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Although lipid excess can impair [beta]-cell function in vitro, short-term high-fat feeding in normal rats produces insulin resistance but not hyperglycemia. This study examines the effect of long-term (10-mo) high polyunsaturated fat feeding on glucose tolerance in Wistar rats. The high fat-fed compared with the chow-fed group was 30% heavier and 60% fatter, with approximately doubled fasting hyperinsulinemia (P < 0.001) but only marginal fasting hyperglycemia (7.5 [+ or -] 0.1 vs. 7.2 [+ or -] 0.1 mmol/l, P < 0.01). Insulin sensitivity was ~67% lower in the high-fat group (P < 0.01). The acute insulin response to intravenous arginine was approximately double in the insulin-resistant high-fat group (P < 0.001), but that to intravenous glucose was similar in the two groups. After the intravenous glucose bolus, plasma glucose decline was slower in the high fat-fed group, confirming mild glucose intolerance. Therefore, despite severe insulin resistance, there was only a mildly elevated fasting glucose level and a relative deficiency in glucose-stimulated insulin secretion; this suggests that a genetic or congenital susceptibility to [beta]-cell impairment is required for overt hyperglycemia to develop in the presence of severe insulin resistance. insulin secretion; arginine; long-chain acyl-coenzyme A; body composition; glucose tolerance

The relationship between episodic growth hormone (GH) secretion and muscle entropy, body composition and physical fitness was analyzed in normal human volunteers via a deconvolution technique. Analysis of lean and fat tissue distribution via computerized tomography and dual-energy X-ray absorption scan indicated the presence of reduced levels of GH secretion in older humans compared to younger volunteers. Furthermore, abdominal fat mass acted as a negative determinant of the amount and pattern of GH release in the fed state.

Diets rich in fats lead to excess fat deposits with little increase in the body weight. Studies with different fat percentages in the diet, reveal that body-fat distribution becomes disproportionate. Dietary fat also causes increase in energy storage and deposition of adipose tissue. In humans such increases in adipose deposits, especially in the viscera, would pose great risks to health.

A study was conducted on hamsters to examine if changes in voluntary exercise contribute to alterations in energy balance during pregnancy or after experimental manipulations of ovarian hormone levels as in other species. The results revealed that Syrian hamsters do not display important alterations in voluntary exercise during pregnancy or in reaction to manipulations of ovarian steroid levels, unlike rats. Therefore, in Syrian hamsters, changes in energy balance caused by pregnancy or steroids, are not affected by changes in food or voluntary exercise.

Magnitude and variation of ratio of total body potassium to fat-free mass: a cellular level modeling study. Am J Physiol Endocrinol Metab 281: E1-E7, 2001.--Potassium is an essential element of living organisms that is found almost exclusively in the intracellular fluid compartment. The assumed constant ratio of total body potassium (TBK) to fat-free mass (FFM) is a cornerstone of the TBK method of estimating total body fat. Although the TBK-to-FFM (TBK/FFM) ratio has been assumed constant, a large range of individual and group values is recognized. The purpose of the present study was to undertake a comprehensive analysis of biological factors that cause variation in the TBK/FFM ratio. A theoretical TBK/FFM model was developed on the cellular body composition level. This physiological model includes six factors that combine to produce the observed TBK/FFM ratio. The ratio magnitude and range, as well as the differences in the TBK/FFM ratio between men and women and variation with growth, were examined with the proposed model. The ratio of extracellular water to intracellular water (E/I) is the major factor leading to between-individual variation in the TBK/FFM ratio. The present study provides a conceptual framework for examining the separate TBK/FFM determinants and suggests important limitations of the TBK/FFM method used in estimating total body fat in humans and other mammals. water distribution; body fat measurement; body composition

