Hyperthermic and anorectic effects of oxazolidines derived from L-ephedrine in rats

Oxazolidines synthesized from (-) ephedrine have been proposed as potential pro-drugs, but no pharmacological data on these compounds has been yet reported. In this study, four such compounds are tested in rats for ephedrine-like activity using the hyperthermia and anorexia models. The compounds were synthesized by reaction of (-) ephedrine with salicylaldehyde, acetone, cyclohexanone, and benzaldehyde, respectively. The results showed that all of the compounds decreased food intake significantly, but only the acetone and the salicylaldehyde derivatives caused a significant elevation of body temperature. All of the compounds were less effective than (-) ephedrine in the anorexia model. The acetone and salicylaldehyde derivatives showed similar potency to (-) ephedrine in the hyperthermia model.     

Hyperammonemia in anorectic tumor-bearing rats

Plasma ammonia concentrations were significantly elevated by 150% in anorectic rats bearing methylcholanthrene sarcomas. Assessment of ammonia levels in blood draining these sarcomas indicated nearly a 20-fold increase as compared with venous blood in control rats, suggesting the tumor mass as the source of this increase in ammonia. Infusing increasing concentrations of ammonium salts produced anorexia and alterations in brain amino acids in normal rats that were similar to those observed in anorectic tumor-bearing rats. Therefore, these results suggest that ammonia released by tumor tissue may be an important factor in the etiology of cancer anorexia.     

Thermogenic effects of dihydrocodeine in the rat

The object of this study was to assess the effects of dihydrocodeine on thermogenesis and brown adipose tissue activity in the rat from measurements of oxygen consumption and blood flow. Acute injection of dihydrocodeine tartrate (s.c.) stimulated resting oxygen consumption (VO2) in Sprague-Dawley rats in a dose-dependent manner (0.5-50 mg/kg), with a peak response (40-45% increase) occurring at 10-25 mg/kg. This effect was also observed in urethane-anaesthetized rats (although the effect was reduced) and in conscious animals following gastric intubation with the drug. Pretreatment of rats with either a beta-adrenergic antagonist (propranolol, 20 mg/kg), ACTH (4 g/kg), or an opiate antagonist (WIN44441-1, 2 mg/kg) significantly reduced the response to dihydrocodeine, whereas corticosterone injection (5 mg/kg) enhanced the effect. Surgical adrenalectomy or hypophysectomy (HYPX) almost completely abolished the thermogenic effect of dihydrocodeine. Dihydrocodeine also stimulated VO2 in lean (58% increase) and genetically obese Zucker rats (69% increase), and in both Zucker genotypes these responses were only slightly affected by HYPX, but enhanced in HYPX rats treated daily with corticosterone (1 mg/kg). Tissue blood flow, assessed from the distribution of radiolabelled microspheres, was unaffected in white adipose tissue, skeletal muscle, testes, kidney, brain, and liver (arterial supply) after a single injection of dihydrocodeine (25 mg/kg), but flow to interscapular and perirenal brown adipose tissue was increased by 9- to 10-fold. Surgical sympathectomy of brown adipose tissue prevented the increase in blood flow.(ABSTRACT TRUNCATED AT 250 WORDS)     

Thermogenic side effects to migratory predisposition in shorebirds

In the calidrine sandpiper red knot (Calidris canutus), the weeks preceding takeoff for long-distance migration are characterized by a rapid increase in body mass, largely made up of fat but also including a significant proportion of lean tissue. Before takeoff, the pectoral muscles are known to hypertrophy in preparation for endurance flight without any specific training. Because birds facing cold environments counterbalance heat loss through shivering thermogenesis, and since pectoral muscles represent a large proportion of avian body mass, we asked the question whether muscle hypertrophy in preparation for long-distance endurance flight would induce improvements in thermogenic capacity. We acclimated red knots to different controlled thermal environments: 26 degrees C, 5 degrees C, and variable conditions tracking outdoor temperatures. We then studied within-individual variations in body mass, pectoral muscle size (measured by ultrasound), and metabolic parameters [basal metabolic rate (BMR) and summit metabolic rate (M(sum))] throughout a 3-mo period enclosing the migratory gain and loss of mass. The gain in body mass during the fattening period was associated with increases in pectoral muscle thickness and thermogenic capacity independent of thermal acclimation. Regardless of their thermal treatment, birds showing the largest increases in body mass also exhibited the largest increases in M(sum). We conclude that migratory fattening is accompanied by thermoregulatory side effects. The gain of body mass and muscle hypertrophy improve thermogenic capacity independent of thermal acclimation in this species. Whether this represents an ecological advantage depends on the ambient temperature at the time of fattening.     

