Weight loss induced by chronic phenylpropanolamine: anorexia and brown adipose tissue thermogenesis

Effect of Metaswitch® dietary supplement on anthropometric parameters, serum lipids, glucose level, oxidative stress and in vivo antioxidant properties in high fat diet-induced overweight Sprague Dawley rats

PURPOSE

Obesity and overweight are metabolic disorders associated with oxidative stress, and risk factors for many chronic diseases. We sought to investigate the effects of Metaswitch dietary supplement on weight gain and associated acute metabolic alterations in a high-fat diet-induced overweight rat model.

METHODS

Female Sprague Dawley (SD) rats were put into 6 groups. Control groups were fed normal (NCD) or high-fat diet (HFD). Treatment groups on HFD receieved 3 different daily doses of Metaswitch for 3 weeks. Another group on HFD received Slimrite® (phenylpropanolamine), a standard drug. Rats on HFD also received cyproheptadine to stimulate appetite. Food consumption and anthropometric parameters were determined weekly. Serum lipids, glucose level, hepatic lipid peroxidation, and antioxidant activity were used to assess overweight in rats.

RESULTS

Food intake remained relatively constant among groups. Rats on HFD had significantly increased body weight compared to rats fed NCD. Metaswitch significantly prevented weight gain; this effect was greater or similar to rats administered Slimrite, but was not dose-dependant. No significant changes occurred in the levels of serum lipids and glucose among the groups. However, serum triglyceride (TG) was significantly increased. The TG/HDL-C ratio revealed significant metabolic alterations which was prevented by Metaswitch. Catalase activity was significantly decreased in the HFD untreated group but was restored in Metaswitch-treated groups.

CONCLUSIONS

A 3-week HFD regimen with cyproheptadine supplementation in female SD rats resulted in a significant increase in body weight and acute metabolic alterations. The aforementioned changes were found to have been prevented with the administration of Metaswitch.

A Systematic Review of the European Rapid Alert System for Food and Feed: Tendencies in Illegal Food Supplements for Weight Loss

Background: Slimming products represent a dynamically growing group of food supplements worldwide. The efficacy of safely usable natural ingredients is usually below consumers' expectations. Certain manufacturers add unauthorized or prohibited ingredients to weight loss supplements in order to increase their efficacy. Hence, many of these products are adulterated and may pose a risk to the consumers' health. Aims: The aim of our work was to give an overview on natural ingredients used in slimming products, to summarize the frequently used synthetic adulterants and also to assess the trends of adulterated and illegal food supplements in the European Union based on the warnings of the Rapid Alert System for Food and Feed (RASFF) in the time period of 1988-2019. Methods: Reports between 1988-2019 were extracted from the RASFF portal on January 1, 2020. Each entry was individually reviewed. Results: 2,559 records of food supplements with quality problems were identified in the RASFF, several of which [319 (12,5%)] were marketed to facilitate weight loss. 202 (63,3%) contained unapproved, synthetic drug ingredients. The major adulterant (113 of 319, 35.4%) was DNP (2,4-dinitrophenol), whereas sibutramine was the second most frequent adulterant agent (69 products, 21,6%) between 1988 and 2019. Conclusion: The number of approved medicines for the indication of weight loss is relatively low and their efficacy (and also that of the natural ingredients) is limited. Therefore, a significant number of weight loss supplements is adulterated to satisfy patients' expectations. Hence, these products may cause serious adverse effects in sensitive patients.

Neurochemical regulators of food behavior for pharmacological treatment of obesity: current status and future prospects

In recent decades, obesity has become a pandemic disease and appears to be an ultimate medical and social problem. Existing antiobesity drugs show low efficiency and a wide variety of side effects. In this review, we discuss possible mechanisms underlying brain-gut-adipose tissue axis, as well as molecular biochemical characteristics of various neurochemical regulators of body weight and appetite. Multiple brain regions are responsible for eating behavior, hedonic eating and food addiction. The existing pharmacological targets for treatment of obesity were reviewed as well.

