The cannabinoid Δ(9)-tetrahydrocannabivarin (THCV) ameliorates insulin sensitivity in two mouse models of obesity.

BACKGROUND: Cannabinoid type-1 (CB1) receptor inverse agonists improve type 2 diabetes and dyslipidaemia but were discontinued due to adverse psychiatric effects. Δ(9)-Tetrahydrocannabivarin (THCV) is a neutral CB1 antagonist producing hypophagia and body weight reduction in lean mice. We investigated its effects in dietary-induced (DIO) and genetically (ob/ob) obese mice. METHODS: We performed two dose-ranging studies in DIO mice; study 1: 0.3, 1, 2.5, 5 and 12.5 mg kg(-1), oral twice daily for 30 days and study 2: 0.1, 0.5, 2.5 and 12.5 mg kg(-1), oral, once daily for 45 days. One pilot (study 3: 0.3 and 3 mg kg(-1), oral, once daily) and one full dose-ranging (study 4: 0.1, 0.5, 2.5 and 12.5 mg kg(-1), oral, once daily) studies in ob/ob mice for 30 days. The CB1 inverse agonist, AM251, oral, 10 mg kg(-1) once daily or 5 mg kg(-1) twice daily was used as the positive control. Cumulative food and water intake, body weight gain, energy expenditure, glucose and insulin levels (fasting or during oral glucose tolerance tests), plasma high-density lipoprotein and total cholesterol, and liver triglycerides were measured. HL-5 hepatocytes or C2C12 myotubes made insulin-resistant with chronic insulin or palmitic acid were treated with 0, 1, 3 and 10 µM THCV or AM251. RESULTS: THCV did not significantly affect food intake or body weight gain in any of the studies, but produced an early and transient increase in energy expenditure. It dose-dependently reduced glucose intolerance in ob/ob mice and improved glucose tolerance and increased insulin sensitivity in DIO mice, without consistently affecting plasma lipids. THCV also restored insulin signalling in insulin-resistant hepatocytes and myotubes. CONCLUSIONS: THCV is a new potential treatment against obesity-associated glucose intolerance with pharmacology different from that of CB1 inverse agonists/antagonists.

A new, highly selective murine peroxisome proliferator-activated receptor δ agonist increases responsiveness to thermogenic stimuli and glucose uptake in skeletal muscle in obese mice.

AIM: We investigated how GW800644, the first pharmacologically selective murine peroxisome proliferator-activated receptor δ (PPARδ) agonist, affects energy balance, glucose homeostasis and fuel utilization by muscle in obese mice. METHODS: Potencies were determined in transactivation assays. Oral glucose tolerance was determined after 14 and 22 days' administration (10 mg/kg body weight, twice daily) to Lep(ob)/Lep(ob) mice. Food intake and energy expenditure were measured during a 26-day experiment, and plasma metabolites and 2-deoxyglucose uptake in vivo at termination. Palmitate oxidation and 2-deoxyglucose uptake by isolated soleus muscles were measured after 14 (in lean and obese mice) and 26 days. RESULTS: GW800644 activated murine PPARδ (EC(50) 2 nM), but caused little to no activation of PPARα or PPARγ up to 10 µM. It did not increase liver weight. GW800644 reduced food intake and body weight in obese mice after 8 days. It did not affect resting energy expenditure, but, compared to pair-fed mice, it increased the response to a ß(3)-adrenoceptor agonist. It improved glucose tolerance. GW800644, but not pair-feeding, reduced plasma glucose, insulin and triglyceride concentrations. It increased 2-deoxyglucose uptake in vivo in adipose tissue, soleus muscle, heart, brain and liver, and doubled 2-deoxyglucose uptake and palmitate oxidation in isolated soleus muscle from obese but not lean mice. CONCLUSIONS: PPARδ agonism reduced food intake and independently elicited metabolic effects that included increased responsiveness to ß(3)-adrenoceptor stimulation, increased glucose utilization and fat oxidation in soleus muscle of Lep(ob)/Lep(ob) but not lean mice and increased glucose utilization in vivo in Lep(ob)/Lep(ob) mice.

Some mathematical and technical issues in the measurement and interpretation of open-circuit indirect calorimetry in small animals.

