Comparison of the time course of the anorectic effect of fenfluramine and amphetamine with drug levels in blood

TPH2 in the Dorsal Raphe Nuclei Regulates Energy Balance in a Sex-Dependent Manner

AbstractCentral 5-hydroxytryptamine (5-HT), which is primarily synthesized by tryptophan hydroxylase 2 (TPH2) in the dorsal Raphe nuclei (DRN), plays a pivotal role in the regulation of food intake and body weight. However, the physiological functions of TPH2 on energy balance have not been consistently demonstrated. Here we systematically investigated the effects of TPH2 on energy homeostasis in adult male and female mice. We found that the DRN harbors a similar amount of TPH2+ cells in control male and female mice. Adult-onset TPH2 deletion in the DRN promotes hyperphagia and body weight gain only in male mice, but not in female mice. Ablation of TPH2 reduces hypothalamic pro-opiomelanocortin (POMC) neuronal activity robustly in males, but only to a modest degree in females. Deprivation of estrogen by ovariectomy (OVX) causes comparable food intake and weight gain in female control and DRN-specific TPH2 knockout mice. Nevertheless, disruption of TPH2 blunts the anorexigenic effects of exogenous estradiol (E2) and abolishes E2-induced activation of POMC neurons in OVX female mice, indicating that TPH2 is indispensable for E2 to activate POMC neurons and to suppress appetite. Together, our study revealed that TPH2 in the DRN contributes to energy balance regulation in a sexually dimorphic manner.

Serotonin and the regulation of mammalian energy balance

Maintenance of energy balance requires regulation of the amount and timing of food intake. Decades of experiments utilizing pharmacological and later genetic manipulations have demonstrated the importance of serotonin signaling in this regulation. Much progress has been made in recent years in understanding how central nervous system (CNS) serotonin systems acting through a diverse array of serotonin receptors impact feeding behavior and metabolism. Particular attention has been paid to mechanisms through which serotonin impacts energy balance pathways within the hypothalamus. How upstream factors relevant to energy balance regulate the release of hypothalamic serotonin is less clear, but work addressing this issue is underway. Generally, investigation into the central serotonergic regulation of energy balance has had a predominantly “hypothalamocentric” focus, yet non-hypothalamic structures that have been implicated in energy balance regulation also receive serotonergic innervation and express multiple subtypes of serotonin receptors. Moreover, there is a growing appreciation of the diverse mechanisms through which peripheral serotonin impacts energy balance regulation. Clearly, the serotonergic regulation of energy balance is a field characterized by both rapid advances and by an extensive and diverse set of central and peripheral mechanisms yet to be delineated.

Effects of chronic fenfluramine administration on hypothalamic neuropeptide mRNA expression

Appetite suppressants lose efficacy when given chronically; the mechanisms are unknown. We gave male rats once-daily dl-fenfluramine (dl-FEN, 5 mg/kg, i.p.) injections for 15 days and measured mRNA expression of corticotropin releasing factor (CRF), neuropeptide Y (NPY) and proopiomelanocortin (POMC) in hypothalamic neurons on days 1, 2 and 15. dl-FEN decreased food intake on days 1-2 but not on day 15. The drug increased CRF mRNA and decreased NPY mRNA on days 1-2; on day 15, NPY mRNA was normal, but CRF mRNA remained elevated. No changes occurred in POMC mRNA. Thus, only the NPY mRNA response to dl-FEN correlated with changes in food intake over time in a manner consistent with the known effects of NPY on food intake.

Effects of positional and geometrical isomerism on the biological activity of some novel oxazolidinones

Some novel oxazolidinone derivatives with benzotriazole as pendant have been synthesized and tested for antibacterial activity. Linearly attached benzotriazole derivative showed more potency compared to angular one in vitro. Out of E/Z-isomers of angularly attached derivatives E-isomer was found to be more potent than Z-isomer. Either less active or inactive molecules were obtained, when benzotriazole was replaced with benzimidazole, benzthiazole, or benzoxazole. Finally, thioacetamide analogue of linear compound gave a lead having activity similar to linezolid in vitro.

Mouse feeding behavior: ethology, regulatory mechanisms and utility for mutant phenotyping

Ingestive behaviors, feeding and drinking, constitute unconditioned, obligatory functions that are tightly regulated in the rodent according to demands of the external and internal milieu. Dependent measures of food intake have been used extensively in rats to infer the identity and function of neurochemical pathways, which mediate energy balance. A recent interest in application of appetitive measures in mice can be attributed jointly to the discovery of novel markers of energy balance in genetically obese mice as well as systematic targeting of known feeding regulatory pathways in bioengineered mutant mice. Accordingly, this review will attempt to provide the reader interested in behavioral phenotyping of knockout or transgenic mice with information regarding the ethology of mouse eating behavior, known mechanisms of appetitive regulation and examples of successes and pitfalls encountered when studying food intake in mutant mice.

