Effects of norepinephrine infusion and exercise on blood pressure in rats.

Two experiments were conducted to test the hypotheses that norepinephrine (NE) infusion would increase blood pressure and wheel running activity level, and, secondly, that voluntary exercise would lower NE-induced increases in blood pressure. NE-bitartrate was infused into male Sprague-Dawley rats using an implanted osmotic pump (3.75 micrograms/kg/min in 0.9% saline). Control rats received the vehicle solution. Systolic blood pressure was measured by the tail-cuff method. Voluntary wheel running activity expressed as wheel revolutions per 24 hr was measured on the 5th, 9th, and 13th day. Blood pressure on the 13th day and wheel running activity on the 9th day were significantly higher in NE-infused rats. The NE content of heart tissue was not altered, but urinary excretion of NE and epinephrine was increased in the NE-infused animals. Food intake, body weight gain, and kidney weight per 100 g body wt were not changed but heart weight per 100 g body wt was increased by NE infusion. Urinary total calcium excretion was higher in the NE-infused rats. Spontaneous voluntary exercise in running wheels attenuated increases of blood pressure in NE-infused rats. The results of the present study suggest that rats receiving exogenous NE exhibit increased blood pressure and voluntary wheel running activity. Voluntary wheel running exercise also reduces blood pressure in NE-infused rats.

Low-protein diet blocks development of hyperphagia and obesity in rats with hypothalamic knife cuts.

The objective of this study was to examine the influence of dietary protein levels on development of hyperphagia and obesity in rats that had been given surgical knife cuts between the ventromedial and lateral areas of the hypothalamus. Under normal conditions, rats with this type of surgery exhibit hyperphagia and become obese when given unlimited access to dietary energy. Earlier studies indicated impaired adaptive diet-induced thermogenesis in response to excess energy intake in this animal model of obesity. Because low protein diets can also stimulate diet-induced thermogenesis, we conducted four experiments which examined how diets containing different levels of protein affect development of hyperphagia and obesity in female rats given bilateral, parasagittal wire knife cuts between the ventromedial and lateral areas of the hypothalamus. For 28 d, knife-cut and sham-operated rats were given unlimited or restricted (1 79 or 1 80 kJ/d) access to diets containing protein at 5, 10 or 20% of total metabolizable energy. Knife-cut rats with unlimited access to 10 or 20% protein diets became obese, gaining 2-3 times more weight and 3-6 times more carcass energy while consuming 55-89% more energy than sham-operated rats. In contrast, energy consumed and gained by knife-cut rats with unlimited access to a 5% protein diet was similar to that of rats given sham surgery. Results indicate that a low protein diet effectively blocks development of hyperphagia and obesity in rats with surgical knife cuts between the ventromedial and lateral regions of the hypothalamus.

An analysis of excessive running in the development of activity anorexia.

Food restriction combined with activity wheel access produces activity anorexia: a combination of excessive running, reduced food intake and rapid weight loss. Temporal distributions of running in activity anorexia were examined in a reversal design with one of 2 x 2 x 2 factorial combinations (pelleted-vs-powdered food x deprivation x wheel access) as the treatment condition. Wheel revolutions were recorded in 30 min intervals; body weights, food and water intakes were measured daily. Only wheel access combined with food deprivation reliably produced activity anorexia. Excessive running occurred in the absence of schedule-induced polydipsia, was unaffected by food form, and showed distributional characteristics of facultative behavior. These results are inconsistent with schedule-induced behavior explanations. Running distributions appeared consistent with chronobiological models with light/dark onset and feeding serving as zeitgebers.

Effects of a behavioral weight-loss program food purchases: instructions to shop with a list.

