Investigation of the index case herd and identification of the genotypes of Theileria orientalis associated with outbreaks of bovine anaemia in New Zealand in 2012.

CASE HISTORY AND CLINICAL FINDINGS: On 7 September 2012 the Ministry for Primary Industries was notified of a dairy cow with regenerative anaemia (haematocrit (HCT) 0.08 L/L) in a herd of 465 Jersey-Friesian cross cows (index case herd) in the Northland region of New Zealand. Organisms consistent with Theileria spp. were present in red blood cells on a blood smear. No other causes of anaemia were detected following examination of affected cows. Blood samples collected from 29 randomly selected cows on 26 September 2012 showed that 24 (83%) were anaemic (HCT≤0.24 L/L) and therefore fitted the case definition for bovine anaemia associated with Theileria orientalis infection. LABORATORY FINDINGS: Using a T. orientalis type-specific PCR assay that targeted the single subunit rRNA gene, all of six animals tested were positive for T. orientalis type Ikeda. Blood samples collected from clinically affected cattle in 11 subsequent outbreaks from throughout the North Island showed that T. orientalis Ikeda type was a common finding, but mixed infections with Chitose type were also identified. In addition, using a PCR assay that targeted the major piroplasm surface gene, T. orientalis type 5 was detected in one cow from the Waikato region. DIAGNOSIS: The presence of T. orientalis type Ikeda, as well as type 5, was confirmed in cattle from outbreaks of bovine anaemia in herds throughout the North Island of New Zealand. CLINICAL RELEVANCE: Two new types of T. orientalis were identified in this investigation, that were associated with a sudden rise in cases of bovine anaemia. The body of evidence showed that the Ikeda type was implicated as the cause of disease observed in this epidemic.

Two cases of inflammatory muscle disease presenting with raised serum concentrations of troponin T.

Troponins T and I are highly sensitive markers of myocardial injury. However, non-cardiac disorders, such as pulmonary embolism, renal failure, subarachnoid haemorrhage, sepsis, eclampsia, chemotherapy, and inflammatory muscle conditions (dermatomyositis and polymyositis), can also result in raised serum troponin concentrations. This article describes two cases that occurred within a month of each other in Craigavon Area Hospital, whereby conditions unrelated to myocardial ischaemia resulted in raised concentrations of cardiac markers. The first patient, in retrospect, underwent unnecessary investigation as an inpatient in the cardiac ward. Experience gained from this case led to more appropriate consultation and management of the second patient.

Interaction of glucose and long chain fatty acids (C18) on antioxidant defences and free radical damage in porcine vascular smooth muscle cells in vitro.

AIMS/HYPOTHESIS: Abnormalities of glucose and fatty acid metabolism in diabetes are believed to contribute to the development of oxidative stress and the long term vascular complications of the disease; therefore the interactions of glucose and long chain fatty acids on free radical damage and endogenous antioxidant defences were investigated in vascular smooth muscle cells. METHODS: Porcine vascular smooth muscle cells were cultured in 5 mmol/l or 25 mmol/l glucose for 10 days. Fatty acids, stearic acid (18:0), oleic acid (18:1), linoleic acid (18:2) and alpha-linolenic acid (18:3) were added with defatted bovine serum albumin as a carrier for the final three days. RESULTS: Glucose (25 mmol/l) alone caused oxidative stress in the cells as evidenced by free radical-mediated damage to DNA, lipids, and proteins. The addition of fatty acids (0.2 mmol/l) altered the profile of free radical damage; the response was J-shaped with respect to the degree of unsaturation of each acid, and oleic acid was associated with least damage. At a lower concentration alpha-linolenic acid (0.01 mmol/l) was markedly different in that, when added to 25 mmol/l glucose it resulted in a decrease in free radical damage to DNA, lipids and proteins. This was accompanied by a marked increase in antioxidant and glutathione concentrations as well as by increased gene expression is of gamma-glutamylcysteine synthetase, the rate-limiting enzyme in glutathione synthesis. CONCLUSIONS/INTERPRETATION: The results clearly show that glucose and fatty acids interact in the production of oxidative stress in vascular smooth muscle cells.

Meal-induced changes in extracellular 5-HT in medial hypothalamus of lean (Fa/Fa) and obese (fa/fa) Zucker rats.

