Adrenalectomy increases serotonin turnover in brains of obese Zucker rats

Because adrenalectomy tends to normalize many metabolic abnormalities of obese Zucker rats, we hypothesized that it would also normalize the depressed serotonergic turnover in their ventromedial nucleus (VMN). Lean (Fa/Fa) and obese (fa/fa) male Zucker rats were adrenalectomized or sham operated when 5 wks old and sacrificed at 11 wks. Their brains were frozen, and 13 areas were dissected for HPLC-EC analysis of monoamines and metabolites. Consistent with previous studies, VMN serotonin turnover (indexed by 5-HIAA/5-HT) was lower in obese than lean sham-operated rats. Monoamine and metabolite concentrations were altered in several other brain areas as well. Adrenalectomy reduced percent body fat and elevated VMN serotonergic turnover more in obese than in lean rats. It also stimulated serotonergic turnover in almost every brain area examined. We conclude that in obese Zucker rats: monoaminergic activity is altered in several brain areas involved in regulating energy balance; adrenalectomy normalizes the reduced VMN serotonergic turnover seen in the obese rats; and adrenalectomy results in a generalized increase in central serotonergic turnover. These data are consistent with serotonin's role in inhibiting food intake and enhancing sympathetic stimulation of energy metabolism.

Chronic protein restriction does not alter energetic efficiency or brown adipose tissue thermogenic capacity in genetically obese (fa/fa) Zucker rats

Attenuated regulatory thermogenesis in genetically obese (fa/fa) Zucker rats involves an impaired capacity to increase sympathetic drive to brown adipose tissue in response to dietary stimuli. Young, growing lean rats fed a low protein diet reduce energetic efficiency to compensate for elevated energy intake; however, it is not known if obese rats adapt similarly to chronic protein restriction by decreasing energetic efficiency and whether this would be accompanied by increased brown adipose tissue thermogenic capacity. Lean (Fa/Fa) and obese Zucker rats were either protein-restricted (protein 8% of total energy) or fed a control diet (21% protein) starting at age 5 wk. At 9 wk, oxygen consumption (VO2) was measured in response to an intubated meal of mixed macronutrient composition. Mass-adjusted food intake (i.e., food intake/body weight 0.67) was greater in protein-restricted than in control lean rats, but not different due to diet in obese rats. Mass-adjusted brown adipose tissue uncoupling protein levels were more than 100% greater in protein-restricted vs. control lean rats, but not different between protein-restricted and control obese rats. The uncoupling protein level was not significantly different in control lean vs. obese rats. Energetic efficiency was 40% lower in protein-restricted vs. control lean, but not different in obese rats; however, the efficiency of protein utilization was significantly greater in obese protein-restricted than in obese control rats. Meal-induced energy expenditure (VO2) did not differ significantly due to diet or genotype. In conclusion, protein restriction led to overfeeding in lean rats which appeared to enhance brown adipose tissue thermogenic capacity and decrease energetic efficiency. Protein efficiency increased to more than two times its original value in obese (fa/fa) rats, but otherwise no metabolic accommodation in the capacity for regulatory thermogenesis was observed in this genotype.

Effects of age and gender on brown fat and skeletal muscle metabolic responses to cold in F344 rats

Older male Fischer 344 (F344) rats do not maintain core temperature as well as do older females during cold exposure. To elucidate factors contributing to the decreased thermoregulatory ability of older males, the metabolic potentials of interscapular brown adipose tissue (IBAT) and skeletal muscle were evaluated at rest (26 degrees C) and during 4 h of cold (6 degrees C) in male and female F344 rats, aged 6, 12, and 26 mo. Compared with 26-mo-old females, cold-exposed 26-mo-old males exhibited a greater drop in core temperature and lower amounts of IBAT mitochondrial uncoupling protein (UCP) and IBAT thyroxine 5'-deiodinase (T5'D) activity. Unlike females, 26-mo-old males showed no cold-induced increase in total IBAT UCP or T5'D activity. In contrast, plasma norepinephrine was higher in cold-exposed 26-mo-old males vs. females, whereas plasma insulin and thyroxine did not differ with gender. Skeletal muscle oxidative capacity (measured by citrate synthase activity) and carbohydrate availability (measured by muscle glycogen and plasma glucose levels) did not differ between the 26-mo-old males and females. Our data suggest that altered regulation of IBAT UCP levels during cold exposure of aged rats, due at least in part to attenuated cold-induced IBAT T5'D activity, contributes to the gender difference in thermoregulatory ability of older males vs. females.

Age and gender effects on glucose utilization in skeletal muscle and brown adipose tissue of cold-exposed rats

We hypothesized that glucose utilization by skeletal muscle is less in cold-exposed older male versus female Fischer 344 (F344) rats and that this reduction may contribute to the poorer cold-exposed thermoregulatory ability of the older males. To test this hypothesis, the rates of in vivo glucose utilization of skeletal muscle in 6-, 12-, and 26-month-old male and female F344 rats were estimated during cold exposure by measuring the cellular incorporation of [14C]-2-deoxyglucose ([14C]-2DG) after its conversion to [14C]-2DG-6-phosphate ([14C]-2DGP). Comparable measurements were also made in the interscapular brown fat depot (IBAT). Four-hour fasted rats, that had been fitted with femoral arterial and venous cannulae 24 hr earlier, were exposed to either 26 degrees or 6 degrees C for 2 hr and then received a bolus infusion of [14C]-2DG (125 microCi/kg body wt). Arterial plasma glucose and [14C]-2DG concentrations were measured periodically for an additional 45 min. Rats were sacrificed, and various skeletal muscles and IBAT were removed and immediately frozen in liquid N2 for subsequent analysis of [14C]-2DGP content. Cold-exposed male rats had significantly lower rectal temperatures than comparably treated females (26-month-old male, 34.8 degrees +/- 0.3 degrees; female, 36.1 degrees +/- 0.2 degrees C). There was no main effect of age, gender, or cold exposure on skeletal muscle glucose utilization when the data were expressed as nmol/min/g. In contrast, when data were expressed relative to total tissue weight (nmol/min), skeletal muscle glucose utilization was significantly higher in male than in female rats. Although estimated glucose utilization in IBAT (nmol/min/g) isolated from cold-exposed rats was significantly greater than that in brown fat isolated from non-cold-exposed animals, there was no main effect of age or gender. However, glucose utilization per IBAT depot (nmol/min) was significantly less in older male than in female rats, and reflected the fact that IBAT weight of older males was more than 50% lower than that of comparably aged females. Thus, our hypothesis that reduced skeletal muscle glucose utilization contributes to the blunted thermoregulatory ability of older male versus female F344 rats is negated.(ABSTRACT TRUNCATED AT 400 WORDS)

Serotonergic activity is depressed in the ventromedial hypothalamic nucleus of 12-day-old obese Zucker rats

We previously reported lower ventromedial hypothalamic nucleus (VMN) serotonergic activity in 11-wk genetically obese vs. lean Zucker rats. To determine whether the activity was secondary to metabolic alterations associated with this established obesity (e.g., significant hyperphagia and hyperinsulinemia), we examined monoaminergic activity in various brain nuclei of 12-day lean (Fa/Fa and Fa/fa) and obese (fa/fa) rats early in the development of obesity. Obese pups had greater percent carcass fat than heterozygotes, both of which were fatter than homozygous lean rats. Obese, but not heterozygous lean, pups were hyperinsulinemic vs. Fa/Fa pups. VMN 5-hydroxy-3-indoleacetic acid levels, an index of serotonin release, were lower in obese and heterozygous than in homozygous lean pups and were not correlated with plasma insulin levels. Although monoamine differences also occurred in several other nuclei, for the most part they appeared to be unrelated to the obese genotype. We conclude that blunted VMN serotonergic activity is not secondary to the obese rat's hyperinsulinemia and may play a significant role in the development of obesity.