Synthesis and antitubercular activity of 3-aryl substituted-2-[1H(2H)benzotriazol-1(2)-yl]acrylonitriles

A series of 22 3-aryl substituted-2-(1H(2H)-benzotriazol-1(2)-yl)acrylonitriles was synthesized for a preliminary in vitro evaluation of antitubercular activity according to an international program with the Tuberculosis Antimicrobial Acquisition & Coordinating Facility (TAACF). This work reports the synthetic approach and analytical and spectroscopic characterization (UV, IR, 1H- and 13C-NMR) of all compounds synthesized. Several compounds showed an interesting activity in the preliminary screening with a percent growth inhibition of the virulent Mycobacterium tuberculosis between 40 and 99% at the concentration of 12.5 microg/mL. The most effective derivatives E-5a and E-5e were also tested against M. avium in vitro.

Determination of d-amphetamine in biological samples using high-performance liquid chromatography after precolumn derivatization with o-phthaldialdehyde and 3-mercaptopropionic acid

An HPLC method is described for the determination of amphetamine using fluorometric detection after derivatization with o-phthaldialdehyde and 3-mercaptopropionic acid. This procedure is more sensitive (detection limit 370 fmol in microdialysate buffer standards, 1.5 pmol in extracted plasma and tissue samples) than most of the previous methods described for the determination of amphetamine with HPLC-fluorescence detection. Due to the stability of the derivative it is also suitable for autosampling after manual derivatization. Investigators currently using o-phthaldialdehyde derivatization and fluorometric detection for amino acid determination should be able to rapidly implement this method.

Are interspecies comparisons in the toxicity of centrally acting drugs valid without brain concentrations? A commentary

Many pharmacological and toxicological studies of centrally acting drugs are undertaken in animals at doses expressed in mg.kg-1, and the results extrapolated to the clinical dose in man. Safety margins based on such no or lowest effect levels may have little relevance since they do not take into account differences in the kinetics and metabolism of the compounds. These deviations are accentuated when extremely high doses are used, and saturation of metabolism occurs.

The use of kinetic-dynamic interactions in the evaluation of drugs

Deterred by the complexity of the mathematics, pharmacologists and clinical pharmacologists have only recently appreciated the usefulness of pharmacokinetics in drug development. Now unfortunately, although the vernacular of the science is known, often the meaning behind the words is lost. It is often assumed that drug levels are linearly related to drug action. Frequently they are not. This review shows, with reference to psychotropic drugs, how, in simple terms, it is possible to relate pharmacokinetics with pharmacodynamics, and how such relationships may provide a greater insight into drug activity and enhance drug development. Assuming that an equilibrium exists between the drug in plasma levels, and at the site of action, the same Michaelis-Menten equations used to relate effect to drug receptor binding can be used for drug level-dynamic interactions. A number of these relationships have been published and are discussed in terms of their derivation and their limitations. The graphical and computerised methods to create complete Emax curves are described and how the parameters of maximal effect, potency, variability and slope can be measured. When the drug is not in equilibrium with its site of action, hysteresis occurs and drug levels are out of phase with activity. Anticlockwise hysteresis, that is, activity increasing with time for a given drug level, can be caused by uptake into an active site, active metabolites, cascade activity, and sensitisation whilst clockwise hysteresis, in which activity decreases with time, can be caused by tolerance, active antagonistic metabolites, learning effects and feedback regulation. Attempts to relate simultaneously kinetics and dynamics by Link models can be difficult and not always necessary. It is assumed in therapeutic drug monitoring that individuals will show the same response for a given drug level. On the contrary, differences in individual subject sensitivity to drugs measured by kinetic-dynamic relationships may provide a greater understanding of the disease itself.

Experimental manipulations of eating: advances in animal models for studying anorectic agents

The material set out in this text has been designed to show the wide range of procedures which have the capacity to modify eating behavior--to produce hyper- or hypophagia, to alter the profile of eating patterns, or to adjust dietary preferences and selection. Accordingly, in investigating anorectic drugs it seems necessary to observe the effects of drug actions in a variety of experimental models. This strategy will provide a more complete description of the effect of a drug, will throw light on the mechanism of action, and will provide a more realistic base for predicting the effects of drugs in man.

