Effect of temperature on lipoprotein lipase and lipogenic enzyme activities in brown adipose tissue of hypophysectomized rats

It has been shown that the same modifications on the composition of brown adipose tissue (BAT) which are normally induced following cold stimulation are also observed in hypophysectomized rats acclimated either at 28 degrees C or 15 degrees C. To test the possibility of BAT stimulation in hypophysectomized rats, we have determined some enzymatic activities known to modulate the energy supply to that organ. Seven week old Long-Evans rats were hypophysectomized. Three weeks later, they were exposed to either 28 degrees C or 15 degrees C ambient temperature for five or six weeks. Hypophysectomized rats were compared to age matched or weight matched controls. Total lipoprotein lipase activity (LPL) (triglyceride uptake) was enhanced in BAT of 28 degrees C hypophysectomized rats compared to controls. Cold acclimation led to a large increased activity. Total LPL activity was comparable in BAT of hypophysectomized and control rats. Total malic enzyme and glucose-6-phosphate dehydrogenase activities (in situ lipogenesis) were doubled in BAT of 28 degrees C hypophysectomized compared to controls. A large enhancement was observed in BAT of either 15 degrees C control or 15 degrees C hypophysectomized rats. Among the studied organs (liver, white adipose tissue, heart, BAT) hypophysectomy promotes the three enzyme activities only in BAT. These variations were discussed with relation to the effect of hypophysectomy on brown adipose tissue at 15 degrees C and 28 degrees C.     

Skeletal and cardiac muscle protein turnover during cold acclimation in young rats

The effect of long-term cold exposure on skeletal and cardiac muscle protein turnover was investigated in young growing animals. Two groups of 36 male 28-day-old rats were maintained at either 5 degrees C (cold) or 25 degrees C (control). Rates of protein synthesis and degradation were measured in vivo on days 5, 10, 15, and 20. Protein mass by day 20 was approximately 28% lower in skeletal muscle (gastrocnemius and soleus) and approximately 24% higher in heart in cold compared with control rats (P < 0.05). In skeletal muscle, the fractional rates of protein synthesis (k(syn)) and degradation (k(deg)) were not significantly different between cold and control rats, although k(syn) was lower (approximately -26%) in cold rats on day 5; consequent to the lower protein mass, the absolute rates of protein synthesis (approximately -21%; P < 0. 05) and degradation (approximately -13%; P < 0.1) were lower in cold compared with control rats. In heart, overall, k(syn) (approximately +12%; P < 0.1) and k(deg) (approximately +22%; P < 0.05) were higher in cold compared with control rats; consequently, the absolute rates of synthesis (approximately +44%) and degradation (approximately +54%) were higher in cold compared with control rats (P < 0.05). Plasma triiodothyronine concentration was higher (P < 0.05) in cold compared with control rats. These data indicate that long-term cold acclimation in skeletal muscle is associated with the establishment of a new homeostasis in protein turnover with decreased protein mass and normal fractional rates of protein turnover. In heart, unlike skeletal muscle, rates of protein turnover did not appear to immediately return to normal as increased rates of protein turnover were observed beyond day 5. These data also indicate that increased rates of protein turnover in skeletal muscle are unlikely to contribute to increased metabolic heat production during cold acclimation.     

Effects of rearing temperature on sympathoadrenal activity in young adult rats

Animals reared at 18 degrees C exhibit enhanced innervation of brown adipose tissue (BAT) and greater cold tolerance as adults, yet gain more weight when fed an enriched diet compared with rats reared at 30 degrees C. To explore this paradox, sympathoadrenal activity was examined using techniques of [(3)H]norepinephrine ([(3)H]NE) turnover and urinary catecholamine excretion in male and female rats reared until 2 mo of age at 18 or 30 degrees C. Gene expression in BAT was also analyzed for several sympathetically related proteins. Although [(3)H]NE turnover in heart did not differ between groups, [(3)H]NE turnover in BAT was consistently elevated in the 18 degrees C-reared animals, even 2 mo after removal from the cool environment. Gene expression for uncoupling proteins 1 and 3, GLUT-4, leptin, and the alpha(1A)-adrenergic receptor was more abundant in BAT and the increase in epinephrine excretion with fasting suppressed in 18 degrees C-reared animals. These studies demonstrate that obesity consequent to exposure to 18 degrees C in early life occurs despite tonic elevation of sympathetic input to BAT. Diminished adrenal epinephrine responsiveness to fasting may play a contributory role.     

