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Affinities and intrinsic activities of dopamine receptor agonists for the hD21 and hD4.4 receptors.

The affinity and intrinsic activity of dopamine receptor agonists were determined at the human dopamine hD21 and hD4.4 receptors. (-)-3-Hydroxy-N-n-propylpiperidine ((-)3-PPP) had an intrinsic activity of 46% and 83%, whereas (+)-N-propylnorapomorphine ((+)-NPA) had intrinsic activities of 61% and 58% at the dopamine hD21 and hD4.4 receptors, respectively. Affinities also varied. A single, or multiple, dopamine D2-type receptor(s) may be involved in schizophrenia and agonists are being tested as therapy. Understanding their properties at the individual dopamine D2-family receptors is important.

Aminoquinolines↗

Dopamine receptor antagonists attenuate conditioned place preference following sexual behavior in female Syrian hamsters.

We assessed the effects of the dopamine D2 receptor antagonists, sulpiride and raclopride, on conditioned place preference produced by sexual behavior in female Syrian hamsters. Female hamsters treated with sulpiride or raclopride showed high levels of sexual behavior (lordosis) that were equivalent to control females receiving vehicle injections. The degree of place preference conditioning for sulpiride-treated females was marginally reduced, whereas females treated with raclopride showed no evidence of conditioning. These results indicate that conditioned place preference is a useful means for probing the appetitive components of female sexual behavior, and that dopamine D2 receptors are involved in this appetitive process.

Animals↗

Trypanosoma brucei and T. vivax: salicylhydroxamic acid and glycerol treatment of acute and chronically infected rats.

In rats infected with monomorphic Trypanosoma brucei brucei, the efficacy of the therapy with salicylhydroxamic acid plus glycerol, i.e., combined therapy, decreased with increasing time after infection. It failed completely after the infection was made chronic by suboptimal treatment for 6 weeks. When this chronic infection had been established and "optimal" treatment was given, viable trypanosomes could still be detected 1 day later in brain and muscle but not in blood. In most organs, the concentrations of salicylhydroxamic acid and glycerol were lower than in the blood plasma; the maximum concentration of glycerol in the brain was only 20% of that in plasma. The most likely explanation for the failure of the combined therapy is that, in certain tissues, the concentration of the drugs remains too low to kill extravascular trypanosomes. Other explanations, such as the selection of a resistant strain or the survival of (extravascular) forms with a more active mitochondrion, could be excluded with a high degree of probability. Suramin was very effective, even after combined therapy had failed repeatedly, while melarsoprol was less effective. As in combined therapy, the dose of melarsoprol that could cure an acute infection was insufficient to cure a chronic infection. Combined therapy failed after a spontaneous chronic infection with T. b. rhodesiense had existed for 5-7 weeks, but it was effective in T. vivax infected rats even when parasitemia had been present for at least 4 days. Effective alternative schedules for combined therapy were not found.

Animals↗

Schistosoma mansoni: salicylanilides as topical prophylactic against cercarial penetration of mice.

Salicylanilide and 37 of its analogs were applied topically to mice as candidate chemoprophylactic agents against Schistosoma mansoni cercarial penetration. The compounds were solubilized in absolute methanol, dimethyl sulfoxide, or isopropanol at concentrations not exceeding 1.25% W/V. The tails of the mice of each experimental group were treated by immersion for 5 min in the test compound solution or in the vehicle. The treated tails of 5 mice from each group were washed for 30 min in flowing tap water 3-4 hr after compound application. Tails of all mice were then exposed to approximately 100 cercariae by tail immersion for 1 hr, 24 hr after treatment. The portal veins were perfused 49 days after exposure and worm burdens were determined. The protective capacity of each compound was calculated by comparing the reduction of the mean worm burdens of the compound treated mice to the worm burdens of those treated with only the vehicle and expressing the resulting value as percentage protection. Of the 38 compounds tested, 20 provided 98% or better protection if the treated tails were not washed before exposure to cercariae. Of these 20 active compounds, 16 provided 98% or better protection from infection by S. mansoni cercariae even after the mouse tails were subjected to the 30 min wash.

Administration, Topical↗

Trypanosoma (Nannomonas) congolense: changes in respiratory metabolism during the life cycle.

