Diurnal Variations of Beta-Endorphin at Rest and After Moderate Intensity Exercise

To determine the effect of time of day on circulating beta-endorphin concentrations 14 men exercised at 75% of their maximal capacity at 0600, 1200, 1800 and 2400 hr. Each trial was separated by 3-5 days and preceded by a normal sleep cycle except for the 0600 hr trials which was preceded by 6 hr sleep. Resting physiological data indicated normal diurnal variations in heart rate, core temperature and oxygen uptake, being lowest during the 0600 hr trials and highest during the 1800 hr trials. Resting plasma beta-endorphin concentrations averaged 11.9 +/- 8.4 pmol/l during the 0600 hr trials, significantly greater than the 2400 hr trials (6.4 +/- 3.6 pmol/l; P less than 0.05). No other significant differences existed at rest. Post exercise beta-endorphin concentrations were elevated and found to be inversely related to time of day with the 0600 hr trials having the highest mean (25.7 +/- 14.7) and the 2400 hr trials the lowest (14.7 +/- 8.3). These data suggest that the plasma beta-endorphin concentrations at rest and after exercise are affected by the time of day. The results also suggest that the changes in beta-endorphin associated with exercise are not major contributors to cardiorespiratory control or changes in psychological effect associated with exercise.     

Comparison of antiprogestin stimulation of uterine prostaglandin synthesis in vitro

Progesterone has an inhibitory effect on prostaglandin synthesis in urine tissue and this effect is reversible with progesterone receptor antagonists. Although antiprogesterone steroids such as RU486 (Mifepristone) are effective at inducing abortion in women they have an improved efficacy when used with exogenous synthetic prostaglandin. In the guinea-pig such antagonists sensitize the uterus but do not result in increased myometrial activity and therefore may not induce endogenous PG synthesis. In this study the effects of antiprogestins on a preparation of rat uterus perifused with progesterone were studied. ZK98 734 caused a rapid and sustained increase in 6-oxoPGF synthesis which rose within the first 90 minutes. This rapid response suggested that some mechanism other than the induction of fresh protein synthesis was involved. A similar increase was not seen with pregnant guinea-pig myometrium/decidua perifused in a similar manner, suggesting that some other mechanism was responsible for the relatively low PG production in pregnancy. However increases in 6-oxoPGF in response to antiprogestins were recorded when pregnant guinea-pig decidua/myometrium was incubated for 4 hours. In these experiments 1 microM ZK98 734 and 1 microM ZK98 299 (Onapristone) gave a 2.7 fold increase in PG production whereas RU486 gave a 1.6 fold increase. Both 1 microM ZK98 734 and 1 microM ZK98 299 also gave a significant increase in PGE production but no increase in PGF was observed. These findings suggest that some antiprogestins might have a better effect on the stimulation of endogenous PG synthesis or on the rate of catabolism of prostanoids.     

Antibodies which recognize the C-terminus of the inhibitory guanine-nucleotide-binding protein (Gi) demonstrate that opioid peptides and foetal-calf serum stimulate the high-affinity GTPase activity of two separate pertussis-toxin substrates.

We investigated the mechanisms of receptor-mediated stimulation of high-affinity GTPase activity in response to opioid peptides and to foetal-calf serum in membranes of the neuroblastoma X glioma hybrid cell line NG108-15. Increases in GTPase activity in response to both of these ligands was abolished by prior exposure of the cells to pertussis toxin. Pertussis toxin in the presence of [32P]NAD+ catalysed incorporation of radioactivity into a broad band of approx. 40 kDa in membranes prepared from untreated, but not from pertussis-toxin-pretreated, cells. Additivity studies indicated that the responses to opioid peptides and to foetal-calf serum were mediated by separate guanine-nucleotide-binding proteins (G-proteins). Whereas opioid peptides produced an inhibition of adenylate cyclase in membranes of untreated cells, foetal-calf serum did not. Affinity-purified antibodies which recognize the C-terminus of the inhibitory G-protein identified a 40 kDa polypeptide in membranes of NG108-15 cells. These antibodies attenuated opioid-stimulated high-affinity GTPase activity, but did not markedly affect the response to foetal-calf serum. We conclude that receptors for the opioid peptides function via the inhibitory G-protein (Gi), whereas foetal-calf serum activates a second pertussis-toxin-sensitive G-protein, which has a C-terminal sequence significantly different from that of Gi.     