Evidence for a cold-induced aldosterone stimulation in the rat

This study was undertaken to determine the secretion of aldosterone by male Long-Evans rats acclimated for six weeks to moderate cold (15 C), in comparison with rats maintained at thermo-neutral temperature (28 C). The following determinations were made: corticosteroids in plasma and adrenals, PRA, and hydromineral balance. Cold acclimation highly increased the plasma and adrenal levels of aldosterone and corticosterone. The cold stimulation of aldosterone was induced neither by the renin-angiotensin system, nor by alterations of hydromineral balance: PRA, plasma sodium and potassium concentrations, blood hematocrit, and hydromineral balance at 15 C and 28 C did not differ. Moreover this stimulation was induced neither by ACTH, nor by any other hypophyseal factors, since plasma aldosterone levels remained high in hypophysectomized rats. This study provides evidence of an aldosterone stimulation which appeared during moderate cold acclimation; the origin of this stimulation must be investigated.     

Contribution of ATP synthase to stimulation of respiration by Ca2+ in heart mitochondria

A variety of experimental conditions were applied with the aim to estimate the correlation between the contribution of ATP synthase to the respiratory flux control and the calcium-induced activation of succinate oxidation in heart mitochondria isolated from rat, rabbit and guinea pig. The sensitivity of respiration in heart mitochondria to the decrease in temperature from 37 degrees C to 28 degrees C decreases in the order rabbit > guinea pig > rat. Ca2+ effect on succinate oxidation rate in state 3 respiration was species- and temperature-dependent and ranged from 0 (rat, 37 degrees C) to +44% (rabbit, 28 degrees C). For mitochondria from all experimental animals, the increase of Ca2+ in physiological range of concentration did not change state 2 respiration rate, and the stimulatory effect of Ca2+ on state 3 respiration was more pronounced at 28 degrees C than at 37 degrees C. The respiratory subsystem was sensitive to Ca2+ ions only in rabbit heart mitochondria. A high positive correlation between Ca2+ ability to stimulate succinate oxidation in state 3 and the control exerted by ATP synthase over the respiratory flux provides argument confirming stimulation of ATP synthase by Ca2+ ions.     

Morpholigic and physiologic repercussions of partial removal of brown adipose tissue in rats acclimated to different temperatures]

Rats were chronically acclimated to 28 degrees C or 5 degrees C or submitted to daily variations of ambiant temperature. Ten or thirty days after removal of about 40% of the total brown adipose tissue (whole interscapular and 25% of abdominal tissues), the weight of the different pads of brown adipose tissue, thyroid and adrenals were determined. In all the groups, there was a large decrease of brown adipose tissue weight for the first ten days due to the shock following the operation. Then, the brown adipose tissue weight was restaured and, only in constant cold accliclimated rats, compensative hypertrophies of axillary and thoracic brown adipose tissue were found. Adrenals weight was significantly increased after the operation; in the two groups of cold acclimated rats, that increase was still significant one month later. However, the corticosterone production rate was not increased. These results are discussed in relation to the physiolocical role of brown adipose tissue in cold acclimated animals.     

Skeletal and heart muscle protein turnover during long-term exposure to high environmental temperatures in young rats