Indirect calorimetry is increasingly used to investigate why compounds or genetic manipulations affect body weight or composition in small animals. This review introduces the principles of indirect (primarily open-circuit) calorimetry and explains some common misunderstandings. It is not widely understood that in open-circuit systems in which carbon dioxide (CO2) is not removed from the air leaving the respiratory chamber, measurement of airflow out of the chamber and its oxygen (O2) content paradoxically allows a more reliable estimate of energy expenditure (EE) than of O2 consumption. If the CO2 content of the exiting air is also measured, both O2 consumption and CO2 production, and hence respiratory quotient (RQ), can be calculated. Respiratory quotient coupled with nitrogen excretion allows the calculation of the relative combustion of the macronutrients only if measurements are over a period where interconversions of macronutrients that alter their pool sizes can be ignored. Changes in rates of O2 consumption and CO2 production are not instantly reflected in changes in the concentrations of O2 and CO2 in the air leaving the respiratory chamber. Consequently, unless air-flow is high and chamber size is small, or rates of change of O2 and CO2 concentrations are included in the calculations, maxima and minima are underestimated and will appear later than their real times. It is widely appreciated that bigger animals with more body tissue will expend more energy than smaller animals. A major issue is how to compare animals correcting for such differences in body size. Comparison of the EE or O2 consumption per gram body weight of lean and obese animals is misleading because tissues vary in their energy requirements or in how they influence EE in other ways. Moreover, the contribution of fat to EE is lower than that of lean tissue. Use of metabolic mass for normalisation, based on interspecific scaling exponents (0.75 or 0.66), is similarly flawed. It is best to use analysis of covariance to determine the relationship of EE to body mass or fat-free mass within each group, and then test whether this relationship differs between groups.

Inhibition of 11beta-hydroxysteroid dehydrogenase type 1 reduces food intake and weight gain but maintains energy expenditure in diet-induced obese mice.

AIMS/HYPOTHESIS: The 11beta-hydroxysteroid dehydrogenase type-1 inhibitor BVT.2733 lowers blood glucose and insulin in mutant mouse models of obesity and diabetes. Its effects on energy balance and body composition, and their contribution to improved glucose homeostasis have received little attention. MATERIALS AND METHODS: BVT.2733 (100 mg/kg, orally) was given twice daily to lean and diet-induced obese mice for 16 or 17 days. A group of obese mice was pair-fed to the amounts consumed by BVT.2733-treated mice. RESULTS: In both obese and lean mice, BVT.2733 reduced food intake and weight gain, but increased water intake. Pair-feeding caused almost as great a decrease in body weight as BVT.2733. Energy expenditure was 38+/-8% higher in the BVT.2733-treated obese mice than in the pair-fed mice. Terminal plasma corticosterone was raised, lean body weight reduced and percentage fat unchanged in the pair-fed mice (control, 47.8+/-2.6%; pair-fed, 47.1+/-1.9%), whereas BVT.2733 did not reduce lean mass, but did reduce percentage fat (40.9+/-2.0%). BVT.2733 but not pair-feeding reduced both the glucose tolerance AUC and the plasma insulin concentration 30 min after giving glucose. CONCLUSIONS/INTERPRETATION: BVT.2733 reduced food intake but prevented a concomitant reduction in lean body mass and energy expenditure. The latter effects may have contributed to improved glucose tolerance.

Modulation of susceptibility to weight gain and insulin resistance in low birthweight rats by treatment of their mothers with leptin during pregnancy and lactation.

OBJECTIVES: To investigate whether administration of leptin to rats during pregnancy and lactation affects placental 11beta-hydroxysteroid dehydrogenase (11beta-HSD2) activity and the susceptibility of their offspring to weight gain and insulin resistance. DESIGN: Pregnant rats fed on a low-protein diet were administered leptin or saline by subcutaneous minipump from day 14 of gestation and throughout lactation. A further group was fed a normal diet and given saline. After weaning, the offspring of each group were fed on a normal diet until 6 weeks of age and then half of each group was transferred to a high-fat diet until 12 months of age. RESULTS: Plasma leptin levels were raised two-fold on days 16-18 of pregnancy in the leptin-treated dams, but, despite a constant rate of infusion, at parturition they dipped to control levels before rising again. The activity of placental 11beta-HSD2 was reduced by the low-protein diet; this reduction was prevented by treating the dams with leptin. The male offspring of the saline-treated dams gained more weight and had higher plasma leptin levels on the high fat than the chow diet, but the offspring of the leptin-treated dams did not. Fasting blood glucose and intraperitoneal glucose tolerance at 6 and 12 months of age was unaffected by the high-fat diet, but only the offspring of the leptin-treated dams achieved this control without raised insulin levels. CONCLUSIONS: The rate of leptin clearance appears to increase at parturition. The administration of leptin to rats during late pregnancy and lactation makes their male offspring less susceptible to high-fat-diet-induced weight gain and insulin resistance.

Retinoid X receptor agonists have anti-obesity effects and improve insulin sensitivity in Zucker fa/fa rats.