Adrenergic modulation of intracellular pH in isolated brown fat cells from hamster and rat

The activity of the uncoupling protein in brown fat mitochondria is enhanced at alkaline pH, leading to the hypothesis that changes in intracellular pH (pHi) may modulate the thermogenic response to sympathetic stimulation. We employed ratio imaging of the fluorescent dye 2',7'-bis(carboxyethyl)-5(6)-carboxyfluorescein to measure pHi in acutely isolated single brown fat cells from hamster and neonatal rat and in cultured rat cells. Basal pHi averaged approximately 7.2 in HCO3- media and 0.1-0.15 pH units lower in nominally HCO3(-)-free media in all cell types. In both HCO3- and HCO3(-)-free media, stimulation with norepinephrine (NE) typically caused an alkalinization of approximately 0.05-0.1 pH units, which was followed by a smaller net acidification occurring primarily after NE was removed. Alkalinization seemed to be mediated predominantly by alpha-adrenergic stimulation, while acidification most often followed beta-adrenergic activation. Similar pHi changes were elicited by NE in rat and hamster cells, but responses were more frequent in hamster cells. Assays of recovery from ammonium prepulse-induced acid loads indicated that rat and hamster cells have both Na(+)-H+ and Na(+)- and HCO3(-)-dependent regulatory systems, while hamster cells have, in addition, a Na(+)-independent recovery mechanism activated at acid pHi. We conclude that alpha-adrenergic alkalinization of brown fat may contribute to the control of thermogenesis.

Adrenergic stimulated skeletal muscle glycogenolysis in perfused hindlimbs of young and old male Fischer 344 rats

Epinephrine (Epi)- and forskolin (FSK)-stimulated glycogenolysis of skeletal muscle was evaluated in perfused hindlimb isolated from male Fischer 344 (F344) rats, ages 6, 12, and 26 mo. Muscle glycogen stores were reduced by sciatic nerve stimulation and replenished by infusing 10 mM glucose, 500 microU insulin, and 5 microCi [14C]glucose via a left carotid artery cannula. Then the hindlimb was perfused with a modified Krebs-Henseleit buffer (pH 7.4). At minute 20 of the perfusion, Epi [0.0 (perfusate), 0.25, 0.50, or 0.75 microM] or 40 microM FSK were infused for 10 min. Radioactivity (14C) in the effluent perfusate was collected every 60 s during a 20-min preinfusion, a 10-min Epi infusion, and a 20-min postinfusion period and was used to determine the rate of muscle glycogen utilization. Total 14C release increased with Epi and 40 microM FSK. However, the pattern of release did not differ significantly with age. In general, the fraction of the perfusate released as 14CO2 increased in the presence of FSK and Epi but did not significantly differ with age. [14C]lactate released in response to Epi increased in the 6-mo-old group, remained unchanged in the 12-mo-old group, and decreased in the 26-mo-old group compared with 0.0 Epi (perfusate) values. It appears that stimulation of skeletal muscle glycogenolysis via adrenergic receptor or postreceptor/adenosine 3',5'-cyclic monophosphate-mediated mechanisms is unaffected by age. However, the utilization of carbohydrate by isolated hindlimb muscle is altered in the aging rat, resulting in a more oxidative metabolism.

Characteristics of the obesity syndrome in Zucker-Brown Norway (ZBN) hybrid rats

The existence of a restriction fragment length polymorphism (RFLP) closely linked to the fatty locus between the Zucker (Z) and Brown Norway (BN) rat strains allows evaluation of early effects of the fatty (fa) gene using offspring of back-crosses (N2) between F1 females and Zucker obese males. We examined several metabolic characteristics of N2 animals to determine if these hybrid animals exhibited similar characteristics of the obese syndrome to those of Zucker rats. Females from crosses of obese male Zucker (fa/fa) and lean female BN (+/+) rats were back-crossed to their sires, resulting in twelve N2 litters. At 9 weeks of age, liver, spleen, interscapular brown fat (IBAT), and gonadal, retroperitoneal (RP), and inguinal fat depots were removed and weighed. Samples of the RP depot were analyzed for cell size and number. Obese N2 rats were hyperphagic, with body weights in the range of those of obese Zucker rats. Obese N2 rats were also hyperinsulinemic [mean +/- SEM, microU/ml: females, 7.9 +/- 0.6 vs. 82.1 +/- 8.4 (lean vs. obese); males, 10.5 +/- 1.6 vs. 128.5 +/- 13.4 (lean vs. obese)] and mildly hyperglycemic [mean +/- SEM, mg/dl: females, 104.1 +/- 2.0 vs. 139.0 +/- 14.7 (lean vs. obese); males, 100.9 +/- 2.6 vs. 132.0 +/- 2.8 (lean vs. obese) p < or = 0.05]. White fat depots in obese rats were 3 to 7 times heavier than those in lean rats; adipocyte numbers in RP depots were 50% greater in obese than in lean rats; and cell size was more than 3 times larger. IBAT, liver, and spleen were also heavier in obese vs. lean rats, while tail lengths were shorter. Percent lean carcass mass and % carcass protein were about 30% greater in lean vs. obese rats, while % carcass fat in obese rats was 5 times greater than that of lean rats. Thus, phenotypic expression of the fa gene in ZBN hybrid animals, with approximately 25% of their genetic background coming from the BN strain, appears to be similar to that in Zucker rats. Given the similarity of phenotypic expression of the fa gene between the Zucker strain and ZBN hybrids, it is plausible to consider using ZBN hybrids for studies of early manifestations of fa gene action prior to onset of detectable obesity.

Effect of age and high sucrose diet on 2-deoxyglucose uptake in perfused hindlimb

The purpose of this investigation was to evaluate insulin-stimulated skeletal muscle glucose uptake in male Fischer 344 rats, age 6, 12, and 27 mo, fed either a sucrose (S: 66.6% sucrose, 17.6% protein, 6.4% fat) or sucrose-free (SF: 66.6% starch, 17.6% protein, 6.4% fat) diet for 3 mo. Skeletal muscle glucose uptake (Rg) in perfused hindlimbs was estimated from the uptake and subsequent phosphorylation of radiolabeled 2-deoxyglucose (2DG) in the gastrocnemius (GN), extensor digitorum longus (EDL), and soleus (SOL) muscles. Rat hindlimbs were perfused at a rate of 10 ml.min-1 with a modified Krebs Henseleit buffer containing bovine red blood cells (hematocrit: 40%) and 5.85 mmole.L-1 glucose along with 358 pmoles.L-1 followed by 3580 pmoles.L-1 insulin. There was no effect of diet on plasma glucose levels measured at weeks 1, 7, and 11 of the dietary period. A significant effect of age on estimated glucose uptake in the GN was demonstrated due primarily to greater uptake in the 27-mo compared to the 6-mo-old animals. This significant effect of age was not evident in the EDL or SOL, nor were there significant effects of diet in any muscle. These data suggest that insulin-stimulated glucose uptake in perfused hindlimbs is not attenuated with senescence or with the feeding of a sucrose diet for 3 months.

Influence of age and gender on brown adipose tissue norepinephrine turnover

We hypothesized that the attenuated brown adipose tissue thermogenic capacity observed previously in cold-exposed 27-month-old male versus female Fischer 344 rats might result, in part, from blunted sympathetic signaling to the tissue. As an index of sympathetic activity to brown fat, norepinephrine (NE) turnover in this tissue was evaluated at rest (22-24 degrees C) and during 1.5 hr of cold exposure (6 degrees C) in male and female Fischer 344 rats, aged 6, 12, and 26 months. Resting NE turnover as well as the rate constant for NE efflux from brown fat, expressed as total and as per gram of tissue protein, did not, in general, differ from age or gender. During cold exposure, rate constants and NE turnover rates increased significantly from those at rest in all groups. Brown fat NE turnover in cold-exposed 26-month-old male rats was greater than that observed in age-matched females, suggesting greater, not less, sympathetic signaling in the males versus females. These data indicate that the attenuated brown fat thermogenic capacity as well as the blunted cold-induced thermogenic responses of cold-exposed older male versus female rats reported previously cannot be explained by diminished release of NE from sympathetic nerves innervating brown adipose tissue.

