Effects Of Chronic Cold Exposure Research Articles

Adipose tissue lipolytic activity and urinary catecholamine excretion in cold-acclimated piglets

This study was designed to investigate the effect of chronic cold exposure (12 degrees C for 3 weeks) on catecholamine production and noradrenaline-induced lipolytic rate to further describe thermoregulatory mechanisms in 5- to 8-week-old pigs. Lipolytic activity in white adipose tissue was assessed in vitro while catecholamine production was estimated by measuring noradrenaline, adrenaline, and dopamine levels in 24-h urine samples. Animals were fed ad libitum and food intake was 20% greater in the cold. In control piglets maintained in a 23 degrees C environment, the addition of increasing amounts of noradrenaline (10(-6), 10(-5), 10(-4) M) stimulates lipolysis (p less than 0.05) and enhances the basal lipolytic rate (5.4 mu equiv. fatty acids.120 min-1.g-1 tissue) by 2.5-, 2.7-, and 3.9-fold, respectively. Three weeks of cold acclimation had no effect on basal lipolytic rate but increased significantly noradrenaline responsiveness: incubation of subcutaneous white fat in the presence of 10(-4) M noradrenaline does increase the basal lipolytic rate by sixfold. Noradrenaline effects were maximally activated by theophylline. Daily dopamine and noradrenaline excretions (3-10 micrograms/24 h) were increased significantly (up to eightfold) after 10 days of cold acclimation. By contrast, adrenaline excretion was quite low (0.6-1.6 micrograms/24 h) and showed no significant variation with time. It is likely that these hormonal and biochemical modifications play a prominent part in the mechanism of cold acclimation in the piglet. Their significance in the development of shivering and nonshivering thermogenesis is discussed in relation to the supply of energy substrates to the fatty acid utilizing tissues and to the possible uncoupling effect of free fatty acids.

Effect of chronic cold exposure and underfeeding on hind-limb tissue metabolism in pregnant sheep

SUMMARYMuscle metabolism was studied in pregnant sheep over the final 4 weeks of pregnancy, between January and March 1985 and between December and March 1986, to investigate the effect of (i) chronic cold exposure, induced by shearing pregnant ewes 8 weeks before lambing and (ii) undernutrition in shorn and unshorn ewes. This was achieved by measuring hind-limb tissue metabolism using a combination of isotopic and arterio–venous difference techniques.The rates of blood flow, oxygen uptake, carbon dioxide production and calculated heat production were all significantly higher across the hind-limb tissues in shorn than in unshorn ewes. The increase in hind-limb energy metabolism in the shorn group was such that 65% of the difference in wholebody heat production between shorn and unshorn groups could be attributed to muscle tissue. Following underfeeding, all of the difference in whole-body heat production between the two groups was completely attributable to muscle tissue.Nonesterified fatty acid (NEFA) oxidation by muscle accounted for 46% of the difference in whole-body NEFA oxidation rate between fed shorn and unshorn groups. Underfeeding significantly increased the mean arterial plasma concentration of NEFA in shorn and unshorn ewes and the rate of NEFA oxidation across the hind-limb tissues in shorn ewes. The difference in whole-body NEFA oxidation between shorn and unshorn groups could, therefore, be completely accounted for by muscle. No significant differences in the arterial plasma concentrations of glucose, lactate or 3-hydroxybutyrate were recorded between shorn and unshorn ewes, although the rate of glucose uptake across the hind-limb tissued was significantly higher in the shorn group. Calculation of the maximum potential contribution of these substrates to hind-limb metabolism demonstrated that NEFA were the predominant energy source in all experimental conditions studied in all ewes. When data from fed and underfed shorn ewes were pooled, regression analysis revealed a significant negative correlation between the arterial plasma concentrations of glucose and 3-hydroxybutyrate, and significant positive relationships between the arterial concentrations of both glucose and 3-hydroxybutyrate and their rate of uptake across the hind-limb tissues. These relationsips were not observed in unshorn ewes.It is concluded that the muscle mass plays a major role in the nonshivering thermogenic adaptation to chronic cold exposure in shorn pregnant sheep and that NEFA are the major substrate utilized for oxidative metabolism in this tissue.

