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Biomedical subjects

G N Wade

Publications and source records attributed to G N Wade.

At least 55 records · Page 3Linked to original sources
PubMed1989

Effects of maternal diet, body weight and body composition on infanticide in Syrian hamsters.

We examined the idea that female hamsters kill and eat their own offspring as part of an organized mechanism that balances litter size with metabolic energy supply. In Experiment 1, females fed diets that made them lighter and leaner cannibalized more offspring and maintained smaller litters than females fed diets that made them heavier and fatter. A greater supply of metabolic energy from the diet and/or from body fat stores may have attenuated cannibalism in heavier mothers. In Experiment 2, food restriction during lactation increased the level of cannibalism to a greater degree in lighter, leaner mothers. Heavier, fatter mothers may have eaten fewer offspring because they were better able to mobilize fatty acids from adipose tissue as an alternative fuel source during food restriction. These results suggest that an important factor influencing cannibalism of pups is the general availability of metabolic fuels from both external (food supply) and internal (adipose tissue) sources.

Animals↗
PubMed1989

Progesterone can either increase or decrease weight gain and adiposity in ovariectomized Syrian hamsters.

We examined the effects of estradiol and progesterone on weight gain, food intake, and carcass composition in Syrian hamsters (Mesocricetus auratus). In ovariectomized (OVX) hamsters injections of 5 micrograms/day estradiol benzoate (EB) alone decreased weight gain and adiposity, whereas treatment with progesterone alone (1 or 5 mg/day) resulted in increased weight gain and adiposity. However, concurrent treatment with progesterone and EB reduced body fat content to levels significantly below those of hamsters treated with EB alone. In a second experiment, 17 beta-estradiol and progesterone were administered via subcutaneous Silastic capsules in doses which produce physiological levels of steroids. Implants of estradiol significantly decreased body weight gain and fat content. As in the first experiment, these effects of estradiol were exaggerated by concurrent progesterone administration. Implants of progesterone alone did not affect body weight or fatness in OVX hamsters. These data indicate that estradiol and progesterone interact to decrease body lipid stores in hamsters, whereas in rats progesterone reverses the adiposity-reducing actions of estradiol. This species difference in responses to progesterone could help to explain why rats increase, whereas hamsters decrease, their body lipid stores during pregnancy, when circulating progesterone levels are elevated.

Adipose Tissue↗
PubMed1989

Effects of norepinephrine and denervation on brown adipose tissue in Syrian hamsters.

Daily injections of either 0.8 or 3.2 mg norepinephrine (NE)/kg for 2 wk failed to stimulate brown adipose tissue (BAT) growth, GDP binding, or cytochrome-c oxidase activity (COA) in Syrian hamsters (Mesocricetus auratus). However, a single injection of 1.6 mg NE/kg produced a small (23%) but significant acute increase in BAT GDP binding without affecting COA. Thus there is some loss of sensitivity to NE with chronic treatment in Syrian hamsters. Unilateral sympathectomy by surgical denervation of the interscapular BAT (IBAT) resulted in decreased GDP binding and COA in the denervated pad. Chronic NE treatment in hamsters with denervated IBAT only partially reversed the denervation-induced decreases in GDP binding and COA. It therefore appears that NE is not solely responsible for the maintenance and stimulation of thermogenic activity and COA in Syrian hamster BAT. Denervation of IBAT also resulted in elevated levels of lipoprotein lipase (LPL) in this tissue, a surprising finding since brown and white adipose tissue LPL activity were both stimulated by chronic NE treatment. Therefore, although NE has a stimulatory effect on LPL activity, the primary influence of the neural input to IBAT on this enzyme is inhibitory. These data exemplify dramatic differences between rats and hamsters in the mechanisms controlling BAT thermogenesis and white and brown adipose tissue LPL activity.

Adipose Tissue, Brown↗
PubMed1989

Regional differences in fat pad responses to short days in Siberian hamsters.

Siberian hamsters exhibit decreased body weight and fat after initial exposure to short photoperiods and increased body weight and fat after extended short photoperiod exposure. The purpose of the present experiments was to determine if uniform changes in white adipose tissue (WAT) pad weights and lipid metabolism correspond to these short photoperiod-induced changes in body fat. Carcass lipid content and testes and fat pad weights [retroperitoneal WAT (RWAT), epididymal WAT (EWAT), and inguinal and dorsal subcutaneous WAT, respectively] were decreased in male hamsters relative to their long day counterparts after 6 and 12 wk of short-day exposure. Moreover, EWAT and RWAT weight, EWAT specific lipoprotein lipase activity, and specific and total lipogenesis were disproportionately decreased relative to the subcutaneous fat pads. The changes in fat pad weight and metabolism were generally reversed coincident with the return to a long-day-like reproductive status after prolonged short-day exposure (24 and 30 wk). In a less detailed experiment, female Siberian hamsters had decreased body, fat pad, and uterine weights after 6 wk of short-day exposure; however, no fat pad-specific changes in weight were observed. The results of these experiments demonstrate that short-day-exposed male Siberian hamsters may be a useful model for examining mechanisms underlying fat pad-specific responses. In addition, gender appears to influence the pattern of short-day-induced lipid depletion in this species.

