Dopaminergic mechanisms in diet-induced thermogenesis and brown adipose tissue metabolism

Rhamnose Displays an Anti-Obesity Effect Through Stimulation of Adipose Dopamine Receptors and Thermogenesis

The imbalance between energy intake and energy expenditure leads to the prevalence of obesity worldwide. A strategy to simultaneously limit energy intake and promote energy expenditure would be an important new obesity treatment. Here, we identified rhamnose as a nonnutritive sweetener to promote adipose thermogenesis and energy expenditure. Rhamnose promotes cAMP production and PKA activation through dopamine receptor D1 in adipose tissue. As a result, rhamnose administration promotes UCP1-dependent thermogenesis and ameliorates obesity in mice. Thus, we have demonstrated a rhamnose-dopamine receptor D1-PKA axis critical for thermogenesis, and that rhamnose may have a role in therapeutic molecular diets against obesity.

Dopamine receptor D1- and D2-agonists do not spark brown adipose tissue thermogenesis in mice

Brown adipose tissue (BAT) thermogenesis is considered a potential target for treatment of obesity and diabetes. In vitro data suggest dopamine receptor signaling as a promising approach; however, the biological relevance of dopamine receptors in the direct activation of BAT thermogenesis in vivo remains unclear. We investigated BAT thermogenesis in vivo in mice using peripheral administration of D1-agonist SKF38393 or D2-agonist Sumanirole, infrared thermography, and in-depth molecular analyses of potential target tissues; and ex vivo in BAT explants to identify direct effects on key thermogenic markers. Acute in vivo treatment with the D1- or D2-agonist caused a short spike or brief decrease in BAT temperature, respectively. However, repeated daily administration did not induce lasting effects on BAT thermogenesis. Likewise, neither agonist directly affected Ucp1 or Dio2 mRNA expression in BAT explants. Taken together, the investigated agonists do not seem to exert lasting and physiologically relevant effects on BAT thermogenesis after peripheral administration, demonstrating that D1- and D2-receptors in iBAT are unlikely to constitute targets for obesity treatment via BAT activation.

Dopamine directly increases mitochondrial mass and thermogenesis in brown adipocytes

Brown adipose tissue (BAT) is key to energy homeostasis. By virtue of its thermogenic potential, it may dissipate excessive energy, regulate body weight and increase insulin sensitivity. Catecholamines are critically involved in the regulation of BAT thermogenesis, yet research has focussed on the effects of noradrenaline and adrenaline. Some evidence suggests a role of dopamine (DA) in BAT thermogenesis, but the cellular mechanisms involved have not been addressed. We employed our extensively characterised murine brown adipocyte cells. D1-like and D2-like receptors were detectable at the protein level. Stimulation with DA caused an increase in cAMP concentrations. Oxygen consumption rates (OCR), mitochondrial membrane potential (Δψ_m) and uncoupling protein 1 (UCP1) levels increased after 24 h of treatment with either DA or a D1-like specific receptor agonist. A D1-like receptor antagonist abolished the DA-mediated effect on OCR, Δψ_m and UCP1. DA induced the release of fatty acids, which did not additionally alter DA-mediated increases of OCR. Mitochondrial mass (as determined by (i) CCCP- and oligomycin-mediated effects on OCR and (ii) immunoblot analysis of mitochondrial proteins) also increased within 24 h. This was accompanied by an increase in peroxisome proliferator-activated receptor gamma co-activator 1 alpha protein levels. Also, DA caused an increase in p38 MAPK phosphorylation and pharmacological inhibition of p38 MAPK abolished the DA-mediated effect on Δψ_m In summary, our study is the first to reveal direct D1-like receptor and p38 MAPK-mediated increases of thermogenesis and mitochondrial mass in brown adipocytes. These results expand our understanding of catecholaminergic effects on BAT thermogenesis.

