Aspirin as a promoter of ephedrine-induced thermogenesis: potential use in the treatment of obesity

Chronic administration of aspirin to obese mice had no effect on energy balance and body composition. In contrast, ephedrine increased energy expenditure by 9% and reduced body weight and body fat by 18% and 50%, respectively: obesity, however, was reduced but not reversed. In the presence of both ephedrine and aspirin, increase in energy expenditure found during treatment with ephedrine alone was doubled, and the obese group lost greater than 75% of body fat: obesity was reversed. These studies indicate that although aspirin administered alone has no influence on energy balance it can markedly potentiate thermogenic properties of ephedrine, effects which led to a normalization of body composition of the obese to that of the lean. Such ephedrine-aspirin mixtures, often found in over-the-counter preparations for asthma and bronchial disorders, could be put to new use as aids for treatment of human obesity.

Reversal of obesity in the genetically obese fa/fa Zucker rat with an ephedrine/methylxanthines thermogenic mixture

Administration of a thermogenic mixture of ephedrine, caffeine and theophylline to grossly obese (11-12 mo old) fa/fa Zucker rats led to a rapid decline in their body weight, which reached lean levels within 9-10 wk, and this postobese weight was maintained for another 5-6 wk. Compared to the no-drug obese controls (O-ND), food intake was reduced by 70% during the dynamic phase of weight loss and by 50% during the postobese period in the food-restricted animals (O-FR) and by about 40% during both phases in the ephedrine/methylxanthines (O-E/Mx) animals. Energy expenditure in the O-FR group was lower than in the O-E/Mx group by 25-33%. Analysis of body composition showed that body fat in both O-FR and O-E/Mx groups was much lower than in the O-ND group, by 2.5- and 4-fold, respectively, and body protein was lower by 50 and 28%, respectively. Thus, compared to the O-ND group, the fat:protein ratio was only 25% lower in the O-FR animals but was three times less in the O-E/Mx group. These findings demonstrate that in the fa/fa rat a mixture of ephedrine and methylxanthines reduces food intake but also minimizes the fall in metabolic rate that usually accompanies such an energy deficit, effects that led to a reversal of their gross obesity. The ability of ephedrine alone or in combination with methylxanthines to reverse obesity in animal models with dietary and hypothalamic etiologies is thus extended to the obesity resulting from the inheritance of a single-gene recessive defect.

Screening of drugs for thermogenic anti-obesity properties: antidepressants

Twelve antidepressant drugs, currently in clinical use, were screened for thermogenic properties on the basis of their ability to stimulate the activity of the sympathetic nervous system via an inhibitory effect on noradrenaline reuptake into the sympathetic neurons. Drug screening was carried out on mice made obese by hypothalamic lesioning using monosodium glutamate. Preliminary experiments, based on changes in body weight and food intake in response to increased doses of the drugs, indicate that most of the twelve antidepressants possess thermogenic potential. In particular, butriptyline, protriptyline and nortriptyline were most effective in causing marked losses in body weight without altering the food intake of the mice. The potent anti-obesity thermogenic properties of these three antidepressants were confirmed during a 10-week energy balance study involving measurements of energy expenditure over the entire period by the comparative carcass method, as well as by measurement of 24 h oxygen consumption. These studies indicate that the methodology employed in the preliminary screening is valid for identifying drugs with thermogenic potential, and demonstrate that many antidepressants currently in clinical use have marked thermogenic properties, and could therefore influence the nutritional status of patients under drug therapy.

The effect of parasympathetic drugs on energy expenditure: relevance to the autonomic hypothesis

The influence of the parasympathetic nervous system in the control of energy expenditure was investigated in obese and lean rodents during chronic administration of drugs that alter parasympathetic transmission. In the genetically obese ob/ob mice and fa/fa rats and in monosodium glutamate induced hypothalamic obese mice, administration of the parasympathetic inhibitors hyoscine, benztropine, and mecamylamine either had no effect on energy balance or caused losses in body weight that could entirely be accounted for by a reduction in food intake; 24-h oxygen consumption in drug-treated animals was no different from that of the nontreated controls. In the lean animals, both the parasympathetic inhibitors (hyoscine, benztropine, and mecamylamine) and stimulators (bethanecol and neostigmine) had no influence on energy balance nor on body composition. These studies refute the concept that an overactive parasympathetic tone underlies the elevated energetic efficiency of obese models and suggests that the parasympathetic nervous system is unlikely to play an important role in the long-term control of energy expenditure.

The thermogenic properties of ephedrine/methylxanthine mixtures: animal studies

An over-the-counter preparation containing ephedrine, caffeine, and theophylline was examined for thermogenic anti-obesity properties. Administration of the methylxanthines to MSG-induced obese mice for 6 wk had no effect on energy balance or body composition. In contrast, treatment with ephedrine alone caused losses of 14% in body weight and 42% in body fat, effects brought about mainly by a 10% increase in energy expenditure. These changes were accentuated when ephedrine was administered together with one or both methylxanthines: energy expenditure was increased by a further 10%, and led to a reduction of about 25% in body weight and 75% in body fat, while the total food intake and body protein were unaltered. These results indicate that dietary methylxanthines like caffeine and theophylline, although alone have little effect on energy balance, can nevertheless markedly potentiate the thermogenic anti-obesity effect of ephedrine and normalize the body composition of the obese to the lean levels.