Acclimatization↗
PubMed1988

Lipectomy influences white adipose tissue lipoprotein lipase activity and plasma triglyceride levels in ground squirrels.

Golden-mantled ground squirrels undergo marked fattening and fat depletion during the prehibernatory and hibernatory phases, respectively, of their annual body weight cycle. Fat regulation was studied by surgical removal (lipectomy) of most of the inguinal-subcutaneous, retroperitoneal, and parametrial fat depots from female squirrels during the weight-gain phase of the annual cycle. Seven weeks after surgery, body weights of lipectomized (Lipx) and Sham-Lipx squirrels were equivalent, although white adipose tissue was not completely recovered in Lipx animals. Lipoprotein lipase (LPL) activity was markedly elevated in subcutaneous adipose tissue of Lipx squirrels, but not in other depots. Plasma triglyceride (TG) levels also were higher in Lipx squirrels 7 weeks after surgery. Changes in LPL activity and plasma TG may contribute to body mass and lipid restoration following lipectomy.

Adipose Tissue↗
PubMed1988

Lipectomy does not impair fattening induced by short photoperiods or high-fat diets in female Syrian hamsters.

Syrian hamsters (Mesocricetus auratus) exhibit seasonal fluctuations in body fat that are triggered by changes in photoperiod and/or diet. Body fat accumulates when hamsters are switched to a short photoperiod or high-fat diet. The effects of surgical reduction of adipose tissue (lipectomy) on these responses were tested in adult female hamsters. Dorsal-inguinal subcutaneous, parametrial, and retroperitoneal white adipose tissues were removed bilaterally from some hamsters, while others received sham surgery. Hamsters from each surgical group were then fed a high-fat diet for the next 12 or 30 weeks, or were exposed to a short photoperiod for 13 weeks. Restoration of previously excised pads was for the most part incomplete, yet all lipectomized hamsters fully regained total body lipid, which suggests compensatory hypertrophy in other depots. Consistent with this, we found a significant increase in the weight of the previously undisturbed axillary subcutaneous pad, but this increase was small and not sufficient to offset the deficits remaining in the regenerated pads. Thus, restoration of total body lipid mass was achieved by a general increase in deposition over all depots rather than a specific renewal of removed tissue. This ability to recover completely from lipectomy is similar to that previously reported in ground squirrels. In contrast, rats and mice are frequently unable to replace lost adipose tissue. Both hamsters and squirrels adjust their levels of body fat according to season, which may afford them an enhanced ability to recover from surgical reductions of adipose tissue.

Adipose Tissue↗
PubMed1988

Inhibition of fatty acid oxidation and glucose metabolism does not affect food intake or hunger motivation in Syrian hamsters.

We examined the interaction of the metabolic fuels, glucose and free fatty acids (FFA), in the control of food intake in Syrian hamsters. Hamsters were treated with a 2-deoxy-D-glucose (2DG) which inhibits glucose utilization, and methyl palmoxirate (MP), which inhibits fatty acid oxidation. The 2DG and MP, alone or in combination did not enhance food intake in hamsters fed a standard rodent chow diet. Determination of the circulating glucose, FFAs, and ketones confirmed that the drugs were having the intended metabolic effects. The 2DG caused marked hyperglycemia and decreased ketones consistent with an inhibition of glycolysis, and the MP caused increased FFAs and decreased ketones indicating inhibition of fatty acid oxidation. A third experiment examined the hamsters' willingness to ingest a diet made highly unpalatable with NaCl, another measure of hunger motivation. Although food-deprived hamsters ingested more of a salt-adulterated diet than did control animals, hamsters treated with MP and 2DG did not. These experiments provide further evidence that the control of food intake in Syrian hamsters is appreciably different than that of laboratory rats.

Animals↗
PubMed1988

Role of fatty acid oxidation in food intake and hunger motivation in Syrian hamsters.

