Brown Adipose Tissue Pads Research Articles

Thermoregulatory deficits following prenatal alcohol exposure: Structural correlates

Prenatal exposure to alcohol delays the development of thermoregulation in newborn rats. This study examined two possible physiological correlates of this effect. In the first experiment, the effect of prenatal alcohol exposure on the availability of brown adipose tissue for nonshivering thermogenesis was investigated in rat pups from birth to weanling age. Male and female pups were chosen from independent litters with one of three prenatal treatment histories: 35% ethanol-derived calories (35% EDC), pair-fed control (0% EDC), or lab-chow control (LC). Prenatal alcohol exposure resulted in decreased body weight from postnatal (PN) day 1 to 20 compared to controls. Similarly, alcohol-exposed subjects had lighter interscapular brown adipose tissue pads than controls. However, the proportion of brown adipose tissue to body weight in alcohol-exposed pups was not different from controls. It appears that thermoregulatory deficits at birth due to prenatal alcohol exposure are not due to decreased substrate availability. In the second experiment, the relative growth rate of the tail compared to the growth rate of the body was measured in male and female pups from the three prenatal treatment groups. Five-day-old rat pups exposed to alcohol prenatally had relatively slower tail growth than control pups. Since tail growth rate has been associated with ambient temperature, these results suggest that alcohol-exposed rat pups may be experiencing transient periods of cold stress in the nest because of their thermoregulatory deficiencies, which, in turn, could have important implications for neural and body growth retardation seen in Alcohol Related Birth Defects.

THYROID FUNCTION IN MALE ZUCKER RATS EXPOSED TO COLD

Non-obese and obese Zucker rats were exposed to 6 degrees C for 20 days. At the end of the experiment thyroid stimulating hormone (TSH), circulating thyroid hormones, and the weights of the thyroid gland and a brown adipose tissue pad were measured. TSH and 3,5,3'-triiodothyronine concentrations and brown adipose tissue weights increased in response to cold in both phenotypes but by larger amounts in obese rats. Free thyroxine was lower in obese rats. There appears to be no defect in thyroid function in congenitally obese rats exposed to cold, or in their ability to develop brown adipose tissue.

Are the short‐photoperiod‐induced decreases in serum prolactin responsible for the seasonal changes in energy balance in Syrian and Siberian hamsters?

Serum prolactin (PRL) decreases in Syrian (Mesocricetus auratus) and Siberian (Phodopus sungorus sungorus) hamsters following short-photoperiod exposure. Both species also exhibit short-photoperiod-induced changes in body and lipid mass, but in opposite directions; Syrian hamsters increase and Siberian hamsters decrease their body weight, changes reflected nearly exclusively in their carcass lipid content. The purpose of these experiments was to determine whether the photoperiod-induced changes in PRL were responsible for the seasonal changes in energy balance in Syrian and Siberian hamsters by using the strategy of experimentally producing serum PRL levels opposite to those normally associated with the photoperiod in which the animals were housed. In long photoperiods serum PRL was reduced to short-day levels by subcutaneous (s.c.) CB-154 (bromoergocryptine, a dopamine agonist) injections. In short photoperiods, serum PRL was elevated to long-day levels in Syrian hamsters by ectopic pituitary explants, and in Siberian hamsters, serum PRL was elevated by chronic s.c. infusions of ovine PRL (oPRL). In both species, manipulations of serum PRL did not affect food intake, carcass composition, or the wet weight of various white and brown adipose tissue pads (WAT and BAT, respectively). Body weight increased in CB-154-treated Syrian hamsters and decreased in Siberian hamsters, an effect partially reversed by coadministration of oPRL in Syrian, but not Siberian, hamsters. Thus, lowering serum PRL to short-day levels in long-day-housed hamsters of both species mimicked the directional change in body weight appropriate for each species when they are exposed to short days. This effect of CB-154 on body weight may be a result of some as yet unidentified effect of dopaminergic stimulation on overall growth since 1) these changes in body weight were not reflected as changes in lipid mass, as occurs naturally following short-day exposure for each species, and 2) neither species exhibited a reciprocal change in body weight when serum PRL was experimentally elevated in short days. Alternatively, it may be that once the energetic responses to short-day exposure have been fully expressed, the ability of PRL to stimulate the target sites of action for PRL for these responses may be decreased. BAT protein content, cytochrome oxidase activity (measures of metabolic growth of this tissue), and retroperitoneal total and specific lipoprotein lipase (LPL) activities were increased by CB-154 treatment in Syrian hamsters.(ABSTRACT TRUNCATED AT 400 WORDS)

Short- and long-term effects of ovariectomy on food intake, body weight, carcass composition, and brown adipose tissue in rats

This experiment examined both the short-term and the long-term effects of ovariectomy on brown adipose tissue growth and function in rats to determine if reduced brown adipose tissue thermogenesis might contribute to the weight gain and adiposity. Brown adipose tissue function was assessed by measuring sympathetic nervous system activity (estimated by the rate of norepinephrine turnover) and mitochondrial proton conductance (estimated by specific GDP binding) in interscapular brown adipose tissue. Rats ( n=12 per group) were killed 0 (sham), 1, 2, 4, and 12 weeks after ovariectomy. During the first five weeks after ovariectomy rats overate and rapidly gained weight. The weight gain was due to increases in all carcass components. Five weeks after ovariectomy food intake returned to control levels, and body weights stabilized 12–16% above sham-operated control weights for the duration of the experiment. Between week 4 and week 12 after surgery there was a redistribution of carcass composition, with decreases in carcass water and fat-free dry weights offset by a further increase in total carcass lipid. Brown adipose tissue pads were heavier in the 1-, 2-, and 4-week ovariectomy groups, but only in the 4-week group was the increase statistically significant. Brown adipose tissue protein, DNA, and norepinephrine content was unchanged 1-, 2-, 4-, or 12-weeks after ovariectomy. There was no difference in either the rate of norepinephrine turnover or specific mitochondrial GDP binding between sham-operated and 1-, 2-, 4-, or 12-week ovariectomized rats. These results indicate that the dynamic phase of ovariectomy-induced weight gain in rats cannot, even in part, be explained by a reduction in brown adipose tissue thermogenesis.

