Takehiro Yahata

Physical training and fasting erythrocyte activities of free radical scavenging enzyme systems in sedentary men

SummaryEffects of 10 weeks of physical training on free radical scavenging enzyme systems in erythrocytes were investigated in 7 sedentary healthy male students. The training consisted of running over 5 km, 6 times/week. Their maximum oxygen uptake and 12 min walk-run performance increased significantly after training. Of the antioxidant enzyme systems examined in the erythrocytes, both catalase activity and concentration and total glutathione reductase (GR) activity also showed significant increases following the training. The erythrocyte GR activity coefficient also increased significantly. These results suggest that chronic aerobic exercise increases riboflavin requirements and has some positive effects on antioxidative processes.

Cross adaption between stress and cold in rats

Three-hour immobilization stress was imposed on male adult rats of Wistar strain by restraining them on a board 6 days a week for 1–8 weeks. The stressed rats showed less body weight gain during the experiment compared to the controls. These stressed animals manifested an improved cold tolerance as shown by no significant fall in colonic temperature in the cold at −5° C for 300 min during the experimental period, while the colonic temperature of the controls fell progressively. Nonshivering thermogenesis as assessed by noradrenaline-induced increase in oxygen consumption was significantly potentiated in the stressed rats. The weight and protein content of the intercapsular brown adipose tissue (BAT) increased and BAT mitochondria were more packed in the stressed rats. Plasma insulin, insulin/glucagon molar ratio and thyroxine levels were lowered in the stressed rats, while the plasma triiodothyronine level remained unchanged. Removal of interscapular BAT led to a loss of improved cold tolerance and a significant reduction of nonshivering thermogenesis in the stressed rats.These results indicate that repetitive stress may induce cross adaptation between stress and cold through an enhanced capacity of nonshivering thermogenesis mediated, at least in part, via stimulation of BAT function.

Hormonal regulation of brown adipose tissue—with special reference to the participation of endocrine pancreas

Abstract 1. 1. The role of pancreatic hormones, especially glucagon in the thermogenic function of brown adipose tissue (BAT) was investigated in rats. 2. 2. Plasma glucagon level increased in the cold-acclimated rats, while it decreased in the heat-acclimated ones. A significant positive relationship was observed between plasma glucagon and blood free fatty acid (FFA) levels as a whole in the warm controls, cold-acclimated and heat-acclimated rats. 3. 3. Glucagon infusion provoked an immediate rise of blood FFA and glucose levels on the venous drainage from the interscapular BAT. The β-adrenergic blocker, propranolol, did not modify these lipolytic and glycogenolytic actions of glucagon. When glucagon infusion was prolonged, the elevation of blood FFA and blood glucose levels was markedly suppressed in the cold-acclimated rats. 4. 4. Glucagon exhibited a marked heat production in the isolated brown adipocytes. 5. 5. Chronic administration of glucagon caused an improved cold tolerance accompanied by enhanced activity of BAT and increased non-shivering thermogenesis. 6. 6.Cold acclimation markedly elevated the content of glucagon as well as insulin in the interscapular BAT, while heat acclimation decreased it. 7. 7.These results would appear to indicate that glucagon as well as insulin is closely involved in the metabolic temperature acclimation, possibly through activation or inhibition of thermogenic mechanism(s) residing in the BAT.

Improved cold tolerance in glucagon-treated rats

Abstract In glucagon-treated rats (50 μg/100g, twice a day, 4 wks, sc) (GTR), the weights of liver and interscapular brown adipose tissue (BAT), and the level of plasma glucagon increased as compared with those in the vehicle-treated controls (VC). Mitochondria of BAT were markedly developed in size and cristae. Cold tolerance as assessed by the rate of fall in colonic temperature at −5 °C was improved. Elevations of colonic temperatures by noradrenaline (40 μg/100g, im) were significantly enhanced in GTR. After cold exposure, blood free fatty acids (FFA) and plasma glucagon levels increased, but blood glucose and β-hydroxybutyrate levels were not changed in VC. Both blood FFA and β-hydroxybutyrate levels increased and blood glucose level decreased, but plasma glucagon levels was not affected by cold exposure in GTR. These results suggest that glucagon is involved in cold acclimation by means of enhanced nonshivering thermogenesis, possibly due to an activation of BAT as well as increased production and utilization of ketone bodies in the liver.