We examined the metabolic control of food intake in Syrian hamsters using methyl palmoxirate (MP), an inhibitor of fatty acid oxidation. If fatty acid oxidation plays a role in the control of food intake in hamsters, as it does in rats, it would be expected that hamsters predisposed toward lipid metabolism would increase food intake in response to inhibition of fatty acid oxidation. To the contrary, female hamsters fed a high-fat diet for several weeks and then treated with MP (0.25-100 mg/kg) did not increase food intake relative to vehicle-treated controls. Furthermore, MP treatment did not enhance food intake in hamsters that had been previously food deprived for 12 hr. Consistent with the inhibition of fatty acid oxidation, plasma levels of total ketone bodies and glucose in the MP-treated hamsters were significantly lower than those of the vehicle-treated controls. Thus, treatment with doses of MP which apparently inhibited fatty acid oxidation did not enhance food intake, even after manipulations which predispose the hamsters toward utilization of fat fuels. The control of food intake in Syrian hamsters is in marked contrast to that of rats and other mammals in which the consequences of glucose and fat metabolism interact to signal changes in food intake.

Animals↗
PubMed1987

Are the short-photoperiod-induced decreases in serum prolactin responsible for the seasonal changes in energy balance in Syrian and Siberian hamsters?

Serum prolactin (PRL) decreases in Syrian (Mesocricetus auratus) and Siberian (Phodopus sungorus sungorus) hamsters following short-photoperiod exposure. Both species also exhibit short-photoperiod-induced changes in body and lipid mass, but in opposite directions; Syrian hamsters increase and Siberian hamsters decrease their body weight, changes reflected nearly exclusively in their carcass lipid content. The purpose of these experiments was to determine whether the photoperiod-induced changes in PRL were responsible for the seasonal changes in energy balance in Syrian and Siberian hamsters by using the strategy of experimentally producing serum PRL levels opposite to those normally associated with the photoperiod in which the animals were housed. In long photoperiods serum PRL was reduced to short-day levels by subcutaneous (s.c.) CB-154 (bromoergocryptine, a dopamine agonist) injections. In short photoperiods, serum PRL was elevated to long-day levels in Syrian hamsters by ectopic pituitary explants, and in Siberian hamsters, serum PRL was elevated by chronic s.c. infusions of ovine PRL (oPRL). In both species, manipulations of serum PRL did not affect food intake, carcass composition, or the wet weight of various white and brown adipose tissue pads (WAT and BAT, respectively). Body weight increased in CB-154-treated Syrian hamsters and decreased in Siberian hamsters, an effect partially reversed by coadministration of oPRL in Syrian, but not Siberian, hamsters. Thus, lowering serum PRL to short-day levels in long-day-housed hamsters of both species mimicked the directional change in body weight appropriate for each species when they are exposed to short days. This effect of CB-154 on body weight may be a result of some as yet unidentified effect of dopaminergic stimulation on overall growth since 1) these changes in body weight were not reflected as changes in lipid mass, as occurs naturally following short-day exposure for each species, and 2) neither species exhibited a reciprocal change in body weight when serum PRL was experimentally elevated in short days. Alternatively, it may be that once the energetic responses to short-day exposure have been fully expressed, the ability of PRL to stimulate the target sites of action for PRL for these responses may be decreased. BAT protein content, cytochrome oxidase activity (measures of metabolic growth of this tissue), and retroperitoneal total and specific lipoprotein lipase (LPL) activities were increased by CB-154 treatment in Syrian hamsters.(ABSTRACT TRUNCATED AT 400 WORDS)

Adipose Tissue↗
PubMed1987

Genetic association between nest building and brown adipose tissue thermogenesis in female house mice.

Mice selectively bred for either high or low levels of thermoregulatory nest building were cold-acclimated (5 degrees C) for 3 weeks without nesting material; then body weight and food intake were measured. The mice selected for low nest building (Lows) of both sexes showed lower feed efficiencies than the high nest-building mice (Highs), although their body weights were not significantly different (Table 1). This adds to a large body of evidence which suggests that nest building and feed efficiency were influenced by a common mechanism (Lacy et al. 1978; Sulzbach and Lynch 1984; Lynch et al. 1981; Lynch and Roberts 1984). Brown adipose tissue mitochondrial GDP binding and cytochrome c oxidase activity were measured in the above mice. In females, the Lows had 100% higher levels of total GDP binding than the Highs, while no difference between the lines was seen in males. Thus in the High females, lower energy expenditure through brown fat thermogenesis may account for their greater feed efficiency. In males, the genetic differences in feed efficiency must be due to differences in either thermogenesis in tissues other than brown fat, or mechanisms which reduce heat loss.

