Uptake inhibitors do not change the effect of imidazoline α2-adrenoceptor agonists on transmitter release evoked by single pulse stimulation in mouse vas deferens

Summary The present study was undertaken to compare the presynaptic interaction of neuronal noradrenaline uptake inhibitors with imidazoline and phenylethylamine ₂adrenoceptor agonists under two different conditions: at low and high noradrenaline concentrations in the biophase.Isolated mouse vasa deferentia were stimulated with trains of 7 pulses given at 0.2 Hz and the inhibition by the ₂-adrenoceptor agonists clonidine, -methylnoradrenaline, and UK-14,304 of twitch responses was measured in the absence and in the presence of either cocaine (12 mol/l) or desipramine (40 nmol/l). The effects were determined for the first (equivalent to single pulse stimulation) and the last stimulus of each train. Both uptake inhibitors antagonized the presynaptic inhibitory effects of imidazolines (clonidine and UK-14,304) on the last twitch; the effects on the first twitch remained unchanged. In contrast, the uptake inhibitors potentiated the inhibitory effect of the phenylethylamine (-methylnoradrenaline) on both the first and the last twitches.These results support the view that the concentration of noradrenaline in the biophase plays a decisive role in the inhibition by a₂-adrenoceptor agonists of the electrically evoked release of noradrenaline. Agonists that are not substrates of neuronal uptake (i.e., clonidine, UK-14,304) become less effective when noradrenaline is present in the biophase while substrates of neuronal uptake (i. e., -methylnoradrenaline) do not. The results argue against the hypothesis that uptake inhibitors interact directly with presynaptic ₂-adrenoceptors or act at some link between uptake and receptor sites. Send offprint requests to S. Guimarães at the above address     

Phase I study of 4′-deoxydoxorubicin (esorubicin) in children with malignant solid tumors

Summary 4 -Deoxydoxorubicin was given to 15 patients with drug-resistant pediatric malignant solid tumors with the objectives of determining the maximum tolerated dosage and dose-limiting toxicity. Maximum tolerated dosage was 36 mg/m₂ given IV once every 3 weeks. Dose limiting toxicity was myelosuppression, which was severe and prolonged. Therapeutic benefits were not observed for these patients.     

2-deoxy-D-glucose inhibits the antitumor effects of α-difluoromethylornithine on the growth of colon cancer in vivo

Summary The glycolytic inhibitor, 2-deoxy-D-glucose (2-DG), has been shown to inhibit the growth of certain cancers. -Difluoromethylornithine (DFMO) is an irreversible inhibitor of ornithine decarboxylase (ODC), the ratelimiting enzyme in polyamine biosynthesis. DFMO has been shown to inhibit cancer growth in a number of models. The present study was designed to investigate the effects of 2-DG alone and combined with DFMO on MC-26 mouse colon adenocarcinoma tumors growing in vivo. Twenty-eight male Balb/c mice were inoculated with 250,000 MC-26 cells, and then randomized into four groups of 7 each: group I served as control; group II received DFMO (3% in drinking water); group III received 2-DG (500 mg/kg/d IP); group IV received a combination of 2-DG and DFMO. Treatment began 5 days after tumor cell inoculation. MC-26 tumor area was reduced 73% by DFMO compared to a 24% reduction caused by 2-DG. The tumor weight was reduced 80% by DFMO and 52% by 2-DG. The tumor contents of DNA, RNA, and protein were significantly reduced by DFMO but not 2-DG. The tumor concentration of the polyamines putrescine and spermidine were reduced by DFMO alone or combined with 2-DG while spermine levels remained unchanged. 2-DG alone did not alter polyamine levels. These results indicate that both 2-DG and DFMO, when added as single agents, inhibit tumor growth. However, the addition of 2-DG to the DFMO regimen inhibited the antitumor effects of DFMO. Survival studies performed on MC-26 cells in vitro corroborated the antagonisms between DFMO and 2-DG that were shown in vivo.Dr. Upp was awarded a fellowship grant from the American Cancer Society Texas Division.     

