the Val34Leu mutant did not differ. During the course of thrombin-induced activation of FXIII fibrin gamma-chain dimerisation and alpha-chain polymerisation developed more rapidly with the Val34Leu mutant. The increased rate of fibrin stabilisation brought about by the Val34Leu FXIII seems to be paradoxically associated with a protective effect against pathological thrombosis.

Val34Leu polymorphism of plasma factor XIII: biochemistry and epidemiology in familial thrombophilia.

Val34Leu polymorphism of the A subunit of coagulation factor XIII (FXIII-A) is located in the activation peptide (AP) just 3 amino acids away from the thrombin cleavage site. This mutation has been associated with a protective effect against occlusive arterial diseases and venous thrombosis; however, its biochemical consequences have not been explored. In the current study it was demonstrated that the intracellular stability and the plasma concentration of FXIII of different Val34Leu genotypes are identical, which suggests that there is no difference in the rate of synthesis and externalization of wild-type and mutant FXIII-A. In contrast, the release of AP by thrombin from the Leu34 allele proceeded significantly faster than from its wild-type Val34 counterpart. By molecular modeling larger interaction energy was calculated between the Leu34 variant and the respective domains of thrombin than between the Val34 variant and thrombin. In agreement with these findings, the activation of mutant plasma FXIII by thrombin was faster and required less thrombin than that of the wild-type variant. Full thrombin activation of purified plasma FXIII of different genotypes, however, resulted in identical specific transglutaminase activities. Similarly, the mean specific FXIII activity in the plasma was the same in the groups with wild-type, heterozygous, and homozygous variants. Faster activation of the Leu34 allele hardly could be associated with its presumed protective effect against venous thrombosis. No such protective effect was observed in a large group of patients with familial thrombophilia.

A simple, quick one-step ELISA assay for the determination of complex plasma factor XIII (A2B2).

A new highly sensitive sandwich ELISA assay was developed for the determination of plasma factor XIII (FXIII). Plasma FXIII is a tetrameric complex of two types of subunits (A2B2). A biotinylated monoclonal capture-antibody against the B-subunit and a peroxidase-labelled monoclonal tag-antibody against the A-subunit were added to the plasma dilution and the amount of the complex attached to streptavidin-coated microplate was quantitated by measuring peroxidase activity. Only the tetrameric plasma FXIII reacted in the assay, non-complexed A or B subunits showed no reaction. The assay is linear up-to 40 microg/L of FXIII in the assay mixture. It is a quick one-step assay which can be performed within two hours. At normal and low FXIII concentration within batch reproducibility was 2.0% and 3.3%, day to day variation was 5.5% and 8.7%, respectively. Its high sensitivity allows reliable measurement at FXIII concentrations below 1% of normal average. Plasma samples can be stored for the assay at -20 degrees C for at least one month. Plasma levels of healthy individuals were normally distributed and no gender difference was observed. A reference interval of 14-28 mg/L (67-133%) was established.

Treatment possibility of hypercholesterolaemia associated with hypertriglyceridaemia.

Thirty patients were investigated with hyperlipoproteinaemia, 15 patients with non-insulin dependent diabetes mellitus (NIDDM) and 15 with primary hyperlipoproteinaemia. The patients took 250 mg acipimox (5-metyl-pyrazine-carboxylic acid 4-oxide) 3 times per day for 2 months. Serum examinations were performed before and after 1 and 2 months of acipimox administration. After treatment the cholesterol and triglyceride levels decreased in both groups. Patients with NIDDM had 11% increase of high density lipoprotein-cholesterol (HDL-C) level at the end of the first, and 18% increase at the end of the second month, while patients with primary hyperlipoproteinaemia did not change significantly. The low density lipoprotein (LDL) level did not change significantly in either groups of patients. The apolipoprotein A 1 (apo A 1) levels increased significantly during the second month of acipimox administration. Uric acid levels decreased in both groups, but significant change could be detected mainly in the NIDDM group. Serum glucose level did not change in the non-diabetic patients, while it decreased significantly in the NIDDM group.

Prostacyclin-like activity in the female rat thoracic aorta and the inferior vena cava after ethinyloestradiol and norethisterone.

1. Female rats were injected with ethinyloestradiol, norethisterone or both compounds for 30 days. Prostacyclin-like activity was measured in the thoracic aorta and inferior vena cava. 2. In the thoracic aorta of rats injected with ethinyloestradiol and ethinyloestradiol/norethisterone, prostacyclin-like activity was significantly increased. Norethisterone alone had no effect. 3. In the inferior vena cava of rats injected with ethinyloestradiol, norethisterone or both compounds, prostacyclin-like activity was not significantly altered. The amount of prostacyclin generated by the inferior vena cava was much lower than that by the aorta. 4. Experimentally induced changes in the vessel wall after the administration of contraceptive steroids must be due to factors other than diminished prostacyclin production.