Thermoregulatory responses of the inbred heat-tolerant FOK rat to cold.
(25/1528)
The responses of inbred heat-tolerant FOK rats to cold were compared with those of Wistar King A/H (WKAH) and Std:Wistar (WSTR) strains. The fall of colonic temperature during cold exposure was unexpectedly smaller in FOK than in other groups, but the onset of shivering was delayed in FOK. Norepinephrine (NE)-induced in vivo oxygen consumption and the mitochondrial uncoupling protein 1 level of brown adipose tissue (BAT) were not different among the groups, but the cold-induced increases in in vivo oxygen consumption as well as plasma glycerol and free fatty acids were higher in FOK than in other groups. In vitro NE-induced oxygen consumption of BAT was less in FOK than WSTR, but not WKAH. The magnitude of the NE-induced increase in blood flow through BAT was higher in FOK than in other groups. These results suggest that FOK paradoxically have a high capacity for nonshivering thermogenesis in spite of their high capacity for heat tolerance, probably due to an increased lipid utilization and improved circulation of BAT. (+info)
Evidence for the presence of several phosphodiesterase isoforms in brown adipose tissue of Zucker rats: modulation of PDE2 by the fa gene expression.
(26/1528)
The present study was undertaken to characterise the phosphodiesterases (PDEs) present in brown adipose tissue (BAT) of Zucker rat pups and to determine whether the capacity for degradation of cyclic nucleotides was affected by the fatty genotype. Regardless of the genotype, PDE2-4 contributed to total PDE activity, the PDE3 activity equalling the sum of PDE2 and 4 activities. In fa/fa compared to Fa/fa rats, (a) PDE2 activity was significantly increased, (b) Western blot analysis of PDE2 revealed two signals at 71 and 105 kDa, with changes in protein being in good parallelism with changes in activity, (c) the PDE2 mRNA concentration was also significantly increased. In good agreement, the cGMP concentration was decreased in BAT from fa/fa pups. (+info)
The promotion effect of anorectic drugs on aflatoxin B(1)-induced hepatic preneoplastic foci.
(27/1528)
The ability of three extensively used anorectic drugs, namely fenfluramine (FN), fluoxetine (FX) and amphetamine (AM), to alter the development of aflatoxin B(1) (AFB(1))-induced gamma-glutamyl-positive (GGT(+)) preneoplastic liver foci was investigated in 135 male weanling F344 rats. Following AFB(1) administration, 15 rats were killed, while the rest were divided into four groups and fed diets containing either FN, FX, AM or control diet, with half of the animals in each group subsequently being killed at 4 weeks and half at 10 weeks. All three anorectic drugs as expected suppressed initial food intake, growth rate, body weight gain and food efficiency. They also tended to suppress body fat mass and to decrease plasma levels of T(3) and T(4). FN significantly (P < 0.05) increased GGT(+) foci number/cm(2) and number/cm(3), while FX significantly increased GGT(+) foci number/cm(2) and the volume fraction of foci. Histopathological staining also revealed that FN- and FX-treated animals had more serious morphological alterations in their liver tissue. In contrast, foci development was, if anything, suppressed by AM feeding. These results indicate that serotoninergic drugs (FN and FX), as opposed to dopaminergic drugs (AM), may have tumor promoter activity, at least for liver tissue. (+info)
Role of the sympathetic nervous system and insulin in enhancing glucose uptake in peripheral tissues after intrahypothalamic injection of leptin in rats.
(28/1528)
Our previous study demonstrated that microinjection of leptin into the ventromedial hypothalamus (VMH) dramatically increased glucose uptake in the heart, brown adipose tissue (BAT), and skeletal muscles, but not in white adipose tissue (WAT) in conscious unrestrained rats, as assessed in vivo by the 2-[3H]deoxyglucose method. Here we examined the role of the sympathetic nervous system and insulin in enhanced glucose uptake by tissues after hypothalamic leptin injection. Pretreatment with guanethidine significantly suppressed the increased glucose uptake by the tissues in response to leptin injected into the VMH, whereas bilateral adrenal demedullation had no significant effect. Treatment with propranolol but not phenoxybenzamine also decreased significantly enhanced glucose uptake by the tissues. We further examined the interaction of the effects of hypothalamic leptin and insulin administered peripherally by clamping the glucose concentrations at a constant level. When leptin was injected into the VMH and a maximal dose of insulin was administered intravenously, the rates of glucose uptake by the heart, BAT, and skeletal muscles, but not by WAT, markedly increased beyond the values reached by insulin stimulation alone. Surgical sympathetic denervation of BAT abolished the enhancement of glucose uptake in this tissue, decreasing to the level stimulated by insulin alone. These results appear to indicate that leptin in the hypothalamus enhances glucose uptake in certain peripheral tissues through mediation of a beta-adrenergic mechanism for the sympathetic nerves innervating the tissues and that central leptin and peripheral insulin have a synergistic role in augmenting tissue glucose uptake. (+info)
Difference in induction of uncoupling protein genes in adipose tissues between young and old rats during cold exposure.
