Hyaluronate-alginate combination for the preparation of new biomaterials: investigation of the behaviour in aqueous solutions.

With the aim of producing a biomaterial for surgical applications, the alginate-hyaluronate association has been investigated. Crossed techniques were used to assess the existence of polymer interactions in aqueous solutions up to 20 mg/ml. Alginate was obtained from algae and hyaluronate was purified from rooster comb. Viscometry measurements using the capillary technique or the Couette flow, together with circular dichroism investigations, evidenced the moderate significance of interactions between the two polysaccharides in dilute solutions. In addition, the case of more concentrated solutions and containing 20 mg/ml alginate was approached by rheological measurements in the flow mode; the behaviour of the polymer associations appeared as a compromise between those of individual polysaccharides.

Differences between A 68930 and SKF 82958 could suggest synergistic roles of D1 and D5 receptors.

The isochroman A 68930 and the benzazepine SKF 82958 are two full dopamine D1 receptor agonists. Responses to these compounds are different in several important aspects. When given to rats in a novel environment, A 68930 caused a dose-dependent (0.019-4.9 mg/kg) suppression of locomotion. SKF 82958 had no such effect at any dose studied (0.051-3.3 mg/kg). In animals habituated to the environment, A 68930 had no effect but SKF 82958 increased locomotor activity. Both A 68930 and SKF 82958 caused a decrease in core temperature at early time points. Both agonists increased c-fos and NGFI-A expression in caudate putamen but only SKF 82958 did so in the accumbens nucleus (at 1.6 mg/kg). Quantitative receptor autoradiography showed that A 68930 is 9-13 times more potent than SKF 82958 at displacing the selective dopamine D1 antagonist [3H]SCH 23390. This difference agrees with the difference observed when the agonists were used to stimulate cAMP formation in cells transfected with the D1 receptor. In contrast, SKF 82958 was 5 times more potent than A 68930 in cells transfected with the D5 receptor. We suggest that the balance between signaling via dopamine D1 and D5 receptors determines the functional effects of agonists at D1/D5 receptors.

Involvement of 5-HT1A and 5-HT1B receptors for citalopram-induced hypothermia in the rat.

OBJECTIVES: To examine the role of 5-HT1A and 5-HT1B receptors for citalopram-induced hypothermia in the rat. METHODS: Core temperature measurements were performed in adult male Wistar rats (305-340 g) using a computer-assisted recording instrument. The temperature readings were automated and gave a printout when the core temperature had stabilised at +/- 0.1 degree C for 10 s. RESULTS: Citalopram (6.25-100.0 mumol/kg) produced a dose-dependent hypothermia. The effect was maximal within 60 min after administration, and had waned off at 120 min. The 5-HT1B receptor agonist anpirtoline (0.25-4.0 mumol/kg) produced a dose-dependent decrease in core temperature. The citalopram-induced hypothermia (25 mumol/kg) was antagonised by pretreatment with either of the 5-HT1A and the 5-HT1B receptor antagonists, WAY-100,635 (0.04 mumol/kg) and NAS-181 (1.0 mumol/kg), respectively, or by the two drugs in combination. Subchronic treatment with the SSRI zimeldine (100 mumol/kg once daily for 2 weeks) resulted in tolerance to the hypothermic effect of citalopram (100 mumol/kg). CONCLUSIONS: The hypothermia produced by acute administration of the SSRI citalopram is mediated via activation of 5-HT1A, as well as 5-HT1B receptors, and this effect is subject to the development of tolerance.

Temperature set-point changes induced by DA D2/3 and 5-HT1A receptor agonists in the rat.

The DA D2/3 receptor agonist 7-OH-DPAT (2 micromol kg(-1)) and the 5HT1A receptor agonist 8-OH-DPAT (0.6 micromol kg(-1)) both produced a marked and similar decrease in core temperature of 3-4 degrees C at 10 and 20 degrees C ambient temperature. At 30 degrees C there were no, or weak, effects. The decrease in core temperature was accompanied by a sudden increase in tail temperature, followed by a decrease as core temperature returned to basal values. The results suggest that the hypothermia produced by the respective DA D2/3 and the 5-HT1A receptor agonists 7-OH-DPAT and 8-OH-DPAT is an active process, in all probability due to changes in a hypothalamic set-point for temperature regulation.

Atypical antipsychotics and dopamine D(1) receptor agonism: an in vivo experimental study using core temperature measurements in the rat.

The study objectives were to examine the effects of the atypical antipsychotic drugs olanzapine, risperidone, and quetiapine on core temperature in the rat in relation to such effects produced by clozapine and to compare possible in vivo intrinsic efficacy of olanzapine, risperidone, and quetiapine at dopamine (DA) D(1) receptors with such effects previously shown for clozapine. Core temperature measurements were made in adult male Wistar rats maintained under standard laboratory conditions using a reversed 12-h daylight cycle. Clozapine (0-32 micromol/kg s.c.), olanzapine (0-32 micromol/kg s.c.), and risperidone (0-4 micromol/kg s.c.) all produced a dose-dependent hypothermia. Except for slight nondose-dependent hyperthermia, there were no effects of quetiapine (0-16 micromol/kg s.c. or i.p.) on the core temperature. The hypothermia produced by clozapine, but not that produced by equipotent doses of olanzapine or risperidone, was fully antagonized by pretreatment with the DA D(1) receptor antagonist SCH-23,390 (0.1 micromol/kg s.c.). On the other hand, quinpirole-induced hypothermia (4 micromol/kg s.c.) was partially antagonized by olanzapine (2 micromol/kg s.c.), risperidone (4 micromol/kg s.c.), and quetiapine (16 micromol/kg s.c.) but not by clozapine (1 micromol/kg s.c.). Clozapine preferentially stimulates DA D(1) receptors in comparison with olanzapine and risperidone, whereas olanzapine, risperidone, and quetiapine preferentially block DA D(2) receptors compared with clozapine. It is suggested that stimulation of DA D(1) receptors, presumably in the prefrontal cortex, is a distinguishing feature of clozapine responsible for its favorable profile on cognitive functioning in schizophrenia.