Adipose Tissue, Brown↗
PubMed1987

Short- and long-term effects of ovariectomy on food intake, body weight, carcass composition, and brown adipose tissue in rats.

This experiment examined both the short-term and the long-term effects of ovariectomy on brown adipose tissue growth and function in rats to determine if reduced brown adipose tissue thermogenesis might contribute to the weight gain and adiposity. Brown adipose tissue function was assessed by measuring sympathetic nervous system activity (estimated by the rate of norepinephrine turnover) and mitochondrial proton conductance (estimated by specific GDP binding) in interscapular brown adipose tissue. Rats (n = 12 per group) were killed 0 (sham), 1, 2, 4, and 12 weeks after ovariectomy. During the first five weeks after ovariectomy rats overrate and rapidly gained weight. The weight gain was due to increases in all carcass components. Five weeks after ovariectomy food intake returned to control levels, and body weights stabilized 12-16% above sham-operated control weights for the duration of the experiment. Between week 4 and week 12 after surgery there was a redistribution of carcass composition, with decreases in carcass water and fat-free dry weights offset by a further increase in total carcass lipid. Brown adipose tissue pads were heavier in the 1-, 2-, and 4-week ovariectomy groups, but only in the 4-week group was the increase statistically significant. Brown adipose tissue protein, DNA, and norepinephrine content was unchanged 1-, 2-, 4-, or 12-weeks after ovariectomy. There was no difference in either the rate of norepinephrine turnover or specific mitochondrial GDP binding between sham-operated and 1-, 2-, 4-, or 12-week ovariectomized rats.(ABSTRACT TRUNCATED AT 250 WORDS)

Adipose Tissue, Brown↗
PubMed1987

Body composition, food intake, and brown fat thermogenesis in pregnant Djungarian hamsters.

Strategies for balancing energy storage and expenditure during pregnancy were examined in the Djungarian hamster. In expt 1, pregnant hamsters lost nearly 50% of their body lipid stores, even though they showed significant increases in body weight and food intake during the latter half of pregnancy. The increase in body weight was accounted for by the growth of the uteri, fetuses, and placentas. The water and fat-free dry contents of the maternal carcasses did not differ from those of the unmated controls. In expt 2, brown fat cytochrome-c oxidase activity (mitochondrial content) was significantly lower in the late- but not early-pregnant females relative to the nonpregnant controls. Specific GDP-binding levels did not differ significantly among these groups. Thus an overall decrease in total thermogenic activity in brown fat would be expected during late pregnancy. The loss of carcass lipid, despite decreased brown fat thermogenesis and increased food intake, suggests that substantial increases in energy expenditure occur in pregnant females that are not related to heat production in brown fat. The present results are not consistent with traditional models of energy balance during pregnancy. Some of the inconsistencies may be related to differences between hoarding and nonhoarding families of rodents, whereas others may be due to the fact that the traditional model is based on a possibly exceptional species, the laboratory rat.

Adipose Tissue↗
PubMed1986

Hypothalamic nuclear progestin receptors and the duration of sexual receptivity in ovariectomized and ovariectomized-hysterectomized rats.

In order to determine if the enhancement of sexual behavior in hysterectomized rats is associated with an increased level of hypothalamic nuclear progestin receptors, ovariectomized (OVX) and ovariectomized-hysterectomized (OVHX) rats were injected with 2 micrograms estradiol benzoate. Twenty-four hr later, animals were injected with 0.5 mg progesterone and were tested for sexual receptivity every 4 hr. Hysterectomy had an overall facilitatory effect on lordosis and increased the duration of the period of sexual receptivity by about 4 hr. In a second experiment, similarly-treated animals were killed 4, 8, or 12 hr after progesterone injection, and hypothalamic nuclear progestin receptor levels were measured. In contrast to what has been reported for guinea pigs, nuclear progestin receptor levels decreased to baseline 8-12 hr before the termination of sexual receptivity. Nuclear progestin receptor concentrations were higher in OVHX rats than in OVX rats at 4 hr after progesterone injection, and there was a trend toward higher receptor concentrations in OVHX rats at 8 hr. These results demonstrate that hysterectomy-induced facilitation of sexual receptivity is associated with an increased level of hypothalamic nuclear progestin receptors. Furthermore, they suggest a fundamental difference in the regulation of nuclear progestin receptor retention between rats and guinea pigs.

Animals↗
PubMed1986

Short day lengths decrease body mass of overweight female meadow voles.