Effect of chronic cold exposure on tyrosine hydroxylase mRNA in rat adrenal gland

The effect of chronic stress on the levels of tyrosine hydroxylase (TH) RNA in rat adrenal gland was investigated by RNA-DNA hybridization using a cloned TH cDNA probe. Results of dot-blot hybridization experiments and northern analysis demonstrate that exposure of animals to cold for 1 week results in a 4-5-fold increase in the relative abundance of TH mRNA. This increase in TH mRNA level may underlie the increase in adrenal TH activity that is known to occur when rats are exposed to such cold stress.

Effects of chronic cold exposure on wheel running, food intake and fatty acid synthesis in Syrian hamsters

Mesocricetus auratus with established wheel running in a thermoneutral environment (23°C) showed an immediate suppression of running when placed in a cold room at 4°C. This suppression was seen in three separate studies and lasted at least 1 month. Food intake of these hamsters rose within 48 hr in the cold, and body weight was maintained. In contrast, hamsters which had been sedentary in the 23°C room showed a slower rise in food intake in the cold and sustained a chronic drop in body weight. In vivo fatty acid synthesis rates were greatly elevated in white and brown adipose tissue, but not liver, of exercise versus sedentary hamsters after 1 month in the cold, despite the relative inactivity of both groups throughout the cold exposure. Previous exercise training predisposes hamsters to efficient energy storage in the cold. The energy demand of the cold environment may be responsible for the decreased voluntary running.

PLASMA GLUCOSE, LACTATE AND FREE FATTY ACID RESPONSES TO ADRENALINE IN CHRONICALLY WARM- AND COLD-EXPOSED SHEEP

The effects of chronic cold exposure, fasting, or both on the plasma metabolite responses to jugular infusions of adrenaline were studied in eight five-mo-old wether lambs. Following maintenance at 20–22 °C or −4 to 10 °C for 2–3 wk the sheep received adrenaline infusions (0.15 μg∙kg−1∙min−1) for 75 min prior to and following a 72-h fast. Plasma samples collected at intervals of 10–15 min before and during adrenaline infusion were analyzed for glucose, lactate and total free fatty acids. Chronic cold exposure had no effect on the pre-infusion plasma glucose, lactate or free fatty acid concentrations. Fasting decreased plasma glucose and lactate and increased plasma free fatty acid concentrations. The plasma glucose response to adrenaline was greater (P < 0.01) in cold- than warm-exposed sheep and fasting depressed this response to a greater extent in the cold-exposed sheep. The plasma lactate response to adrenaline was not influenced by temperature treatment or fasting. Both groups of fasted sheep showed a large increase in plasma free fatty acids during adrenaline infusion but when fed the response was minimal.

Effects of cold exposure on the synthesis and release of growth hormone and prolactin.

The anterior pituitary functions of synthesizing and releasing growth hormone (GH) and prolactin were determined in vitro after exposing the rat to mild (6°C) or severe cold (1°C) for periods ranging from 4 hr to 7 days.1) Mild or severe cold exposure for 12 hr depressed the GH synthesis function. Severe cold exposure for 12 hr stimulated the GH release function.2) Mild cold exposure stimulated the prolactin synthesis function within 4 hr and severe cold exposure within 2 hr. Severe cold exposure for 12 hr stimulated the prolactin release function.3) The effects of chronic cold exposure for 7 days were substantially the same as mentioned above.4) Pituitary whole protein synthesis was depressed by mild or severe cold exposure within 12 hr, and the effects lasted for a 7-day exposure period. Whole protein hormone release did not change significantly.5) The serum level of free fatty acids (FFA) was elevated by severe cold exposure within 4 hr and returned to the normal level by 7 days. Serum glucose and protein did not change throughout the cold exposure period.The observed facts suggested that the cold stimulus acts directly on the hypothalamus through neural pathways and that the altered pituitary functions of synthesizing and releasing GH and prolactin play a role in metabolic readjustment to a cold environment.

