Development of fatty acid-synthetic capacity in interscapular brown adipose tissue during suckling in genetically obese Zucker rats.

The development of the lipogenic capacity in brown adipose tissue was studied in suckling lean (Fa/fa) and obese (fa/fa) Zucker pups aged from 7 to 22 days. In both lean and obese pups, activities of the two key lipogenic enzymes, fatty acid synthetase and acetyl-CoA carboxylase, and of citrate cleavage enzyme rose from the early to the late suckling period. Compared with lean pups, 7-day-old fa/fa pups showed a 35% increase in fat accumulation in interscapular brown adipose tissue and a 25% increase in fatty acid synthetase activity. By 10 days of age, fat deposition, lipogenesis in vivo (assessed by the incorporation of 3H from 3H2O into fatty acids) and fatty acid synthetase activity were 1.5-2-fold higher in pre-obese than in lean pups. Compared with lean pups, the increased lipogenesis in vivo observed in brown adipose tissue of 10-day-old pre-obese pups could not entirely account for the difference in fat deposition observed in this tissue, suggesting that additional mechanisms are at play to explain the increased fat content of this tissue.     

Plasma catecholamines in rats during rewarming from induced hypothermia

The present study sought to quantitate the levels of plasma catecholamines [norepinephrine (NE), epinephrine (E), and dopamine (DA)] during induction and rewarming from hypothermia. Male rats (317 +/- 8 g) were made hypothermic by exposure to 0.9% halothane at -10 to -15 degrees C while blood pressure (carotid artery), heart rate, and colonic temperature (Tc) were monitored. Anesthesia was discontinued when Tc reached 28 degrees C. Tc continued to fall but was held at 20-20.5 degrees C for 30 min. Rewarming was then initiated by raising ambient temperature to 22 degrees C. Arterial blood samples were taken 1) before cooling, 2) just before rewarming, 3) when Tc reached 22 degrees C during rewarming, and 4) when Tc reached 27 degrees C during rewarming. Plasma was assayed radioenzymatically for catecholamines using both phenylethanolamine-N-methyltransferase and catechol-O-methyltransferase procedures, and hypothermic induction resulted in significant increases in NE, E, and DA above control levels (P less than 0.01). With rewarming to Tc = 22 degrees C, all catecholamines increased above the level observed during hypothermia (P less than 0.01), and NE and DA increased still further (P less than 0.01) when Tc reached 27 degrees C. The levels of plasma catecholamines observed during hypothermia and during the rewarming phase indicate a role of the sympathoadrenal medullary system in the metabolic adjustments associated with hypothermia and recovery. During rewarming, the levels of E and NE attained exceed those at which both substances may be expected to act as circulating hormones.     

Thermoregulation in rats during early postnatal maturation: importance of nitric oxide

Experiments were carried out to determine the role of nitric oxide in mediating autonomic and behavioral thermoregulatory control in rat pups on postnatal days 1-2, 5-6, and 10-11. For an experiment, each pup received a subcutaneous injection of vehicle, NG-nitro-D-arginine methyl ester (D-NAME; 100 mg/kg), or NG-nitro-L-arginine methyl ester (L-NAME; 100 mg/kg) before being placed in a metabolic chamber or in a thermocline with a linear temperature gradient of 23 to 43 degrees C. In the metabolic chamber, oxygen consumption and core temperature were measured as ambient temperature was decreased from 40 to 15 degrees C over a 60-min period. Decreasing ambient temperature elicited an increase in oxygen consumption in all age groups that received vehicle or d-NAME. The lower critical temperature and peak oxygen consumption upon exposure to cold after vehicle were 41 +/- 10 ml x kg(-1) x min(-1) at 30 degrees C, 43 +/- 12 ml x kg(-1) x min(-1) at 28 degrees C, and 55 +/- 11 ml x kg(-1) x min(-1) at 25 degrees C in the 1- to 2-, 5- to 6-, and 10- to 11-day-old pups, respectively. Administration of L-NAME abolished the oxygen consumption response to cold in the 1- to 2- and 5- to 6-day-old pups and significantly attenuated the oxygen consumption response to cold in the 10- to 11-day-old pups. Selected ambient temperature in the thermocline was not significantly affected by prior administration of D-NAME or L-NAME compared with vehicle. Thus our data provide evidence that the nitric oxide system plays a role in mediating autonomic but not behavioral thermoregulatory control in rat pups during early postnatal maturation.     