Interrupting activator protein-1 signaling in conscious rats can modify neuropeptide Y gene expression and feeding behavior of phenylpropanolamine

The mechanism for phenylpropanolamine (PPA)-induced anorexia has been attributed to its inhibitory action on hypothalamic neuropeptide Y (NPY), an orexigenic agent abundant in the brain. However, molecular mechanisms behind this effect are not well known. In this study, we investigated whether activator protein-1 (AP-1) signaling was involved. Rats were daily treated with PPA for 4 days. Changes in hypothalamic NPY, c-fos, c-jun, superoxide dismutase (SOD)-1, and SOD-2 mRNA contents were measured and compared. Results showed that c-fos and c-jun mRNA levels were increased following PPA treatment, which were relevant to a reduction in NPY mRNA level. To further determine if c-fos/c-jun genes were involved in PPA anorexia, infusions of antisense oligonucleotide into cerebroventricle were performed before daily PPA treatment in freely moving rats. Results showed that either c-fos or c-jun knock down could block PPA anorexia and restore NPY mRNA content to normal level. It is suggested that AP-1 signaling may participate in the central regulation of PPA-mediated appetite suppression via the modulation of NPY gene expression. Moreover, this modulation might be partly because of the neuroprotective effect of AP-1 since SOD gene was activated during PPA treatment.

Acute administration of phenylpropanolamine fails to affect resting energy expenditure in men of normal weight

Studies have consistently found that dieters using over-the-counter weight control products containing phenylpropanolamine (PPA) are more successful at losing weight than those who do not. To explore the possibility that drug-induced metabolic changes contribute to weight loss associated with this compound, this study investigated the effects of PPA on resting metabolic rate in 20 healthy men of normal weight between the ages of 18 and 29. After the arrival of the subjects to the laboratory, blood pressure was taken and resting energy expenditure (REE) and respiratory quotient (RQ) were assessed for 20 minutes (Baseline) via indirect calorimetry. Half of the subjects were then given 75 mg of immediate-release PPA (administered orally via a gelatin capsule), while the other half received placebo. Immediately after drug administration, metabolic rate was measured for an additional 95 minutes (During Drug). After this assessment, blood pressure was again measured. Although significant increases in both systolic and diastolic blood pressure were observed after PPA administration, the drug had no effect on REE or RQ. These results, consistent with that previously reported in mildly overweight women, further establish that it is unlikely that drug-induced metabolic changes contribute to PPA-induced weight loss in humans.

Effects of the alpha 1a-adrenoceptor antagonist RS-17053 on phenylpropanolamine-induced anorexia in rats

Activation of alpha 1-Adrenergic receptors via systemic administration of drugs such as phenylpropanolamine (PPA) and cirazoline results in the suppression of feeding in rats. Whether PPA acts via activation of the three currently identified alpha 1-Adrenoceptor subtypes is unknown. The intent of the present study was thus to examine the effects of systemic administration of the novel alpha 1a-Adrenoceptor antagonist RS-17053 on PPA-induced anorexia. Adult male rats (n = 6 to 8 per group) were pretreated (IP) with either 0, 0.1, 0.5, 2.5, or 10.0 mg/kg RS-17053 or with 2.0 mg/kg of the prototypical alpha 1-Adrenoceptor antagonist prazosin. Five minutes later, each rat was treated (IP) with either 0, 5, 10 or 15 mg/kg PPA. Food and water intakes were recorded for a 30 min period starting 10 min after the the treatment injection. Rats pretreated with vehicle and then treated with PPA exhibited a dose-dependent suppression of feeding with a maximal effect evident at the 15 mg/kg dose of PPA. Pretreatment with 2.0 mg/kg prazosin reversed the anorexic activity of PPA. Pretreatment with RS-17053 (0.1-2.5 mg/kg) did not alter either baseline feeding or the anorexic action of PPA. These results suggest that PPA does not act via the alpha 1a-Adrenergic receptor subtype to suppress food intake.