Effects of instructions to shop with a list on subsequent food purchases were evaluated in the context of a 12-week behavioral/nutritional weight loss program. In the fifth class, subjects were taught to prepare a weekly menu, convert the menu to a shopping list, adjust the list for foods already on hand and organize the list to be consistent with supermarket layout. Subjects were told to attempt to restrict their purchases to items and amounts on the list. Food purchases were reduced from 16,188 kcal per person per week prior to the shopping class to 9625 kcal during the remainder of the treatment period in five subjects losing greater than or equal to 4.5 kg during treatment and from 14,620 kcal to 12,305 kcal for five subjects losing less than 4.5 kg during the treatment. The decrease for subjects losing less than 4.5 kg did not reach significance, but a further decrease to 10,254 kcal during follow-up was significantly less than pre-intervention purchases. Reductions posted by the greater than or equal to 4.5 kg subjects were maintained over a 12-week post-treatment follow-up period. A non-equivalent control group of six shoppers who were not attempting to lose weight did not change over the same time period, (averaging 14,470, 14,939 and 12,636 kcal at pre-intervention, post-intervention and follow-up respectively), ruling out seasonal factors as an alternative explanation. Food purchases were also analyzed for qualitative changes.

Temporal adjustments in sympathoadrenal activity in rats with obesity-producing hypothalamic knife cuts.

Sympathoadrenal activity was assessed in adult rats with obesity-producing hypothalamic knife cuts prior to and after the onset of gross obesity by measuring urinary excretion of norepinephrine and epinephrine and by determining rates of norepinephrine turnover in selected organs. Urinary excretion of norepinephrine, as an index of overall sympathetic nervous system activity, was approximately doubled throughout the 4-week study in knife-cut rats, as was intake of the high-fat diet. Three days after knife-cut surgery (before the onset of gross obesity) rates of norepinephrine turnover (ng X organ-1 X hr-1) were 23-33% lower in three of the four organs examined than in the corresponding organs of control rats; rates of norepinephrine turnover were depressed in pancreas, interscapular brown adipose tissue, and abdominal white adipose tissue and unchanged in hearts. Four weeks after surgery when gross obesity was evident, rates of norepinephrine turnover were accelerated in heart (+82%) and pancreas (+63%), but remained low in interscapular brown adipose tissue (-27%) and abdominal white adipose tissue (-28%). Adrenal medullary activity, assessed by urinary excretion of epinephrine, was suppressed within the 1st day after knife-cut surgery and remained suppressed for several weeks. Brown adipose tissue and white adipose tissue appear to be selectively excluded from the generalized activation of the sympathetic nervous system in adult hyperphagic rats with obesity-producing hypothalamic knife cuts. Activation of the sympathetic nervous system was associated with reciprocal suppression of adrenal medullary responses in knife-cut rats.

Energy balance in rats with obesity-producing hypothalamic knife cuts: effects of adrenalectomy.

Rats with obesity-producing, hypothalamic knife cuts (KC) were fed a purified high fat diet for 9 wk. KC rats consumed more energy (+70-100%) and retained energy with a much higher efficiency than control rats. Adrenalectomy of KC rats 1 wk (before gross obesity was evident) or 5 wk (when KC rats were 70% overweight) after KC surgery caused a reduction in energy intake to levels approximating those of control rats. Furthermore, energy retention in adrenalectomized KC rats was depressed more than could be explained on the basis of the reduction in energy intake. Two factors associated with the reduction in energy retention, urinary excretion of norepinephrine, an indicator of sympathetic nervous system activity, and GDP binding to brown adipose tissue mitochondria, an indicator of the thermogenic capacity of the tissue, were higher in vadrenalectomized KC rats than in pair-fed KC rats. Removal of the adrenals not only suppressed hyperphagia in KC rats fed a high fat diet, but also increased energy expenditure per kilocalorie consumed.

Impaired thermoregulation in cold-exposed rats with hypothalamic obesity.