A study was undertaken to determine the long-term effects of a hot environment on protein turnover in skeletal and cardiac muscles of young homeothermic animals. Three groups of 36 male 28 day old rats were housed at 35 degrees C (hot group), 25 degrees C (control group), or 25 degrees C but pair-fed to the intake of the hot group (pair-fed group). Rates of protein synthesis and degradation were measured in vivo on days 5, 10, 15, and 20. By day 20, soleus and gastrocnemius (skeletal muscle) protein masses were 7 and 14% lower in the hot group and 31 and 21% lower in the pair-fed group compared with the control group (P < 0.05). The fractional rate of protein synthesis (k(syn)) was on average 11% lower (P < 0.05) in the hot group compared with control rats and was not different from pair-fed rats. The fractional rate of skeletal muscle protein degradation (k(deg)) in hot rats was slightly lower than in control rats; k(deg) was on average 18% higher (P < 0.05) in the pair-fed group compared with the hot group and this difference appeared to be most prominent on day 5. In heart, by day 20, protein mass was 30% lower in the hot group and 40% lower in the pair-fed group compared with control rats (P < 0.05). k(syn) was on average 19% lower (P < 0.05) in the hot group compared with the control group, but not different from pair-fed rats. In the heart there were no differences in k(deg) among treatments. Plasma triiodothyronine (T3) concentration was lower in the hot group, but not in the pair-fed group, compared with controls. In conclusion, chronic exposure to hot environments was associated with lower skeletal and cardiac muscle mass and protein turnover; lower protein mass in this tissue was due to decreased k(syn); this is consistent with lower plasma T3 concentrations. In pair-fed rats, k(syn) was also reduced, but interestingly k(deg) was not, resulting in a greater loss of skeletal muscle mass. These results suggest that heat exposure invokes physiological adaptations to preserve skeletal muscle mass despite decreased food intake. In the heart, loss of protein was a result of decreased k(syn), which can be primarily ascribed to lower food intake.     

Postnatal development of hepatic xanthine oxidase in baby pigs and turnover of purine catabolites at reduced ambient temperature.

1. The activity of xanthine oxidase in liver samples of baby pigs up to 4 weeks of age was investigated. On the 3rd day of life the turnover of hypoxanthine and of uric acid were measured after intravenous injection of 3H- and 14C-labelled tracers into animals kept at normal (32 degrees C) and reduced (20 degrees C) ambient temperature. 2. Hepatic xanthine oxidase activity increased progressively from 2 to 28 days of age (r = 0.689; P < 0.001). The increase of Vmax and of KM within 3-4 weeks was about 4.5-fold. 3. In 3-day-old baby pigs kept at normal temperature, pool size and turnover was about 10-fold higher for hypoxanthine than for uric acid. 4. At reduced ambient temperature, the pool size of uric acid increased 3.9-fold (P < 0.01) and turnover 1.6-fold (P < 0.05). For hypoxanthine the increases were insignificant.     

The role of insulin in norepinephrine turnover and thermogenesis in brown adipose tissue after acute cold-exposure

The role of insulin in norepinephrine turnover (NE) and thermogenesis in brown adipose tissue (BAT) after acute cold-exposure was studied using streptozocin (STZ)-induced diabetic rats. NE turnover was estimated by the NE synthesis inhibition technique with alpha-methyl-p-tyrosine. BAT thermogenesis was estimated by measuring mitochondrial guanosine-5'-diphosphate (GDP), cytochrome oxidase activity and mitochondrial oxygen consumption in BAT at an ambient temperature of 22 degrees C and during a six-hour cold-exposure at 4 degrees C. In insulin-deficient diabetic rats, the NE turnover, mitochondrial GDP binding, cytochrome oxidase activity and mitochondrial oxygen consumption in BAT at 22 degrees C were significantly reduced, compared with those of control rats. Treatment of STZ-induced diabetic rats with insulin prevented a decrease in NE turnover and BAT thermogenesis. Acute cold-exposure increased the NE turnover of BAT in insulin-deficient diabetic rats. The BAT thermogenic response to acute cold-exposure, however, did not occur in insulin-deficient diabetic rats. These results suggest that insulin is not essential in potentiating NE turnover in BAT after acute cold-exposure, but is required for cold-induced thermogenesis.     

Glycerokinase activity and lipolysis regulation in brown adipose tissue of cold acclimated rats.

Glycerol release by brown adipocytes from constant cold adapted rats was not stimulated by norepinephrine. On the contrary, the release was stimulated in rats adapted to a nycthemeral fluctuatiing temperature from 5 degrees to 28 degrees C. Glycerokinase activity was greatly increased in brown adipose tissue by cold adptation ; there was no change in the liver. However this increased activity cannot entirely explain the lack of norepinephrine stimulation of glycerol release in the brown adipose tissue of cold adapted rats.     