Effects of chronic phenylpropanolamine infusion and termination on body weight, food consumption and water consumption in rats

The present study determined the effect of chronic PPA infusion and withdrawal on weight regulation. Male Sprague-Dawley rats received PPA (0, 90 or 180 mg/kg) via miniosmotic pumps for 2 weeks. Body weight and food and water consumption were measured daily before, during, and for 2 weeks after PPA infusion. Additionally, body weight was measured once 6 weeks after the last day of drug administration. PPA infusion produced dose-dependent reductions in body weight and food consumption throughout drug administration. During the first week of PPA termination, food consumption returned to control levels; however, body weights of drug-treated animals remained below those of controls throughout the 6-week post-drug period. PPA depressed water intake during the first week of drug administration, but tolerance to this effect developed by the second week of administration. These results suggest chronic PPA infusion produces persistent appetite suppression and weight loss and that discontinuation of PPA does not result in hyperphagia or rapid weight gain. These findings may have clinical significance for the many individuals who wish to lose weight but have difficulty reducing intake without pharmacologic assistance.

Lack of involvement of 4-hydroxynorephedrine in phenylpropanolamine-induced anorexia in rats

The anorexic effects of phenylpropanolamine (PPA) appear to be qualitatively different in humans and rats. One factor that may account for these differences is that PPA is excreted essentially unchanged in humans, while nearly 30% is metabolized into 4-hydroxynorephedrine (4-OHN) in rats. To investigate the contribution of 4-OHN to the anorexic properties of PPA, this experiment compared the effects of equal doses (0.0-20.0 mg/kg, IP) of both drugs on eating and drinking during restricted feeding trials in the same group of food-deprived, female rats. Both 15.0 and 20.0 mg/kg of PPA significantly decreased eating when compared to saline vehicle, while 5.0-20.0 mg/kg of the drug reduced prandial drinking. In comparison, only the highest dose of 4-OHN (20.0 mg/kg) significantly suppressed food and water intake. When the percentage of reduction produced by corresponding doses of the two drugs was compared, PPA proved to be more than twice as potent as 4-OHN. It is concluded that, at the doses used, 4-OHN is unlikely to significantly contribute to reductions in deprivation-induced eating produced by the acute administration of PPA.

Comparison between phenylpropanolamine and structurally related compounds on gastric transit in the rat

Our laboratory previously reported several pharmacological differences between phenylpropanolamine [PPA; (+/-)-norephedrine] and its structurally related compounds in regard to their activity on cardiovascular and appetite-suppressant parameters. The present study investigates the pharmacological differences between PPA, [1R,2R]-(-)-norephedrine [(-)-NOR], [1S,2S]-(+)-norephedrine [(+)-NOR], [1R,2S]-(-)-ephedrine [(-)-EPH], [1S,2R]-(+)-ephedrine [(+)-EPH], [1R,2S]-(-)-norpseudoephedrine [(-)-NORP], [1S,2R]-(+)-norpseudoephedrine [(+)-NORP], [1R,2R]-(-)-pseudoephedrine [(-)-PSE], and [1S,2S]-(+)-pseudoephedrine [(+)-PSE], as determined by their ability to inhibit gastric transit in the rat. (-)-Norephedrine was approximately three times more potent in inhibiting gastric transit than (+)-NOR (p < 0.01). As anticipated, the racemic mixture, PPA, demonstrated an ED50 (25.1 mg/kg) of approximately the mean of the ED50s from the component enantiomers (14.7 and 47.0 mg/kg, respectively). Similarly, administration of 20 mg/kg of either (-)-EPH, (+)-EPH, (-)-PSE, or (+)-PSE significantly decreased gastric transit by 26% (p < 0.001), 12% (p < 0.01), 10% (p < 0.01), and 11% (p < 0.01), respectively. Administration of (-)-NORP and (+)-NORP were without effect. These data confirm and extend previous findings demonstrating pharmacological differences between PPA and its structurally related compounds.

