Effects of amphetamine and phenylpropanolamine on food intake in rats with ventromedial hypothalamic or dorsolateral tegmental damage

Inhibition of gastric emptying and intestinal transit by amphetamine through a mechanism involving an increased secretion of CCK in male rats

1. The effect of amphetamine on gastrointestinal (GI) transit and the plasma levels of cholecystokinin (CCK) were studied in male rats. 2. Gastric emptying was inhibited both acutely and chronically by the administration of amphetamine. GI transit was decreased by the acute administration of amphetamine but not affected by the chronic administration of amphetamine. 3. Plasma CCK levels were increased dose-dependently by amphetamine. 4. Proglumide, a CCK receptor antagonist, prevented amphetamine-induced inhibition of gastric emptying and the decrease in GI transit in male rats. 5. The selective CCK(A) receptor antagonist, lorglumide, dose-dependently attenuated the amphetamine-induced inhibition of gastric emptying in male rats. In contrast, the selective CCK(B) receptor antagonist, PD 135,158, did not reverse the effect of amphetamine on gastric emptying. 6. Both lorglumide and PD 135,158 reversed the inhibitory effect of amphetamine on GI transit in male rats. 7. These results suggest that amphetamine-induced inhibition of gastric emptying and intestinal transit is due in part to a mechanism associated with the hypersecretion of endogenous CCK.

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.

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.

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.

Heart rate changes during consumption of preferred and non-preferred food under amphetamine treatment

Heart rate was recorded in five dogs while they ate three kinds of foods varying in preference. Heart rate increased during the initial phase of eating, to the greatest extent with the most preferred food. dl-Amphetamine sulfate (0.2 mg/kg) injected intramuscularly produced a general decrease of heart rate. Nevertheless, the heart rate increase during first period of eating was as great as before treatment. Furthermore, the difference in heart rate increase between the most and least palatable foods was still present, and in some dogs even enhanced. It was concluded that amphetamine at this dose in dogs does not attenuate the hedonic properties of food, but may even intensify them. Therefore, the food intake-reducing effect of amphetamine cannot be due to its suppression of hedonic value of food but is the result of its action on other mechanisms such as hunger drive or control of movement.

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.

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.

Effect of phenylpropanolamine on diet selection in rats

Four doses of phenylpropanolamine (PPA; i.e., dl-norephedrine: 2.5, 5, 10, and 20 mg/kg) and saline were injected intraperitoneally in female rats maintained on a dietary self-selection paradigm. Intake of all three macronutrients (carbohydrate, fat, and protein) was equally affected by high doses of PPA. Lower doses decreased fat and protein more than carbohydrate.

Phenylpropanolamine decreases food intake in rats made hyperphagic by various stimuli

Phenylpropanolamine (PPA, d,l-norephedrine), found in many over-the-counter appetite suppressants and nasal decongestants, induces anorexia by a yet unidentified mechanism. The present study evaluates the effects of PPA on different types of non-drug- and drug-induced hyperphagias (i.e., food deprivation, 2-deoxy glucose, ketocyclazocine and insulin). Phenylpropanolamine (15, 25 and 35 mg/kg IP) significantly reduced food intake in a dose-related fashion at the 1 hr and 3 hr time intervals in the food deprivation-, insulin- and 2-deoxy glucose-induced hyperphagic models. Phenylpropanolamine produced a non-dose-related 99% reduction of food intake in the ketocyclazocine-induced model at the 1 and 3 hr measurement, which was most likely due to a combination of the appetite suppressant activity of PPA and the sedation produced by ketocyclazocine in combination with PPA. We conclude that PPA is capable of suppressing appetite in rats made hyperphagic by various stimuli.

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.

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.

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

The effects of chronic treatment with phenylpropanolamine (PPA) on body weight (BW), food intake (FI), and water intake (WI) and interscapular brown adipose tissue (IBAT) thermogenesis in adult male Sprague-Dawley rats were evaluated in 2 experiments. In Experiment 1, rats were treated (IP) twice daily (0900 and 2100 hr) for 12 days with either saline or 5, 10, or 20 mg/kg dl-PPA. Rats treated with 20 mg/kg dl-PPA exhibited significant decreases in both FI and BW but not WI. Basal IBAT temperature was slightly increased in chronic 20 mg/kg dl-PPA rats and there was no evidence of tolerance to the acute IBAT thermogenic effect of 20 mg/kg dl-PPA. In Experiment 2, rats were treated twice daily (0900 and 2100 hr) for 12 days with either saline or 20 mg/kg of either d-PPA or l-PPA. There was a 2-fold difference in the potency of these PPA isomers on FI, BW and IBAT thermogenesis. Body composition analyses revealed that l-PPA, but not d-PPA, induced a significant loss of carcass lipid without significant changes in carcass ash, water or protein levels. These data suggest that the weight-reducing action of PPA may reflect a combined effect of this drug on both food intake and BAT thermogenesis.

Electrolytic current parameters in the dorsolateral tegmental obesity syndrome in rats

Female rats received lesions in the dorsolateral tegmentum formed by the 20 sec passage of 0.25, 0.5, or 0.75 mA anodal or 0.5, 0.75, 1.0, 1.25, or 1.5 mA cathodal current. Although all lesion parameters induced roughly comparable body weight gains, the largest effect was seen with 1.25 mA cathodal current. Anodal lesions were much larger and induced transient periods of hyperactivity that confounded the effects of the lesions on body weight gain.

Hyperinsulinemia and obesity in the dorsolateral tegmental rat

Adult female rats (N = 26) were prepared with either sham lesions or electrolytic lesions of the dorsolateral tegmentum (DLT). Body weight gain, adiposity, 72-hour food intake and day/night food intake, serum glucose and serum insulin levels were measured 15 and 17 days post-operatively. Dorsolateral tegmental lesions produced moderate weight gains and enhanced adiposity as assessed by the Lee Index. Although dorsolateral tegmental rats were hyperphagic only at night, hyperinsulinemia was observed during the day and the night. Hyperinsulinemia may contribute to the obesifying action of tegmental lesions in rats fed high-fat diets.