Pressor and tachycardic responses to intravenous substance P in anesthetized rats

Intravenous injection of 3–33 nmol/kg of substance P (SP) caused pressor and tachycardic responses in anesthetized rats. The responses were not blocked by a ganglion nicotinic receptor antagonist or by pithing. Pretreatment with reserpine blocked both responses. β-Adrenoceptor blockade attenuated only the tachycardic response, and -adrenoceptor blockade attenuated only the pressor response. These findings indicated that the effects of SP to increase blood pressure and heart rate are due to sympathetic ganglion stimulation. Studies with adrenalectomized rats showed that stimulation of the adrenals by SP contributes to both responses but makes a greater contribution to the tachycardic response. These observations raise the possibility that the tachykinin innervation of sympathetic ganglia and the adrenal medulla may be involved in the local regulation of blood pressure and heart rate.     

Acclimation of rats following stepwise or direct exposure to heat

The physiological changes in male rats during acclimation were studied following direct or stepwise exposure to heat (32.5 degrees C) in a controlled-environment room. The animals were exposed to each temperature for 10 days beginning at 24.5 degrees C and returning to 24.5 degrees C in the reverse order of initial exposure. Relative humidity of 50 +/- 2% and a 12-h light-dark photoperiod (light from 0900 to 2100 h) were maintained. Physiological changes in metabolic rate (MR), evaporative water loss (EWL), plasma corticosterone, body water turnover, and food and water intake were measured. The results indicate a significantly (P less than 0.001) elevated plasma corticosterone and MR in rats exposed directly to heat from control temperature (24.5 degrees C) but not in those animals exposed stepwise via 29.0 degrees C. All kinetic parameters of water pool changed (P less than 0.01) on direct exposure to heat, whereas rats exposed in a stepwise manner increased only pool turnover. In addition, exposure to experimental temperatures resulted in reduced (P less than 0.05) relative food intake and increased (P less than 0.05) water intake. Compared with the control condition of 24.5 degrees C, EWL was significantly (P less than 0.05) elevated when the animals were exposed either directly or in a stepwise fashion to 32.5 degrees C. These data suggest that the response to elevated temperatures is influenced by the temperature to which the rat is acclimated.     

Effect of breeding temperature on the growth and composition of brown fat in the newborn rat]

The weight and the lipid, water and norepinephrine contents of the interscapular brown adipose tissue from 1, 3, 7, 11, 14 and 21 day aged rats were measured. The animals were maintained at an ambiant temperature of 16 degrees, 23 degrees or 28 degrees C from birth. It is concluded that nonshivering thermogenesis is not necessary after 3 days of age in animals kept at 28 degrees C and after 11 days of age in the ones kept at 23 degrees C. However that thermogenesis persists for all the suckling period in those kept at 16 degrees C.     

Influence of temperature on the secretion of insulin and glucagon induced by stimulation of cholinergic receptors in the presence of glucose]

In the presence of a glucose concentration of 1.5 g/1 the secretion of insulin from the isolated perfused rat pancreas is clearly weaker at 28 degrees C than at 37.5 degrees C. In response to cholinergic stimulation, the absolute increase of insulin secretion rate is less at 28 degrees C than at 37.5 degrees C. However, when evaluated in percentage in relation to the baseline value, this increase is more important at the lower temperature. As to glucagon secretion, lowering of the temperature from 37.5 degrees C to 28 degrees C modifies neither this secretion in the presence of glucose alone, nor the increased secretion provoked by the cholinergic stimulation.     