Differential effects of suramin on the coupling of receptors to individual species of pertussis-toxin-sensitive guanine-nucleotide-binding proteins.

The anti-helminthic drug suramin inhibited the basal high-affinity GTPase activity of both C6 BU1 glioma and NG 108-15 neuroblastoma x glioma hybrid-cell membranes with an IC50 (concentration causing half-maximal inhibition) value close to 30 micrograms/ml. This effect was shown to occur via a non-competitive mechanism in which the binding affinity of the G-proteins for GTP was not altered, but the maximal velocity of the subsequent hydrolysis was reduced. In NG 108-15 membranes, both opioid peptides and foetal-calf serum stimulated high-affinity GTPase activity in a pertussis-toxin-sensitive manner. These effects have previously been shown to be mediated by different G-proteins [McKenzie, Kelly, Unson, Spiegel & Milligan (1988) Biochem. J. 249, 653-659]. Suramin completely prevented the opioid-peptide-stimulated increase in GTP hydrolysis, but did not prevent the opioid peptide from binding to its receptor. Suramin, however, did not block the foetal-calf-serum-stimulated GTPase response. This selective action of suramin provides further evidence for distinct roles for two separate pertussis-toxin-sensitive G-proteins in signal transduction in NG 108-15 membranes and provides the first evidence for a selective effect of a drug on the functions of different G-proteins.     

Respiration-driven proton translocation in Thiobacillus versutus and the role of the periplasmic thiosulphate-oxidizing enzyme system

The periplasmic location of enzymes A and B of the thiosulphate-oxidizing multienzyme system of Thiobacillus versutus has been further confirmed by differential radiolabelling of periplasmic and cytoplasmic proteins. The stoichiometries of respiration-driven proton translocation in T. versutus were determined using the oxygen pulse and the initial rate methods. A value for the H⁺/O quotient (number of protons translocated per oxygen atom reduced) of about 2.8 was found for the oxidation of thiosulphate, and of about 2.5 for sulphite. The H⁺/O quotient for endogenous respiration was about 5.7. The data are shown to be in good agreement with the scheme proposed previously for thiosulphate oxidation by this organism. Proton generation during the oxidation of thiosulphate or sulphite is indicated to occur in the periplasm rather than by pumping across the cytoplasmic membrane. The results also suggest that a H⁺/O quotient of six occurs during NADH oxidation (from endogenous metabolism measurements) and that the terminal cytochrome oxidase, aa₃, does not function as a proton pump.Abbreviations DCCD dicyclohexyl carbodiimide - FCCP carbonyl cyanide p-trifluoromethoxyphenylhydrazone - HQNO 2-n-heptyl-4-hydroxyquinoline N-oxide - TMPD N,N,N,N-tetramethyl-p-phenylenediamine - IEF isoelectric focusing - HIC hydrophobic interaction chromatography - EAI ethyl acetimidate hydrochloride - IAI isethionyl acetimidate     

Dopamine Receptor Stimulation Does Not Affect Phosphoinositide Hydrolysis in Slices of Rat Striatum