Calorigenic effects of noradrenaline and glucagon on white adipocytes in cold- and heat-acclimated rats.

Calorigenic actions of noradrenaline and glucagon on isolated epididymal fat cells from warmacclimated controls, cold-acclimated and heatacclimated rats were measured by the use of a twin-type conduction microcalorimeter. Both noradrenaline and glucagon stimulated heat production in isolated adipocytes maximally in doses of 1 μg/ml and 10μg/ml, respectively. Maximal responsiveness of adipocytes per unit cell to noradrenaline was not influenced by cold acclimation, while it was reduced by heat acclimation. Maximal response in total epididymal fat cells to noradrenaline was increased in cold acclimation and not changed in heat acclimation at increased numbers of adipocytes in both cold-acclimated and heatacclimated animals. Maximal response per unit cell as well as per total epididymal fat cells to glucagon was increased in cold acclimation and reduced in heat acclimation.The present results indicate that the modified responses of target adipocytes to noradrenaline and glucagon are involved in the development of temperature acclimation.

In vitro thermogenic activity of rat brown adipose tissue in neonatal period.

The roles of noradrenaline (NA) and glucagon in ontogeny of nonshivering thermogenesis (NST) were investigated in rats. The relative brown adipose tissue (BAT) mass to body weight was larger in the neonates compared with those of adult animals. The NA level in BAT was low at birth and then increased rapidly to adult level, whereas glucagon level at birth was as high as that in the adult. The thermogenic function of BAT was estimated by measuring the in vitro oxygen consumption of the tissue blocks. NA and glucagon stimulated the oxygen consumption of BAT maximally in a dose of 1 microgram/ml, respectively. The response of the tissue to NA from the neonates just after birth was high compared with that in adult animals. The high values persisted throughout the early neonatal period, and decreased around the weaning period. The response to glucagon exhibited similar pattern. These results indicate that glucagon as well as NA play a significant role in NST in BAT during the early stage of neonatal period.

Comparison of in vitro thermogenesis of brown adipose tissue in cold-acclimated rats and guinea pigs

Abstract 1. 1. Effects of noradrenaline (NA) and glucagon (G) were investigated on in vitro brown adipose tissue (BAT) thermogenesis by measuring oxygen consumption with an oxygen electrode on finely minced tissue blocks incubated in Krebs-Ringer phosphate buffer at 37°C. 2. 2. The interscapular BAT weight increased in rats, while it rather decreased in guinea pigs by cold acclimation. Fat percentage in BAT decreased in the cold-acclimated rats and guinea pigs. 3. 3. Na- and G-stimulated oxygen consumptions of BAT expressed per mg tissue weight were suppressed in the cold-acclimated rats, but were enhanced in the cold-acclimated guinea pigs as compared with those in the warm control animals. Adenosine deaminase did not affect the result in the cold-acclimated rats However, the oxygen consumption per BAT pad did not differ between the cold-acclimated and warm control animals. 4. 4. These findings reveal species differences in the in vitro responsiveness of BAT of cold-acclimated animals to the thermogenic factors. It is further suggested that some compensatory mechanisms such as hyperplasia and/or increased blood flow induce an enhanced thermogenesis in BAT during cold acclimation.