Age related changes in noradrenaline,noradrenaline turnover and adrenaline in brainstem nuclei of wistar kyoto and spontaneously hypertensive rats

Noradrenaline and noradrenaline turnover were determined in regions enriched in catecholamine nuclei of the brainstem (A1, A2, C1, C2 and C3), in the locus coeruleus (A6) and in the nucleus tractus spinalis n. trigemini (Sp5C) of Wistar Kyoto and spontaneously hypertensive rats at four ages from 6 to 40 weeks. Adrenaline levels were also determined but were only consistently detected in the C1 and C2 regions. There was an age-related decline in noradrenaline concentrations in both strains of rats in all brainstem catecholamine nuclei however noradrenaline turnover decreased only in the A2 and C3 regions and this may contribute to the progressive rise in blood pressure with age in spontaneously hypertensive and Wistar Kyoto rats. Adrenaline levels did not alter with age providing evidence of a functional disassociation between adrenaline and noradrenaline neuronal systems. There were several strain-related differences in noradrenaline and adrenaline concentrations in the regions studied, however noradrenaline turnover was reduced only in the A2 and C2 regions (nucleus tractus solitarius) of spontaneously hypertensive rats which is consistent with the sympathoinhibitory role of this nucleus in central blood pressure regulation.     

Thermogenic capacity of the brown adipose tissue of developing rats; effects of rearing temperature

A chronological study was performed to investigate the postnatal development of the thermogenic capacity of the brown adipose tissue (BAT) comparing rats born and reared at 16 degrees C (cold) or 28 degrees C (control). Mitochondrial mass, cytochrome-c-oxidase activity (index of oxidative capacity) and GDP binding to mitochondria (uncoupling test) were investigated in rats from 1 to 33 days of age. Specific cytochrome-c-oxidase activity was the same in both groups during the first week, then increased in the cold group and decreased in controls; from the 9th day it was always twice as high in the former as in the latter. Specific binding of GDP to mitochondrial proteins remained almost constant in control rats during the first week contrasting with a rapid increase in that for cold rats. Afterwards it decreased in both groups until weaning but remained five times as high in cold rats as in control rats. As growth of BAT is faster and mitochondrial content greater in cold reared rats, the capacity of the tissue for thermogenesis appeared to be greatly temperature dependent soon after birth and during the entire suckling period. However the mechanisms of this stimulation remain to be elucidated.     

Sympathetic response to exercise in various tissues with advancing age

It was the purpose of this investigation to examine any age-related changes in norepinephrine turnover (NEt) in four tissues at rest and during exercise. Fischer 344 rats 6 (n = 20) and 25 mo of age (n = 20) were received from the National Institute on Aging. NEt was determined at rest, during 30 min of submaximal exercise, and at maximal exercise by administration of alpha-methyl-p-tyrosine, a competitive inhibitor of tyrosine hydroxylase. Resting NE declined with age in both heart (38.2 vs. 30.5 ng.g-1.h-1) and liver (11.2 vs. 6.4 ng.g-1.h-1). NEt was greater in the older animals compared with the young animals in heart (120.9 vs. 169.5 ng.g-1.h-1), liver (23.1 vs. 38.9 ng.g-1.h-1), and adrenals (74.0 vs. 98.4 ng.mg-1.h-1) during submaximal exercise. In response to maximal exercise, NEt varied depending on age and tissue. It was concluded that, in response to exercise stress, the older animals generally demonstrated a higher NEt (reflecting elevated sympathetic activity) perhaps because of a decreased adrenergic receptor sensitivity and/or responsiveness.     

Effect of heat treatment on oxidase activity and proton-pumping capability of proteoliposome-incorporated beef heart cytochrome aa3

By incubating beef heart cytochrome c oxidase at 43-45 degrees C, selective inactivation of the H+-pumping function is possible without affecting cytochrome c oxidase activity; proteoliposomes reconstituted with heated enzyme (43.5 degrees C for 60 min at pH 7.0) showed an apparent H+/e- ratio of only 0.3 and a turnover with cytochrome c plus ferrocyanide as substrate of 20 s-1, while those with the intact enzyme showed an apparent H+/e- ratio somewhat greater than 1.0 and a turnover of 19 s-1. This decrease in the H+/e- ratio could not be attributed to a stimulation of H+ permeability upon heating, since the respiratory control ratio and the magnitude of membrane potential formation remained almost the same in the two cases. A pH-dependent Em (midpoint redox potential) change of cytochrome a in the presence of cyanide was still observed after the heat treatment. Heating induced a small spectral shift in the Soret region of the oxidized (resting) enzyme; the peak of the heated enzyme was at 421 nm, while that of the intact enzyme was at 419 nm. The spectral shift obtained by pulsing the enzyme with oxygen under turnover conditions is also altered.     