Rats with obesity-producing, hypothalamic knife cuts were fed a high fat diet and placed in the cold (2 degrees C) for six days starting 3, 11, or 24 days after surgery. Between surgery and cold exposure, knife-cut rats consumed 90% to 122% more energy and gained more weight (32 +/- 4, 112 +/- 5, and 241 +/- 9 g) than sham-operated rats (15 +/- 2, 34 +/- 2, and 58 +/- 3 g). When exposed to cold, sham-operated rats increased (22% to 30%) energy intake whereas knife-cut rats decreased (5% to 51%) intake. After 24 hours at 2 degrees C body temperatures of knife-cut rats were 1.2, 0.7, and 0.7 degrees less than those of control rats; body temperatures continued to decrease to 2.9, 3.0 and 2.5 degrees less than control rats after six days at 2 degrees C. Fasting for 12 hours at 2 degrees C caused a further reduction in body temperature to 4.9, 4.8, and 5.9 degrees less than in control rats. Cold exposure increased urinary excretion of norepinephrine and epinephrine (indicators of sympathoadrenal activity) in all rats. Guanosine diphosphate (GDP) binding to brown adipose tissue (BAT) mitochondria (an indicator of the thermogenic capacity of the tissue) was similar in cold-exposed, knife-cut, and sham-operated rats. Cold acclimation before hypothalamic knife-cut surgery prevented the cold-induced decrease in body temperatures of knife-cut rats.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of a warm environment on energy balance in obese (ob/ob) mice.

Low rates of thermoregulatory heat production associated with low metabolic activity of brown adipose tissue, the primary site of thermoregulatory heat production, contribute substantially to the high efficiency of energy retention in obese (ob/ob) mice housed at 20 degrees C to 28 degrees C. To eliminate the need for thermoregulatory heat production lean and ob/ob mice were housed at 34.5 degrees C. At this temperature ob/ob mice still retained energy with a greater efficiency than lean littermates. Next, we investigated the possibility that the high efficiency of energy retention in ob/ob mice housed at 34.5 degrees C was related to depressed dietary-induced thermogenesis associated with low metabolic activity of brown adipose tissue. The sympathetic nervous system is a primary regulator of brown adipose tissue metabolism. Therefore, rates of norepinephrine (NE) turnover in brown adipose tissue, as an indicator of sympathetic nervous system stimulation of the tissue, were measured. Lean and ob/ob mice housed at 34.5 degrees C had equally low rates of NE turnover in their brown adipose tissue. Thus, the high efficiency of energy retention in ob/ob mice maintained at 34.5 degrees C is caused by factors other than low sympathetic stimulation of brown adipose tissue.

Hypothalamic obesity, brown adipose tissue, and sympathoadrenal activity in rats.

Obesity-producing, hypothalamic knife cuts and ventromedial hypothalamic (VMH) lesions in ad libitum-fed adult rats increased intake of a high-fat diet (123 and 130%) and energy retention (880 and 1,099%) during the 4-wk period postsurgery; even when pair fed to control rats, energy retention of the knife-cut and lesioned rats was still elevated (105 and 155%). Thermogenic capacity of brown adipose tissue (BAT), estimated from guanosine diphosphate (GDP) binding to BAT mitochondria, was unchanged in hyperphagic knife-cut and VMH-lesioned rats and was reduced approximately 50% when these rats were pair fed to controls. Urinary excretion of norepinephrine (NE) was approximately twofold higher in ad libitum-fed, knife-cut, and lesioned rats than in control rats; restriction of energy intake decreased NE excretion to control values. Rates of NE turnover in heart paralleled urinary NE excretion, whereas NE turnover in BAT was generally not increased in the hyperphagic rats. Urinary epinephrine excretion, an index of adrenal medullary activity, was depressed in all knife-cut and VMH-lesioned rats. Hyperphagia coupled with a lack of increased heat production in BAT causes gross obesity in ad libitum-fed, knife-cut, and VMH-lesioned rats, whereas obesity in pair-fed rats develops in part at least as a result of reduced heat production by BAT.

Adrenalectomy increases norepinephrine turnover in brown adipose tissue of obese (ob/ob) mice.