Effects of phenylpropanolamine infusion and withdrawal on body weight and dietary composition in male and female rats

Male and female rats with ad lib access to separate sources of carbohydrate, fat, and protein were implanted with minipumps providing one of three dosages (0.0, 40.0, or 80.0 mg/kg/day) of phenylpropanolamine (PPA) for 2 weeks. Body weight, macronutrient intake, and water consumption were measured daily before, during, and after PPA treatment. Phenylpropanolamine lowered body weight and caloric intake in males and females, and water consumption in females, but did not alter dietary composition in either sex. After PPA termination, caloric intake returned to control levels in both males and females. However, body weight returned to control levels in males only, while PPA-treated females continued to weigh less than controls. Phenylpropanolamine termination was associated with significant increases in water consumption and the percentage of total calories consumed from protein and reductions in the percentage of calories from carbohydrate in males. In contrast, water and macronutrient consumption was similar comparing PPA-treated females to controls after drug termination. These results suggest there are sex differences in the effects of PPA termination on water and macronutrient consumption that result in differential weight gain in males and females.

Effects of phenylpropanolamine on regulatory and nonregulatory ingestion in adult rats

This experiment examined the effects of phenylpropanolamine (0.0, 5.0, 10.0, 20.0 mg/kg PPA) on regulatory (RG) and nonregulatory (NRG) eating and drinking in rats using a within-subjects design. Administration of PPA produced dose-dependent reductions in eating in animals deprived to 80-85% of baseline weight, and reduced drinking after 23.5-h of water deprivation. Nonregulatory eating, elicited by tail pinch in nondeprived animals, was similarly inhibited. Nonregulatory drinking was elicited in the schedule-induced polydipsia (SIP) paradigm. Water consumption, locomotion, licking, lick efficiency (licks/ml water), and entries into the food magazine were simultaneously measured. At the lowest dose, only locomotion was significantly reduced. At 10.0 mg/kg, lick efficiency and entries into the food magazine were also significantly reduced, while all measured behaviors, including licking and water consumption, were decreased by the highest dose of PPA. The reduction in lick efficiency suggested a PPA-induced motor impairment in the capacity for licking. Considered together, these results indicated that the observed decreases in regulatory and nonregulatory eating and drinking could be at least partially accounted for by the drug's effects on behaviors contributing to ingestion, as well as apparent motor impairments in ingestive behavior at higher doses.

Effects of intra-PVN injections of d- and l-norephedrine on feeding in rats

Phenylpropanolamine (PPA) is thought to inhibit feeding by activation of alpha 1-adrenergic receptors within the paraventricular hypothalamus (PVN). Systemic injections of the PPA component enantiomers, d- and l-norephedrine (NEP), result in differential suppression of feeding (l-NEP more potent than d-NEP). Whether the norephedrine racemates induce differential anorexia subsequent to injection into the PVN is unknown. In the present study, adult male rats received intra-PVN injections of the d- and l-norephedrine enantiomers (0, 80, 160, and 240 nmol). Significantly greater anorexia was obtained for l-NEP relative to d-NEP. These results document a stereospecific effect of the norephedrine enantiomers within the PVN in inhibiting food intake and suggest that the interaction of these enantiomers with PVN alpha 1-adrenoceptors may mediate the similar difference in potency noted for systemic injections of d- and l-norephedrine.