Reactive oxygen species in pregnant rats: effects of exercise and thermal stress

With the aim of evaluating the effect of interaction between physical training or exercise only during pregnancy and thermal stress on oxidative stress, and antioxidant mechanism sedentary pregnant rats (PS), exercised pregnant rats only during pregnancy (PE) and trained rats submitted to also exercise during pregnancy (PT) were compared (N=63). Exercise sessions consisted of swimming at 80% of maximal work load supported into water at 28 degrees C (hypothermia, PS 28, PE28, PT28) or 35 degrees C (thermal neutrality, PS35, PE35, PT35) or 39 degrees C (hyperthermia, PS39, PE39, PT39), for 30 min. The initial body weight in all groups of rats was from 177 to 207 g. On the 20th day of pregnancy, 24 h after the last immersion or swimming session venous blood was collected to determine oxidative stress. Plasma concentrations of means malondialdehyde (MDA) values measured as thiobarbituric acid reactive substances (TBARS); total glutathione (GSH) and vitamin E were determined. The oxidative stress index was calculated from the ratio TBARS/GSH and TBARS/Vitamin E. TBARS did not change on the group PE at different temperatures of water; TBARS were higher for PS28 than PS35 and PS39; PT35 had higher values than PT28 and PT39. For GSH, PS39 was lower than PS35; PE28 was higher than PE35 and PE39 and PT35 were lower than PT28 and PT39. Plasma concentration of vitamin E did not present any difference for sedentary rats at different water temperatures, but for PE28, the values were lower than for PE35 and PE39, whereas PT39 was lower than PT35 and PT28. In relation to TBARS/GSH, it was verified an increase in oxidative stress for PS28 (in relation to PS35 and PS39), PE35, and PT35 (in relation to PE28 and PE39 or PT28 and PT39); regarding the ratio TBARS/vitamin E, the highest values were obtained at 35 degrees C for PS and PT groups and at 39 for PE group. These results have shown the great complexity of the interaction between physical training, thermal stress and pregnancy. Apparently, hypothermia produces large index of oxidative stress only in sedentary rats, but this index was greater at 35 degrees C in relation to extreme temperatures for trained rats. These results have suggested that physical training allows a more efficient activation of antioxidant mechanisms under thermal stress.     

Saturated glucose uptake capacity and impaired fatty acid oxidation in hypertensive hearts before development of heart failure

Abnormalities in energy metabolism may play an important role in the development of hypertensive heart failure. However, the transition from compensated hypertrophy to heart failure is not fully understood in terms of energy metabolism. In Dahl salt-sensitive (DS) and salt-resistant (DR) rats, myocardial fatty acid and glucose uptake values were determined using (131)I- or (125)I-labeled 9-methylpentadecanoic acid ((131)I- or (125)I-9MPA), and [(14)C]deoxyglucose ([(14)C]DG), fatty acid beta-oxidation was identified using thin-layer chromatography, and insulin-stimulated glucose-uptake was observed using a euglycemic hyperinsulinemic glucose clamp. Six-week-old rats were fed a diet that contained 8% NaCl, which resulted in development of compensated hypertrophy in DS rats at 12 wk of age and ultimately led to heart failure by 18 wk of age. Uptake of [(14)C]DG increased markedly with age in the DS rats, whereas (131)I-9MPA uptake was marginally but significantly increased only in animals aged 12 wk. The ratio of (125)I-9MPA beta-oxidation metabolites to total uptake in the DS rats was significantly lower (P < 0.05) at 12 (37%) and 18 (34%) wk compared with at 6 (45%) wk. Insulin increased [(14)C]DG uptake more than twofold in the DS rats at 6 wk, although this increase was markedly attenuated at 12 and 18 wk (11 and 8%, respectively). Our data suggest that in a hypertrophied heart before heart failure, fatty acid oxidation is impaired and the capacity to increase glucose uptake during insulin stimulation is markedly reduced. These changes in both glucose and fatty acid metabolism that occur in association with myocardial hypertrophy may have a pathogenic role in the subsequent development of heart failure.