The hyperphagia and rapid body weight gain normally observed in young obese (ob/ob) mice were abolished by removal of their adrenal glands, whereas food intake and weight gain of lean mice were not significantly affected by adrenalectomy. Adrenalectomy lowered body energy density (kcal/g carcass) in obese mice more than could be attributed to reduced food intake per se, suggesting that their energy expenditure was also increased. In control obese mice, low stimulation of brown adipose tissue by the sympathetic nervous system, as indicated by the low fractional rates of norepinephrine (NE) turnover in their brown adipose tissue may have contributed to the reduced energy expenditure in these animals. Adrenalectomy increased the rates of NE turnover in brown adipose tissue of obese mice to rates nearly equal to those observed in lean mice without affecting NE turnover in this tissue of lean mice. Likewise, removal of the adrenals normalized the low rates of NE turnover in hearts of obese mice without affecting lean mice. Rates of NE turnover in two other organs, white adipose tissue and pancreas, of control and adrenalectomized obese mice were similar to rates observed in lean counterparts. The adrenal may thus contribute to both the hyperphagia and the low energy expenditure by brown adipose tissue that together cause gross obesity in ob/ob mice.

Consumption of a low protein diet increases norepinephrine turnover in brown adipose tissue of adult rats.

Adult rats were fed diets containing 5 or 15% casein to determine effects of low protein intake on efficiency of energy retention and on brown adipose tissue metabolism. Efficiency of energy retention of rats fed the 5% casein diet for 4 or 8 weeks was approximately 40% lower than was efficiency of energy retention of rats fed the 15% casein diet. Rats fed the 5% casein diet also exhibited an enhanced norepinephrine (NE)-stimulated metabolic rate and an accelerated NE turnover in their brown adipose tissue relative to responses of rats fed the 15% casein diet. Additionally, NE turnover in white adipose tissue, but not heart, was accelerated in rats fed the 5% casein diet. The reduced efficiency of energy retention in rats fed the low protein diet may be linked to accelerated NE turnover and heat production by their brown adipose tissue.

Effects of dietary carbohydrate, fat, and protein on norepinephrine turnover in rats.

To investigate effects of diet composition on rates of norepinephrine (NE) turnover in sympathetically innervated organs, weaning rats were fed for 2 to 21/2 weeks diets varying in carbohydrate (74.2% to 7.4% of total metabolizable energy) and fat (5.2% to 72.0%), or diets varying in protein (9.9% to 39.6%) and carbohydrate (77.8% to 48.1%). Changing the proportions of carbohydrate and fat in the diet, while maintaining similar intakes of energy and all other essential nutrients did not affect rates of NE turnover in heart, white adipose tissue (WAT), liver or pancreas and only minimally affected NE turnover in interscapular brown adipose tissue (IBAT). Decreasing the proportion of protein in the diet from 39.6% to 9.9% accelerated rats of NE turnover in heart (52%), IBAT (20%), WAT (42%), and liver (37%). When rats fed a diet containing 19.8% protein were also given a 10%(wt/vol) sucrose solution to drink for three days, their rates of NE turnover increased in heart (45%), IBAT (17%), liver (71%), and pancreas (55%). This response to sucrose depended on the protein content of the diet, since rats fed a 9.9% protein diet in which rates of NE turnover was already accelerated had no further increase in NE turnover when given the sucrose solution to drink. These data demonstrate that diet composition can affect activity of the sympathetic nervous system, as indicated by changes in rates of NE turnover. Changing the proportion of protein in the diet was more effective in altering NE turnover than changing the proportion of carbohydrate or fat.

Reduced sympathetic nervous system activity in rats with ventromedial hypothalamic lesions.

To determine if alterations in sympathetic nervous system (SNS) activity occur in rats with ventromedial hypothalamic (VMH) lesions, norepinephrine (NE) turnover rates were examined in various tissues of lesioned and control, weanling rats. VMH-lesioned rats fed a high-carbohydrate diet ad libitum for 4 weeks following surgery were not hyperphagic, but they gained 50% more body energy than control rats. VMH lesions extended the half-life of 3H-NE in interscapular brown adipose tissue (BAT) by 42%, in abdominal white adipose tissue (WAT) by 201%, in heart by 61% and in pancreas by 85%, and reduced total NE turnover (ng/organ/hr) in BAT (38%), WAT (57%), heart (30%) and pancreas (53%). Reduced SNS activity in BAT is consistent with the decreased energy expenditure (heat production) and increased energy efficiency observed in VMH-lesioned rats. In WAT, decreased SNS activity coupled with hyperinsulinemia would facilitate energy storage as fat by reducing lipid mobilization. In the pancreas, reduced SNS activity would contribute to hyperinsulinemia. These results support the hypothesis that VMH lesions decrease SNS activity in several organs. This change in autonomic tone is very likely a major factor in the development of obesity in VMH-lesioned animals.