Reversal of cirazoline- and phenylpropanolamine-induced anorexia by the α1-receptor antagonist prazosin

Phenylpropanolamine (PPA) is a phenethylamine anorectic drug that exerts direct agonist effects predominantly on alpha 1-adrenoceptors, with some alpha 2-adrenergic activity. Microinjections of PPA, as well as the alpha 1-adrenergic receptor agonists cirazoline, methoxamine, and 1-phenylephrine, into rat paraventricular nucleus (PVN) suppress feeding. The present study further evaluates the alpha 1-adrenergic basis of PPA-induced anorexia by examining the effects of systemic injections of the alpha 1-adrenergic antagonist prazosin (PRAZ, 2 and 5 mg/kg, IP) on the anorexia induced by systemic injections of PPA (5, 10, and 20 mg/kg, IP), as well as cirazoline (0.05, 0.1, and 0.2 mg/kg, IP). Although neither PRAZ dose alone altered food intake in the present study, 2 mg/kg PRAZ effectively reversed the feeding-suppressive effects of both PPA and cirazoline. These results strongly support the hypothesis that alpha 1-adrenoceptor stimulation mediates the anorexia induced by drugs such as PPA and cirazoline.

Effects of the α1-adrenergic agonist cirazoline on locomotion and brown adipose tissue thermogenesis in the rat

Anorexia is induced by injection of alpha 1-adrenergic receptor agonists into the hypothalamic paraventricular nucleus (PVN) in rats. Of the agonists tested to date, cirazoline is the most potent when administered either into the PVN or systemically. The present experiments assess the effects of systemically administered cirazoline, at doses that suppress food intake, on dopamine and norepinephrine systems as evident in locomotion and stereotypy and in the induction of brown adipose tissue (BAT) thermogenesis. In Experiment 1, adult male rats were treated with either vehicle (0) or 0.05, 0.1, 0.2 or 0.4 mg/kg cirazoline (IP) prior to 30 minutes assessment of horizontal and vertical locomotion and stereotypy in Omnitech activity chambers. Horizontal activity and stereotypy were significantly suppressed at 0.05 mg/kg cirazoline but these effects waned at higher cirazoline doses. In Experiment 2, interscapular BAT temperature in adult male rats was monitored for 30 minutes after injection (IP) of either vehicle or 0.4 mg/kg cirazoline. Cirazoline, at 0.4 mg/kg did not influence BAT temperature whereas a positive control treatment (phenylpropanolamine: 40 mg/kg) rapidly increased BAT temperature during a 15 minute period after injection. These results suggest that cirazoline-induced anorexia is not the result of competing motor responses and that this drug, at a dose that produces maximal suppression of feeding, does not alter BAT thermogenesis.

Abuse of drugs associated with eating disorders

Concomitant bulimia nervosa and drug abuse are common in women. Drugs used by this group include diuretics, emetics, laxatives, and diet pills, as well as alcohol, cigarettes, and illicit street drugs. This paper applies principles from behavioral pharmacology to the problem of drug use by women with bulimia nervosa. The prevalence of use, primary effects, toxicity, detection, tolerance, withdrawal, and effects on appetite and weight are discussed for drugs used by bulimic women to reduce appetite or weight or to induce purging (e.g., diuretics, emetics, laxatives, and diet aids). Alternatives in the diagnosis and treatment of drug use in women with eating disorders are discussed.

A review of the physiological bases of the anorexic action of phenylpropanolamine (d,1-norephedrine)

Phenylpropanolamine (PPA) is a phenethylamine that induces a variety of effects including anorexia and weight loss. The present review compares the acute anorexic effects of PPA with those of amphetamine in animals and humans, describes the persistent chronic effects of PPA on feeding as well as differences in anorexic potency between the norephedrine enantiomers (d-norephedrine less than 1-norephedrine) and summarizes the generality of PPA anorexia. The review also describes the putative mechanisms by which PPA is thought to reduce feeding behavior including alteration of gastric emptying and interaction with central nervous system neurons.