Bromocriptine for diabetes mellitus type II

A quick-release formulation of bromocriptine is the latest drug approved by the US Food and Drug Administration for the treatment of type 2 diabetes mellitus. Most interestingly, the development of this drug stems from studies of hibernation in rodents. This article will review the physiology that led to the development of this new drug, as well as its indications, clinical use, benefits, and contraindications.

Effects of paradoxical sleep deprivation and cocaine on genital reflexes in hyperlipidic-fed rats

The present study was designed to investigate the effects of a hyperlipidic diet (HD) on penile erection (PE) and ejaculation (EJ) induced by cocaine in paradoxical sleep deprived (PSD) rats. Secondly, we aimed to verify the influence of HD cafeteria diet on steroid hormone levels. Twenty-one day-old male Wistar rats were randomly assigned into two groups: rats fed with commercial chow diet and rats fed with a palatable HD containing chow mixed with peanuts, milk chocolate and sweet cookies in the proportion of 3:2:2:1. After nine weeks of treatment, the animals were submitted to PSD or maintained as home cage control group for 96 h and challenged with cocaine (7 mg/kg, i.p.). Results showed that the HD led to a reduction in the frequency of erection in the PSD+cocaine group when compared to the PSD+cocaine fed with standard diet. Regardless of the diet, testosterone concentrations were significantly lower and progesterone was higher in the PSD rats than in the respective home-cage control rats. Although there were no hormonal alterations, the findings showed that a long-term HD might modify the stimulating effects of cocaine in potentiating genital reflexes in PSD rats.

Protein-induced changes in energy expenditure in young and old individuals

Resting energy expenditure (EE) has recently been shown to be reduced in elderly human subjects even after adjustment for body size and composition. The present study extended this examination of EE in relation to age by comparing the thermic effect of a protein meal in young men (YM 20-26 yr, n = 9), old men (OM 70-89 yr, n = 9), and old women (OW 67-75 yr, n = 6). EE was measured before and from 1 to 6 h after presentation of 60 g protein and of a control noncaloric meal on separate occasions. Despite substantial differences in body size and composition, the protein-induced increment in EE was similar in all groups [maximum increase: YM 0.21 +/- 0.05, OM 0.17 +/- 0.12, and OW 0.17 +/- 0.04 (SE) kcal/min]. Although fasting plasma norepinephrine (NE) levels differed among all three groups (YM less than OM less than OW), NE concentrations were not affected by protein ingestion. Because protein administration acutely promotes synthesis of dopamine (DA) and serotonin (5-HT), which are both capable of stimulating EE, blockade of extraneuronal synthesis of DA and 5-HT with carbidopa, a competitive inhibitor of aromatic-L-amino acid decarboxylase, failed to suppress (and actually increased) postprandial EE. These data demonstrate that not all mechanisms responsible for EE decline with age and that protein-induced changes in EE are more a function of the oral load itself than of the size, age, or antecedent diet of the individual ingesting the protein.

Influence of fasting and dopamine on the tissue catecholamines diurnal variations

To define the role of catecholamines (CA) in the metabolic adaptation to fasting we examined the effect of exogenous dopamine(DA) on heat production(HP) and CA content in the interscapular brown adipose tissue(IBAT) and adrenals of control-fed and 2-day fasted rats in the morning(M) and in the evening(E). DA stimulates HP in fed rats in the M by 45% but the thermogenic effect of this CA is markedly higher in the E. However, DA had no thermogenic effect in fasted rats. The tissue CA in fed rats fluctuates diurnally: in the IBAT noradrenaline(NA) was much higher in the E while adrenaline(A) in adrenals was lower. DA in fed rats did not change the adrenal A but reduced NA content both in the adrenals and in the IBAT all over the day. Fasting depleted A from adrenals but increased NA content both in the M and in the E. Unlike the adrenals in the IBAT fasting did not affect NA content. In the adrenal gland of fasted rats DA significantly increased the A content to the equal degree during the day, while this CA had no effect on NA content of the IBAT.