Hypothalamic serotonin (5-HT) is involved in appetite regulation and sympathetic stimulation of thermogenesis. This study tested the hypothesis that the enhanced energetic efficiency of obese Zucker rats involves blunted serotonergic release within the medial hypothalamus (MH). We used microdialysis and HPLC-EC to measure dynamic changes in extracellular 5-HT levels in the MH of 10-13-week-old male lean (Fa/Fa) and obese (fa/fa) Zucker rats before and after a meal. No differences were noted in basal levels of 5-HT between lean and obese rats. Consistent with the suggestion that hypothalamic 5-HT plays a physiological role in feeding, extracellular 5-HT levels increased significantly in both lean and obese rats given a meal. This increase was observed in the 20 min interval in which they ate the 8.1 kcal meal and remained for an additional 60 min. The net release of 5-HT during the meal interval was comparable in the lean (1.46+/-0.38 fmol/microl) and obese (1.21+/-0.82 fmol/microl) rats. However, the 5-HT levels of the leans (1.80+/-0.29 fmol/microl) plateaued in the next 20 min interval, whereas they continued rising (2.74+/-0.53 fmol/microl) in obese rats and were significantly higher than those in the leans during the 40 and 60 min intervals after the meal was presented. This resulted in a total net release during the meal plus the next three 20 min intervals that was significantly higher in obese (9.83+/-1.16 fmol/microl) than in lean (5.59+/-0.85 fmol/microl) rats. Thus, the enhanced energetic efficiency of the obese Zucker rats may not be associated with attenuated serotonin release in response to a meal. Rather their enhanced release of 5-HT in the MH may reflect compensatory mechanisms for the elevated orexigen NPY, the reduction in meal-induced CCK release, and/or a functional resistance to 5-HT.

Reduced feeding response to neuropeptide Y in senescent Fischer 344 rats.

The anorexia of aging syndrome in humans is characterized by spontaneous body weight loss reflecting diminished food intake. We reported previously that old rats undergoing a similar phenomenon of progressive weight loss (i.e., senescent rats) also display altered feeding behavior, including reduced meal size and duration. Here, we tested the hypothesis that blunted responsiveness to neuropeptide Y (NPY), a feeding stimulant, occurs concurrently with senescence-associated anorexia/hypophagia. Young (8 mo old, n = 9) and old (24-30 mo old, n = 11) male Fischer 344 rats received intracerebroventricular NPY or artificial cerbrospinal fluid injections. In response to a maximum effective NPY dose (10 microg), the net increase in size of the first meal after injection was similar in old weight-stable (presenescent) and young rats (10.85 +/- 1.73 and 12.63 +/- 2.52 g/kg body wt (0.67), respectively). In contrast, senescent rats that had spontaneously lost approximately 10% of body weight had significantly lower net increases at their first post-NPY meal (1.33 +/- 0.33 g/kg body wt (0.67)) than before they began losing weight. Thus altered feeding responses to NPY occur in aging rats concomitantly with spontaneous decrements in food intake and body weight near the end of life.

Systemic administration of the immunophilin ligand GPI 1046 in MPTP-treated monkeys.

Systemic administration of immunophilin ligands provides trophic influences to dopaminergic neurons in rodent models of Parkinson's disease (PD) resulting in the initiation of clinical trials in patients with Parkinson's disease. We believe that prior to clinical trials, novel therapeutic strategies should show safety and efficacy in nonhuman models of PD. The present study assessed whether oral administration of the immunophilin 3-(3-pyridyl)-1-propyl (2S)-1-(3,3-dimethyl-1,2-dioxopentyl)-2-pyrrollidinecarboxylate (GPI 1046) could prevent the structural and functional consequences of n-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) administration in nonhuman primates. Twenty-five rhesus monkeys received daily oral administration of vehicle (n = 5) or one of four doses of GPI 1046 (0.3 mg/kg, n = 5; 1.0 mg/kg, n = 5; 3.0 mg/kg, n = 5; 10.0 mg/kg, n = 5). Two weeks after starting the drug treatment, all monkeys received a unilateral intracarotid injection of MPTP-HCl (3 mg). Daily drug administration continue for 6 weeks postlesion after which time the monkeys were sacrificed. Monkeys were assessed for performance on a hand reach task, general activity, and clinical dysfunction based on a clinical rating scale. All groups of monkeys displayed similar deficits on each behavioral measure as well as similar losses of tyrosine hydroxylase (TH)-immunoreactive (ir) nigral neurons, TH-mRNA, and TH-ir striatal optical density indicating that in general treatment failed to have neuroprotective effects.