Effects of paraventricular hypothalamic microinjections of phenylpropanolamine and d-amphetamine on mash intake in rats

The present experiment compared the effects of unilateral microinjections (40, 80 and 160 nmol/0.5 microliter) of phenylpropanolamine (PPA: d,l-norephedrine) and d-amphetamine sulfate within the paraventricular hypothalamus (PVN) on consumption of a palatable sweetened-mash diet in 15-hour food-deprived adult male rats. Intracranial microinjections were administered 5 minutes prior to each 30-minute feeding trial. PPA, at a dose of 160 nmol, suppressed feeding by 42%, whereas a similar dose of amphetamine suppressed feeding by 49%. Amphetamine or PPA doses of 40 and 80 nmol were without significant effect on feeding behavior. A relatively high dose of 160 nmol amphetamine was required to suppress feeding after injection into the PVN whereas much lower amphetamine concentrations are required to suppress feeding after injection into the perifornical hypothalamus. In contrast, PPA has some anorexic activity within the PVN but not within the perifornical hypothalamus.

Enantiomers of phenylpropanolamine suppress food intake in hyperphagic rats

Phenylpropanolamine (PPA, d,l-norephedrine), available in many over-the-counter nasal decongestants and appetite suppressants, is a racemic mixture of the enantiomers d- and l-norephedrine. The present study evaluates the effects of the individual PPA enantiomers on a variety of nondrug (food deprivation) and drug-induced hyperphagias (2-deoxyglucose and insulin). Racemic PPA has been shown to significantly suppress food intake in these hyperphagic models. Both l-norephedrine (5-50 mg/kg) and d-norephedrine (5-150 mg/kg), administered intraperitoneally, significantly suppressed feeding after a 4-hr fast during the dark cycle. During the light period, l-norephedrine (7.5, 10, 15 mg/kg) and d-norephedrine (75, 100, 150 mg/kg) significantly reduced food intake at the 1-hr and 3-hr time intervals in the 24-hr food deprivation-, insulin- and 2-deoxyglucose-induced hyperphagic models. Only 7.5 mg/kg l-norephedrine in the insulin-induced hyperphagia at 3 hr failed to significantly suppress feeding. These results indicate that each individual PPA enantiomer possesses the ability to suppress food intake in rats made hyperphagic by various stimuli.

Effects of haloperidol on anorexia induced by l-norephedrine and d-amphetamine in adult rats

Although amphetamine anorexia has been linked to activation of dopaminergic receptors within the lateral aspects of the hypothalamus, the receptor type by which phenylpropanolamine (PPA: the racemic mixture of d- and l-norephedrine) induces anorexia has not been identified. In the present experiment, separate groups of adult male rats were pretreated (IP) with either 0.9% saline or haloperidol (either 0.4 or 0.8 mg/kg) 45 minutes prior to treatment (IP) with either saline or 20 mg/kg l-NEP (the active enantiomer of PPA) and were then allowed 180 minutes access to food and water. Treatment with 20 mg/kg l-NEP induced comparable reductions in food intake of approximately 30% in rats pretreated with either dose of haloperidol or saline. In a sub-experiment, it was demonstrated that 1.0 mg/kg d-amphetamine sulfate reduced food intake by 25%, but this anorexic action was completely attenuated by 0.8 mg/kg haloperidol given 45 minutes prior to feeding. These results add to a growing body of literature that documents important differences between the mechanisms by which amphetamine and PPA produce their anorexic actions.

Effects of perifornical hypothalamic microinjections of phenylpropanolamine and amphetamine on latency to feed and mash intake in rats

To determine whether phenylpropanolamine (PPA) and amphetamine act on a common satiety mechanism, the present experiment compared the effect of unilateral microinjections (40, 80, and 160 nmol) of phenylpropanolamine hydrochloride (PPA: d,1-norephedrine) and of d-amphetamine sulfate within the perifornical hypothalamus (PFH) on consumption of a palatable sweetened-mash diet in adult male rats. Microinjection of d-amphetamine (40-160 nmol) within the PFH induced dose-dependent anorexia, whereas PPA microinjections were without effect on feeding. These results document that amphetamine and PPA do not act at a common CNS site, such as the PFH, to induce anorexia.