Immunohistochemical evidence for the existence of a dopamine- and cyclic AMP-regulated phosphoprotein (DARPP-32) in brown adipose tissue of pigs

The indirect immunofluorescence technique was used to study the cellular localization of DARPP-32, a dopamine- and cyclic AMP-regulated phosphoprotein, in brown adipose tissue of newborn piglets. Clusters of strongly DARPP-32-immunoreactive cells were found in brown adipose tissue from the interscapular area and around lymph nodes close to the kidneys, adrenal glands, descending aorta, and great veins in the neck. The DARPP-32-immunoreactive cells contained multilocular lipid droplets, had round, centrally located nuclei, and were polygonal in shape, thus possessing characteristics and location sites typical for brown fat cells. The results indicate that brown adipose tissue from the newborn pig contains DARPP-32, an intracellular third messenger for dopamine. Together with recent functional data, these results strongly suggest that dopaminergic D1 mechanisms--i.e., activation of adenylate cyclase and formation of cyclic AMP--may be involved in cold-induced, nonshivering, and/or diet-induced thermogenesis.

Fluorescent histochemical demonstration of catecholamines in brown adipose tissue from obese (ob/ob) and lean mice acclimated at different temperatures

Fluorescent histochemistry was used to visualize catecholamines in brown adipose tissue (BAT) of lean and genetically obese mice after they had been acclimated at different temperatures. At all temperatures, strong catecholamine-dependent fluorescence, attributable to the sympathetic innervation, was seen around the blood vessels of BAT from both lean and obese animals. Additionally, catecholamine-dependent fluorescent varicosities, in direct contact with the adipocytes were seen in abundance in lean mice acclimated at 23 degrees, 13 degrees or 4 degrees C and in obese mice acclimated at 13 degrees C. This latter compartment was greatly reduced in lean mice acclimated at 33 degrees C and in obese mice acclimated at 23 degrees and 33 degrees C. Three acute treatments (pretreatment with a monoamine oxidase inhibitor; 24 h food deprivation; and short-term cold exposure followed by short-term warm exposure) all increased the varicose fluorescence associated with adipocytes in obese mice housed at 23 degrees C, which suggests that the low resting level in these animals is attributable, at least in part, to subthreshold concentrations of catecholamines in existing varicosities rather than the absence of sympathetic varicosities per se. These results are in accordance with the results from noradrenaline turnover studies which suggest that the difference in sympathetic nervous system (SNS) activity in BAT from lean and obese (ob/ob) mice is best demonstrated at normal environmental temperatures. The reduced SNS activity in BAT of obese mice (which our studies show to be at the 'cellular' level) is likely to be a major factor in their reduced non-shivering thermogenesis and resultant high efficiency of energy storage as previously suggested by other workers.

The effect of dopamine upon oxidative metabolism of brown fat adipocytes

The effect of dopamine upon the oxygen consumption (QO2) of brown fat adipocytes was measured by polarography. The results showed a marked stimulation of QO2 by dopamine, similar to that induced by noradrenaline. The dopamine response could be blocked by haloperidol, butaclamol, propranolol and by high concentrations of tolazoline. These results suggest a role for dopamine in energy release from brown fat.

(Na+,K+)-ATPase stimulation by sucrose feeding: prevention by 6-hydroxydopamine

The effects of sucrose feeding on parameters associated with (Na+,K+)-ATPase in brown adipose tissue were compared in rats treated with parenteral 6-hydroxydopamine and vehicle. Sucrose feeding significantly increased K+-p-nitrophenylphosphatase and ouabain binding in brown adipose tissue from rats treated with vehicle. By contrast, sucrose feeding had no effects on these measurements in rats treated with parenteral 6-hydroxydopamine. 6-hydroxydopamine did not significantly alter sucrose consumption and there were no significant effects on weight gain during the short experimental period.