Thermogenic capacity of the brown adipose tissue of developing rats; effects of rearing temperature

A chronological study was performed to investigate the postnatal development of the thermogenic capacity of the brown adipose tissue (BAT) comparing rats born and reared at 16 degrees C (cold) or 28 degrees C (control). Mitochondrial mass, cytochrome-c-oxidase activity (index of oxidative capacity) and GDP binding to mitochondria (uncoupling test) were investigated in rats from 1 to 33 days of age. Specific cytochrome-c-oxidase activity was the same in both groups during the first week, then increased in the cold group and decreased in controls; from the 9th day it was always twice as high in the former as in the latter. Specific binding of GDP to mitochondrial proteins remained almost constant in control rats during the first week contrasting with a rapid increase in that for cold rats. Afterwards it decreased in both groups until weaning but remained five times as high in cold rats as in control rats. As growth of BAT is faster and mitochondrial content greater in cold reared rats, the capacity of the tissue for thermogenesis appeared to be greatly temperature dependent soon after birth and during the entire suckling period. However the mechanisms of this stimulation remain to be elucidated.     

Comparison of the effects of fenfluramine and other anorectic agents in different feeding and drinking paradigms in rats

Fenfluramine (2.5 and 5 mg/kg) significantly suppressed the food intake of rats following food deprivation, administration of 2-deoxy-D-glucose (2DG), and during tail pressure. This suggests that fenfluramine has relatively general anorectic potency. Other "serotonergic" anorectics were studied for comparison. In a second experiment we determined that norfenfluramine and quipazine greatly suppressed food intake following food deprivation but, at the same doses, had relatively small effects on water intake following water deprivation. This was true for intraperitoneal and cerebroventricular routes of administration. The data have relevance for specificity of action of these agents and for the possible contribution of dopamine antagonist properties.     

Thermogenic and lipogenic activities in brown adipose tissue of I-strain mice.

Specific binding of 125I-labelled human somatotropin was demonstrated in isolated hepatocytes from male mice. In the presence of divalent cations (Ca2+ and Mg2+) the binding of 125I-labelled human somatotropin was competitive with ovine prolactin. Scatchard analysis of competition data indicated a KD of 1.4 +/- 0.2 nM and a binding capacity of 13 000 +/- 2000 sites/cell. In the absence of divalent cations and in the presence of EDTA, human and bovine somatotropins were found to be equally effective to displace bound 125I-labelled human somatotropin, while ovine prolactin showed a weak competition. In this case, the binding capacity was 8400 +/- 1500 sites/cell and the KD was 1.1 +/- 0.1 nM.     

PEGylation of cholecystokinin prolongs its anorectic effect in rats

The anorectic compound CCK-9 was coupled to polyethylene glycol 5 kDa, 10 kDa, 20 kDa and 30 kDa, under different reaction conditions. Conjugates were purified by HPLC and characterized by MALDI-TOF MS. A 96% PEGylation yield was obtained in buffer pH 7.5 after 6h reaction at 20 degrees C. The anorectic activity was tested in vivo in rats. A single bolus intra-peritoneal injection of non-modified CCK-9 resulted in a significant initial food intake reduction 30 min after food presentation (87% compared to paired control group). When PEG-CCK-9 conjugates modified with polymers of molecular weight up to 20 kDa were injected, lower but statistically significant initial food intake reductions were obtained (76% for PEG 10 kDa-CCK-9 conjugate compared to control group). The cumulative food intake reduction of non-modified CCK-9 is normalized within 1-2h, whereas the PEG-CCK-9 molecules showed a prolonged anorectic activity lasting for 6h for PEG 5 kDa-CCK-9; 23 h for PEG 10 kDa-CCK-9 and between 8h and 23 h for PEG 20 kDa-CCK-9. For PEG 30 kDa-CCK-9 conjugate, neither an initial nor a cumulative FI reduction was observed. PEG-CCK-9 conjugates show a significantly prolonged anorectic activity in comparison to the non-modified peptide. This effect is most evident for the PEG 10 kDa-CCK-9 conjugate.     