The thermogenic properties of ephedrine/methylxanthine mixtures: human studies

The thermogenic effect of an over-the-counter preparation containing 22 mg ephedrine, 30 mg caffeine and 50 mg theophylline was investigated in human volunteers with a predisposition to obesity and also in the lean. The ephedrine/methylxanthines mixture was twice as effective as ephedrine alone in increasing the fasting metabolic rate of both subject groups, and it normalized the reduced thermogenic response to a 1.25-MJ meal observed in those predisposed to obesity. Measurements of 24-h energy expenditure in a respirometer indicate that the mixture had no effect on the daily metabolic rate of the lean, but was effective in causing a significant 8 percent increase in the 24-h energy expenditure of those subjects predisposed to obesity. These studies indicate that relatively mild doses of dietary methylxanthines in combination with ephedrine can raise daily energy expenditure of those predisposed to obesity, mainly by correcting their defective thermogenic response to food. Such ephedrine/methylxanthine preparations could be useful as aids in the treatment of obesity.

Genetic and dietary influences on the levels of diet-induced thermogenesis and energy balance in adult mice

Genetic and dietary influences on energy balance and diet-induced thermogenesis were investigated in 5 strains of adult mice fed either a stock diet or a varied and palatable cafeteria diet for 4 weeks. Compared to their stock-fed controls, the total metabolisable energy intake of mice fed a cafeteria diet increased by 60, 45, 28, 50 and 35% in the ob/+ or +/+, C57BL/6, DBA/2, BALB/C and CFLP strains, respectively, while energy expenditure, over the entire period, was increased by 53, 21, 24, 53 and 34%, respectively. The results show the presence of diet-induced thermogenesis in most strains studied, and also indicate that variations in food intake were more strongly determined by diet, whereas variations in energy efficiencies were more strongly influenced by genetics.

Increased body fat due to elevated energetic efficiency following chronic administration of inhibitors of sympathetic nervous system activity

The effects on energy balance of drugs known to inhibit the sympathetic nervous system at different sites and with various modes of action were studied in lean mice of the CFLP strain. Metabolizable energy intake was monitored continuously over seven-week experimental periods and energy expenditure was determined by the comparative carcass method as well as by measurements of 24-hour oxygen consumption. Administration of either propranolol, phenoxybenzamine, clonidine, or mecamylamine had no influence on energy balance nor on body composition. On the other hand, administration of alpha-methyl para tyrosine, reserpine, and bethanidine, ie, drugs capable of reducing the levels of noradrenaline at sympathetic terminals, resulted in significant increases in body fat by 38%, 24%, and 46% respectively: this effect was brought about by a reduction in the metabolic rate of these drug-treated groups and the efficiency of energy utilization (both gross and net) was increased by three to nine times. These studies indicate that chronic administration of drugs that act at the receptor level to inhibit sympathetic activity fail to influence metabolic rate, thereby suggesting that thermogenesis under noradrenaline control may involve mechanisms other than the alpha and beta classification of adrenergic receptors. Nonetheless, the ability of some drugs which both reduce noradrenaline levels and decrease metabolic rate would support the concept of an important role of the sympathetic nervous system in the overall control of thermogenesis and in energy balance regulation.

A comparative study of the effects of white sugar, unrefined sugar and starch on the efficiency of food utilization and thermogenesis

Energy balance studies with weanling rats and mice were carried out to investigate the chronic effects of diets containing white sugar, unrefined sugar, and starch as sole carbohydrate on body composition and energetic efficiency. The results show no significant differences in energetic efficiency and in body composition of both rats and mice fed the different carbohydrate diets. However, there is a tendency for the sugar-fed animals to have higher metabolizable energy intakes, but rarely was this sufficient to increase body energy since there were corresponding increases in metabolic rate. These studies indicate that differences in energy balance between sugar and starch are small and that any increase in thermogenesis that occurred in some of the groups fed sugar-rich diets was in response to the higher energy intake rather than due to a lower efficiency of utilization of sucrose per se.

Thermogenic drugs for the treatment of obesity: sympathetic stimulants in animal models

Thirty-three drugs known to stimulate the sympathetic nervous system have been screened for thermogenic properties. The results presented are for seven of them. The drugs were tested in five animal models of obesity (genetic (mice and rats), hypothalamic (mice) and dietary (mice and rats] as well as in lean mice. Energy-balance studies were undertaken using the comparative-carcass technique as well as by measurement of daily oxygen consumption. All seven drugs in obese animals tended to reduce body-weight and fat without loss of body protein: they acted by increasing metabolic rate without increasing food intake. They were much less effective in lean animals. These findings lend support to the concept that obesity is due to a diminished activity of the sympathetic nervous system. Differences in the effectiveness of the drugs are discussed in relation to differences between the animal models of obesity. Ephedrine and tranylcypromine were found to be the most effective drugs in this series of experiments and a prima facie case is made for human clinical trials.

Energy balance following sympathetic denervation of brown adipose tissue

The effects of sham, bilateral surgical denervation or excision of interscapular brown adipose tissue on body composition and energetic efficiency were studied in young CFLP mice kept at 25 degrees C and fed a laboratory stock diet. A preliminary experiment showed that 15 weeks following surgery, total body fat was increased by 42% in the denervated group and by 72% in the excised group while body protein was unchanged. In another 7-week energy balance experiment, body fat was also significantly higher by 15 and 18% in the denervated and excised group, respectively, but metabolizable energy intake was slightly lower than that of sham controls. Determination of energy expenditure both by the comparative carcass slaughter technique and by measurement of daily oxygen consumption showed that the metabolic rate was reduced in the denervated nd excised groups. The capacity for thermogenesis, as measured by an increase in oxygen consumption following injections of noradrenaline (600 micrograms/kg body weight) was similar in energetic efficiency, and indicates an important role of the sympathetic nervous system in the regulation of animal heat production by brown adipose tissue and in the overall control of thermogenesis.