Phenylpropanolamine and amphetamine disrupt postprandial satiety in rats

Two tests of the behavioral specificity of the anorectic effects of amphetamine (AM) and phenylpropanolamine (PPA) were done. Intraperitoneal injections of each drug reduced the size of condensed milk test meals in 30-min pellet-deprived rats. The dose-response relations in semi-log coordinates were linear and parallel, but AM (ED50, 2.0 +/- 0.1 mumol/kg) was about ten times more potent than PPA (ED50, 24.6 +/- 0.1 mumol/kg). Periprandial behaviors were observed using a time-sampling technique. Both AM and PPA disrupted the normal behavioral sequence of postprandial satiety throughout their anorectic ranges, but they did so differently. AM increased postprandial exploratory behavior, decreased or eliminated resting, and, at larger doses, elicited stereotypy. In contrast, PPA inhibited both grooming and exploration, and increased resting. The drugs' effects on water intake were tested in 17-hr water-deprived rats. AM's adipsic effect (ED50, 2.3 +/- 0.1 mumol/kg) was similar to its anorectic effect. PPA also inhibited drinking, although slightly less potently (ED50, 56.6 +/- 0.1 mumol/kg) than it did feeding. Thus, under conditions maximizing the anorectic potencies of systemically administered AM and PPA in rats, both drugs inhibited feeding nonspecifically rather than by eliciting normal postprandial satiety.

Ephedrine-induced thermogenesis as an adjunct to cognitive restructuring and covert conditioning: a proposal for treatment of obese individuals

Experimental investigators have discussed the therapeutic potential of ephedrine as a thermogenic agent in the treatment of obese individuals. Because research into thermogenesis and the role of sympathetic nervous system stimulation in weight control primarily has emphasized pharmacological interventions, the authors suggest that cognitive restructuring and covert conditioning procedures could be valuable psychotherapeutic additions to a pharmacologically derived weight-loss regimen. Furthermore, it is concluded that additional clinical research is necessary to determine the efficacy of integrating ephedrine therapy and cognitive-behavioral psychotherapeutic procedures as adjuncts to a multidimensional program for treating obesity.

Effects of amphetamine and phenylpropanolamine on latency to feed and cumulative liquid diet intake in rats

The purpose of the present experiment was to compare the actions of d-amphetamine sulfate (AMP) and phenylpropanolamine hydrochloride (PPA: d,l-norephedrine) on feeding of a liquid diet. Adult rats were deprived of food for 22 hours and treated with 1.0 and 2.0 mg/kg AMP and with 15 and 30 mg/kg PPA 30 minutes prior to a 60-minute feeding test. Latency to begin feeding was recorded at the start of the feeding session with cumulative liquid diet intake recorded every 5 minutes during the test. Amphetamine and PPA significantly increased latency to feed but PPA, at the doses used here, produced a greater reduction in overall feeding during the test sessions than did amphetamine. Eating rate was reduced by both AMP and PPA during the first 20 minutes of the test session, but eating rate after AMP was significantly higher during the latter portion of the test session. Although amphetamine and PPA are often likened as similar in structure and function, these results suggest important qualitative differences between the anorexic activities of these two drugs.

Inhibition of feeding and hoarding behaviors by phenylpropanolamine in the adult rat

The mechanism by which phenylpropanolamine (PPA) reduces feeding and body lipid is unknown. To determine if malaise associated with PPA treatment mediates its anorexic action, the present study compared the actions of PPA on feeding and hoarding behavior with that of lithium chloride at dose levels that induce comparable conditioned taste aversions. Adult male rats were injected (IP) 30 minutes prior to a test of feeding and hoarding behavior with either 0.9% saline, 32 mg/kg lithium chloride or with 10 mg/kg, 20 mg/kg or 40 mg/kg PPA. Although 32 mg/kg lithium chloride was without effect on either feeding or hoarding behaviors, PPA significantly suppressed both behaviors. These results do not support the notion that malaise is a critical aspect of the anorexic property of PPA and that hoarding behavior may represent a sensitive index of anorexic drug potency.