Altered alpha 1-adrenoceptor binding in intact and adrenalectomized obese Zucker rats (fa/fa)

While many autonomic and metabolic defects associated with genetic obesity in the Zucker rat are corrected by adrenalectomy (Adx), brain adrenoceptor function has not been examined in this context. Here, 3 weeks after Adx or sham surgery, brains of 11 weeks old lean (Fa/Fa) and obese (fa/fa) male Zucker rats were assayed for alpha 1-([3H]prazosin; [3H]PRZ) and alpha 2-adrenoceptor ([3H]paraminoclonidine; [3H]PAC) binding by autoradiography. By genotype, obese rats had 19-256% higher [3H]PRZ binding than lean rats in the amygdala (central [ACN], basolateral [ABL], basomedial [ABM] and medial [MAN] nuclei [n.]), hypothalamus (dorsomedial n. [DMN] and lateral [LH]) and somatosensory cortex. In the ABL and ACN, increased maximal binding (Bmax) in obese rats was associated with decreased affinity (increased Kd). Three weeks after surgery, sham-operated obese rats gained 27% more weight than lean rats but lean and obese Adx rats gained the same amount of weight. Adx reduced [3H]PRZ binding in both lean and obese rats by 37-70% in the amygdala (ABM, ACN, MAN) compared to sham-operated rats. But, Adx selectively reduced [3H]PRZ binding only in lean rats in the ABL, DMN, ventromedial hypothalamic n. (VMN) and ventroposteromedial thalamic n. In most areas, decreases in maximal binding (Bmax) associated with Adx were accompanied by decreases in Kd. Unlike [3H]PRZ binding, there was no consistent genotype difference in [3H]PAC binding although Adx was followed by increased binding in obese and decreased binding in lean rats in the ABL. In only the VMN, obese rats had a 21% higher alpha 2- to alpha 1-adrenoceptor ratio than lean rats.(ABSTRACT TRUNCATED AT 250 WORDS)

Litter size, adrenalectomy and high fat diet alter hypothalamic monoamines in genetically lean (Fa/Fa) Zucker rats

To determine if diet-induced obesity is associated with depressed serotonergic activity (as is genetic obesity), we examined hypothalamic biogenic amines in 11-wk-old genetically lean (Fa/Fa) male Zucker rats raised in small (3 pups/dam) or control (8-9 pups/dam) litters. Five-week-old rats were adrenalectomized or sham-operated and, 1 wk later, fed either 11% of energy as fat (low fat) or 68% of energy as fat (high fat) diets for 5 wk. Tissue punches from the ventromedial nucleus (VMN), the paraventricular nucleus and the preoptic area were assayed via HPLC. Rats fed high vs. low fat had a greater percentage of body fat and brown fat mitochondrial GDP binding, whereas serotonergic turnover was lower. Small litter vs. control litter animals had lower VMN and preoptic concentrations of 3,4-dihydroxyphenylacetic acid, a major metabolite of dopamine. Although adrenalectomy resulted in smaller, leaner rats, it did not differentially affect the rats that became fatter. Because VMN and preoptic dopaminergic activities were depressed in small litter vs. control litter rats but the percentage of body fat was unchanged, this decreased dopamine metabolism is probably not causal to the obesity development. However, the same cannot be said for the attenuated serotonergic activity, although such activity may not be directly related to the degree of obesity.

Photocontrol of the Accumulation of Plastid Polypeptides during Greening of Tomato Cotyledons : Potentiation by a Pulse of Red Light

A pulse of red light acting through phytochrome accelerates the formation of chlorophyll upon subsequent transfer of dark-grown seedlings to continuous white light. Specific antibodies were used to follow the accumulation of representative subunits of the major photosynthetic complexes during greening of seedlings of tomato (Lycopersicon esculentum). The time course for accumulation of the various subunits was compared in seedlings that received a red light pulse 4 h prior to transfer to continuous white light and parallel controls that did not receive a red light pulse. The light-harvesting chlorophyll-binding proteins of photosystem II (LHC II), the 33-kD extrinsic polypeptide of the oxygen-evolving complex (OEC1), and subunit II of photosystem I (psaD gene product) all increased in the light, and did so much faster in seedlings that received the inductive red light pulse. The red light pulse had no significant effect on the abundance of the small subunit of ribulose 1,5-bisphosphate carboxylase/oxygenase (Rubisco), nor on several plastid-encoded polypeptides: the large subunit of Rubisco, the beta subunit of the CF(1) complex of plastid ATPase, and the 43- and 47-kD subunits of photosystem II (CP43, CP47). Subunits I (cytochrome b(6)f) and III (Rieske Fe-S protein) of the cytochrome b(6)f complex showed a small or no increase as a result of the red pulse. The potentiation of greening by a pulse of red light, therefore, is not expressed uniformly in the abundance of all the photosynthetic complexes and their subunits.

Effect of cold on serum substrate and glycogen concentration in young and old Fischer 344 rats

This investigation evaluated the hypothesis that the age-related decline in cold-induced thermogenesis observed in male (F344) rats is associated with altered substrate concentrations of glucose, lactate, and/or liver and muscle glycogen. Body mass-independent O2 consumption, core temperature, and serum glucose and lactate concentrations were measured at rest and during 4 h of exposure to 5 degrees C in male F344 rats ages 6, 12, and 26 months. At the end of the 4-h cold exposure, liver, soleus, and gastrocnemius tissues were removed, frozen, and analyzed for glycogen concentration and/or citrate synthase activity. Core temperature decreased during cold exposure and was consistently less in the 26-month versus the 6- and 12-month rats. There were no significant differences between the 6- and 12-month-old rats with respect to cold-induced O2 consumption, but measures were significantly lower in the 26-month-old rats. During cold exposure, serum lactate and glucose concentrations increased in the 26-month-old animals compared to those in the 6- and 12-month-old rats, while liver glycogen concentrations decreased in all groups, and gastrocnemius glycogen contents decreased in the 12- and 26-month-old rats. Citrate synthase specific activity (mumol.[min.microgram.protein] -1) did not differ with age. These data suggest that carbohydrate availability (as measured by serum glucose and muscle glycogen) is not a limiting factor in the attenuated cold-exposed thermogenic response of the 26-month-old male F344 rat. However, it appears that the 26-month-old rat may have a diminished capacity to fully oxidize carbohydrate during cold exposure.

The gene encoding rat liver glycogen phosphorylase contains multiple polyadenylation signal sequences

RNA blot analysis of rat liver and adipose tissues detected two glycogen phosphorylase (GP)-encoding transcripts. The polymerase chain reaction was used to characterize the 3'-noncoding region of the gene (L-GP) encoding liver-GP (L-GP) from the lean Zucker rat (Fa/Fa). Three distinct classes of colinear cDNA clones were identified by nucleotide (nt) sequence analysis, demonstrating that the L-GP gene contains at least three functional polyadenylation sites. The predominant L-GP transcript was generated by polyadenylation 130 nt 3' from the end of the coding region. A previously uncharacterized L-GP transcript is generated by polyadenylation at 346 nt 3' of the first polyadenylation site. Polyadenylation site selection does not appear to be regulated in a tissue-specific fashion. The relative steady-state L-GP mRNA levels in the different types of adipose tissues were comparable to, or exceeded transcript levels in liver.