Changes in body composition of adult obese (ob/ob) and lean mice fed restricted levels of diets high in carbohydrate, fat or protein.

Adult obese (ob/ob) and lean male mice were fed severely-restricted amounts (approximately 20 to 30 per cent of ad-libitum intake) of either a high-carbohydrate, high-fat or high-protein diet for three weeks. All mice were fed an equal amount of metabolizable energy. Total body fat, total body nitrogen and skeletal-muscle nitrogen were measured in separate groups of mice initially and following three weeks of energy restriction. Obese mice lost 38 to 75 per cent more body energy than did lean mice. Fat accounted for most of the total energy lost (80 to 95 per cent). Obese mice lost more fat, but less protein, than lean mice. Of the total body protein lost by lean mice, 40 to 50 per cent was from skeletal muscle; but obese mice lost very little skeletal-muscle protein. Composition of the diet fed did not significantly affect losses of body weight, fat or protein in either obese or lean mice; mice fed the high-protein diet had heavier livers and kidneys. These results suggest that adult obese mice expend more total energy than lean mice. In addition, loss of body protein during restricted energy intake may be more closely related to remaining body fat stores than to composition of the diet.

Na+,K+-ATPase enzyme units in lean and obese (ob/ob) thyroxine-injected mice.

The possible involvement of Na+,K+-ATPase in the etiology of obesity in the obese (ob/ob) mouse was explored. The number of Na+,K+-ATPase enzyme units in skeletal muscle, liver, and kidneys from 4- and 8-wk-old obese and lean mice was estimated from saturable [3H]ouabain binding to particulate fractions. Neither phenotype nor age altered the Kd value for ouabain binding in these three tissue preparations. The total number of [3H]ouabain binding sites in hindlimb muscles was 35--55% lower in 4- and 8-wk-old obese mice than in their lean counterparts. However, the total number of [3H]ouabain binding sites in liver and kidneys of obese mice was similar to values observed in their lean counterparts. Because it has been suggested that ob/ob mice are hypothyroid, we investigated the response of Na+,K+-ATPase in these mice to thyroid hormone treatment (approximately 5 microgram thyroxine/day for 2 wk). The number of [3H]ouabain binding sites in the three tissues increased in both obese and lean mice injected with this relatively large dose of thyroxine, but the obese mice were 2--3 times more responsive than lean mice.

Maintenance energy requirements, energy retention and heat production of young obese (ob/ob) and lean mice fed a high-fat or a high-carbohydrate diet.

Female obese (ob/ob) and lean mice were weaned at 21 days of age, placed in wire-mesh cages maintained at 25 to 30 degrees, and fed a high-fat or a high-carbohydrate diet for 21 days. The body energy balance procedure was utilized to determine the maintenance energy requirements, and the efficiency of dietary energy utilization, above maintenance, in these mice. Heat production of each mouse was measured weekly in a gradient-layer calorimeter. Regressions of changes in body energy per kg3/4 on metabolizable energy intake per kg3/4 indicated that the maintenance energy requirement averaged 72 kcal/kg3/4/day for obese mice and 124 kcal/kg3/4/day for lean mice. Diet composition did not influence the maintenance energy requirements, but utilization of energy, above maintenance, in obese mice fed the high-fat diet was 41% more efficient than observed in obese mice fed the high-carbohydrate diet and 38 to 71% more efficient than observed in lean mice. Heat production, per unit body weight was lower in obese mice than in lean mice. The lowest heat production was observed in obese mice fed the high-fat diet. The 40% lower maintenance energy requirement of the obese mice is a major factor contributing to the high efficiency of energy retention in these mice. Consumption of a high-fat diet further improved the ability of the obese mice to retain dietary energy.