Testosterone in a Cyclodextrin-Containing Formulation: Behavioral and Physiological Effects of Episode-like Pulses in Rats

Testosterone, administered in the form of an inclusion complex with 2-hydroxypropyl--cyclodextrin by subcutaneous injection, enters the circulation in a manner markedly similar to the natural episodic release by the testes. The effects of a regimen of once-a-day administration of complexed testosterone to adult (castrated or intact) rats and to senescent (intact) rats were investigated. Although this procedure left the castrated animals with concentrations of circulatory hormone far below physiological levels for much of the day, a significant improvement in androgen-sensitive behavior and physiology was obtained. Furthermore, the testosterone effects were more pronounced when high doses were used periodically rather than when the same total amount of testosterone was equally divided among doses. The same supplementation to intact rats intensified androgen-sensitive behavior and physiology over normal levels. In senescent rats uniform pulses of the testosterone complex also improved behavior and physiology. Specifically, spermatogenesis was stimulated and, notably, the treatment increased muscle weight without substantial enlargement of the prostate. Since the testosterone–cyclodextrin complex also can be effectively administered as a sublingual tablet, the data suggest that similar regimens may be recommended for elderly men suffering from decreases in muscle mass.     

Radioreceptor Assay of Metoprolol in Human Plasma: Comparison with an Enantiospecific High-Performance Liquid Chromatographic (HPLC) Procedure

Plasma concentrations of metoprolol after acute and repetitive administration of R/S-metoprolol to healthy volunteers were measured by a -adrenoceptor subtype-specific radioreceptor assay (RRA) and by an enantiospecific high-performance liquid chromatographic (HPLC) method. In the RRA, R/S-metoprolol showed a 20-fold ₁-subtype selectivity: the S-( – )-enantiomer was 35-fold more potent than the R-( + )-enantiomer. A comparison between S-( – )-metoprolol concentrations detected in the plasma samples by HPLC and those detected by RRA yielded a 1/1 relationship, indicating that active metabolites are not present to a significant extent. These results were independent of the widely scattering metabolic clearance of metoprolol (with the potential of differences in the rate and extent of formation of active metabolites) in the volunteers. In general, HPLC methods can be validated by comparison with RRA in order to clarify whether active metabolites are present and—on the basis of the K_i value from RRA—whether the detection limit of the physicochemical procedure is sufficient to cover the therapeutically relevant range.     

Distribution of 2-naphthol sulphotransferase and its endogenous substrate adenosine 3′-phosphate 5′-phosphosulphate in human tissues

The activity of sulphotransferase towards 2-naphthol and the concentration of its endogenous substrate, adenosine 3'-phosphate 5'-phosphosulphate (PAPS), have been measured in five specimens of human liver, lung, and kidney, and the mucosa from the ileum and the ascending, descending and sigmoid colon. The activity of 2-naphthol sulphotransferase (mean nmol.min-1.mg-1 protein) was 1.82 (liver); 0.034 (kidney); 0.19 (lung); 0.64 (ileum); 0.47 (ascending colon); 0.50 (descending colon); 0.40 (sigmoid colon). The concentration of PAPS (mean nmol.g-1 wet tissue) was 22.6 (liver); 4.8 (kidney); 4.3 (lung); 12.8 (ileum); 8.1 (ascending colon); 7.5 (descending colon); 6.2 (sigmoid colon). The concentration of PAPS and the activity of 2-naphthol sulphotransferase were higher in the liver than in the extrahepatic tissues. There was significant difference between ileum and ascending colon, both the activity of sulphotransferase and the concentration of PAPS being higher in the former. 2-Naphthol sulphotransferase activity and the concentration of PAPS have consistent distribution patterns. Differences between the tissues studied were more marked for sulphotransferase than for its endogenous substrate.     