Animal models of obesity: genetic aspects

Among the candidate genes that have been reviewed herein, adipsin, calcitonin, cholecystokin, Gi alpha and Gs subunits of G proteins, insulin I and II, and lipoprotein lipase have all been mapped to specific chromosomes in mouse or rat or both. In none of these cases is the chromosomal location syntenic with murine obesity genes db (on chromosome 4), or ob (on chromosome 6). Thus, all of these genes that code for metabolic modulators that are altered in obese animals but not in lean animals can be ruled out as possible loci of the primary genetic defect, at least for the murine models of obesity. In the case of neuropeptide Y, growth hormone, glucose transporter GLUT-4, the insulin receptor, and glyceraldehyde-3-phosphate dehydrogenase, chromosomal mapping has not yet been reported. However, in each of these cases, the evidence available strongly argues against any one of these physiologic modulators as the likely site of the primary defect for any one of the obesity mutations. Rather, in all of these cases, regardless of whether or not the gene has been mapped, the evidence suggests that posttranscriptional and/or post-translational processes are involved in bringing about the specific alterations in level or activity of the protein product that is seen in the obese animal. Often hormonal regulation is invoked as a possible explanation for the changes observed in gene expression. The hormones most commonly identified as having a mediating effect on the particular metabolic pathways involved are insulin and/or the adrenal glucocorticoids. Since in each of the obese mutants, circulating amounts of these hormones are elevated, severely so in the case of insulin, it would not be surprising to find that they influence the levels and activities of many protein products involved in a variety of central nervous system and peripheral metabolic pathways. Glucocorticoids are known to exert direct effects on gene expression; however, with respect to adipsin gene expression, a direct effect has not been found. Furthermore, insulin itself has been considered as a candidate for the genetic lesion in these animals and has been ruled out by chromosomal localization. Thus, while it may certainly prove to be the case that both insulin and glucocorticoids affect these systems in some way, their effects appear to be indirect. The work by Platt and colleagues in transgenic mice provides the first evidence of signal transduction between an obese mutant allele and the promoter sequence for a gene that shows significantly altered expression in the obese animal.(ABSTRACT TRUNCATED AT 400 WORDS)

Exercise decreases fat selection in female rats during weight cycling

Weight cycling (weight loss and regain) increases fat intake in rats allowed to self-select a diet from protein, carbohydrate, and fat sources. This study reports the effects of exercise on macronutrient self-selection. Female Sprague-Dawley rats (5 mo old) self-selected their diet. After 3 wk, rats were assigned to one of the following three groups: ad libitum fed sedentary (Con), sedentary food restricted to 40% Con intake (R-Sed), or treadmill exercised (20 m/min, 1 h/day, 6 day/wk) food restricted to 40% Con intake (R-Ex). Food restriction was for 3 wk followed by 5 wk of refeeding. This was repeated for a second cycle. During restriction, body weight decreased by 30% in R-Sed and by 33% in R-Ex than in R-Sed, fat regain was greater in R-Sed. By week 3 of refeeding, total caloric consumption did not differ. However, fat selection increased in R-Sed (56% kcal) vs. R-Ex (30%) and Con (35%). Fat selection in R-Sed increased further during cycle 2 (73% kcal). Resting oxygen consumption decreased during food restriction in R-Sed and R-Ex. After refeeding, resting metabolic rate in R-Ex was significantly greater than in R-Sed. In conclusion, weight cycling increases dietary fat selection and adiposity. Exercise mitigates this effect.

Effect of photoperiod on body weight and food intake of obese and lean Zucker rats

Although the rat is usually not considered to be sensitive to photoperiod, under some experimental conditions photoperiod responses are unmasked. In addition, we have observed photoperiod-induced changes in body weight gain in lean and obese Zucker rats. In this experiment, body mass, food intake, body composition, brown adipose tissue (BAT) thermogenic state, and blood concentrations of corticosterone, insulin, and glucose were evaluated under one of two lighting conditions: a short (10 h light: 14 h dark) or a long (14 h light: 10 h dark) photoperiod. Plasma corticosterone and glucose concentrations measured under fasting conditions were unaffected by photoperiod in either genotype. The amount of BAT mitochondrial protein isolated was less in long photoperiod rats. BAT mitochondrial GDP binding was unaffected by photoperiod in the lean rats, but tended to be lower in long photoperiod obese rats than in short photoperiod obese rats. Although, photoperiod had no effect on daily food intake of rats exposed to the short versus long photoperiod, body mass was heaviest in obese rats raised in long photoperiod. Plasma insulin was increased in both lean and obese rats in long photoperiod. In addition, fat storage appeared to shift to internal depots in the lean rats exposed to long photoperiod. Our data demonstrate that photoperiod does have an effect on male Zucker rats with respect to body weight and fat distribution, with the obese rats being more sensitive to changes in photoperiod than the lean rats.

Similarity between Cytokinin and Blue Light Inhibition of Cucumber Hypocotyl Elongation

The cytokinin benzyladenine inhibited endogenous hypocotyl elongation in intact etiolated seedlings of cucumber (Cucumis sativus L.). In hypocotyl segments, the inhibitory effect of benzyladenine on growth was clearly detectable in the presence of indoleacetic acid. Fusicoccin-induced elongation was unaffected by the presence of cytokinin. The effect of cytokinin on elongation of the segments was determined by measuring changes in fresh weight, a linear function of extension growth. The effect of benzyladenine on hypocotyl growth was at least as large in segments prepared from red-light-grown seedlings as in those from seedlings grown in total darkness. A comparison was made between the inhibitory effects of cytokinin and blue light. The use of the calcium chelator ethyleneglycol-bis(beta-aminoethyl ether)-N, N'-tetraacetic acid indicated that calcium ions are required for manifestation of benzyladenine-induced inhibition.

Neuronal activity in hypothalamic nuclei of obese and lean Zucker rats

Central neural activity was assessed by measuring relative cytochrome oxidase (CO) activity in the ventromedial nucleus (VMN; thermogenesis regulation), the parvocellular paraventricular nucleus (PVN; feeding regulation), and the magnocellular PVN (secretion of vasopressin and oxytocin) in 10 age-matched pairs of 39- to 42-day-old Zucker rats. When obese (fa/fa) were compared to lean (Fa/Fa) rats, relative CO activity was significantly lower (approximately 10 percent) in the VMN and parvocellular PVN, but not in the magnocellular PVN. Cell diameters did not differ. To determine if there were corresponding differences in levels or release of hypothalamic monoamines, we compared 7 pairs of 90- to 94-day-old lean (Fa/?) and obese (fa/fa) rats at rest and after 2 h of 9 degrees C. Tissue punches from frozen PVN, VMN, and preoptic area (the latter being a site of thermosensitive units modulating VMN output) were assayed. In obese vs. lean noncold-exposed rats, we observed lower concentrations of: 5-hydroxyindoleacetic acid (5HIAA; metabolite of serotonin, 5HT) in the VMN; 3-methoxy-4-hydroxyphenylglycol (MHPG; metabolite of norepinephrine, NE) and NE + MHPG (index of total NE) in the preoptic area; and 3,4-dihydroxyphenylacetic acid (DOPAC; metabolite of dopamine, DA) in the PVN. Additionally, in the VMN, cold exposure resulted in: elevated concentrations of MHPG and MHPG + NE in both lean and obese rats; elevated concentrations of 5HT, 5HIAA, and 5HT + 5HIAA in obese rats, with no significant changes in these variables in lean animals; decreased ratio of 5HIAA/5HT in obese rats and increased ratio in leans. In the preoptic region, cold exposure led to increased concentrations of MHPG, NE + MHPG, 5HT, and 5HT + 5HIAA in obese but not lean rats. In the PVN, 5HT concentrations were increased in cold-exposed obese but not lean rats. Our data support the hypothesis that neuronal activity in obese rats differs from that of lean rats at rest and during cold exposure and suggest that several monoamine systems play a role in such differences.

Phytochrome regulation of greening in wild type and long-hypocotyl mutants ofArabidopsis thaliana

A brief pulse of red light (R) given to darkgrown seedlings ofArabidopsis thaliana (L.) Heyn. potentiates rapid synthesis of chlorophyll upon transfer to continuous white light. The time course for potentiation of rapid greening shows that a R pulse in the LF (low fluence) range has maximal effect within a few hours, and that there is a small VLF (very low fluence) component as well. Partial reversal of the effect of R by far-red light (FR) indicates that the pulse acts through phytochrome. As it does in the wild-type (WT), a pulse of R accelerates greening of long-hypocotyl (hy) mutants. The extent of induction by the R pulse was about the same in the WT and in allhy mutants studied. Reversibility by FR was greatly decreased in thehy-1 andhy-2 strains. It is possible that these mutants contain a species of phytochrome with defective phototransformation kinetics. If there is such a defective phytochrome species, it nevertheless appears to be active in the potentiation of rapid greening.