Additive hypothermic effects of the 5-HT1A receptor agonist 8-OH-DPAT and the dopamine D2/3 receptor agonist 7-OH-DPAT in the rat.

The objective of this study was to examine possible interactions between serotonergic and dopaminergic agents lowering core temperature via stimulation of 5-HT1A and dopamine (DA) D2 receptors, respectively. The effects of the 5-HT1A receptor agonist (+/-)-8-hydroxy-2-(di-n-propylamino)tetralin HBr (8-OH-DPAT) and the DA D2/3 receptor agonist 7-OH-DPAT on core temperature was monitored in adult male Wistar rats, approximately 300 g body weight. The temperature probe was connected to a PC-assisted temperature instrument, and an automated printer device was activated when the temperature reading had stabilized (+/-0.1 degrees C) for 10 s. As expected, 7-OH-DPAT [0.5 and 2.0 micromol x kg(-1) subcutaneous (s.c.)] as well as 8-OH-DPAT (0.15-2.4 micromol x kg(-1) s.c.), produced a dose-dependent hypothermia. When combined, there were additive effects of the two compounds, although the effects of 7-OH-DPAT were attenuated by 8-OH-DPAT at the higher doses (0.6-2.4 micromol x kg(-1)), in all probability because of emerging DA D2 receptor blocking properties of the latter compound.

Hyaluronate-alginate gel as a novel biomaterial: mechanical properties and formation mechanism.

With the aim of producing a biomaterial for surgical applications, the alginate-hyaluronate association has been investigated to combine the gel-forming properties of alginate with the healing properties of hyaluronate. Gels were prepared by diffusion of calcium into alginate-hyaluronate mixtures, with an alginate content of 20 mg/mL. The hyaluronate source was shown to have significant effect on the aspect and the properties of the gels. The gels have viscoelastic behaviour and the transient measurements carried out in creep mode could be interpreted through a Kelvin-Voigt generalised model: experimental data led to the steady state hardness and a characteristic viscosity of the gel. Gels prepared from Na rooster comb hyaluronate with weight ratio up to 0.50 have satisfactory mechanical properties, and fully stable gels are obtained after a few days; on the contrary, use of lower molecular weight hyaluronate led to loose gels for hyaluronate contents over 0.25. Gel formation was investigated by measurements of the exchange fluxes between the calcium chloride solution and the forming gel, which allowed thorough investigations of the occuring diffusion phenomena of water, calcium ion and hyaluronate. Strong interactions of water with hyaluronate reduce significantly the rate of weight loss from the gel beads and allows higher water content in steady-state gels. Calcium content in the gel samples could be correlated to the actual alginate concentration, whatever the nature and the weight ratio of hyaluronate.

High interaction alginate-hyaluronate associations by hyaluronate deacetylation for the preparation of efficient biomaterials.

The paper presents fundamental investigations of alginate-hyaluronate association with significant polymer interactions for preparation of efficient biomaterials. For this purpose, acetamide functions of hyaluronate were partly cleaved by hydrazine at high temperature, yielding amino groups accessible to carboxylic functions of the alginate chain. Alginate-hyaluronate association was studied both in dissolved state by rheological measurements and CD, and in the form of gel slabs prepared after calcium diffusion. Appreciable interaction between carboxylic groups of alginate and the released amino groups of hyaluronate was put into evidence by enhanced values of the viscosity of mixed solutions, and by assessment of the properties of the gel formed: moderate deacetylation allowed gels of improved hardness and viscosity. Nevertheless, high deacetylation was observed to hinder the gel formation by Ca(2+) complexation of alginate, by the significant competition of COOH-NH(2) association. Interaction between alginate and modified hyaluronate results in regular gel structure, with small cavities.

Separation and quantification by ion-association capillary zone electrophoresis of unsaturated disaccharide units of chondroitin sulfates and oligosaccharides derived from hyaluronan.

An analytical method has been developed for assay of unsaturated disaccharides of chondroitin sulfates and of oligosaccharides (tetra- and hexasaccharides) of hyaluronan, using ion-association capillary zone electrophoresis. Samples were applied at the anode (the usual polarity), using a borate buffer modified by an ion-pairing reagent, tetrabutylammonium (TBA) phosphate, and the effect of the concentration of the ion-pairing reagent on various electrophoretic parameters (electroosmotic flow, electrophoretic mobility of products, capacity factors) was observed. Increasing concentrations of the reagent led to a decrease of zeta potential, probably due to specific adsorption of the quaternary ammonium ion onto the capillary wall. The authors propose a mechanism of separation, in which anionic borate complexes are formed and interact with TBA ion inside the capillary tube. The capillary electrophoretic system described is potentially a powerful method for specific measurement of the concentrations in joint tissues of chondroitin 4-sulfate, chondroitin 6-sulfate, and hyaluronan, whose relative abundances may vary in various diseases or after local treatments with, for example, antiinflammatory drugs, chondroprotective agents, or orthopedic implants.