Suckling in rats extended by continuous living with dams and their preweanling litters

To evaluate the role of the dam and littermates in weaning, rats were separated from their biological mothers, beginning at 21 days of age, and housed with a succession of dams and their 16–21-day-old litters. Suckling persistence was evaluated every 5 days until rats reached 70 days of age or no longer suckled. Rats housed in such a preweaning environment continued to suckle well past the normal age of weaning. Specifically, 50% suckled until day 55, and 15% suckled until they were 70 days of age and sexually active. In addition, the interactions among three dams and their litters composed of 16–21-day-old pups and a 45–50-day-old rat that had been housed with similar litters were analysed from time-lapse video-recordings. Experimental rats routinely suckled in the nest and withdrew milk from the dam, but did so only when most of the younger pups had already attached. These data suggest that the maternal and social milieu plays a role in the maintenance of suckling behaviour.     

Shivering and nonshivering thermogenesis in exercised cold-deacclimated rats

Norepinephrine (NE)-induced increase in oxygen consumption (VO2) and colonic temperature (Tc) was greater in cold-acclimated rats housed at 4 degrees C for 4 weeks (CA) than warm-acclimated controls housed at 24 degrees C for 4 weeks (WA). On the other hand, shivering activity measured at 4 degrees C was less in CA than in WA, while propranolol administration eliminated the difference between these two groups by enhancing shivering in CA. Wet weight and protein content of interscapular brown adipose tissue (IBAT) were greater in CA than in WA. Following cold acclimation, CA were deacclimated at 24 degrees C for 5 weeks. During deacclimation, half of this latter group were forced to run (15 m.min-1 for 1 h) every day (CD-T) while the remaining rats remained sedentary (CD-S). Shivering activity assessed at 4 degrees C 4 weeks after commencing cold deacclimation was significantly less in CD-T than in CD-S and the difference disappeared following propranolol injection. VO2 and Tc responses to NE injection measured 1, 2 and 5 weeks after commencing cold deacclimation did not differ between CD-S and CD-T. Although IBAT weight was lighter in CD-T than in CD-S, its total protein content was not different between the latter two groups of rats. These results suggest that a greater degree of NE-independent nonshivering thermogenesis (NST) is retained in rats that are exercised during the process of deacclimation as compared with animals that are sedentary. This difference in NST would not seem to be directly related to BAT thermogenic capacity.     

Gastrin release in obese Zucker rats

In this study, gastrin release in the obese Zucker rat was investigated by in vivo and in vitro experiments. Obese rats exhibited normal plasma gastrin levels at 3 weeks (preobese), were moderately hypergastrinemic at 3 months and severely hypergastrinemic at 5 months, compared to lean littermates. Following oral peptone, plasma gastrin levels doubled in both lean and obese rats. Basal and vagally stimulated gastrin release from perfused stomachs was greater in obese compared to lean rats and atropine had no effect on basal gastrin release in either group. Basal somatostatin release from the perfused stomach was found not to differ in both groups of animals. Morphological studies revealed an increase in the number of gastrin-containing G-cells in adult obese rats compared to lean littermates, but not in 3-week-old pups compared to lean littermates, indicating a strong correlation between cell number and plasma gastrin levels. These data indicate that the obese Zucker rat exhibits fasting hypergastrinemia in vivo, a condition which appears after weaning and increases in severity with age. Gastrin hypersecretion persists from the vascularly perfused stomach preparation. The basal hypergastrinemia of the obese Zucker rat is independent of a hyperactive postganglionic cholinergic drive but is associated with and probably causally related to an increase in antral G-cell numbers.     

