Conditioned taste aversion and unconditioned suppression of water intake induced by phenylpropanolamine in rats

Conditioned taste aversion in rats induced by the alpha 1-adrenoceptor agonist cirazoline

Recent studies have indicated that alpha 1-adrenoceptor agonists such as phenylpropanolamine (PPA), cirazoline, amidephrine, and SK&F-89748 suppress food intake in rats. These compounds activate alpha 1-adrenoceptors within the paraventricular hypothalamic nucleus (PVN) and may excite efferent fibers that inhibit feeding. Studies of the effects of alpha 1-agonists suggest a specificity for feeding behavior, but no study to date has evaluated whether these agonists may suppress feeding behavior by the induction of malaise. Accordingly, the present experiment examined the ability of systemically administered cirazoline (0.1, 0.2, and 0.4 mg/kg, IP) to induce conditioned taste aversion (CTA) to a saccharin solution. Significant CTA was noted for 0.2 and 0.4 mg/kg cirazoline but not for 0.1 mg/kg cirazoline, compared to a vehicle treatment. The ED50 for cirazoline-induced aversion was computed to be 0.3 mg/kg, which contrasts with an ED50 value of 0.09 mg/kg for the effect of cirazoline on food intake (computed in other studies). More importantly, a 0.1 mg/kg dose of cirazoline, which is slightly greater than that of the ED50 value for suppression of feeding, did not induce significant CTA in the present study. These results suggest that malaise is not a prominent factor in the suppressive activity of cirazoline on food intake and advocate the use of cirazoline as an effective appetite suppressant.

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.

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.

Conditioned taste reactivity in rats after phenylpropanolamine, d-amphetamine or lithium chloride

That an aversive property of phenylpropanolamine (PPA) in part contributes to its anorexic capacity is suggested by the demonstration of conditioned taste avoidance to PPA doses ranging from 10-40 mg/kg. In order to further evaluate the putative aversive property of PPA, the present experiment compared the effects of PPA on multiple measures of aversion (chin rubs, gaping) in the taste reactivity (TRT) paradigm with those produced by the classic agent lithium chloride and by amphetamine. Male rats were infused via an intraoral cannula with 0.5 M sucrose followed by injection with either vehicle, 127 mg/kg lithium chloride (LiCl), 1.5 or 3.0 mg/kg amphetamine or by 10, 20 or 40 mg/kg PPA. LiCl and 40 mg/kg PPA induced significant chin rub responses during conditioning but only the aversive response induced by 40 mg/kg PPA persisted during extinction trials. In contrast, lower doses of PPA (10 mg/kg, 20 mg/kg) were not aversive in the TRT paradigm. These results suggest that an aversive component is not contributing to anorexia induced by PPA within the dose range of 10-20 mg/kg, but that higher doses may further suppress appetite via an aversive action.

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.

Self-administration of phenylpropanolamine (PPA) by rats previously trained to self-administer amphetamine

Central nervous system stimulation, similar to that observed for amphetamine, has been attributed to phenylpropanolamine (PPA). However, formal tests, using evaluation of locomotion or of self-administration, fail to reveal that PPA is a stimulant. Self-administration studies have trained rats to self-administer cocaine and then have attempted to switch rats to PPA with no success of transfer. The present study further examined the reinforcing properties of PPA (0.08, 0.16, and 0.32 mg/infusion, IV) in rats that were initially trained to self-administer d-amphetamine (0.005-0.08 mg/infusion) in a two-lever paradigm. Self-administration of amphetamine was a function of dose with 0.01 mg/infusion producing reliably high responding on the active lever. The proportion of active/inactive lever presses remained constant (0.60-0.80) across the amphetamine dose range. PPA was dose-dependently self-administered during the first hour of each session with rats responding at approximately 70% on the active lever. In contrast, responding on the active lever dropped off to approximately 48% when saline was substituted for amphetamine. These data document that rats with prior exposure to amphetamine will self-administer PPA during the initial portion of a three-hour test.

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.

Rewarding and aversive effects of stimulant drugs in infant rats

Four experiments investigated the reinforcing effects of cocaine, amphetamine, and phenylpropanolamine using odor as the conditioned stimulus and infant rats as the subjects. At the age of 2 days the rats were injected with saline or with one of the three drugs and placed for 30 min in a plastic bag with almond-scented shavings. At the age of 18 days the rats were deprived of water for 12 hr and then given two tests that required different responses. In the consumption test they were given 30 min access to two water spouts, one surrounded by almond-scented cotton and the other surrounded by plain cotton. In the place test, they spent 5 min in a shuttle box with almond-scented shavings under one side and plain shavings under the other side. Compared to saline, all three drugs decreased water intake from the almond-scented spout and increased time spent over the almond-scented shavings.

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.