Thermoregulatory responses of the inbred heat-tolerant FOK rat to cold

The responses of inbred heat-tolerant FOK rats to cold were compared with those of Wistar King A/H (WKAH) and Std:Wistar (WSTR) strains. The fall of colonic temperature during cold exposure was unexpectedly smaller in FOK than in other groups, but the onset of shivering was delayed in FOK. Norepinephrine (NE)-induced in vivo oxygen consumption and the mitochondrial uncoupling protein 1 level of brown adipose tissue (BAT) were not different among the groups, but the cold-induced increases in in vivo oxygen consumption as well as plasma glycerol and free fatty acids were higher in FOK than in other groups. In vitro NE-induced oxygen consumption of BAT was less in FOK than WSTR, but not WKAH. The magnitude of the NE-induced increase in blood flow through BAT was higher in FOK than in other groups. These results suggest that FOK paradoxically have a high capacity for nonshivering thermogenesis in spite of their high capacity for heat tolerance, probably due to an increased lipid utilization and improved circulation of BAT.The responses of inbred heat-tolerant FOK rats to cold were compared with those of Wistar King A/H (WKAH) and Std:Wistar (WSTR) strains. The fall of colonic temperature during cold exposure was unexpectedly smaller in FOK than in other groups, but the onset of shivering was delayed in FOK. Norepinephrine (NE)-induced in vivo oxygen consumption and the mitochondrial uncoupling protein 1 level of brown adipose tissue (BAT) were not different among the groups, but the cold-induced increases in in vivo oxygen consumption as well as plasma glycerol and free fatty acids were higher in FOK than in other groups. In vitro NE-induced oxygen consumption of BAT was less in FOK than WSTR, but not WKAH. The magnitude of the NE-induced increase in blood flow through BAT was higher in FOK than in other groups. These results suggest that FOK paradoxically have a high capacity for nonshivering thermogenesis in spite of their high capacity for heat tolerance, probably due to an increased lipid utilization and improved circulation of BAT.

Effect of sucrose-induced overfeeding on brown adipose tissue—With special reference to in vitro thermogenesis and fatty acids compositions

Effect of overfeeding induced by sucrose solution (32%) was investigated on in vitro oxygen consumption and fatty acids (FA) compositions of interscapular brown adipose tissue (BAT) in rat. Sucrose group (S) was fed standard diet with sucrose solution as drinking water. Food intake was greater by 10–24% in S as compared with that in standard diet control group (C). Colonic and skin temperatures were higher in S. The weight and DNA content of BAT were greater in S. In vitro basal and noradrenaline- or glucagon-stimulated oxygen consumption did not differ between the groups when expressed per DNA, while they were significantly greater in S in terms of whole tissue pad. In S BAT triglyceride (TG) and phospholipid (PL) levels as well as tissue contents were higher. In TG-FA of S saturated FA and monounsaturated FA were higher, while polyunsaturated FA were lower. In PL-FA of S monounsaturated FA were higher, while saturated FA and polyunsaturated FA were lower. These findings imply that sucrose-induced overfeeding increases BAT thermogenesis through tissue hyperplasia and higher PL-FA unsaturation as indicated by higher proportions of monounsaturates.

GLUCAGON AND TEMPERATURE ACCLIMATION

Publisher Summary Physiological and pathological significance of glucagon has been evidenced for several years. Glucagon is believed to be responsible for the physiological responses to energy need such as fasting and physical exercise. Glucagon plays a part in the metabolic aspects of temperature acclimation in concert with other humoral factors such as catecholamines, thyroid, and adrenocortical hormones that have been shown to be involved in temperature acclimation. This chapter describes an experiment involving a few cold-acclimated rats, in which plasma glucagon level significantly increased at the early stage of acclimation at 2 weeks, but it returned to the control value with the development of cold acclimation. As for the heat-acclimated rats, the plasma glucagon level was reduced and remained low throughout the acclimation period for 4 weeks. The blood free fatty acid (FFA) level also exhibited the corresponding changes to those observed in plasma glucagon, and there was a positive correlation between plasma glucagon and blood FFA levels.