Effects of 2 G on adiposity, leptin, lipoprotein lipase, and uncoupling protein-1 in lean and obese Zucker rats.

Male Zucker rats were exposed to 2 G for 8 wk to test the hypothesis that the leptin regulatory pathway contributes to recovery from effects of 2 G on feeding, growth, and nutrient partitioning. After initial hypophagia, body mass-independent food intake of the lean rats exposed to 2 G surpassed that of the lean rats maintained at 1 G, but food intake of the obese rats exposed to 2 G remained low. After 8 wk at 2 G, body mass and carcass fat were less in both genotypes. Leptin and percent fat were lower in lean rats exposed to 2 G vs. 1 G but did not differ in obese rats exposed to 2 G vs. 1 G. Although exposure to 2 G did not alter uncoupling protein-1 levels, it did elicit white fat pad-specific changes in lipoprotein lipase activity in obese but not lean rats. We conclude that 2 G affects both genotypes but that the lean Zucker rats recover their food intake and growth rate and retain "normal" lipoprotein lipase activity to a greater degree than do the obese rats, emphasizing the importance of a functional leptin regulatory pathway in this acclimation.

Extracellular hypothalamic serotonin levels after dorsal raphe nuclei stimulation of lean (Fa/Fa) and obese (fa/fa) Zucker rats.

Serotonin (5-HT), acting in the medial hypothalamus (MH), is involved in appetite/satiety and sympathetic stimulation of thermogenesis. This study tested the hypothesis that the enhanced energetic efficiency of obese Zucker rats is associated with a reduced capacity of activated dorsal raphe (DR) neurons to release 5-HT in the MH. We used microdialysis and HPLC-EC to measure dynamic changes in extracellular 5-HT levels in the MH of urethane-anesthetized, 10-14 week old male lean and obese Zucker rats. These concentrations did not differ significantly between the two genotypes prior to stimulation (mean+/-S.E.M.=3.8+/-0.5 fmol/microl, lean; 3.6+/-1.0 fmol/microl, obese) or following DR stimulation at 25 Hz (200 microA). The latter elicited initial net increases of 0.54+/-0.15 fmol/microl in lean and 0.58+/-0.20 fmol/microl in obese rats; and 20 min post-stimulus, 5-HT values were still elevated and comparable in the two genotypes. Although a 50-Hz (200 microA) stimulus evoked initial increases that were similar in lean (1.37+/-0.23 fmol/microl) and obese (0.95+/-0.24 fmol/microl,) rats, the net increase in 5-HT concentration during the next 20-40 min period was higher in the lean (2.03+/-0.55 fmol/microl vs. 1.18+/-0.24 fmol/microl in the obese animals). Also, in the lean, but not obese rats, extracellular 5-HT levels were significantly greater at 50 vs. 25 Hz. These results support the hypothesis that the capacity of midbrain serotonergic neurons to release 5-HT at the MH is reduced in obese Zucker rats, consistent with their blunted responsiveness to dietary stimuli and greater energetic efficiency.

Effects of 2G exposure on lean and genetically obese Zucker rats.

Changes in the ambient force environment alter the regulation of adiposity, food intake and energy expenditure (i.e., energy balance). Lean (Fa/Fa) and obese (fa/fa) male Zucker rats were exposed to 2G (twice Earth's normal gravity) for eight weeks via centrifugation to test the hypothesis that the Fa/Fa rats recover to a greater degree from the effects of an increased ambient force environment on body mass and food intake, than do the fa/fa rats which have a dysfunctional leptin regulatory system. The rats (lean and obese exposed to either 1G or 2G) were individually housed in standard vivarium cages with food and water provided ad libitum. The acute response to 2G included a transient hypophagia accompanied by decreased body mass, followed by recovery of feeding to new steady-states. In the lean rats, body mass-independent food intake had returned to 1G control levels six weeks after the onset of centrifugation, and body mass increased towards that of the 1G rats. In contrast, food intake and body mass of the 2G obese rats plateaued at a level lower than that of the 1G controls. Although percent carcass fat was reduced more in the 2G leans vs. 2G obese rats, the latter lost significantly more grams of fat than did the leans. Our data suggest that with respect to food intake and body mass, the lean rats recover from the initial effects of 2G exposure to a greater degree than do the fatty rats, a difference that likely reflects the functionality of the leptin regulatory system in the leans.

