Tremorigenic Effect and Inhibition of Tryptamine and Serotonin Receptor Binding by β-Carbolines

Abstract: The abilities of some naturally occurring β-carbolines (BCs), dihydro-BCs and tetrahydro-BCs to inhibit the specific binding of ³H-tryptamine (TA), ³H-serotonin (5-HT) and ³H-ketanserine to rat brain membranes and to induce tremor in mice were studied. These compounds, particularly DHBCs and BCs, showed higher affinity for TA binding sites than to 5-HT₁ or 5-HT₂ binding sites inhibiting the former at nanomolar and the two latter ones at micromolar or high micromolar concentrations. The K_i values for norharmane, harmaline and harmine (17, 18 and 74 nM, respectively) for TA sites indicate the highest affinity so far described for natural β-carbolines to any receptor sites and thus may indicate their major site of action. Among the BC derivatives studied, the before mentioned harmala alkaloids were the most potent inducers of tremor in mice, although the orders of the tremorogenic potency and the binding to TA site did not correlate. It is suggested that especially the tremorigenic effect of BC derivatives is partly based on the binding to specific tryptamine receptors.     

Polyene antibiotics increase the ionic permeability of synaptosomal plasma membranes

The effects of antifungal heptaene antibiotics candicidin and amphotericin B were investigated in isolated cerebral cortical nerve terminals (synaptosomes). The synaptosomes were incubated with candicidin or amphotericin B in the presence or absence of external Ca2+. Candicidin (0.4-0.8 I.U./mL) increased intrasynaptosomal free Ca2+ significantly. This increase was not significantly suppressed by 30 microM verapamil or 2 microM nifedipine. In the absence of extrasynaptosomal Ca2+ intrasynaptosomal free Ca2+ was not changed by candicidin. Amphotericin B increased intrasynaptosomal free Ca2+ as well. Candicidin (0.05-0.6 I.U./mL) increased the respiration rate up to 3.5-fold above the basal rate. This response was not affected by the absence of extracellular Ca2+. Ouabain completely blocked the increase of respiration caused by candicidin, whereas tetrodotoxin was ineffective. The plasma membrane depolarized in a dose-dependent manner after candicidin (0.2-0.8 I.U./mL). The mitochondrial membrane potential was little affected and only at the highest concentrations. The results indicate that heptaene polyenes increase synaptosomal ionic permeability, which is reflected in increased Ca2(+)-influx and accelerated respiration. The increment in synaptosomal free calcium takes place probably as a nonspecific leak via typical polyene-cholesterol channels. The respiration is accelerated by increased Na(+)-permeability through the plasma membrane which stimulates the function of Na+, K(+)-ATPase and thus increases the energy demand.     

Mitotic index in the subrenal capsule assay as an indicator of the chemosensitivity of ovarian cancer

The subrenal capsule assay (SRCA) is used in clinical oncology to assess the sensitivity of individual malignant tumors to various anticancer agents and their combinations. Mitotic indices reflect cancer cell proliferation and have prognostic value in epithelial neoplasms, including ovarian carcinoma. We combined the two tests (SRCA, mitotic index) by evaluating the numbers of mitotic figures per square millimeter of neoplastic epithelium (M/V) in paraffin-embedded tumor samples after SRCA. The M/V index was compared with the tumor size measurement (dTS), which is used in conventional SRCA to predict the drug response. Histology examination showed insignificant changes in the size of tumor transplants due to host reaction but disclosed a number of potential errors in the use of dTS to evaluate transplant growth and drug effects. In our series of 62 patients with advanced ovarian carcinoma the M/V value was superior to the dTS in explaining the clinical response after 6 months as assessed at second-look laparotomy. Patients showing no response had significantly higher M/V values than did those displaying complete or partial responses (P < 0.033). The use of 6 mitotic figures/mm² as a limit differentiating responders from nonresponders resulted in an overall predictive accuracy of 79% in the logistic regression analysis. In comparison to the FIGO stage, residual tumor size, and the dTS, the M/V value obtained for the cytostatic combination given to the patient was the single most significant factor predicting the 6-month clinical response. The results indicate that the combined use of the M/V index and SRCA is a promising new approach to prediction of the drug response in ovarian adenocarcinoma. Received: 20 October 1996 / Accepted: 9 June 1997     

Feed intake after inhibition of histamine catabolism

It has been reported that histamine and its precursor histidine have a feeding-suppressing effect. The present study shows that metoprine (20 mg/kg i.p.), which increases brain histamine levels by inhibiting its catabolism, also significantly decreases daily feed intake in rats. The reduced feed consumption is evident in different states of water balance. These results agree with an involvement of histaminergic systems in the regulation of feeding behaviour.     