The effect of dopamine receptor stimulation on the accumulation of labelled inositol phosphates in rat striatal slices under basal and stimulated conditions was examined following preincubation with [3H]inositol. Incubation of striatal slices with the selective D-1 agonist SKF 38393 or the selective D-2 agonist LY 171555 for 5 or 30 min did not affect the basal accumulation of labelled inositol mono-, bis-, tris-, and tetrakisphosphate. Resolution by HPLC of inositol trisphosphate into inositol-1,3,4-tris-phosphate and inositol-1,4,5-trisphosphate isomers revealed that under basal conditions dopamine did not influence the accumulation of inositol-1,4,5-trisphosphate. Depolarisation evoked by KCl, or addition of the muscarinic receptor agonist carbachol, produced a marked increase in the accumulation of labelled inositol phosphates in both the presence and absence of lithium. Addition of dopamine did not reduce the ability of KCl or carbachol to increase inositol phospholipid hydrolysis. In the presence of lithium, dopamine (100 microM) enhanced KCl-stimulated inositol phospholipid hydrolysis, but this effect appears to be mediated by alpha 1 adrenoceptors because it was blocked by prazosin. SKF 38393 (10 microM) or LY 171555 (10 microM) also did not affect carbachol-stimulated inositol phospholipid hydrolysis. These data, in contrast to recent reports, suggest that striatal dopamine receptors do not appear to be linked to inositol phospholipid hydrolysis.     

Irreversible Binding and Recovery of the Norepinephrine Uptake System Using an Alkylating Derivative of Norepinephrine

The effects of bromoacetylaminomenthylnorepinephrine (BAAN) on the sodium-dependent, high-affinity norepinephrine (NE) uptake system in rat brain synaptosomes and CNS neuronal cultures were investigated. BAAN inhibited [3H]NE uptake into synaptosomes in a dose- and time-dependent manner (IC50, 6.5 microM). Pretreatment of cortical synaptosomes or neuronal cells with BAAN alone, followed by washing to remove free drug, reduced the Vmax but did not alter the Km value for [3H]NE uptake. The BAAN-induced reduction in Vmax was attenuated by concurrent pretreatment with desipramine and blocked by the reaction of BAAN with dithiothreitol or cysteine. In contrast, BAAN was 19-fold less potent at inhibiting [3H]dopamine uptake in striatal synaptosomes, and no change in the Vmax or Km value for [3H]dopamine uptake was observed after a pretreatment with BAAN followed by washing. Furthermore, the irreversible beta-antagonist, bromoacetylalprenololmentane, was equipotent to BAAN for inhibiting [3H]NE uptake into cortical synaptosomes, but did not alter the Vmax or Km for [3H]NE after pretreatment. In neuronal cultures, BAAN inhibited sodium-dependent uptake of [3H]NE (IC50, 5.6 microM) with no effect on sodium-independent uptake. After pretreatment of cultures with 30 microM BAAN followed by washing, there was a 74% decrease in the Vmax for [3H]NE uptake. Following a 24-h lag period, uptake recovered to the control level within 48 h; however, recovery was completely blocked by cycloheximide. The data indicate that BAAN irreversibly binds to the [3H]NE uptake system in both CNS synaptosomes and neuronal cultures and may be a useful probe for studying the turnover of the [3H]NE uptake system.     

Pyruvate Dehydrogenase Activity in Osmotically Shocked Rat Brain Mitochondria: Stimulation by Oxaloacetate

Pyruvate dehydrogenase complex activity (PDHC) measured by CO2 release isotopic assay has generally been much lower than activity measured by the spectrophotometric arylamine acetyltransferase assay (ArAT). Decarboxylation of [1-14C]pyruvate was measured in osmotically shocked rat brain cortical mitochondria. Activity is dependent on the concentration of the substrate pyruvate. Activity of 74.6 units +/- 12.3 SD (n = 22) was observed at 4 mM pyruvate (1 unit = 1 nmol pyruvate decarboxylated/min/mg protein). Activity was dependent on added NAD, CoA, and thiamine pyrophosphate, implying increased mitochondrial permeability after osmotic shock. Freeze/thaw with sonication of the mitochondrial preparation reduced PDHC activity to 11.5 units +/- 3.0 SD (n = 4). Oxaloacetate produced a marked stimulation of activity. The optimal assay contained 3 mM oxaloacetate, and without oxaloacetate activity fell to 15.4 units +/- 9.9 SD (n = 8). These studies highlight the importance of optimal substrate concentrations in the CO2 release isotopic PDHC method. Higher PDHC activity is found with intact mitochondria and thus activity values should be interpreted in the light of the presence or absence of intact mitochondria in individual preparations.