Altered Phytochrome Regulation of Greening in an aurea Mutant of Tomato

A brief pulse of red light accelerates chlorophyll accumulation upon subsequent transfer of dark-grown tomato (Lycopersicon esculentum) seedlings to continuous white light. Such potentiation of greening was compared in wild type and an aurea mutant W616. This mutant has been the subject of recent studies of phytochrome phototransduction; its dark-grown seedlings are deficient in phytochrome, and light-grown plants have yellow-green leaves. The rate of greening was slower in the mutant, but the extent (relative to the dark control) of potentiation by the red pulse was similar to that in the wild type. In the wild type, the fluence-response curve for potentiation of greening indicates substantial components in the VLF (very low fluence) and LF (low fluence) ranges. Far-red light could only partially reverse the effect of red. In the aurea mutant, only red light in the LF range was effective, and the effect of red was completely reversed by far-red light. When grown in total darkness, aurea seedlings are also deficient in photoconvertible PChl(ide). Upon transfer to white light, the aurea mutant was defective in both the abundance and light regulation of the light-harvesting chlorophyll a/b binding polypeptide(s) [LHC(II)]. The results are consistent with the VLF response in greening being mediated by phytochrome. Furthermore, the data support the hypothesis that light modulates LHC(II) levels through its control of the synthesis of both chlorophyll and its LHC(II) apoproteins. Some, but not all, aspects of the aurea phenotype can be accounted for by the deficiency in photoreception by phytochrome.

Induction of Trichoderma sporulation by nanosecond laser pulses: evidence against cryptochrome cycling

An important question in the study of photoreceptor action in morphogenesis is whether the chromophore is unidirectionally photobleached, or whether it is recycled, allowing each receptor molecule to be counted more than once. The common soil fungus Trichoderma harzianum grows vegetatively in the dark and sporulates in response to a pulse of blue or UV-A light. Colonies were grown at 26 degrees C, transferred to 3 degrees C, illuminated with non-saturating light, and then put back at 26 degrees C to sporulate. The fluence-response curves for photoinduction in the cold and at 26 degrees C were identical, indicating that there are no enzymatic transduction processes during irradiation. Regions of the perimeter of dark-grown colonies were given single pulses (maximum duration, 30 ns) at 355 nm with a neodymium laser. We obtained a complete fluence-response curve for the laser pulses, which agreed with data for irradiations in the second to minute range. Photoinduction at 3 degrees C, and validity of Bunsen-Roscoe reciprocity from nanoseconds to minutes, support the hypothesis that the inductive event is a simple first-order photobleaching reaction.

The effects of 2-deoxy-D-glucose and sympathetic denervation of brown fat GDP binding in Sprague-Dawley rats

Central administration of 2-deoxy-D-glucose (2-DG) decreases brown fat thermogenesis. This effect is suggested to be mediated via a central control mechanism. Our study was designed to determine the importance of the sympathetic nervous system in the response of brown fat to intraperitoneal (i.p.) injection of 2-DG. Unilateral denervation of interscapular brown adipose tissue (IBAT) was performed on male Sprague-Dawley rats (300 g body weight). Nine days after surgery, rats were injected i.p. with either saline vehicle (0.9% sodium chloride) or 2-DG (360 mg/kg wt) and then killed one hour later. Sympathetic denervation resulted in 50% decreases in total IBAT protein and in mitochondrial protein recovered. In the denervated lobes, mitochondrial GDP binding (expressed as nmol/mg mitochondrial protein and as total activity recovered) was decreased to 36% and 18%, respectively. Injection of 2-DG did not change mitochondrial protein content in either the innervated or denervated IBAT. In the innervated lobes, 2-DG significantly lowered GDP binding to 55% of that in saline-treated animals, whether expressed per mg mitochondrial protein or as total recovered activity. In contrast, 2-DG did not further decrease GDP binding in the denervated lobes. In conclusion, the effects of i.p. injection of 2-DG on brown fat thermogenesis (as evidenced by GDP binding) appear to be primarily mediated via the sympathetic nervous system.

Maternal brown fat metabolism returns to control level by four weeks postweaning in rats

We studied body composition, white and brown adipose tissue cellularity, lipoprotein lipase activity and metabolic enzyme activity in three groups of rats: nonpregnant controls, lactating dams and nonlactating dams (i.e., dams not permitted to suckle their young). Nine to 11 rats in each group were killed on d 12 postpartum (study d 34) and on d 40 postpartum (study d 62). During lactation, brown fat citrate synthase, beta-hydroxyacylCoA dehydrogenase (HOAD) and lipoprotein lipase activities were significantly lower in the lactating than in the nonlactating dams or virgin controls. Although the nonlactating dams had their pups removed within 24 h after delivery, by d 12 postpartum citrate synthase and HOAD activities were significantly lower than those of nonpregnant controls. By the end of the study there were no differences among the three groups except in the case of HOAD. HOAD activity in the lactation group was significantly lower than in the nonlactation group. White fat cell number in the parametrial depot was significantly increased in the nonlactation groups by d 12 postpartum. In the lactation group, increased white fat cell number in this depot was detectable at d 40 postpartum, when carcass fat stores and fat cells had been repleted. These results demonstrate that both lactating and nonlactating dams undergo cellular hyperplasia, at least in the parametrial depot. This may predispose them to obesity. Also, decreased brown fat metabolism in the nonlactating dams may be contributing to their significantly greater carcass fat content at d 12 postpartum.

Effect of gender on the response to a high fat diet in aging Fischer 344 rats

The purpose of this study was to describe the effects of high fat (HF) and low fat (LF) diets in male and female Fischer 344 (F344) rats ages 5, 23 and 27 mo. Rats were fed the diet for 3 mo, and then resting metabolic rate, body composition and adipose tissue cellularity were evaluated. Although body mass was greater in rats fed the HF diet, this difference was due to a rapid increase in mass within the first 2 wk. There was no difference in the rate of body mass gain after this period. Resting mass-independent metabolic rate did not significantly differ due to age, diet or gender. In general, percentage fat mass was greater in rats fed the HF diet and in female than in male rats in both diet groups. However, lean body mass (%) was not altered due to diet or age. Cell number of the retroperitoneal depot increased with age and diet between 5 and 23 mo of age in both male and female rats. There was no effect of age, diet or gender on retroperitoneal cell size or gonadal cell number and size. These data suggest that age, gender and diet do not significantly alter the ability of F344 rats to regulate body composition or fat cell proliferation.

Effect of age and gender on thermoregulation

Previous investigations have shown that during cold exposure 24-mo-old male Fischer 344 (F344) rats do not thermoregulate as well as do 12-mo-old animals. To determine if this deficiency also occurs in female rats, we measured oxygen consumption (thermogenesis) and colonic temperature of male and female rats 5, 23, and 27 mo of age at rest and during 6 h of exposure to 6 degrees C. In addition, nonshivering thermogenesis (NST) was evaluated from the capacity of brown adipose tissue (BAT) mitochondria isolated from cold-exposed rats to bind guanosine 5'-diphosphate (GDP). Neither age nor gender had a significant effect on resting or cold-exposed oxygen consumption expressed on a mass-independent basis (l/kg body mass0.67) or on a lean body mass independent basis (l/kg lean body mass0.67). The drop in colonic temperature in response to cold was greater in the male rats. However, females exhibited increased BAT mass and relatively constant GDP binding with advancing age, whereas males showed decreased mass and GDP binding. Although the data suggest greater NST capacity in the female rats, rates of cold-induced oxygen consumption were similar in older female vs. male rats. Taken together, our data indicate that gender has a significant impact on thermoregulation and that, under the cold exposure conditions of the study, this effect involves differential heat conservation rather than heat production.

Regional blood flow of exercise-trained younger and older cold-exposed rats

O2 consumption (thermogenesis) and regional blood flows (measured using radioactively labeled microspheres) were evaluated in younger (12 mo) and older (24 mo) sedentary and exercised male Fischer 344 (F-344) rats. These variables were measured at rest and during exposure to 6 degrees C. Exercise-trained rats were run on a motor-driven treadmill 5 days/wk, 1 h/day, at 20 m/min for 6 mo. Resting rates of O2 consumption did not differ with age or exercise training. However, thermogenesis during cold exposure was significantly greater in the older exercised rats than in the other three groups. This difference did not reflect a greater contribution from brown fat as indicated by the fact that total blood flow to the brown fat depots during cold exposure was not greater in the older exercised vs. the other rat groups. Neither exercise training nor age had a significant effect on specific resting blood flow (expressed as ml.min-1.g tissue mass-1) to most of the organs measured, including heart, kidney, brown fat, white fat, and skeletal muscle. The notable exception to this was in the spleen of the older sedentary animals where flow was diminished compared with that in the older exercised animals. We conclude that aging, between 12 and 24 mo of age, and/or exercise training have only a minor effect on regional blood flow of F-344 rats during rest or cold exposure and that the enhanced thermogenesis seen in cold-exposed older exercised vs. sedentary F-344 rats cannot be explained by a greater contribution from brown fat.