Caffeine and ephedrine stimulated thermogenesis in LA-corpulent rats

Resting metabolic rate (RMR), as well as caffeine (CAF) and ephedrine (EPH) stimulated thermogenesis (VO2) were measured in young adult corpulent (corp) LA/N-cp (LA-corpulent) rats. RMR of lean was greater than corp. Administration of EPH, CAF and EPH + CAF resulted in 32, 48 and 50% increases in VO2, respectively, in both lean and corp rats. The time to attain maximal VO2 was similar for both drugs in both phenotypes, but the duration of maximal VO2 averaged 50, 26 and 42% longer in corp than lean for EPH, CAF and EPH + CAF, respectively. Acute weight loss following these treatments was greater for corp than lean, and corresponded with the duration of elevated VO2. These results are consistent with a normally functioning end-organ sympathomimetic receptor system in the corp phenotype of the LA/N-cp rat, and suggest that obesity in this model may be caused by factors other than defective brown fat thermogenesis at the end organ level.     

Studies on the anorectic effect of N-acylphosphatidylethanolamine and phosphatidylethanolamine in mice

N-acyl-phosphatidylethanolamine is a precursor phospholipid for anandamide, oleoylethanolamide, and other N-acylethanolamines, and it may in itself have biological functions in cell membranes. Recently, N-palmitoyl-phosphatidylethanolamine (NAPE) has been reported to function as an anorectic hormone secreted from the gut and acting on the brain (Gillum et al., [5]). In the current study, two of our laboratories independently investigated whether NAPE metabolites may be involved in mediating the anorectic action of NAPE i.p. injected in mice. Thus, the anorectic activity of a non-hydrolysable NAPE analogue, having ether bonds instead of ester bonds at sn1 and sn2 was compared with that of NAPE in molar equivalent doses. Furthermore, the anorectic effect of NAPE in NAPE-hydrolysing phospholipase D knockout animals was investigated. As negative controls, the NAPE precursor phosphatidylethanolamine and the related phospholipids phosphatidylcholine and phosphatidic acid were also tested. All compounds except one were found to inhibit food intake, raising the possibility that the effect of NAPE is non-specific.     

Nonadditive interactive effects of polychlorinated biphenyl congeners in rats: role of the 2,3,7,8-tetrachlorodibenzo-p-dioxin receptor

Administration of 3,3',4,4',5,5'-hexa-,3,3',4,4',5-penta-, and 2,3,3'4,4'5-hexa-chlorobiphenyl to immature male Wistar rats caused a thymic atrophy at high dose levels (1.25, 1.0, and 100 mumol/kg, respectively) and induced the hepatic cytochrome P-448 dependent monooxygenases (benzo[a]pyrene hydroxylase and ethoxyresorufin O-deethylase) at both high and low (0.25, 0.01, and 5 mumol/kg, respectively) doses. In contrast, 2,2',4,4',5,5'-hexachlorobiphenyl (HCBP) (300 mumol/kg) did not elicit any of these effects but elevated hepatic 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) cytosolic receptor protein levels (threefold) as previously reported. The effects of hepatic receptor modulation by 2,2',4,4',5,5'-HCBP (300 mumol/kg) on the enzyme induction activities of 3,3'4,4',5-penta-, 3,3'4,4',5,5'-hexa-, and 2,3,3',4,4',5-hexa-chlorobiphenyl were dose-dependent; no interactive effects were observed at high (toxic) doses of these compounds, whereas apparent synergistically increased hepatic microsomal monooxygenase induction activities were noted at the lower submaximal induction doses. It was concluded that the increased responsiveness of the rats was due to elevated hepatic 2,3,7,8-TCDD receptor levels.     