Fenfluramine discrimination in obese and lean Zucker rats: serotonergic mediation of effect

Genetically obese Zucker rats and their lean littermates were trained to discriminate between the stimulus properties of 2.0 mg/kg fenfluramine and its vehicle in a two-lever, food-motivated operant task. Both groups learned the discrimination at the same rate and all rats showed a dose-related decrease in discriminative performance with lower fenfluramine doses. Analysis of the dose-response curves indicated an ED50 for the obese rats of 0.56 mg/kg and for the lean group of 0.42 mg/kg. Time-course experiments indicted that the obese rats maintain errorless discrimination through 90 min post-injection but discriminate significantly less than the lean rats at 960 min post-administration. These results suggest a similar sensitivity to fenfluramine in obese and lean rats with a difference in the time-course of drug action. Pre-treatment with the specific serotonin receptor antagonist pirenperone significantly attenuated fenfluramine discrimination in lean rats without a similar effect in the obese rats. Possible reasons for this observation are offered.

Serotoninergic mechanisms in human feeding: the pharmacological evidence

This paper reviews the evidence of serotoninergic mechanisms in human feeding by considering the effects of 5-HT agonists, precursors and receptor antagonists on hunger, food intake and weight change in normal volunteers, obese people and psychiatric patients. Although there is compelling evidence for a serotonin (5-HT) mechanism being involved, the paper highlights the considerable individual variation in response to pharmacological manipulation of 5-HT. Such variation may reflect differences in the bio-availability of the drugs used. Subtle psychological factors may also play a role in blurring the pharmacological evidence for 5-HT involvement in the highly complex activity of human feeding.

Dissociation of the anorectic actions of 5-HTP and fenfluramine

The possible peripheral anorectic actions of 5-hydroxytryptophan (5-HTP) and fenfluramine were examined in food-deprived rats. In a 1-h feeding test the peripherally acting 5-HT antagonist, xylamidine, attenuated the reductions in food intake induced by 5-HT and 5-HTP but not fenfluramine. Thus, the anorectic action of 5-HTP appears to be mediated in part by peripheral 5-HT receptors. Microstructural analyses showed that 5-HTP and fenfluramine induced decreases in eating rate and bout size. Xylamidine reversed the effect of 5-HTP on eating rate, and induced a slight increase in bout size in its own right. Therefore, the peripheral effect of 5-HTP appears to be a slowing of eating rate. No effects of xylamidine on fenfluramine induced changes in feeding were observed. The results indicate a dissociation of the anorectic effects of 5-HTP and fenfluramine based on a peripheral action of 5-HTP. The peripheral action of 5-HTP differs from the previously reported reductions in bout size and bout duration induced by 5-HT. Possible mechanisms for this difference in the peripheral actions of 5-HT and 5-HTP are discussed.

The effect of previous d-amphetamine treatment on the disposition and lethality of fenfluramine in the rat

In an earlier study, it was found that a 15-day ip postfeeding session d-amphetamine treatment rendered an apparent "tolerance" to the feed intake suppressant effects of fenfluramine. The purpose of the present study was to determine if such d-amphetamine treatment altered the disposition of fenfluramine in a way which might account for this decrement in the feed intake suppressant effect of fenfluramine. In addition, the effect of d-amphetamine on fenfluramine toxicity was also examined in an attempt to further characterize and correlate fenfluramine dispositional changes. It was found that plasma and, to some extent, brain concentrations of fenfluramine were elevated in the d-amphetamine-treated rats as compared to a saline control group. The acute, ip LD50 for fenfluramine in d-amphetamine-treated rats was 68 mg/kg (95% CI = 64.8 to 71.4), a value significantly lower than that observed in the saline-treated animals (97 mg/kg; 95% CI = 93.3 to 100.9). The overall results of this study suggest that the anorectic tolerance conferred toward fenfluramine by previous subchronic treatment with d-amphetamine does not result from decreased plasma or brain concentrations of fenfluramine. In fact, such concentrations are increased by prior d-amphetamine treatment, and this increase may in part account for the increased lethality of fenfluramine observed in these animals.

Protein and carbohydrate self-selection: modification of the effects of fenfluramine and amphetamine by age and feeding regimen

Age and daily restricted feeding are two frequently manipulated procedural variables that have been shown to alter dietary self-selection of protein and carbohydrate in rats. This study examined whether age and restricted feeding could further interact with drugs such as fenfluramine and amphetamine that are used to manipulate dietary self-selection. At the time of peak blood levels, fenfluramine spared relative intake of protein (as reflected in an increase in %P-E ratio of protein to total energy consumed). This effect, however, was significant at only some doses of fenfluramine and in some groups. At the times of peak blood levels of amphetamine, sparing of protein intake was never observed. In contrast, amphetamine tended to suppress protein intake (decrease in %P-E). This effect was dose-related (0.5, 1.0 and 2.0 mg/kg) in the adult, free-feeding rats, but not apparent in food-restricted rats. Consequently the effect of drugs on the self-selection of protein and carbohydrate diets is influenced by both age and feeding regimen. These results have implications for proposed neurochemical and hormonal hypotheses of protein and carbohydrate regulation as well as the design and interpretation of self-selection experiments.