Prolactin stimulates food intake in the absence of ovarian progesterone

Increases in serum estrogen inhibit food intake. Conversely, progesterone stimulates food intake, probably via its antiestrogenic action. We have reported that elevated serum prolactin also stimulates food intake in female rats. It is unclear whether this effect is mediated through elevated levels of progesterone. The present study investigated the effects of prolactin on food intake and brown fat activity in the absence of progesterone. Female Osborne-Mendel rats were assigned to one of six groups: sham operated (Sham, n = 10), ovariectomized (OVX, n = 10), OVX + low estrogen (EL, n = 11), OVX + EL + prolactin (PIT, n = 9), OVX + high estrogen (EH, n = 10), and OVX + EH + PIT (n = 8). Estrogen levels were elevated by Silastic implants. Prolactin levels were elevated through pituitary transplants placed under the kidney capsule. Nine days postsurgery, food intake was significantly higher in OVX vs. Sham rats. Estrogen-treated rats (OVX + EL and OVX + EH) had significantly suppressed food intake values compared with both Sham and OVX animals. Finally, hyperprolactinemic rats (OVX + EL + PIT and OVX + EH + PIT) ate significantly more food than did estrogen-treated rats without pituitary explants. Despite the hyperphagia, no significant differences in brown fat GDP binding were observed. These data indicate that prolactin stimulates food intake in the absence of ovarian progesterone.

Thermogenic responses of younger and older rats to cold exposure: comparison of two strains

Oxygen consumption and colonic temperatures at rest and during 6 hours at 6 degrees C, body composition, adipose tissue cellularity, and the binding of guanosine 5'-diphosphate (GDP) to isolated brown fat mitochondria were measured in younger (12 months) and older (24 months) male Fischer 344 (F344) and Osborne-Mendel (O-M) rats. The rates of resting mass-independent oxygen consumption, the total cold-induced oxygen consumption expressed as body mass-independent (L.kg body mass-.67) or as lean body mass-independent (L.kg lean body mass-.67) did not differ among the four groups. Although the absolute (g) and the percentage of carcass mass as lean body tissue did not differ within the strains, these measures were significantly greater in the younger and older O-M rats compared to the F344 counterparts. In contrast, cold-exposed O-M rats showed significantly greater total specific GDP binding to isolated brown fat mitochondria than did the O-M animals (an index of brown fat thermogenic capacity); GDP binding did not differ between 12 and 24 months in either strain except when expressed in terms of body mass to the 0.67 power. In general, the results presented here showed no significant age-related loss in oxygen consumption in either strain. However, there did appear to be strain-related differences in brown fat mitochondrial GDP binding, and body composition.

Prolactin stimulates food intake in a dose-dependent manner

Lactation in the rat is marked by pronounced hyperphagia and suppression of brown fat (BAT) thermogenic capacity. We previously examined the possibility that elevated prolactin levels mediate these changes. The present study evaluated the effect of varying prolactin levels on food intake, BAT mitochondrial GDP binding, and carcass adiposity. Female rats were injected daily for 10 days with ovine prolactin at one of three doses: high = 3.0, medium = 1.0, or low = 0.3 micrograms/g body wt. Controls were injected with 0.9% NaCl. A group of uninjected rats served as an additional control. Cumulative food intake was significantly elevated in a dose-dependent manner in the prolactin-treated animals relative to the saline-injected and uninjected controls. Compared with the saline controls, the mean cumulative food intake was greatest at the high dose (20% increase), intermediate at the medium dose (17%), and smallest at the low dose (12%). Prolactin-treated rats gained significantly more weight during the experiment than did controls. Despite the hyperphagia in the prolactin-treated rats, no significant differences in BAT mitochondrial GDP binding were observed among the five groups. These data indicate that elevated prolactin levels stimulate food intake in a dose-dependent manner and that this hyperphagia is not accompanied by an increase in BAT mitochondrial GDP binding.

Hyperprolactinemia prevents short photoperiod-induced changes in brown fat

Previous studies demonstrated that short photoperiod exposure significantly decreases circulating prolactin levels. The present study investigated the possibility that concomitant changes in brown fat tissue mass, protein content, thermogenic capacity, and carcass composition are dependent on this change in prolactin levels. Male golden (Syrian) hamsters were sham operated and exposed to a short (10L:14D) or long (14L:10D) photoperiod. A third group was implanted with exogenous pituitaries under the right kidney capsule and exposed to a short photoperiod. In experiment I, 4 wk of short- vs. long-photoperiod exposure did not result in significant changes in circulating prolactin levels, nor was there an increase in brown fat mass, protein content, or thermogenic capacity. Four weeks of short-photoperiod exposure did significantly increase carcass lipid content. However, this increase did not occur in hamsters exposed to 4 wk of short photoperiod but made hyperprolactinemic (implanted with two exogenous pituitaries). Ten weeks of short photoperiod significantly reduced circulating prolactin levels. Concomitantly, brown fat mass, protein content, and thermogenic capacity, as well as carcass fat, were increased. These short-photoperiod-induced changes were not observed in similarly exposed hamsters that were made hyperprolactinemic via two implanted pituitaries. In experiment II, similar changes in brown fat and body composition occurred in sham-operated hamsters exposed to 10 wk of short photoperiod. These changes were prevented in hamsters exposed to 10 wk of short photoperiod but made hyperprolactinemic via only one implanted pituitary. These results suggest that decreased prolactin is a necessary condition for the increased brown fat mass, protein content, and thermogenic capacity that occurs when golden hamsters are exposed to short photoperiod.

Light effects on several chloroplast components in norflurazon-treated pea seedlings

Changes occurring in several chloroplast components during Norflurazon-induced photobleaching of Pisum sativum seedlings were investigated. mRNA steady state levels of the chlorophyll a/b-binding protein of photosystem II, ferredoxin I, the small and large subunits of ribulose 1,5-bisphosphate carboxylase, and pEA214 and pEA207, two other light-responsive genes, were determined during chlorophyll photooxidation. Relative transcription rates were assayed in isolated nuclei. The results illustrate a complex set of interactions regulating expression of the nuclear and chloroplast genomes. Photobleaching was found to affect the expression of the various genes in different ways. While transcript levels of the chlorophyll a/b-binding protein decreased by more than 80% under photooxidative light conditions in carotenoid-deficient peas, levels of ferredoxin, the small and large subunits of ribulose 1,5-bisphosphate carboxylase, and pEA214 mRNAs were reduced by less than 50%. pEA207 mRNA levels, on the other hand, were resistant to the effects of photobleaching. Analyses of chlorophylls a and b and the chlorophyll a/b-binding protein suggest that accumulation of the protein and its mRNA are coordinated with chlorophyll abundance at several steps. In addition to post-transcriptional regulation at the level of mRNA and protein stability, there may exist coordination at the transcriptional stage.

Nonshivering thermogenesis and brown fat in spontaneously hypertensive rats

Oxygen consumption was measured before and during infusion of the catecholamine isoproterenol in age-matched spontaneously hypertensive (SHR) and Wistar-Kyoto (WKY) normotensive rats. Mass-independent rates of oxygen consumption of anesthetized 7-week-old rats were similar in the WKY and SHR rats (11.08 +/- 0.74 and 11.33 +/- 0.82 ml O2 min-1 kg-.67, respectively). Catecholamine infusion elicited increased total oxygen consumption in both WKY and SHR animals (15.0 +/- 1.0 and 14.9 +/- 1.2 ml O2 min-1 kg-.67, respectively), and the magnitude of these increases did not significantly differ. To assess whether there were changes in the metabolic state of brown adipose tissue, the major site of catecholamine-induced thermogenesis in rats, enzymes whose activity is proportional to aerobic capacity were assayed in vitro. In both the interscapular and cervical brown fat depots, maximal citrate synthase and maximal HOAD (beta-hydroxyacyl-CoA dehydrogenase) activities were similar in SHR and WKY rats. There were also no significant differences in brown fat protein content, suggesting no differential growth of this tissue in the two rat strains. Our results indicate that the nonshivering thermogenic capacity of the hypertensive SHR rats does not differ from that of the normotensive WKY animals.