All four life cycle stages (bloodstream, procyclic, epimastigote, and metacyclic) of Trypanosoma congolense IL 3000 were assayed with an oxygen electrode (polarograph) for the presence of terminal oxidases and carbon-source preference. In addition, these stages were used for histochemical analysis of mitochondrial activity using rhodamine 123, nitroblue tetrazolium, and diaminobenzidine. Morphometry was used to compare mitochondrial volumes and surface area among the different life cycle stages. It was found that in contrast to epimastigote forms, which were metabolically almost identical to procyclic forms, metacyclic forms showed characteristics of, and seemed preadapted to, differentiation into the bloodstream stage. While mitochondrial NAD+ diaphorase activity and an electrochemical potential were detected in all life cycle stages, metacyclic metabolism was glucose-based and terminal oxidase activity was primarily dependent upon the trypanosome alternative oxidase with the contribution of cyanide-sensitive respiration accounting for only 20-30% of the total respiratory capacity.

Adenosine Triphosphate↗

Reticulocyte lipoxygenase, ingensin, and ATP-dependent proteolysis.

Lipoxygenase purified from rabbit reticulocyte lysate has a molecular mass of 68 kDa on SDS gel and a pI of 5.97. Lipoxygenase is inhibited by nordihydroguaiaretic acid (NDGA), 3-amino-1-(m-(trifluoromethyl)phenyl)-2-pyrazoline (BW755C), 5,8,11,14-eicosatetraynoic acid (ETYA), salicylhydroxamate (SHAM) or hemin. Metal ions or nucleotides do not affect its activity. The addition of certain of these inhibitors to the reticulocyte extract also inhibited the ATP-dependent proteolysis of casein, one of the distinct characteristics of reticulocytes. No clear correlation between lipoxygenase activity and ATP-dependent proteolysis could be detected. Hemin and NDGA inhibited both processes, but the concentrations necessary for inhibition were quite different. SHAM completely inhibited lipoxygenase, but not proteolysis. o-Phenanthroline inhibited ATP-dependent proteolysis, but had no effect on lipoxygenase activity. We have also purified a high-molecular-mass protease, ingensin, from reticulocyte extract. This protease accounted for more than 90% of the casein-degrading activity in reticulocyte extract. NDGA inhibited ingensin at the same concentrations required for inhibition of ATP-dependent proteolysis. These results suggest that lipoxygenase is not indispensable for the ATP-dependent proteolysis and the novel high-molecular-mass protease, ingensin, may be involved in the process.

4,5-Dihydro-1-(3-(trifluoromethyl)phenyl)-1H-pyraz↗

Trypanosoma brucei brucei: the catabolism of glycolytic intermediates by digitonin-permeabilized bloodstream trypomastigotes and some aspects of regulation of anaerobic glycolysis.

1. The production of pyruvate, glycerol and glycerol-3-phosphate by intact and digitonin-permeabilized Trypanosoma brucei brucei has been studied with glucose or the glycolytic intermediates as substrates. 2. Under aerobic conditions hexosephosphates gave maximal glycolysis in the presence of 40-60 micrograms digitonin/10(8) trypanosomes while the triosephosphates gave it at 20-30 micrograms digitonin/10(8) trypanosomes. 3. In the presence of salicylhydroxamic acid, and the glycolytic intermediates, permeabilized trypanosomes produced equimolar amounts of pyruvate and glycerol-3-phosphate and no glycerol. Under the same conditions, glucose catabolism produced glycerol in addition to pyruvated and glycerol-3-phosphate. 4. In the presence of salicylhydroxamic acid and ATP or ADP intact trypanosomes produced equimolar amounts of pyruvate and (glycerol plus glycerol-3-phosphate) with glucose as substrate. 5. A carrier for ATP and ADP at the glycosomal membrane is implicated. 6. It is apparent that glycerol formation is regulated by the ATP/ADP ratio and that it needs intact glycosomal membrane and the presence of glucose.

Adenosine Diphosphate↗

Evidence for glycerol 3-phosphate:glucose transphosphorylase activity in bloodstream Trypanosoma brucei brucei.

1. Anaerobic glycolysis in intact bloodstream Trypanosoma brucei brucei was studied. 2. Fructose, glucose and mammose were aerobically catabolized at rates of 3.4, 3.0 and 2.5 and anaerobically at rates of 0.38, 2.75 and 2.35 mumol hexose/hr/10(8) trypanosomes respectively. 3. Glycerol 3-phosphate and ADP accumulated approximately to the same level from anaerobic catabolism of the three hexoses. However, fructose catabolism stopped within 15-20 min but addition of glucose to these already immobilized trypanosomes temporarily caused a rapid characteristic drop in glycerol 3-phosphate level at a rate of 40 nmol/min/10(8) trypanosomes and correspondingly glucose 6-phosphate, glycerol and pyruvate levels were raised. 4. These observations are not consistent with the proposed requirements for the reverse glycerol kinase in anaerobic net ATP production. Instead, we propose a glycerol 3-phosphate:glucose transphosphorylase that catalyses the formation of glycerol and glucose 6-phosphate.

Adenine Nucleotides↗