(29/1528)
Induction of uncoupling protein (UCP) genes in adipose tissues from young and old rats exposed to cold was compared. UCP1 mRNA expression in brown adipose tissue (BAT) was enhanced in both young and old rats after cold exposure, but the expression was downregulated at 72 h after the exposure only in the young rats. The UCP2 gene was induced notably in BAT of young rats instead of the downregulation of the UCP1 gene, whereas the induction in old rats was almost blunted. The pattern of UCP3 expression was similar to that of UCP1 expression in each group. The effect of cold exposure on the expression of UCP2 genes was also observed in white adipose tissue from the young rats. These results indicate a change in induction of UCP genes in adipose tissues with aging. (+info)
Leptin has acute effects on glucose and lipid metabolism in both lean and gold thioglucose-obese mice.
(30/1528)
Leptin is reported to have effects in peripheral tissues that are independent of its central effects on food intake and body weight. In this study, the acute effects of a single dose of recombinant mouse leptin on lipid and glucose metabolism in lean and gold thioglucose-injected obese mice were examined. Changes were measured 2 h after leptin injection. In lean mice, liver and white adipose tissue (WAT) lipogenesis was inhibited. The activity of the pyruvate dehydrogenase complex (PDHCa), the rate-determining step for glucose oxidation, was reduced in heart, liver, quadriceps muscle, and both brown and white adipose tissues. Muscle and liver glycogen and liver triglyceride (TG) content was unchanged, but muscle TG was decreased. In obese mice, liver and WAT lipogenesis was inhibited and PDHCa reduced in heart and quadriceps muscle. Muscle and liver glycogen was decreased but not TG. Serum insulin was reduced in obese but not lean mice. These results are consistent with a role for leptin in the maintenance of steady-state energy stores by decreasing lipid synthesis and increasing fat mobilization, with decreased glucose oxidation occurring as a result of increased fatty acid oxidation. (+info)
The bioenergetics of brown fat mitochondria from UCP1-ablated mice. Ucp1 is not involved in fatty acid-induced de-energization ("uncoupling").
(31/1528)
The bioenergetics of brown fat mitochondria isolated from UCP1-ablated mice were investigated. The mitochondria had lost the high GDP-binding capacity normally found in brown fat mitochondria, and they were innately in an energized state, in contrast to wild-type mitochondria. GDP, which led to energization of wild-type mitochondria, was without effect on the brown fat mitochondria from UCP1-ablated mice. The absence of thermogenic function did not result in reintroduction of high ATP synthase activity. Remarkably and unexpectedly, the mitochondria from UCP1-ablated mice were as sensitive to the de-energizing ("uncoupling") effect of free fatty acids as were UCP1-containing mitochondria. Therefore, the de-energizing effect of free fatty acids does not appear to be mediated via UCP1, and free fatty acids would not seem to be the intracellular physiological activator involved in mediation of the thermogenic signal from the adrenergic receptor to UCP1. In the UCP1-ablated mice, Ucp2 mRNA levels in brown adipose tissue were 14-fold higher and Ucp3 mRNA levels were marginally lower than in wild-type. The Ucp2 and Ucp3 mRNA levels were therefore among the highest found in any tissue. These high mRNA levels did not confer on the isolated mitochondria any properties associated with de-energization. Thus, the mere observation of a high level of Ucp2 or Ucp3 mRNA in a tissue cannot be taken as an indication that mitochondria isolated from that tissue will display innate de-energization or thermogenesis. (+info)
Influence of thyrotrophin-releasing hormone on thermoregulatory adaptation after birth in near-term lambs delivered by caesarean section.
(32/1528)
We investigated the hypothesis that exogenous stimulation with thyrotrophin-releasing hormone (TRH) immediately prior to umbilical cord clamping can improve thermoregulatory adaptation after birth in near-term lambs delivered by Caesarean section. Lambs received an umbilical vein injection of saline +/- TRH (8 microg) prior to cord clamping. The rate of change in colonic temperature and oxygen consumption after birth were not influenced by TRH, but TRH-treated lambs exhibited a greater incidence of shivering compared with controls over the first hour of neonatal life. Two and a half hours after birth, TRH-treated lambs possessed brown adipose tissue (BAT) with a higher thermogenic activity (i.e. GDP binding to mitochondrial protein), but their BAT had a reduced DNA content and they had less hepatic glycogen than control lambs. TRH administration had no effect on iodothyronine 5' deiodinase activity in BAT and liver, or on plasma concentrations of total triiodothyronine, thyroxine, cortisol or free fatty acids. Three TRH-treated but no control lambs, failed to establish continuous breathing, so tissues from these treated lambs together with time-matched controls were sampled 25 min after birth. These 'non-surviving' TRH-treated lambs had very high plasma catecholamine concentrations, but their lung weights were similar to controls. 'Surviving' TRH-treated lambs possessed lungs with less DNA than non-surviving TRH-treated lambs. It is concluded that umbilical vein injection of TRH prior to umbilical cord clamping increases the recruitment of both shivering and non-shivering thermogenesis after birth. (+info)