Cold-induced thermogenesis in younger and older Fischer 344 rats following exercise training

The inability of old rats to maintain body temperature during cold exposure has been well documented. This study evaluated the effect of exercise on the rates of cold-induced O2 consumption and the contribution of nonshivering thermogenesis (NST) to these rates. Younger (12 mo) and older (24 mo) male Fischer 344 (F344) rats were divided into exercised and sedentary groups. Exercised rats were run on a motor-driven treadmill 60 min/day, at 19-24 m/min, 5 days/wk for 6 mo. At the conclusion of the 6-mo training period, O2 consumption of all four groups was measured at thermoneutrality (26 degrees C) and during 6 h of exposure to 6 degrees C. Rectal temperatures were recorded before and after cold exposure. NST was estimated from the ability of isolated brown fat mitochondria to bind guanosine 5'-diphosphate (GDP). Core temperature of older sedentary rats fell 5.1 +/- 0.4 degrees C after cold exposure (36.3 +/- 0.3 vs. 31.2 +/- 0.8 degrees C). Exercise training in older animals prevented this fall from occurring (36.4 +/- 0.2 vs. 35.3 +/- 0.3 degrees C). Core temperatures of cold-exposed younger exercised and sedentary rats did not differ from thermoneutral values. Exercise did not alter the rates of resting body mass-independent (ml.min-1.kg body mass-0.67) O2 consumption in younger or older rats. However, body mass-independent and lean body mass (LBM)-independent (ml.min-1.g LBM-0.67) cold-induced O2 consumptions of older exercised rats were significantly elevated relative to those of older sedentary animals. This effect of exercise was not seen in younger rats.(ABSTRACT TRUNCATED AT 250 WORDS)

Cold- and norepinephrine-induced thermogenesis in younger and older Fischer 344 rats

Older rats exposed to low environmental temperatures show attenuated thermogenesis. However, the mechanisms responsible for this attenuation are not clear. This investigation evaluated the possibility that reduced nonshivering thermogenic capacity is associated with this attenuation. O2 consumption was measured in male Fischer 344 rats ages 7 and 24 mo at thermoneutrality (26 degrees C), during exposure to cold (6 degrees C) for 2 h, and during norepinephrine (NE) infusion (an in vivo measure of nonshivering thermogenesis). In addition, the binding of GDP to isolated mitochondria of brown fat, an in vitro estimate of nonshivering thermogenesis, was also measured. Resting mass-independent O2 consumption (ml.min-1.g body mass -0.67) was not different between the two age groups. However, mass-independent O2 consumption was significantly greater in the younger vs. older rats during 2 h of cold exposure (younger, 2.86 +/- 0.19 l/kg body mass 0.67; older, 2.39 +/- 0.10 l/kg body mass 0.67) and during 20 min of maximum NE infusion (younger, 410.4 +/- 15.1 ml/kg body mass)] was greater in younger than ml/kg body mass 0.67). Brown fat mass [absolute (g) as well as relative (g tissue/kg body mass)] was greater in younger than in older rats. Furthermore, younger rats had significantly greater binding of GDP to isolated mitochondria of brown fat than did the older rats. This effect was true whether the data were expressed as nanomoles bound per milligram mitochondrial protein (32% lower in older rats), bound nanomoles recovered (57% lower), or bound picogram per kilogram body mass 0.67 (59% lower).(ABSTRACT TRUNCATED AT 250 WORDS)

Phytochrome Regulation of Greening in Pisum: Chlorophyll Accumulation and Abundance of mRNA for the Light-Harvesting Chlorophyll a/b Binding Proteins

A brief pulse of red light eliminates or reduces the lag in chlorophyll accumulation that occurs when dark-grown pea seedlings are transferred to continuous white light. The red light pulse also induces the accumulation of specific mRNAs. We compared time courses, escape from reversal by far-red light, and fluence-response behavior for induction of mRNA for the light-harvesting chlorophyll a/b binding proteins (Cab mRNA) with those for induction of rapid chlorophyll accumulation in seedlings of Pisum sativum cv Alaska. In both cases the time courses of low fluence and very low fluence responses diverged from each other in a similar fashion: the low fluence responses continued to increase for at least 24 hours, while the very low fluence responses reached saturation by 8 to 16 hours. Both responses escaped from reversibility by far-red slowly, approaching the red control level after 16 hours. The fluence-response curve for the Cab mRNA increase, on the other hand, showed threshold and saturation at fluences 10-fold lower than threshold and saturation values for the greening response. Therefore, the level of Cab mRNA, as measured by the presence of sequences hybridizing to a cDNA probe, does not limit the rate of chlorophyll accumulation after transfer of pea seedlings to white light. The Cab mRNA level in the buds of seedlings grown under continuous red light remained high even when the red fluence rate was too low to allow significant greening. In this case also, abundance of Cab mRNA cannot be what limits chlorophyll accumulation.

Thyroid function and cold acclimation in the hamster, Mesocricetus auratus

Basal metabolic rate (BMR), thyroxine utilization rate (T4U), and triiodothyronine utilization rate (T3U) were measured in cold-acclimated (CA) and room temperature-acclimated (RA) male golden hamsters, Mesocricetus auratus. Hormone utilization rates were calculated via the plasma disappearance technique using 125I-labeled hormones and measuring serum hormone levels via radioimmunoassay. BMR showed a significant 28% increase with cold acclimation from 4.50 +/- 0.05 to 5.77 +/- 0.10 ml O2 X h-1 X g-2/3. The same cold exposure also produced a 32% increase in T4U (10.75 +/- 0.51 vs. 14.19 +/- 0.75 ng X day-1 X g-2/3), and a 204% increase in T3U (5.51 +/- 0.53 vs. 16.77 +/- 1.35). The much greater increase in T3U implies that previous assessments of the relationship between cold acclimation and thyroid function may have been underestimated and that cold exposure induces both quantitative and qualitative changes in thyroid function. It is concluded that in the cold-acclimated state, T3U more accurately reflects thyroid function than does T4U. A mechanism for the cold-induced change in BMR is proposed, for which alterations in four aspects of thyroid function are required: a decrease in plasma T4 binding, an elevation of the pituitary T4 "set point," a preferential shift in deiodinase activity from reverse T3 to T3 production, and an increase in the thyroidal secretion of T3.

Thermogenic capacity and brown fat in rats exercise-trained by running

Brown adipose tissue, a major effector of nonshivering thermogenesis (NST) in mammals, is activated by the sympathetic neurotransmitter norepinephrine. Prolonged increases in norepinephrine levels, whether elicited by cold exposure or exogenous application of catecholamines, lead to increased NST and increased thermogenic capacity of brown fat. Exercise training is also accompanied by enhanced sympathetic activity. The possibility exists that this enhancement may alter brown fat function. The present study was designed to assess the effect of a running exercise regimen on whole animal NST and the in vivo response of brown fat. Rats were trained by running on a treadmill (an average of 17 m/min, 0 degrees incline, for 90 min/d) for a period of at least 6 weeks. Whole animal NST capacity was assessed by monitoring oxygen consumption in response to infusion of norepinephrine. As a measure of the contribution of brown fat to whole body NST, the mass and norepinephrine-stimulated blood flow (microsphere technique) to the tissue were measured. None of these variables differed between the exercised (n = 10) and sedentary (n = 10) groups. That is, there were no significant differences between the two groups with respect to resting oxygen consumption, norepinephrine-induced oxygen consumption, brown fat mass, and brown fat blood flow--whether expressed per gram of tissue or as total tissue blood flow (ie, tissue mass X blood flow per gram). Further study is needed to explain the differential responses of brown fat to the increased sympathetic activity occurring during exercise v that occurring during cold exposure.