Effects of d-amphetamine and fenfluramine on feeding pattens and activity of obese and lean Zucker rats

The effects of two doses of d-amphetamine and fenfluramine on male Zucker rats maintained ad lib on solid and liquid diets were investigated using the technique of meal pattern analysis. Amphetamine-induced anorexia was of short duration in both obese and lean rats. In the lean rats, anorexia was followed by rebound feeding resulting in little or no reduction in total daily intake. The drug reduced meal sizes of obese but not lean rats and caused a transient decrease in meal frequency. Increased spontaneous activity paralleled the decreased food intake. In contrast, anorexia following fenfluramine was greater, more prolonged and of equivalent magnitude in obese and in lean rats. No rebound feeding was observed. Reduction in intake was achieved primarily by changes in meal size rather than in meal frequency. These data demonstrate that food intakes of genetically obese Zucker rats are more susceptible to the action of d-amphetamine than those of lean rats, and are consistent with reports of differential neurotransmitter levels in the obese and lean rats.

Amphetamine-induced hypodipsia and its implications for conditioned taste aversion in rats

According to the conditioned anorexia hypothesis, conditioned taste aversions occur when flavour stimuli are classically conditioned to the anorexigenic or hypodipsic effects of drugs. The effects on water intake of a range of doses of amphetamine and of several related compounds have therefore been examined in an attempt to correlate their known potentices in tate aversion experiments with their hypodipsic potencies (+)-Amphetamine was more potent than (-)-amphetamine in suppressing water intake but under similar experimental conditions, the isomers were equipotent in the conditioning of taste aversions. Methamphetamine and p-chloromethamphetamine were equipotent in suppressing water intake, but the latter was a more potent agent for conditioning taste aversions. Furthermore, fenfluramine produced taste aversions at doses well below those which suppressed water intake. It was concluded that the ability of the drugs to induce taste aversion was not related to their unconditioned, hypodipsic effects. However, it was confirmed that when drugs with different durations of action are compared for anorexic or hypodipsic potency, the outcome can be greatly influenced by the time over which measurements are made.

Tolerance pattern of the anorexigenic action of amphetamines, fenfluramine, phenmetrazine and diethylpropion in rats

The tolerance pattern to anorectic drugs was studied in starved rats by measuring two consecutive 2 h food intakes. 2 There was a reduction in the first 2 h food intake with development of complete tolerance after fenfluramine and phenmetrazine, and of partial tolerance after amphetamine, (+)-amphetamine and diethylpropion. 3 During the second 2 h intake, the anorectic effect was transient after fenfluramine and diethylpropion; while there was an absolute increase in the intake after amphetamine and (+)-amphetamine. 4 A pair-feeding experiment revealed that the increase in the second 2 h food intake was not a direct effect of the drug but a consequence of the deficit in food intake during the preceding 2 hours. 5 There was an overall correlation between the food and water intake. 6 A significant loss in body weight was observed after amphetamine, fenfluramine and phenmetrazine but not after (+)-amphetamine or diethylpropion. 7 The results indicate that so-called tolerance to the anorexigenic effect of drugs is apparent rather than real and that the duration of food access is a determining factor. The body weight changes may be brought about by the metabolic effects of these drugs rather than their effect on food and water intake.

Differences between the anorexic actions of amphetamine and fenfluramine--possible effects on hunger and satiety

The inhition of feeding in rats brought about by amphetamine and fenfluramine was continuously monitored for periods of up to 24 h using a pellet detecting eatometer. For rats tested under conditions of food deprivation the two drugs gave rise to distinctive anorexic profiles: amphetamine delayed the onset of eating whereas fenfluramine allowed eating to commence normally but brought about an early termination of the initial bout of feeding. When the drugs were administrated to rats with free access to food, analysis of the meal pattern showed that amphetamine gave rise to a small increase in the inter-meal interval while fenfluramine brought about a clear reduction tion in meal size. It is suggested that the contrasting modes of action of these drugs represent an effect of amphetamine upon hunger and an action of fenfluramine on satiety. This suggestion is in keeping with the proposed mechanisms of action of these drugs, amphetamine acting upon a hpothalamic motivational system and fenfluramine acting by means of a postulated serotoninergic satiety system. Use of the continuous monitoring technique has pointed pointed to certain limitations in the assessment of anorexic drug action by means of discrete food sampling periods.