Groups of adult ovariectomized (ovx) voles and sham-ovx controls were placed in a short photoperiod or left in the original long photoperiod (10 or 14 hr light/day). In the next 12 weeks long-day ovx voles increased their body mass by 11.3%, whereas animals transferred to the short-day photoperiod manifested an 11.9% decline in body mass. Short photoperiods not only reversed pre-existing weight gains attributable to ovariectomy, but also prevented further increases in body mass associated with the withdrawal of ovarian hormones. Fat-free dry carcass mass was increased by ovariectomy and decreased by short photoperiods; lipoprotein lipase activity of white adipose tissue was unaffected by ovariectomy or photoperiod. We suggest that reductions in body mass in voles transferred to the short photoperiod are mediated by changes in pineal melatonin secretion.

Adipose Tissue↗
PubMed1986

Effects of estrous cycles and ovarian steroids on body weight and energy expenditure in Syrian hamsters.

In Experiment 1, highly significant changes were observed over the estrous cycle in body weight gain, but not in food intake, daytime resting oxygen consumption or brown fat thermogenesis in Syrian hamsters. In Experiments 2 and 3, body weight and composition, food intake, resting oxygen consumption, and brown fat thermogenesis were measured following estradiol or estradiol plus progesterone treatment in ovariectomized hamsters. The significant changes in body weight could not be explained by changes in food intake, and were not accompanied by significant alterations in daytime oxygen consumption or brown fat thermogenic activity. In Experiment 4, resting oxygen consumption and body weight were measured every 6 hours over the estrous cycle. There was a striking absence of the usual nocturnal peak in resting oxygen consumption on the night of estrus (the night of the largest body weight gain). However, brown fat thermogenic activity did not differ among groups of hamsters killed on different nights of the estrous cycle. Estradiol-induced changes in energy storage may be mediated by changes in the daily rhythm of energy expenditure which are not dependent on alterations in brown fat thermogenesis.

Adipose Tissue, Brown↗
PubMed1986

Short photoperiod stimulates brown adipose tissue growth and thermogenesis but not norepinephrine turnover in Syrian hamsters.

This experiment examined the effect of short photoperiod on food intake, body weight, carcass composition, and brown adipose tissue (BAT) activity in female Syrian hamsters (Mesocricetus auratus). BAT function was assessed by measuring sympathetic nervous system (SNS) activity in BAT (estimated by the rate of norepinephrine (NE) turnover), BAT mitochondrial content (estimated by cytochrome c oxidase activity), and BAT mitochondrial proton conductance (estimated by guanosine-5'-diphosphate (GDP) binding to isolated BAT mitochondria). Food intake and body weight were both increased in short photoperiod-housed hamsters (8-hr light, 16-hr dark; LD 8:16) when compared to those of the long photoperiod-housed controls (LD 16:8). The weight gain was entirely due to an increase in carcass lipid. Interscapular BAT (IBAT) pads from short photoperiod-housed hamsters were 53% heavier and contained comparably more protein and DNA. Short photoperiod produced a 118% increase in BAT cytochrome c oxidase activity and a 41% increase in specific mitochondrial GDP binding. Whether expressed per mg wet tissue or per pad, neither the endogenous concentration of NE nor its rate of turnover were changed by short photoperiod exposure. These results demonstrate a dissociation of BAT thermogenesis from SNS activity in BAT from short photoperiod-housed Syrian hamsters.

Acclimatization↗
PubMed1986

Effects of diet and photoperiod on NE turnover and GDP binding in Siberian hamster brown adipose tissue.

This experiment examined the effects of diet and photoperiod on food intake, body weight, and brown adipose tissue (BAT) activity in female Siberian hamsters (Phodopus sungorus sungorus). BAT function was assessed by measuring both the sympathetic nervous system activity of BAT [estimated by the rate of norepinephrine (NE) turnover] and BAT thermogenic activity (estimated by GDP binding to BAT mitochondria). Nineteen weeks of high-fat feeding in long photoperiod [16:8 light-dark cycle (LD)] caused a 20% increase in food intake but did not affect body weight. Both NE turnover rate and GDP binding in interscapular BAT (IBAT) were increased four- to eightfold relative to that from chow-fed controls. Thus it appears that in Siberian hamsters BAT can serve the same energy-dissipating function during diet-induced overeating previously established in rats and mice. Nineteen-week exposure to a short photoperiod (LD 8:16) produced a reduction in body weight but did not affect food intake. Both NE turnover rate and GDP binding in IBAT were increased two- to fourfold relative to that from long-photoperiod controls. Thus it appears that in Siberian hamsters the photoperiod-induced improvements in thermogenic capacity are mediated via the same mechanisms as are cold- or diet-induced thermogenesis.

Adipose Tissue, Brown↗