Metabolism at thermoneutrality and in the cold is reduced in the neonatal preobese Zucker fatty (fa/fa) rat

Minimum and maximum rates of oxygen consumption (VO2) were determined in 2-, 6- and 8-d-old lean (Fa/?) and preobese (fa/fa or "fatty") Zucker rats. On each study day, three or four naive littermate male pups were placed in individual respiration chambers submerged in a water bath and studied simultaneously over a range of ambient temperatures (24-35 degrees C). The purpose of the cold exposure was to elicit maximal oxygen consumption and to determine the ability of the rat to maintain body temperature during cold stress. Minimum rates of oxygen consumption were observed at 33-34 degrees C in both groups. As ambient temperature was reduced, VO2 increased and rectal temperature decreased. Regression analysis revealed a significantly reduced oxygen consumption in the preobese pups within the thermoneutral zone and during cold exposure. A defect in energy expenditure for heat production was evident in the preobese (fa/fa) pups as indicated by their attenuated cold-induced rate of oxygen consumption and decreased ability to maintain body temperature during cold stress relative to their lean (Fa/?) littermates. Their lower VO2 within the thermoneutral zone implies that the preobese (fa/fa) pups have a decreased metabolic rate even under conditions in which cold-induced thermogenic mechanisms are turned off.

Blood flow to brown fat in lean and obese adrenalectomized Zucker rats

The Zucker obese rat is characterized by decreased capacity for diet-induced and for nonshivering thermogenesis. This decrease is due, in large part, to reduced thermogenesis in depots of brown adipose tissue, a major source of heat production in rats. Adrenalectomy retards the weight gain observed in the obese rats and also normalizes brown fat guanosine 5'-diphosphate (GDP) binding, an in vitro measure of brown fat thermogenic capacity. This study examined the effect of adrenalectomy on brown fat blood flow, an in vivo measure of the tissue's function, and on norepinephrine-induced O2 consumption (NST) of 11-wk-old obese (fa/fa) and lean (Fa/?) rats. Adrenalectomy had little effect on weight gain, NST, or norepinephrine-stimulated blood flow to brown fat in lean rats. However, adrenalectomy produced profound changes in the obese animals, preventing the weight gain normally occurring in the obese rats and normalizing both NST capacity and norepinephrine-stimulated blood flow to brown fat. These findings provide further support for the importance of brown fat thermogenesis and glucocorticoids in modulating the obesity of the Zucker rat.

Decreased testosterone levels do not mediate short-photoperiod-induced brown fat changes

Previous studies showed that short photoperiod increased brown fat (BAT) mass and reduced gonadal size and gonadal hormone secretion in hamsters. The present study investigated the possibility that the effects on BAT were dependent on reduced levels of gonadal hormones. BAT from male Syrian hamsters exposed to short photoperiod for 10 wk was significantly greater in mass, protein content, and total maximal citrate synthase and beta-hydroxyacyl-CoA dehydrogenase activities than was BAT from long-photoperiod hamsters, These differences between short- and long-photoperiod exposure were observed in hamsters housed at 21 as well as at 8 degrees C. Short photoperiod also increased the total recovered mitochondrial GDP binding, a finding consistent with increased BAT thermogenic capacity. These short-photoperiod effects were neither mimicked by castration of long-photoperiod hamsters nor prevented by high levels of testosterone administered to short-photoperiod animals. Castration did attenuate the effects of short photoperiod on BAT growth if, after surgery and prior to short-photoperiod exposure, the animals were housed at a long photoperiod for 2-3 wk. In contrast, in hamsters immediately placed at short photoperiod after surgery, castration did not inhibit short-photoperiod effects. The present three experiments demonstrate that, in addition to increasing BAT mass, short photoperiod elevates the thermogenic capacity of BAT, and this elevation does not require the absence or a much reduced testosterone level.

Hyperprolactinemia stimulates food intake in the female rat

Lactation in the rat is marked by extreme hyperphagia. The present study examined the possibility that elevated prolactin levels contribute to this increase. It also evaluated the effects of hyperprolactinemia on brown adipose tissue and carcass composition. Virgin Osborne-Mendel rats were made hyperprolactinemic via ectopic pituitary transplants (PIT, n = 9) or were sham-operated (SHAM, n = 8). Eight lactating rats (LACT) served as additional controls. Food intake, body weight and rectal temperature were recorded daily. Eleven days postsurgery (or 11-12 days postpartum), the rats were sacrificed, and brown fat (scapular, axillary, cervical and thoracic) was excised, weighed, and assayed for GDP binding, one indicator of thermogenic capacity. Carcasses were subjected to body composition analysis. Although prior to surgery, PIT and SHAM rats weighed the same, PIT rats gained significantly more weight during the experiment than did SHAMs. Percent body fat and food intake (both total intake and intake relative to metabolic body size) were significantly elevated in the PIT rats. GDP binding in both PIT and LACT rats was significantly less than in SHAMs. This was true whether GDP binding was expressed per mg mitochondrial protein or per total amount of mitochondrial protein recovered. These data confirm that brown fat thermogenic capacity is suppressed during lactation. They also demonstrate that elevations of serum prolactin, to levels that are well within physiological limits, are capable of stimulating food intake and white fat deposition in the female rat. It is presently unclear whether these results are a direct or an indirect effect of hyperprolactinemia.

Brown fat mediates increased energy expenditure of cold-exposed overfed neonatal rats

Genetically lean rat pups, overfed by being raised in small litters of three from day 1 postpartum, rapidly become obese compared with pups raised in standard sized litters of eight. Because of the rapid onset of their obesity, we expected that overfed pups would exhibit defective brown fat thermogenesis as is seen in neonatal genetically obese rodents. O2 consumption (VO2) was measured in 2-, 4-, 6-, and 8-day-old homozygous lean (Fa/Fa) Zucker pups from each treatment. We determined minimum rate of VO2 at thermoneutrality and maximum VO2 in response to progressively colder ambient temperatures. Overfed pups were fatter than standard-fed pups (P less than 0.001). But contrary to our prediction, overfed pups had a significantly increased maximum VO2 in response to acute cold exposure. To test the hypothesis that brown fat mediated the increased VO2 in the overfed pups, scapular brown fat lipectomies were performed on a new group of overfed pups at 2 days of age and compared with sham-operated littermate controls. On day 8, no differences in minimum VO2 were seen at thermoneutrality when brown fat is turned off. But maximum VO2 in response to cold, when brown fat is turned on maximally, was significantly reduced in the lipectomized overfed pups compared with sham-operated overfed littermates. These data suggest that manipulations of diet, accomplished by raising pups in small litters, can increase brown fat thermogenic function. The results of the lipectomy experiment imply that brown adipose tissue is a primary mediator of the increased energy expenditure in response to acute cold exposure in the overfed pups.

Modified Light-Induced Absorbance Changes in dim Y Photoresponse Mutants of Trichoderma

A brief pulse of blue light induces the common soil fungus Trichoderma harzianum to sporulate. Photoresponse mutants with higher light requirements than the wild type are available, including one class, dim Y, with modified absorption spectra. We found blue-light-induced absorbance changes in the blue region of the spectrum, in wild-type and dim Y mutant strains. The light-minus-dark difference spectra of the wild type and of several other strains indicate photoreduction of flavins and cytochromes, as reported for other fungi and plants. The difference spectra in strains with normal photoinduced sporulation have a prominent peak at 440 nm. After actinic irradiation, this 440 nanometer difference peak decays rapidly in the dark. In two dim Y photoresponse mutants, the difference spectra were modified; in one of these, LS44, the 440 nanometer peak was undetectable in difference spectra. Detailed study of the dark-decay kinetics in LS44 and the corresponding control indicated that the 440 nanometer difference peak escaped detection in LS44 because it decays faster than in the control. The action spectrum of the 440 nm difference peak is quite different from that of photoinduced sporulation. The light-induced absorbance changes are thus unlikely to be identical to the primary photochemical reaction triggering sporulation. Nevertheless, these results constitute genetic evidence that physiologically relevant pigments participate in these light-induced absorbance changes in Trichoderma.