Short photoperiod stimulates brown adipose tissue growth and thermogenesis but not norepinephrine turnover in Syrian hamsters

This experiment examined the effect of short photoperiod on food intake, body weight, carcass composition, and brown adipose tissue (BAT) activity in female Syrian hamsters (Mesocricetus auratus). BAT function was assessed by measuring sympathetic nervous system (SNS) activity in BAT (estimated by the rate of norepinephrine (NE) turnover), BAT mitochodrial content (estimated by cytochrome c oxidase activity), and BAT mitochondrial proton conductance (estimated by guanosine-5′-diphosphate (GDP) binding to isolated BAT mitochondria). Food intake and body weight were both increased in short photoperiod-housed hamsters (8-hr light, 16-hr dark; LD 8:16) when compared to those of the long photoperiod-housed controls (LD 16:8). The weight gain was entirely due to an increase in carcass lipid. Interscapular BAT (IBAT) pads from short photoperiod-housed hamsters were 53% heavier and contained comparably more protein and DNA. Short photoperiod produced a 118% increase in BAT cytochrome c oxidase activity and a 41% increase in specific mitochondrial GDP binding. Whether expressed per mg wet tissue or per pad, neither the endogenous concentration of NE nor its rate of turnover were changed by short photoperiod exposure. These results demonstrate a dissociation of BAT thermogenesis from SNS activity in BAT from short photoperiod-housed Syrian hamsters.

The effects of supplementation of the diet with highly palatable foods upon energy balance in the rat.

Full energy balance studies have been performed for 9 weeks on four groups of four adult female rats housed in a continuously running indirect calorimeter; for four weeks two of the groups received highly palatable foods in addition to a standard pelleted diet. A further sixteen groups, of which eight received the palatable foods, provided additional carcass composition data. All practicable precautions were taken to measure energy exchange accurately. Comparison of 'start-to-finish' apparent energy balance with carcass composition changes showed a systematic error of approx. +3% of energy throughput. This was most probably caused by losses of energy in food and excreta, which led to over-estimation of energy intake. Variations among individual balance periods added a standard error of approx. +/- 1%: the source of error here was probably imperfect matching of animals analysed at intermediate stages. The rats offered the palatable foods increased their metabolizable energy (m.e.) intake by 106 kJ/day, 51% of the control groups' intake, in the first week of supplementation. Over the whole 4 weeks of supplementation the increase was 64 kJ/day, or 31%. Withdrawal of the palatable foods led to an immediate fall in intake to about two-thirds of control level, and a return to control level over the next 2-3 weeks. Energy expenditure rose more slowly than intake, reaching a fairly steady level ca. 5 days after introduction of the palatable foods. Expenditure was then ca. 22 kJ/day above control level; an increase of 12% above control expenditure or, allowing for systematic and random errors, 33-37% of the additional m.e. intake. Expenditure returned to control level over the 2 weeks after ceasing supplementation. The experimental groups gained weight at a declining rate throughout the period of supplementation. The gain in live body weight at the end was ca. 32 g, but this comprised a carcass weight gain of 37 g and a loss of 5 g gastrointestinal tract contents. The carcass weight gain comprised 27 g fat (i.e. ca. 70% of the weight gained), 9 g lean tissue and 1 g additional water. The gain of carcass energy was 1100 kJ. There was a small increase in body length, an increase in liver weight, and an increase in the weight of the interscapular brown adipose tissue pad. Regression analysis showed that the increase in the weight of the interscapular brown adipose tissue pad reflected the increase in total body fat.(ABSTRACT TRUNCATED AT 400 WORDS)

Palmitate metabolism and norepinephrine sensitivity in brown adipose, liver, and white adipose tissues of Zucker rats.

AbstractInterscapular brown adipose tissue (BAT) in vitro utilization of palmitate (0.5 mM) and glucose (5.0 mM) were examined at 0, 0.1, 1.0, and 10.0 μg norepinephrine-bitartrate (NE)/ml. With increasing NE concentrations, in vitro palmitate oxidation was stimulated and glucose oxidation was inhibited in BAT of nonobese rats. This characterization of BAT metabolism provided the constraints for our analysis of fatty acid utilization and norepinephrine sensitivity at submaximal response concentrations in BAT of lean and obese Zucker rats. Liver and inguinal white adipose were used for tissue comparisons. In comparison to its lean littermates, it was demonstrated that the obese rat: (i) had heavier interscapular BAT pads, (ii) oxidized a similar amount of palmitate to CO2 per 100 mg of BAT, (iii) oxidized more palmitate in response to NE stimulation of BAT, and (iiii) had slower rates of hepatic ketogenesis and palmitate oxidation. Altered palmitate oxidation or NE sensitivity in BAT was not contributing t...