Augmentation of spontaneous hypertension by chronic stress in rats.

The alteration of blood pressure in Spontaneously Hypertensive Rats (Okamoto and Aoki, hereafter abbreviated as SHR) was observed under various kinds of stresses and their hypertensive vascular lesions were histologically examined. 1) Effect of immobilization Seventy to 90 day-old SIR (male 38, female 16) and age-matched normotensive rats of Wistar strain (male 33, female 5, hereafter abbreviated as NR) were restrained supinely on a board for 2-10 hours daily, 100-130 hours in total during 20-30 days. a) Stress-loaded SIR showed a highly significant increase (p< 0.001) in blood pressure (male 29±16, female 29±11 mmHg) at the end of a series of stress-loadings in comparison with either control SIR (male 11±8, female 10±8 mmHg) or control NR (male 8±6, female 5±3 mmHg), and maintained it even one month after the final stress, while a slight elevation of blood pressure (11±8 mmHg) was observed only at the end of the stress-loadings in male NR. b) Stress-loaded SIR developed severe hypertension (over 210mmHg) during or after the stress-loadings in 8 out of 38 males, and pathological studies made on them revealed cerebral hemorrhage, abdominal hemorrhage, retinal bleeding, malignant and benign nephrosclerosis, periarteritis nodosa and angionecrosis in the various organs, some of which corresponded to the lesions in malignant hypertension. 2) Effect of combined visual, auditory and electric stimuli SIR and NR were loaded with a combined stress of high pitched buzzer (duration 3-7 sec., 5-6 times per min.), flickering of incandescent lamp (100V, 100W, 40-60 times per min.) and electric shock (20-40 V Alternating current of 60Hz, 0, 5-1 sec., 5-6 times per min.) for 1-4 hours daily from the 40th day up to the 18th week after birth. a) Stress-loaded NR (male 5, 141±7mmHg) showed a significantly (p<0.05) higher blood pressure (by 11-15 mmHg) than control NR (male 10, 126±7 mmHg) after the 6th week following the onset of the stress-loadings. b) Rise in blood pressure in stress-loaded SIR (male 4, 205 ±8 mmHg) was significantly (p< 0.01) greater than that in control SIR (male 4, 175±5 mmHg), and the increment of blood pressure ( 17-31 mmHg) in the former compared with the latter was evidently larger in comparison with that (11-15mmHg) of stress-loaded NR compared with control NR. 3) Effect of chronic cold exposure Ten SIR and 1 5 NR were exposed to cold temperature (2-10°C) from 3 to 4 months after birth for 7 weeks. In the 3rd week and 7th week of cold exposure the exposed SIR showed significantly (p<0.05, p<0.01) higher blood pressure (186±16, 207±15 mmHg) than nonexposed SIR (171±13, 182±21 mmHg), respectively, while no difference was noted between the exposed NR and nonexposed 13 NR. 4) These results provided an evidence that some kinds of chronic stress-loadings augment hypertension and aggravated hypertensive lesions in SIR and it is speculated that stress might activate the causative mechanisms of the spontaneous hypertension hypothetically supposed in the hypothalamo-medullary-autonomic nervous system and the hypothalamo-adeno-hypophyseo-adrenocortical and -thyroidal systems.

Cold-acclimatization and intermediary metabolism of carbohydrates

The activities of 14 enzymes participating in the intermediary metabolism of carbohydrates have been measured in the livers of rats to study the effects of chronic cold exposure. Based upon significant alterations in the activities of rate-limiting enzymes, it is concluded that an improved capacity for gluconeogenesis is the major change in hepatic carbohydrate metabolism associated with cold-acclimatization. No significant alterations in the activities of enzymes which are rate-limiting for glycolysis, glycogenesis, or glycogenolysis were found in the livers of rats exposed to 4 ° for 28 days.