Effects of rearing temperature and level of food intake on organ size and tissue composition in piglets

Piglets are particularly susceptible to cold and nutritional stress because of their poor insulation and low body fat. The purpose of this study was to examine how ambient temperature and level of food intake affect development in piglets. Thirty-two piglets were reared individually from 14 to 56 days of age in either a cold (10 degrees C) or a warm (35 degrees C) environment. Two feeding regimens, restricted and ad libitum, were used to assess the effect of food intake on organ mass. The ad libitum fed pigs in both environments gained weight at the same rate. Paired t-tests of organ weights of ad libitum fed pigs revealed that the mass of the heart, liver, kidneys, stomach, and small intestine, and total nitrogen and the length of the small intestine were greater in cold-reared than in warm-reared littermates of the same body weight. The skin mass and total fat mass, the lengths of the body, extremities, and individual long bones, and the total surface area were greater in warm-reared than in cold-reared individuals. A regression analysis showed body weight was the most important determinant of size for all tissues measured except fat mass, which was affected slightly more by rearing temperature. Of the organs and tissue components that differed in size in warm- and cold-reared pigs, heart, kidney, stomach, skin, nitrogen, and fat mass, and small intestine length and surface area were generally affected more by rearing temperature than by level of food intake. Liver and small intestine mass and femur length were affected more by level of food intake.(ABSTRACT TRUNCATED AT 250 WORDS)     

The effects of rearing-temperature on body composition in young pigs

Pigs were reared for 23, 35, 42, or 59 days in a cold (10 degrees C) or a warm (35 degrees C) environment. They were fed to grow at the same rate. The total amount of fat was greater in warm-reared than in cold-reared pigs and fat was distributed differently in the two groups. Warm-reared pigs had more fat in the subcutaneous layer while cold-reared pigs had more fat in their abdominal tissues and skeletal muscle. The total amount of nitrogen was greater in cold-reared than in warm-reared pigs and no difference was found in its distribution.     

Effect of precocene II on fatty acid metabolism in the pea aphid, Acyrthosiphon pisum, under cold stress

Pea aphids, Acyrthosiphon pisum (Harris), reared at 10 degrees C contain higher levels of fatty acids than those reared at 25 degrees C. This is primarily the result of an accumulation of triacylglycerols containing myristic acid. When aphids reared at 25 degrees C were transferred to 10 degrees C there was a gradual increase in triacylglycerol content that reached a maximum at 16 days post-transfer. Treatment of aphids with precocene II prior to transfer to 10 degrees C blocked the accumulation of fatty acids including myristic acid. A single application of 2 microg precocene II/aphid or two applications of 0.5 microg precocene II/ aphid administered on consecutive days resulted in aphids moved to 10 degrees C maintaining the same fatty acid profile as aphids maintained at 25 degrees C. Aphids that were treated with precocene II and maintained at 25 degrees C did not show changes in fatty acid profiles. Rearing aphids at 10 degrees C resulted in lower rates of reproduction and lower total numbers of progeny with longer longevity. Treatment with precocene II significantly decreased the total number of progeny produced at both temperatures. Precocene II did not reduce life span of aphids reared at 25 degrees C, however, the life span of treated aphids reared at 10 degrees C was decreased. The mechanism by which precocene II prevents the accumulation of myristic acid in aphids reared at 10 degrees C remains to be determined.     

Thermoregulation and diurnal rhythms in 1-week-old rat pups

This paper reviews the ontogeny of thermoregulation and diurnal rhythmicity in rats. Additionally, original data are presented that indicate the emergence of an endogenous circadian core temperature rhythm during the first postnatal week. Despite neurological immaturity, newborn rats display autonomic and behavioral thermoregulatory responses within 24 h of birth. Their "biological clock" is already running before birth. The thermal environment of pups changes cyclically owing to diurnal variations in maternal behavior, but the core temperatures of 1-week-old pups huddling in the absence of the dam also show marked diurnal fluctuations. Five- to 8-day-old lean Zucker rat pups artificially reared in the absence of 24-h cycles of ambient temperature and food intake show diurnal changes in core temperature similar to those in huddling mother-reared pups. Diurnal core temperature changes, evident only when regulatory effectors are not overwhelmed, are one of the first self-maintained diurnal rhythms to appear. Because thermoregulation and circadian rhythmicity both appear before maturation of the neural networks believed to be critical for their control in adult animals, studying the immature rat might increase our understanding of the control of these processes in the more complex mature central nervous system.     