Leptin extends the anorectic effects of chronic PYY(3-36) administration in ad libitum-fed rats

Acute administration of peptide YY(3-36) [PYY(3-36)] results in a reduction in food intake in several different vertebrates. However, long-term continuous administration of PYY(3-36) causes only a transient reduction in food intake, thus potentially limiting its therapeutic efficacy. We hypothesized that a fall in leptin levels associated with reduced food intake could contribute to the transient anorectic effects of continuous PYY(3-36) infusion and thus that leptin replacement might prolong the anorectic effects of PYY(3-36). Seven-day administration of 100 microg x kg body wt(-1) x day(-1) PYY(3-36) using osmotic minipumps caused a significant reduction in food intake of ad libitum-fed rats, but only for the first 2 days postimplantation. Circulating levels of leptin were reduced 1 day following continuous infusion of PYY(3-36), and combined leptin infusion at a dose of leptin that had no anorectic effects on its own (100 microg x kg body wt(-1) x day(-1)) prolonged the anorectic actions of PYY(3-36) in ad libitum-fed rats for up to 6 days postimplantation and yielded reduced weight gain compared with either peptide alone. The inhibitory effects of 100 microg x kg body wt(-1) x day(-1) PYY(3-36) on food intake were absent in rats refed after a 24-h fast and substantially reduced at a dose of 1,000 microg x kg body wt(-1) x day(-1) PYY(3-36). Leptin replacement was unable to recover the anorectic effects of PYY(3-36) in fasted rats. Our results suggest that an acute fall in leptin levels is not solely responsible for limiting duration of action of chronic PYY(3-36) infusion, yet chronic coadministration of a subanorectic dose of leptin can extend the anorectic effects of PYY(3-36).     

Thermogenic responses to selective and nonselective beta-adrenerg agonists in hypothyroidism of Sprague-Dawley rats.

Resting oxygen consumption (VO2) and mitochondrial GDP binding were measured in hypothyroid and euthyroid rats after administration of selective and nonselective beta-adrenoceptor agonists (BRL 35135A and Isoprenaline--BRL, ISO). Resting VO2, VO2 increment and mitochondrial GDP binding after beta-agonists were lower in hypothyroid rats than in the euthyroid group. The reduced response was more marked for ISO than for BRL. These results suggest that BRL is acting on a beta-adrenoceptor which differs from beta-1 and beta-2 adrenoceptors, responsible for the effect of ISO. Activation of thermogenesis via this beta-3 adrenoceptor seems to be less dependent on permissive levels of thyroid hormones than on activation via beta-1 and/or beta-2 adrenoceptors.     

Effect of desmethylimipramine on tissue distribution and anorectic activity of chlorphentermine in rats

The anorectic effect and tissue distribution of chlorphentermine (CP) have been measured in the presence and absence of desmethyl-imipramine (DMI) in rats, following the finding that DMI was a potent displacer of CP from lung tissue in vitro. CP (10 mg/kg) produced significant anorexia for 4–5 hours after intraperitoneal administration and reduced food intake in a manner similar to that of fenfluramine; that is, CP decreased the rate of eating without affecting onset of eating. DMI caused dose-related changes in CP-induced anorexia; 5 mg/kg DMI inhibited the effects of CP (10 mg/kg) while, with 7.5 mg/kg DMI, there was potentiation. DMI (7.5 mg/kg) significantly (P<0.05) decreased CP (10 mg/kg) concentrations in lung tissue and increased concentrations in brain, liver and blood for up to four hours after treatment, but did not affect kidney or skeletal muscle levels. The CP tissue concentration-time profiles for liver, brain and kidney were significantly different in the presence and absence of DMI, suggesting non-linear kinetics, probably due to saturable tissue binding. Using a simple model to describe eating behaviour, the increased anorexia was found to be linearly related to the higher brain levels of CP seen in the presence of DMI.     