Evidence for monoaminergic involvement in triadimefon-induced hyperactivity

Triadimefon is a triazole fungicide that produces hyperactivity in both mice and rats similar to that seen following administration of compounds with catecholaminergic activity (e.g., d-amphetamine). To determine whether the triadimefon-induced hyperactivity is due to an action on CNS catecholaminergic systems, we evaluated the effects of combined treatment of triadimefon with either the tyrosine hydroxlase inhibitor d,l--methyl-p-tyrosine methyl ester HCl (MPT) or the amine depletor reserpine. Adult male Long-Evans hooded rats, approximately 70 days of age were used. Dosage-effect functions were determined for MPT (0–200 mg/kg IP), reserpine (0–2.5 mg/kg IP), d-amphetamine (0–3 mg/kg IP), and methylphenidate (0–40 mg/kg IP). Motor activity was measured as photocell interruptions in figure-eight mazes. The interaction between triadimefon and MPT was determined with the following groups: 1) vehicle control; 2) 200 mg/kg triadimefon PO; 3) 100 mg/kg MPT; and 4) both MPT and triadimefon. A similar design was used to determine the interaction between triadimefon and reserpine (0.62 mg/kg), MPT and d-amphetamine (1.5 mg/kg), and reserpine and methylphenidate (5.0 mg/kg). In the first experiment MPT did not block the increased motor activity produced by triadimefon (i.e., both triadimefon alone and MPT in combination with triadimefon produced significant increases in motor activity). MPT did, however, block d-amphetamine-induced hyperactivity. Since MPT did not antagonize the effect of triadimefon, these data suggest that increased motor activity produced by triadimefon is not mediated through release of newly synthesized catecholamines. In contrast, pretreatment with reserpine blocked the hyperactivity induced by both triadimefon and methylphenidate, which suggests that triadimefon-induced hyperactivity may be due to an interaction with CNS catecholamines stored in reserpine-sensitive pools.The research described in this article has been reviewed by the Health Effects Research Laboratory, US Environmental Protection Agency, and approved for publication. Approval does not signify that the contents necessarily reflect the views and policies of the Agency nor does mention of trade names or commercial products constitute endorsement or recommendation for use. Presented in part at the Annual Meeting of the Society for Neuroscience, New Orleans, LA, November, 1987     

Behavioural effects of selective μ-, κ-, and δ-opioid agonists in neonatal rats

The behavioural effects of selective -, - and -opioid agonists in 5-, 10- and 20-day-old rats were investigated by observational analysis. The predominant response to -agonists was behavioural depression. High doses (10 mg/kg IP) of morphine and DAGO (d-Ala², NMe-Phe⁴, Glyol⁵-enkephalin) produced overt sedation in all the age groups and also induced catalepsy which was particularly apparent in the 5- and 10-day-old animals. These compounds did not produce any signs of behavioural activation in the neonatal rats. In contrast, rat pups treated with the -agonists U50,488H and PD 117,302 (1,10 mg/kg IP) exhibited marked hyperactivity with increases in wall-climbing and locomotion. Sedative effects of the highest dose of the -agonists began to emerge, however, as the animals grew older, resulting in significant decreases in behaviours such as gnawing and grooming at 20 days of age. The -agonist (+)-tifluadom (0.1–10 mg/kg), but not its corresponding (-)-isomer, produced an increase in activity in 5-day-old rats, thus extending the observations made with U50,488H and PD 117,302 and establishing the stereoselective nature of the response. The involvement of -receptors in opioid-induced hyperactivity was further substantiated by using a variety of opioid antagonists. In this context, the increase in activity induced by U50,488H (10 mg/kg) in 5-day-old neonates was attenuated by naltrexone (1 mg/kg IP) but not by larger doses (10 mg/kg) of either M8008 (which has low affinity for -receptors) or the selective -receptor antagonist ICI 174,864. Finally, DPDPE (d-Pen², d-Pen⁵-enkephalin) which acts selectively at -opioid receptors, did not exert any behavioural effects in either the 5-, 10- or 20-day-old rat pups at doses of up to 10 mg/kg. These results demonstrate behavioural effects of - and -but not -agonists in neonatal rats. There is a clear differentiation between - and -receptor effects and both - and -mediated behaviours show dissimilarities from the adult profile.     

The effects of clonidine and yohimbine on human information processing

The effects of clonidine and yohimbine on human information processing were tested in six normal volunteers ages 18–30 years. Subjects were tested in a pre-post design with sessions conducted at weekly intervals. Three drug conditions were: Placebo (lactose), 0.2 mg clonidine, and 30 mg yohimbine. Two choice reaction time (RT) tasks were used. One was a stimulus evaluation-response selection task (SERS) that has been shown to be sensitive tod-amphetamine, methylphenidate and scopolamine. The other task was to assess stimulus pre-processing and used spatial frequency as a discriminative stimulus. The principle finding was that clonidine slowed RT; this effect was significant for both tasks. In contrast, yohimbine tended to speed RT, but the effects were significant only for the spatial frequency task on some analyses while not for others. RTs to high spatial frequency stimuli were speeded more than for low spatial frequency. The effects of these two NE drugs were compared with findings withd-amphetamine and scopolamine and interpreted within the framework of a serial information processing model proposed by Callaway (1983). Specifically, it is suggested that yohimbine and clonidine affect an early pre-processing stage.