Endogenous 24-hour cycle of core temperature and oxygen consumption in week-old Zucker rat pups

Summary Experiments were designed to test whether or not the 24-h core temperature fluctuations in week-old rat pups are of endogenous origin. Lean (Fa/-) Zucker rat pups born on the same day to mothers maintained in two different colonies with light/dark cycles 12 h out of phase with each other were mother-reared through the first 3–4 days of life and then artificially reared simultaneously in constant dim light. Continuous, automatic measurement of core temperature and oxygen consumption during artificial rearing showed clear 24-h rhythms in 5- to 8-day-old pups. Each rhythm reached a daily minimum at a time corresponding to the beginning of the light period in the colony of origin. The amplitude of these rhythms did not diminish during artificial rearing, nor did the phase difference between the rhythms of pups originating in the two colonies systematically change. The persistent 12-h phase differences between these two groups of pups prove that the observed rhythms are not caused by exogenous stimuli. We conclude that the rat pup possesses an endogenous time-keeping mechanism that permits the expression of overt rhythmicity at the age of 1 week.Abbreviations Tc core temperature - LD-pups born to a mother entrained to a 7:00 to 19:00 light cycle, then artificially reared in constant dim light - DL-pups born to a mother entrained to a 19:00 to 7:00 light cycle, then artificially reared in constant dim light - SCN suprachiasmatic nucleus     

Reproductive responses to variation in temperature and food supply by house mice: II. Lactation

Lactating HS/Ibg house mice housed at 21 degrees C and 5 degrees C were assigned to 3 feeding regimes: ad libitum, daily rations of 80% of ad libitum, or 60% of ad libitum beginning on the day that they bore litters. Significant interaction between temperature and food restriction was found for litter survivorship, pup survivorship, litter size, female body weight, and cumulative biomass production. The interaction was due to a magnification of the effects of food restriction at the colder temperature: i.e. mice fed ad libitum were similar at the two temperatures, mice fed the 80% ration differed, and mice fed the 60% ration differed to a greater extent. The dominant response to food restriction was cannibalism by females, which might be associated with the rate of loss in body weight by the female on the days preceding cannibalism of one or more pups. Incidents of cannibalism tended to involve a limited number of pups and to be repeated until a sustainable litter size was reached. In 3 of the food-restricted treatments, females weaned relatively large litters of relatively small pups, but in the most severe treatment (in the group fed the 60% ration at 5 degrees C), the females weaned small litters of large pups. The patterns of cannibalism and variable relative investment in individual pups reflect the aggressive breeding strategy of this classic colonizing species.     

Serotonin content of the interscapular brown adipose tissue of growing rats.

In brown fat of newborn rats the serotonin (5HT) content is high during the first five days of life. This may play a part in the lipid repletion of the tissue, lipids being the main fuel for nonshivering thermogenesis. Subsequently 5HT increases more in young rats reared at 16 degrees C than in those reared at 28 degrees C but to a lesser extent than norepinephrine (NE) content. A possible role of 5HT in thermoregulation of the rat during the early postnatal period is discussed.     

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.     

Pronounced juvenile circadian core temperature rhythms exist in several strains of rats but not in rabbits

Torpor-like circadian variations of core temperature are well documented for suckling-age Zucker rat pups. To determine (1) whether this juvenile circadian rhythm is as strongly expressed in other rat strains, and (2) whether a similar rhythm is expressed in rabbit pups, we recorded core temperature and metabolic rate of artificially reared pups. Wistar, Brown Norway, and Long Evans pups were studied for 30 h under moderate cold loads (ambient temperature=28°C) when 9–11 days old, i.e. at the age and ambient temperature for which the rhythm has been most thoroughly characterized in Zucker rats. Chinchilla bastard rabbit pups were studied under similar conditions when they were 3–8 days old, the youngest age at which the rhythm can be easily detected in rats. Rat pups of each strain showed clear circadian rhythms with sharp decreases of core temperature and metabolic rate in subjective morning. Core temperature amplitudes were in the order Wistar < Brown Norway < Zucker < Long Evans strain. In contrast, the rabbit pups maintained stable high levels of core temperature and metabolic rate throughout the day. A torpor-like decrease of core temperature in the morning is thus not a pecularity of the Zucker rat strain but also occurs in other pigmented rat strains, whereas rabbit pups at a similar developmental stage do not show a circadian core temperature rhythm.     

