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.     

Effect of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) on tryptophan and glucose homeostasis in the most TCDD-susceptible and the most TCDD-resistant species,guinea pigs and hamsters

 We have previously reported that in rats 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) lethality is associated (although not necessarily causally) with changes in brain serotonin (5-HT) metabolism. In the present study, we have examined whether this holds for other species by comparing the effect of TCDD in the most TCDD-susceptible and the most TCDD-resistant species, guinea pigs and hamsters, respectively. Body weight gain of guinea pigs exposed to TCDD (0.3–2.7 μg/kg) diminished dose dependently, while the effect was marginal in hamsters (900–4600 μg/kg). Brain 5-hydroxyindoleacetic acid (the main metabolite of brain 5-HT), brain tryptophan (the precursor amino acid of 5-HT), and plasma free and total tryptophan were not affected at any dose in guinea pigs. In contrast, 4 days after exposure, the levels of plasma free and total tryptophan were consistently increased in hamsters. These, as well as brain tryptophan, were still elevated 10 days after exposure. TCDD did not affect plasma glucose level in either species. Liver glycogen was decreased in a dose-dependent manner in TCDD-treated guinea pigs as well as in their pair-fed controls on day 10. There was no change in liver glycogen in hamsters. The activity of the gluconeogenic enzyme, phosphoenolpyruvate carboxykinase was only depressed in hamsters by all doses of TCDD. We conclude that changes in tryptophan metabolism or in carbohydrate homeostasis cannot explain the wide interspecies differences in susceptibility to the acute lethality of TCDD, although they may correlate with some aspects of its toxicity in certain species. Received: 12 January 1995 / Accepted: 27 February 1995     

Office and laboratory blood pressures as predictors of daily blood pressure level in normotensive subjects and borderline and mild hypertensive subjects

A series of standardized laboratory tests [10 min sitting and supine, 9 min standing, dynamic; cycle ergometer (ERG) and isometric exercise; handgrip (HG)] were performed during intra-arterial blood pressure (BP) recording in 97 healthy unmedicated men, initially classified as normotensive (NT, n = 34), borderline hypertensive (BHT, n = 29) or mildly hypertensive (HT, n = 34) by repeated office blood pressure (OBP) measurements. After testing, a 24-h intra-arterial ambulatory BP (IABP) recording was obtained while subjects performed their normal activities. Day and night periods were analysed as well as 24-h averages for systolic BP (SBP) and diastolic BP (DBP) using Pearson correlations and multiple linear regressions. In normotensive subjects, the supine SBP predicted IABP measurements best (r range 0·39–0·69, P<0·05–0·001). In multiple regression, supine SBP explained 49% of 24-h SBP variance (F = 12·4, P = 0·001). For BHT, supine SBP was also the best predictor (r range 0·09–0·64, P NS to P<0·001), and it explained 37% of 24-h SBP variance (F = 15·6, P = 0·0005). In HT, ERG DBP correlated best with IABP (r range 0·52–0·75, P<0·01–0·001). ERG SBP explained 49% of 24-h SBP (F = 31·0, P = 0·0000) and ERG DBP explained 56% of 24-h DBP (F = 35·4, P = 0·0000) variance. Laboratory BP correlations were generally better with day than with night measurements. OSBP correlated moderately well with IABP in NT, and weakly in BHT and HT; ODBP instead correlated with IABP in NT and HT but not significantly in BHT. In conclusion, OBP is less closely related to IABP than laboratory BP, but even laboratory BP generally explains less than 50% of IABP variance. Stressors such as exercise are useful only in HT. For BHT, the prediction of IABP with laboratory measures was even weaker than in other groups, and thus ambulatory measurements cannot be replaced by short-duration laboratory measurements and stress tests.     

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.