The effect of propranolol phentolamine and pimozide on drug-induced anorexia in the mouse

Pimozide was a potent antagonist of (+)amphetamine, diethylpropion, mazindol and phentermine anorexia in the mouse. Phentolamine and propranolol produced no such antagonism, but either potentiated or had no effect on the drug-induced anorexia. Although the mechanism of action of the four anorectic agents appears to involve dopamine receptor agonist activity, an antagonist or partial agonist effect at noradrenergic receptors may also be involved.

Relationship between anorectic and reinforcing properties of appetite suppressant drugs: implications for assessment of abuse liability

A quantitative ratio measure was developed which permitted comparisons between the reinforcing and anorectic potency of eight phenylethylamine anorectics and cocaine in laboratory baboons. The ordering of these compounds based upon this ratio bears a reasonable correspondence to clinical drug evaluations. The measure may provide information for preclinical evaluation of relative abuse potential of anorectic drugs.

Lysosomal alterations in cultured macrophages exposed to anorexigenic and psychotropic drugs

Cultured rat macrophages were used for an in vitro study of drug-induced lipidosis. Cells were exposed for 24 hours to equimolar concentrations (5 X 10(-5) and 1 X 10(-4) M) of the following amphiphilic (amphipathic) cationic drugs: chlorphentermine, amitriptyline, 1-chloro-amitriptyline, iprindole, noxiptiline, chlorpromazine. In addition the less amphiphilic drug phentermine was used. Ultrastructurally, the cytologic changes essentially consisted of formation of multilamellated cytoplasmic inclusions, which possessed acid phosphatase activity. The abnormal inclusions are interpreted to result from intralysosomal accumulation of polar lipids. Under the present in vitro conditions all drugs except phentermine, had similar potencies to induce such lysosomal alterations, quite in contrast to the great quantitative differences previously observed under in vivo conditions. The present results lend further support to a concept that regards a pronounced amphiphilic (amphipathic) character to be responsible for the lipidosis-inducing action of various cationic compounds. Cultured macrophages are suggested as a useful tool to investigate this structure-activity relationship, which under in vivo conditions may be obscured by superimposed parameters such as drug metabolism.

On the role of serotonin in the pathogenesis of pulmonary hypertension induced by anorectic drugs; an experimental study in the isolated perfused rat lung, II. Fenfluramine, mazindol, mefenorex, phentermine and R 800

1. The influence of the anorectic drugs fenfluramine, mazindol, mefenorex, phentermine and R 800, an experimental compound, on pulmonary vascular resistance has been studied in the isolated, perfused rat lung. 2. R 800 caused a strong vasoconstriction, which was not antagonized by methysergide of phentolamine; the other drugs listed did not alter vascular resistance. 3. Mazindol and phentermine significantly prolonged the vasoconstrictive effect of serotonin due to inhibition of its metabolic breakdown. 4. Although fenfluramine inhibited serotonin metabolism it also prevented the vasoconstrictive effect of serotonin, due to its ability to act as a serotonin antagonist. 5. Mefenorex did not affect pulmonary vascular resistance, either directly or indirectly via a serotoninergic mechanism.

Inhibition of synaptosomal accumulation of l-norepinephrine II: N-aryloxyalkylphentermines, quaternary d-amphetamines, and 3-aryloxypropylamines

The inhibitory potencies of a series of N-substituted phentermines on the synaptosomal uptake of l-norepinephrine were found to be similar to those of the corresponding amphetamines. Quaternization of N, N-dimenthyl-d-amphetamine diminished, but did not abolish, its inhibitory potency, indicating that a permanently charged cation is also effective. Since the addition of an aromatic moiety at the end of a four-atom chain originating at the nitrogen of amphetamine or phentermine significantly increased inhibitor strength, several 3-aryloxypropylamines and 4-phenylbutylamine were tested, but they were much weaker inhibitors than dl-amphetamine. Thus, the observed increase in inhibitor potency apparently was not simply the result of a specific interaction of the "nonmimic" portion of the N-substituted amphetamines or phentermines.

The pharmacokinetics of phentermine and chlorphentermine in chronically treated rats

Young rats were treated with [3H]labelled phentermine or chlorphentermine for varying periods (1 day to 8 weeks). The plasma tissue and concentrations of the drugs were determined. The distribution of phentermine reflected a partition, the tissue: blood ratios remaining constant for the entire period. In contrast, chlorphentermine was increasingly accumulated the longer the treatment lasted, as indicated by rising tissue: blood ratios. Chlorphentermine proved to be tightly bound to tissue components. The highest tissue: blood ratio (160 after 8 weeks) was found in lungs and the highest increase in the accumulation rate (10 fold in 8 weeks) was for the adrenals. These results, together with biochemical and ultra-structural findings, suggest that the highly amphiphilic chlorphentermine induces an impairment of phospholipid metabolism resembling lipidosis.

The central hypotensive action of amphetamine, ephedrine, phentermine, chlorphentermine and fenfluramine

The influence of amphetamine, ephedrine, phentermine, chlorphentermine and fenfluramine on blood pressure after infusion into the vertebral artery was studied in anaesthetized cats. All drugs lowered blood pressure after infusion into the vertebral artery but showed hypertensive properties upon intravenous administration in the same dosage, although chlorphentermine (i.v.) decreased pressure after a minor initial rise. The hypotensive action of amphetamine was blocked by piperoxan or yohimbine (α-adrenoceptor blocking agents) and by haloperidol which is known to block central adrenoceptors. The hypotensive action of amphetamine was abolished in reserpinized cats and usually a small increase in blood pressure was observed in these animals after infusion of amphetamine in the vertebral artery. The hypotensive action of amphetamine is probably due to the mobilization of noradrenaline in the brain. The results suggest that the drugs show central hypotensive properties probably brought about by stimulation of central α-adrenoceptors, thus causing a decrease in peripheral sympathetic tone. This general principle would also explain the central hypotensive properties of α-methyl- dopa, α-methylnoradrenaline, l-dopa and m-tyrosine.