Lean (Fa/Fa) but not obese (fa/fa) Zucker rats release cholecystokinin at PVN after a gavaged meal.

Neuropeptides play an important role in the integration of dietary signals. Cholecystokinin (CCK) has been implicated in regulating ingestive behavior, particularly satiety. The primary objective of this study was to examine whether the hyperphagia characteristic of obese (fa/fa) rats involves impaired neural CCK secretion. Dynamic release of CCK at the hypothalamic paraventricular nucleus (PVN) of age-matched lean (Fa/Fa) and obese Zucker rats was determined using push-pull perfusion. The gavage of a 10.3-kcal (6 ml) liquid diet during lights off was followed by increased CCK release in lean rats (from 13.6 +/- 1.1 to 22.1 +/- 1.4 fmol in the 1st postprandial period and 18.4 +/- 2.5 fmol in the 2nd postprandial period). An identical meal load resulted in no postprandial increase in CCK release in obese rats, despite the fact that high-K+ artificial cerebrospinal fluid evoked CCK outflow in all animals. Intubation of 6 ml of nonnutritive 1% carboxymethylcellulose had no effect. These results are consistent with the suggestion that hypothalamic CCK plays a physiological role in satiety, and they demonstrate that obese Zucker rats have blunted hypothalamic CCK release in response to dietary cues.

Adiposity and serum leptin increase in fatty (fa/fa) BNZ neonates without decreased VMH serotonergic activity.

Decreased ventromedial hypothalamic (VMH) serotonergic activity occurs in genetic and diet-induced animal models of obesity. We previously found that this activity was lower in adult and in 12-day-old Zucker fa/fa vs. Fa/Fa pups, the fa/fa animals being identified by their greater adiposity. In the present study, we evaluated fa/fa rats (Brown Norway-Zucker hybrids) at ages 2, 4, 7, and 12 days to test the hypothesis that lower VMH serotonergic activity occurs before increased adiposity and/or attenuated energy expenditure. Our results negate this hypothesis. VMH serotonergic activity showed no consistent genotype differences even at 12 days of age. In contrast, by day 7, fa/fa vs. Fa/Fa pups had higher serum leptin concentrations, greater percent body fat, lower resting and cold-induced energy expenditure, and lower activity of brown fat thyroxine 5'-deiodinase, an enzyme that converts thyroxine to triiodothyronine. We conclude that the onset of increased adiposity induced by the fa gene does not require decreased VMH serotonergic activity and that the lower serotonergic activity seen in older fa/fa pups may be secondary to metabolic consequences of the disruption of the leptin regulatory pathway.

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.

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.

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.

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.

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.

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)

Norepinephrine depolarizes sartorius but hyperpolarizes soleus muscles in vitro.

Having previously found that in vivo administration of norepinephrine (NE) depolarizes the membrane of hamster sartorius muscle cells, the present study evaluated NE effects in vitro where alterations in blood flow were eliminated. Muscles were submerged in a temperature-controlled chamber, held at their resting length, and impaled with glass microelectrodes. Norepinephrine addition (maximum concentration of 10-20 microM at the muscle surface) induced significant depolarization in sartorius muscle cells and significant hyperpolarization in soleus muscle cells (P less than 0.05). Ascorbic acid (final concentration 15-25 microM), the vehicle for NE, evoked no significant alteration in resting membrane potentials of either muscle. Isoproterenol, a beta-adrenoceptor agonist, elicited responses similar to those of NE; phenylephrine, an alpha-adrenoceptor agonist, had no significant effect. The data suggest that the NE response is mediated through the beta-adrenergic pathway and that in the hamster, both hyperpolarization and depolarization can be observed under the same experimental conditions, depending on the muscle in question.