OBJECTIVE: To investigate whether retinoid X receptor agonists act as insulin sensitizers and compare their effects with that of thiazolidinedione BRL 49653 in obese Zucker rats. DESIGN: In two independent studies, obese Zucker rats were dosed orally once daily for 14 days with one of the following treatments: LG 100268 (20 mg/kg), LG 100324 (20 mg/kg), BRL 49653 (3 mg/kg) or vehicle. MEASUREMENTS: Daily food intake and body weight gain, blood glucose, plasma and pancreatic insulin, whole body glucose disposal (by euglycaemic-hyperinsulinaemic clamp) and tissue glucose utilization. RESULTS: The retinoid X receptor agonists (rexinoids) LG 100268 and LG 100324 caused a reduction in the food intake of obese Zucker rats relative to controls and to rats receiving BRL 49653. The two rexinoids also produced a marked decrease in the body weight gain, whereas the growth rate of rats treated with BRL 49653 tended to increase. Both rexinoids and BRL 49653 reduced the plasma insulin concentration of fed rats. LG 100268 and LG 100324 also significantly lowered blood glucose concentrations after 1 week of treatment. The 5 h fasted plasma insulin concentration was significantly lower in the rexinoid-treated groups and the terminal insulin level (at the end of the clamp) tended to be lower in all treated groups compared with animals given the dosing vehicle. However, pancreatic insulin content was not affected by any of the treatments. Under euglycaemic-hyperinsulinaemic clamp conditions, there were no significant differences in the rate of hepatic glucose output and whole body glucose disposal, except that, in experiment 1, BRL 49653 caused significant increase in the glucose infusion rate and muscle glucose utilization. In experiment 2, a similar glucose infusion rate to the controls was achieved in all treatment groups but the steady-state insulin concentration in the treated animals was only about 50% of that in the control animals, despite the fact that all rats received a similar insulin infusion concentration. This suggests that both the rexinoids and BRL 49653 increased insulin clearance. CONCLUSIONS: Chronic administration of retinoid X receptor agonists LG 100268 and LG 100324 to Zucker fa/fa rats reduces food intake and body weight gain, lowers plasma insulin concentrations while maintaining normoglycaemia, indicating an improvement of insulin sensitivity.

Beta-cell tropin- and glucose-induced hypersecretion of insulin and amylin from perfused fatty rat pancreas.

The neurointermediate pituitary peptide beta-cell tropin (BCT) has potent insulin-releasing and lipogenic properties and is elevated in obesity and type-2 diabetes. The effects of BCT and glucose on the release of insulin and amylin from the perfused pancreas of obese 'fatty' (fa/fa) rats and lean (Fa/?) controls were measured. Pancreata were perfused, sequentially, with buffer containing: 5.6 mmol glucose/l (basal); basal glucose +/- 0.5 nmol BCT/l; 16.7 mmol glucose/l (high). Insulin and amylin release during basal glucose treatment was eight to nine times greater from pancreata from fatty than from lean rats. BCT induced a fivefold greater monophasic insulin and amylin release from fatty compared with lean pancreata. When not preceded by BCT there was a twofold greater high glucose-induced amylin release from fatty pancreata but no difference in insulin secretion. When preceded by BCT stimulation, high glucose induced twofold greater insulin and fourfold larger amylin release from fatty compared with lean pancreata. Molar secretion ratios of insulin:amylin varied between 30:1 and 50:1. In view of the elevated levels of BCT found in the fatty rat and in the light of the above findings, it is concluded that the peptide may have a role in the development of hyperinsulinaemia, hyperamylinaemia and insulin resistance in this animal model of obesity and diabetes.

Text-scanning patterns of blind readers using Optacon and braille.

Tactual reading usually requires the coordinated use of the forearm/hand motor and tactile sensory systems. Therefore, in a series of studies of tactual reading behavior, we chose to record the text-scanning patterns of adult blind readers in an attempt to gain further insight into the nature of this process. Reading behavior for four modes of tactual reading was recorded (embossed braille one-hand, embossed braille two-hands, Optacon/letterprint, and Optacon/Inkbraille) by detecting and recording the instantaneous position of light-emitting diodes unobtrusively attached to the finger(s) or the Optacon camera. In addition to the comparative evaluation of the four sets of reading patterns, the salient features of the Optacon/letterprint patterns were quantitatively analyzed in an attempt to characterize this particular mode of reading. The text-scanning patterns of Optacon readers have not been previously reported. In general the text-scanning behavior for all modes of tactual reading seems to be similar; the only remarkable difference appears to be in the reading rates. Regarding Optacon/letterprint performance, reading rate was found to be significantly and negatively correlated with line-changing time and the number of regressions. No significant correlation was evident between rate and regression magnitude.

Inkbraille as a potential new reading system for the blind.

Inkbraille, a reduced size ink-image version of the familiar braille code, was conceived in an attempt to sidestep the major disadvantages of embossed braille, while retaining the unsurpassed reading rates achieved by the blind using that code. Inkbraille would ultimately be translated by a specially designed hand-held electronic device with appropriate tactile output. Such a device is not yet available, so in this study we test the readability of Inkbraille when read by means of a commercially available electronic reading aid, the Optacon, which presents its output tactually on a field of vibrating pins which are sensed with a finger. Three modes of tactual reading were compared: conventional embossed braille, and the Opticon's vibrating-pinfield presentation of typed letters and its presentation of Inkbraille. All subjects were able to read Inkbraille upon initial exposure. Subjects who were tested in multiple sessions exhibited significant increases in Inkbraille reading rates after only limited exposure. Since Inkbraille and letterprint reading rates were the same in this study, the results led the authors to conclude that a rate limitation may have been imposed by the device (the Optacon) that was used to translate both the Inkbraille and the letterprint.