Effects of food deprivation and high fat diet on immunoreactive beta-endorphin levels in brain regions of Zucker rats

The levels of immunoreactive beta-endorphin (ir-beta-EP) were measured in the brain and pituitary of lean Zucker rats subjected to food deprivation for 72 h and to a high fat diet, and in fatty Zucker rats after food deprivation for 72 h. Ir-beta-EP was increased in the neurointermediate (NI-) pituitary lobe but reduced in the medulla-pons of fatty rats when compared to lean littermates fed ad libitum. Food deprivation decreased ir-beta-EP in the cortex and medulla-pons of lean rats and in the cortex, midbrain and NI-pituitary of fatty rats. In contrast, ir-beta-EP was increased in the anterior pituitary of lean rats and in the striatum of fatty rats after deprivation. The high fat diet produced a decrease in ir-beta-EP in the cortex, midbrain and NI-pituitary with an increase in the striatum and hypothalamus of lean rats. These results suggest that the ir-beta-EP concentration could be differentially affected in different brain regions of Zucker rats by changes in the energy balance.     

The effect of overfeeding the young in early postnatal ontogeny on brown fatty tissue

We studied the effects of overfeeding of neonatal Wistar rats on O2 consumption by the interscapular brown adipose tissue and DNA content in the tissue. The overfeeding was induced by reducing the litter size to two to three pups per dam compared with standard litters of five to ten pups. All animals were allowed free access to water and forage and were kept at 24 +/- 1 degrees C. Newborn and 16-day-old rat pups were used in the experiments. The body weight of overfed pups was significantly higher than that of standard fed pups (p < 0.001). There were no differences between groups of 16-day-old rats in the resting metabolic rate. The mass of dried brown adipose tissue relative to the body mass in overfed pups was lower than in the control pups (p < 0.01). O2 consumption in the rats from small litters was 35% higher (p < 0.001). DNA content (mg/g brown adipose tissue) in overfed rats was 35% lower as compared to the control pups (p < 0.001). These results indicate that overfeeding at the preweaning stage of life affects growth, cellularity, and thermogenic function of brown adipose tissue.     

Splanchnic sympathetic nerve activity and circulating catecholamines in the hyperthermic rat

The mechanisms responsible for the initial rise in splanchnic vascular resistance with environmental heating are controversial, and those responsible for the subsequent fall in splanchnic resistance in the severely hyperthermic animal are unknown. Thus we examined the effect of environmental heating on plasma catecholamine concentration, splanchnic sympathetic nerve activity (SNA), and select blood chemistries. In one study, 25 male Sprague-Dawley rats (270-300 g) were assigned to one of five groups on the basis of their core temperature (Tc, 37, 39, 41, 43, or 44 degrees C) at death. Heart rate (HR), mean arterial pressure (MAP), and Tc were monitored during heat stress under alpha-chloralose anesthesia (12.5 mg.ml-1.h-1). At each predetermined Tc, an aortic blood sample was drawn and analyzed for mean plasma concentration of norepinephrine (NE), epinephrine (E), Na+, K+, and lactate. From 41 to 43 degrees C, NE and E rose significantly, and the animals became hyperkalemic and lactacidemic. In a separate study, we quantitated SNA from the greater splanchnic nerve during heat exposure of artificially respired animals anesthetized with pentobarbital sodium (50 mg/kg). MAP, splanchnic SNA, and Tc were recorded. Tc was elevated from 37.0 +/- 0.12 to 41.3 +/- 0.18 degrees C in 70 min by increase of ambient temperature to 38 degrees C in an environmental chamber. Splanchnic SNA was 54 +/- 8 spikes/s at a Tc of 37 degrees C and increased significantly as Tc exceeded 39 degrees C (P less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)     

The effects of corticosterone, cold exposure and overfeeding with sucrose on brown adipose tissue of obese Zucker rats (fa/fa).

GDP binding to brown-adipose-tissue mitochondria was decreased in obese Zucker rats. Adrenalectomy restored both GDP binding and serum tri-iodothyronine of obese rats to values observed in lean rats. The effects of adrenalectomy on GDP binding and serum tri-iodothyronine were reversed by corticosterone. Decreasing food intake had no effect on brown-adipose-tissue GDP binding in obese rats. Young (5-week-old) obese rats showed a normal increase in brown-adipose-tissue mitochondrial GDP binding after housing at 4 degrees C for 7 days, but this response was attenuated in 10-week-old obese rats. Overfeeding with sucrose increased brown-adipose-tissue thermogenesis in lean, but not in obese, rats. After adrenalectomy, overfeeding with sucrose enhanced brown-adipose-tissue mitochondrial GDP binding in obese rats.