Ciglitazone is not itself thermogenic but increases the potential for thermogenesis in lean mice

Chronic dietary administration of the oral hypoglycaemic ciglitazone (3 g/day for 14–28 days) to lean, non-diabetic CD1 mice resulted in increased brown adipose tissue mitochondrial GDP binding and a marked increase in the thermic effect of the beta-adrenoceptor agonist BRL 26830A. However, ciglitazone was not itself thermogenic after an acute dose, nor did it raise resting metabolic rate during chronic dietary dosing.     

Caladium bicolor (Araceae) and Cyclocephala celata (Coleoptera, Dynastinae): a well-established pollination system in the Northern Atlantic rainforest of Pernambuco, Brazil

Flowering, pollination ecology, and floral thermogenesis of Caladium bicolor were studied in the Atlantic Rainforest of Pernambuco, NE Brazil. Inflorescences of this species are adapted to the characteristic pollination syndrome performed by Cyclocephalini beetles. They bear nutritious rewards inside well-developed floral chambers and exhibit a thermogenic cycle which is synchronized to the activity period of visiting beetles. Heating intervals of the spadix were observed during consecutive evenings corresponding to the beginning of the female and male phases of anthesis. Highest temperatures were recorded during the longer-lasting female phase. An intense sweet odour was volatized on both evenings. Beetles of a single species, Cyclocephala celata, were attracted to odoriferous inflorescences of C. bicolor and are reported for the first time as Araceae visitors. All the inflorescences visited by C. celata developed into infructescences, whereas unvisited inflorescences showed no fruit development. Findings of previous studies in the Amazon basin of Surinam indicated that Cyclocephala rustica is a likely pollinator of C. bicolor. This leads to the assumption that locally abundant Cyclocephalini species are involved in the pollination of this species.     

Mitochondrial Proton Leak and the Uncoupling Proteins

An energetically significant leak of protons occurs across the mitochondrial inner membranesof eukaryotic cells. This seemingly wasteful proton leak accounts for at least 20% of thestandard metabolic rate of a rat. There is evidence that it makes a similar contribution tostandard metabolic rate in a lizard. Proton conductance of the mitochondrial inner membranecan be considered as having two components: a basal component present in all mitochondria,and an augmentative component, which may occur in tissues of mammals and perhaps ofsome other animals. The uncoupling protein of brown adipose tissue, UCP1, is a clear exampleof such an augmentative component. The newly discovered UCP1 homologs, UCP2, UCP3,and brain mitochondrial carrier protein 1 (BMCP1) may participate in the augmentativecomponent of proton leak. However, they do not appear to catalyze the basal leak, as this isobserved in mitochondria from cells which apparently lack these proteins. Whereas UCP1plays an important role in thermogenesis, the evidence that UCP2 and UCP3 do likewiseremains equivocal.     

Dynamics and precision of thermoregulatory responses of eastern skunk cabbage Symplocarpus foetidus

Inflorescences of the arum lily Symplocarpus foetidus are thermogenic and thermoregulatory. The spadix increases respiratory heat production rate as ambient temperature decreases. This study examined the relationships between spadix temperature (T_s), respiration rate () and ambient temperature (T_a) at equilibrium and during transient responses to step changes in T_a. Intact inflorescences inside a miniature constant temperature cabinet in the field showed the most precise temperature regulation yet recorded; over a 37.4 °C range in T_a (?10.3 to 27.1 °C), T_s changed only 3.5 °C (22.7 to 26.2 °C). Regulated temperatures were not related to spadix size (1.9–7.3 g) or circadian cycle. Dynamic responses to step changes in T_a involved a phasic change in T_s, first in the same direction as T_a, then reversing at 38.3 min, and finally approaching equilibrium at 87.6 min, on average. Meanwhile changed in a monotonic curve toward equilibrium. Models revealed that the dynamics of temperature change were inconsistent with simply a physical lag in the system, but involved some form of biochemical regulation, possibly by changes in activity of a rate‐limiting functional protein.     

Increased uncoupling protein-2 and -3 gene expressions in skeletal muscle of STZ-induced diabetic rats

Streptozotocin (STZ)-induced diabetic animals are vulnerable to cold stress. Uncoupling proteins (UCPs) play an important role in regulating thermogenesis. We investigated the gene expressions of UCPs in brown adipose tissue (BAT), white adipose tissue (WAT), liver and gastrocnemius muscle of STZ-diabetic rats using Northern blot. UCP-1, -2 and -3 mRNA expressions in BAT were all remarkably lower in STZ-diabetic rats than those in control rats. Both UCP-2 and -3 gene expressions in gastrocnemius muscle were substantially elevated in STZ-diabetic rats and insulin treatment restored UCP gene expressions to normal levels. These results suggest that in STZ-diabetic rats, the overexpression of UCP-2 and UCP-3 in skeletal muscle provides a defense against hypothermogenesis caused by decreased UCPs in BAT.     

Nitric oxide reduces the thermogenic changes induced by lateral hypothalamic lesion

The experiment described here tests the effect of intracerebroventricular (icv) injection of nitric oxide (NO) precursors, such as L-arginine (L-arg) and nitroprusside (NP), on the thermogenic changes induced by lesion of the lateral hypothalamus (LH). The firing rate of the nerves innervating interscapular brown adipose tissue (IBAT), along with IBAT and colonic temperatures (T_IBAT and T_C) were monitored in urethane-anesthetized male Sprague-Dowley rats lesioned in the LH. These variables were measured before and after and icv injection of 4 μmol L-arg or 400 nmol NP. The same variables were also monitored in: a) lesioned rats with icv administration of saline; b) sham-lesioned animals with icv injection of L-arg or NP; c) sham-lesioned rats with icv injection of saline. The results show that L-arg or NP injection reduces the increases in firing rate, T_IBAT, and T_C induced by LH lesion. These findings suggest that NO plays a key role in the thermogenic changes following LH lesion.