The effects of phenylpropanolamine on food intake and body weight in the genetically obese (ob/ob) mouse

The purpose of the present study was to compare the actions of the anorexigen phenylpropanolamine (PPA) on chronic feeding and body weight in lean and in genetically obese mice. Adult (8-week-old) female C57BL/6J ob/ob mice and female +/? lean control mice were treated (i.p.) twice daily (at 0800 hrs and 2000 hrs) for 21 days with either 0.9% saline or with 10 or 20 mg/kg PPA. Analyses of cumulative 72-hour food intake revealed that PPA induced significant and dose-dependent anorexia in ob/ob mice but that PPA was without significant anorectic effect in lean mice. PPA dose levels of 10 mg/kg and 20 mg/kg reduced food intake in ob/ob mice by 14 and 21%, but reduced food intake in lean mice by only 3 and 6%, respectively. Analyses of body weight, however, did not reveal significant changes in body weight induced by either PPA dose in ob/ob or lean mice. The enhanced anorexic effects induced by PPA and other adrenergic agents in the ob/ob mouse are discussed.

Effects of phenylpropanolamine on gastric retention in the adult rat

Phenylpropanolamine (PPA) induces anorexia and weight loss via an as yet unidentified mechanism. In the present study, we evaluated the inhibitory action of PPA on gastric emptying. Adult female Sprague-Dawley rats consumed a wet-mash test meal and were then treated (IP) with either saline or 5, 10, 20 or 40 mg/kg PPA. Gastric retention (ratio of weight of gastric content to weight of mash consumed) was evaluated immediately after the meal in a group of saline-treated rats or 3 hours after the meal in the drug groups and another saline-treated group. Rats treated with saline exhibited minimal retention (0.21) over a 3 hour period whereas rats treated with 5, 10, 20 or 40 mg/kg dl-PPA exhibited increased gastric retention ratios of 0.29, 0.66, 0.63, and 1.38, respectively. These data demonstrate that PPA has a marked inhibitory action on gastric emptying and suggest that further studies are warranted to evaluate the possible contribution of gastric retention to the anorexic action of PPA.

Effects of nicotine on body weight, food intake and brown adipose tissue thermogenesis

Chronic treatment with nicotine results in reduced body weight gain without a change in food intake. To evaluate the role of brown adipose tissue (BAT) thermogenesis in this effect of nicotine, male Sprague-Dawley rats were chronically treated (3X daily, IP) over a 14 day period with either saline, 0.8 mg/kg nicotine, 10 mg/kg caffeine or a combination of 0.8 mg/kg nicotine and 10 mg/kg caffeine and were pretreated (once daily) with either saline or 20 mg/kg nadolol, a long-acting beta-adrenergic receptor blocker. Nicotine significantly reduced body weight gain but not food intake and nadolol did not reverse the effect of nicotine on body weight gain. To evaluate whether nicotine induces BAT thermogenesis, rats were injected IP with either saline or 0.8, 1.2 or 1.6 mg/kg nicotine hydrogen tartrate, with 5 mg/kg dl-phenylpropanolamine (dl-PPA) or with a combination of 0.8 mg/kg nicotine and 10 mg/kg caffeine with interscapular BAT (IBAT) temperatures recorded for 30 minutes after injection. No dose of nicotine produced a change in IBAT temperature whereas a combination of caffeine and nicotine produced a temperature increase in IBAT (0.95 degree C) 63% of that induced by 5 mg/kg dl-PPA. These data suggest that changes in body weight gain induced by nicotine treatment are not the result of an action of nicotine on BAT thermogenesis.