3H-dopamine uptake and 3H-haloperidol binding in striatum after administration of methyl mercury to rats

Methyl mercury inhibits dopamine (DA) and serotonin (5-HT) uptake by brain synaptosomes and decreases antagonist binding to striatal dopaminergic D₂ receptors in vitro. To assess the effects in vivo, adult rats were given methyl mercury, either as a single dose (10 mg/kg by gavage) or a cumulative total dose of 50 mg/kg in 2 weeks. The repeated dosing decreased body weight and caused neuromuscular dysfunction. In spite of this overt toxicity, neither ³H-DA uptake nor ³H-haloperidol binding changed in striatal synaptosomes. There were no significant alterations in ³H-5-HT uptake by hypothalamic synaptosomes or ³H-flunitrazepam binding in cerebellar synaptosomes. The results suggest that monoaminergic synapses and the benzodiazepine binding sites, associated with cerebellar GABA receptors, remain functionally normal at doses of methyl mercury that are otherwise toxic. The results also emphasize the importance of due care when extrapolating cellular or biochemical data to the level of the whole organism.     

Effect of anticonvulsant drugs on (35S)t-butylbicyclophosphorothionate binding in vitro and ex vivo

Using several concentrations of eight anticonvulsant drugs in clinical use (carbamazepine, clonazepam, phenytoin, phenobarbital, ethosuximide, primidone, sodium valproate, and D,L-gamma-vinyl GABA), we studied their abilities in vitro to displace (35S)t-butylbicyclophosphorothionate (35S-TBPS) from its binding site in a homogenate of rat brain. Thereafter ethosuximide (150 mg/kg), phenobarbital (30 mg/kg), clonazepam (0.3 mg/kg), or phenytoin (100 mg/kg) was injected intraperitoneally into rats for 16-20 days; and the effect of drug administration on 35S-TBPS binding was studied in the cortex and hippocampus ex vivo. Phenobarbital (100 microM, P less than 0.001), ethosuximide (500 microM, P less than 0.001), and phenytoin (40 microM, P less than 0.001) decreased the specific 35S-TBPS binding in vitro by 10-16%. After drug administration of phenobarbital (concentration in plasma 168 microM), the number of binding sites decreased and the binding affinity (P less than 0.05) in the cortex increased. Other anticonvulsants did not modulate 35S-TBPS binding in vitro at the concentration analogous to therapeutic plasma levels or ex vivo at the dose used. These results suggest that the use of phenobarbital may modulate the TBPS binding site, but the role of the present findings in the anticonvulsant action of phenobarbital needs to be further studied.     

Drinking water mutagenicity and gastrointestinal and urinary tract cancers: an ecological study in Finland.

OBJECTIVES. The purpose of this study was to investigate the relationship between exposure to mutagenic drinking water and cancers of the gastrointestinal and urinary tract. METHODS. Past exposure to drinking water mutagenicity was assessed in 56 Finnish municipalities for the years 1955 and 1970. The cases of bladder, kidney, stomach, colon, and rectum cancers were derived from two periods (1967 to 1976 and 1977 to 1986). Age, sex, social class, urban living, and time period were taken into account in the Poisson regression analysis. RESULTS. Statistically significant exposure-response association was observed between exposure and incidence of bladder, kidney, and stomach cancers. In an ordinary municipality using chlorinated surface water, this exposure would indicate a relative risk of 1.2 for bladder cancer and of 1.2 to 1.4 for kidney cancer compared with municipalities where nonmutagenic drinking water was consumed. CONCLUSIONS. The acidic mutagenic compounds present in drinking water may play a role in the etiology of kidney and bladder cancers, but, because the results are based on aggregate data, they should be interpreted with caution.     

The clinical indications for identical pathogenesis of isolated and non-isolated testicular relapses in acute lymphoblastic leukaemia

In the present population-based study, we compared the clinical data of testicular relapses with and without concurrent bone marrow relapse and clinical data of the relapses in other locations among boys with acute lymphoblastic leukaemia (ALL), in order to study the possible evidence of early sequestration and local regulation of leukaemic lymphoblast in the testis of humans. The results suggest that the pathogenesis of isolated testicular relapse (T) and testicular relapse with a concurrent bone marrow relapse (T+BM) is likely to be similar. Isolated and non-isolated testicular relapses appeared late after the achievement of remission (T 34±16 months, T+BM 32±15 months) in ALL compared to relapses in other locations (CNS 23±11 months, BM 25±19 months). The better prognosis after testicular relapses (estimated second event free survival probability, 2-EFS: T 0.63, T+BM 0.32) compared to bone marrow relapse (2-EFS: BM 0.13) further suggests that testicular relapse with a concurrent bone marrow relapse possibly originates from the isolated testicular relapse, and that the isolated testicular relapse is a separate entity and not a manifestation of systemic recurrence. Higher frequencies of isolated and non-isolated testicular relapses (T 9%, T+BM 5%) were observed among boys with onset of ALL in early puberty (10-12y) compared to those among younger (T 4%, T+BM 2%) and older (T 0%, T+BM 0%) boys. The late occurrence, the possible association with hormonal maturation and the good prognosis after testicular relapses suggest a possible local regulation of the residual leukaemic lymphoblast in human testis.