Thermogenic responses of high-altitude adapted rats on low temperatures and low pressures

The male rats were raised in two groups, one at Mt. Yatsugatake (2,100 m above sea level, the average ambient temperature 12.5 degrees C) for 30 days, and the other at a laboratory of Matsumoto (610 m above sea level, the average temperature 20 degrees C). The steady-state oxygen consumptions (VO2) and the rectal temperatures (TR) were measured under exposure conditions of various temperatures combined with different simulated altitudes. The values of VO2 and TR for a control group at 610 m-20 degrees C were regarded as 100% and the relative changes to the control values were obtained at various temperatures in the respective low-pressure condition. When measured at a simulated altitude of 2,000 m on the 2nd day after the rats raised at Mt. Yatsugatake were translocated to Matsumoto, the values at 0 degrees C and 10 degrees C room temperatures, VO2 and TR, were still significantly increased as compared with those of rats raised at Matsumoto. On the 40th day after the translocation from Mt. Yatsugatake, however, the values turned out to exhibit no significant difference in both groups. These results indicated that the greater thermogenesis of high-altitude adapted rats had been established by combined stimuli of low temperatures and low pressures as compared with those of Matsumoto-level adapted rats, but the responses returned to the control level by deadaptation process at 40 days after the translocation.     

Comparison of anorectic drugs in rats trained to discriminate between satiation and deprivation

Eight male rats were trained to discriminate between the internal states produced by food deprivation of 3 hours (satiation) and that produced by food deprivation of 27 hours duration (deprivation). One lever, in a two-lever operant chamber, had to be pressed to receive reinforcement in the satiation state, whereas pressing the other lever was required when the rat was in the deprivation state. Once the rats were trained, increasing the number of hours of food deprivation, from 1 to 48 hours, resulted in more deprivation-appropriate lever responses in the two-lever operant task. Administration of doses of fenfluramine (0.5-1.5 mg.kg), its active metabolite norfenfluramine (0.25-1.0 mg/kg) or d-amphetamine (0.5-1.5 mg/kg) produced a dose-responsive decrease in deprivation-appropriate responses when each drug/dose was injected (i.p.) 15 min prior to deprivation (27 hours) testing. Norfenfluramine was 1.5 times more potent than fenfluramine which was 1.5 times more potent than amphetamine.     

Endogenous amylin contributes to the anorectic effects of cholecystokinin and bombesin

Previous studies indicated that amylin contributes to the anorectic effects of cholecystokinin (CCK) and bombesin (BBS), possibly by enhancing the release of pancreatic amylin or by modulating their anorectic actions within the central nervous system (CNS). To elucidate the interaction between amylin and CCK or BBS, respectively, we investigated the influence of an IP injection of CCK or BBS on feeding in amylin-deficient mice (IAPP(-/-)). The anorectic effects of CCK and BBS were nearly abolished in IAPP(-/-) mice compared to wildtype (WT) mice (e.g. 20 microg/kg CCK, 1-h food intake: WT/NaCl 0.53 +/- 0.03 g; WT/CCK 0.16 +/- 0.03 g (P < 0.001); IAPP(-/-)/NaCl 0.49 +/- 0.05 g; IAPP(-/-)/CCK 0.39 +/- 0.04 g). Acute amylin replacement restored the anorectic effect of CCK in IAPP(-/-) mice.To find out whether CCK or BBS enhance the feeding-induced release of pancreatic amylin, we injected rats with CCK-8 (0.5-50 microg/kg) or BBS (5 microg/kg) and measured plasma amylin levels after injections. Neither CCK nor BBS increased the plasma amylin level in rats. We suggest that the mediation of the anorectic effects of CCK and BBS by amylin is not dependent on a CCK- or BBS-induced release of pancreatic amylin, but may rather be due to a modulation of their effects by amylin within the CNS.