Lange, Kai Henrik Wiborg, Fredrik Isaksson, Anders Juul, Michael Hojby Rasmussen, Jens Bulow, and Michael Kjaer. Growth hormone enhances effects of endurance training on oxidative muscle metabolism in elderly women. Am J Physiol Endocrinol Metab 279: E989-E996, 2000.--The present study investigated whether recombinant human (rh) growth hormone (GH) combined with endurance training would have a larger effect on oxidative capacity metabolism, and body fat than endurance training alone. Sixteen healthy, elderly women, aged 75 yr, performed closely monitored endurance training on a cycle ergometer over 12 wk. rhGH was given in a randomized, double-blinded, placebo-controlled design in addition to the training program. GH administration resulted in a doubling of serum insulin-like growth factor I levels. With endurance training, peak oxygen uptake increased by -18% in both groups, whereas the marked increase in muscle citrate synthase activity was 50% larger in the GH group compared with the placebo group. In addition, only the GH group revealed an increase in muscle L-3-hydroxyacyl-CoA dehydrogenase activity. Body weight remained unchanged in both groups, but the GH group showed significant changes in body composition with a decrease in fat mass and an increase in lean body mass. Twenty-four-hour indirect calorimetry performed in four subjects showed a marked increase in energy expenditure with increased relative and absolute fat combustion in the two subjects receiving rhGH. In conclusion, rhGH adds to the effects of endurance training on muscle oxidative enzymes and causes a reduction in body fat in elderly women. insulin-like growth factor I; enzymes; exercise; calorimetry; body composition

Resting energy expenditure-fat-free mass relationship: new insights provided by body composition modeling. Am J Physiol Endocrinol Metab 279: E539-E545, 2000.--The relationship between resting energy expenditure (REE) and metabolically active fat-free mass (FFM) is a cornerstone in the study of physiological aspects of body weight regulation and human energy requirements. Important questions, however, remain unanswered regarding the observed linear REE-FFM association in adult humans. This led us to develop a series of REE-body composition models that provide insights into the widely used simple linear REE-FFM prediction model derived experimentally in adult humans. The new models suggest that the REE-FFM relationship in mammals as a whole is curvilinear, that a segment of this function within a FFM range characteristic of adult humans can be fit with a linear equation almost identical to that observed from a composite review of earlier human studies, and that mammals as a whole exhibit a decrease in the proportion of FFM as high metabolic rate organs with greater FFM. The present study thus provides a new approach for examining REE-FFM relationships, advances in a quantitative manner previously observed albeit incompletely formulated REE-body composition associations, and identifies areas in need of additional research. energy metabolism; body composition

Illner, Kirsten, Gisbert Brinkmann, Martin Heller, Anja Bosy-Westphal, and Manfred J. Muller. Metabolically active components of fat free mass and resting energy expenditure in nonobese adults. Am. J. Physiol. Endocrinol. Metab. 278: E308--E315, 2000.--Resting energy expenditure (REE) and components of fat-free mass (FFM) were assessed in 26 healthy nonobese adults (13 males, 13 females). Detailed body composition analyses were performed by the combined use of dual-energy X-ray absorptiometry (DEXA), magnetic resonance imaging (MRI), bioelectrical impedance analysis (BIA), and anthropometrics. We found close correlations between REE and [FFM.sub.BIA] (r = 0.92), muscle [mass.sub.DEXA] (r = 0.89), and sum of internal [organs.sub.MRI] (r = 0.90). In a multiple stepwise regression analysis, [FFM.sub.BIA] alone explained 85% of the variance in REE (standard error of the estimate 423 kJ/day). Including the sum of internal [organs.sub.MRI] into the model increased the [r.sup.2] to 0.89 with a standard error of 381 kJ/day. With respect to individual organs, only skeletal [muscle.sub.DEXA] and liver [mass.sub.MRI] significantly contributed to REE. Prediction of REE based on 1) individual organ masses and 2) a constant metabolic rate per kilogram organ mass was very close to the measured REE, with a mean prediction error of 96 kJ/day. The very close agreement between measured and predicted REE argues against significant variations in specific REEs of individual organs. In conclusion, the mass of internal organs contributes significantly to the variance in REE. body composition; muscle mass; organ mass; dual-energy X-ray absorptiometry; magnetic resonance imaging; bioelectrical impedance analysis; anthropometrics

Burguera, Bartolome, David Proctor, Niki Dietz, ZengKui Guo, Michael Joyner, and Michael D. Jensen. Leg free fatty acid kinetics during exercise in men and women. Am. J. Physiol. Endocrinol. Metab. 278: E113-E117, 2000.--We previously reported that epinephrine stimulates leg free fatty acid (FFA) release in men but not in women. The present studies were conducted to determine whether the same is true during exercise. Six men and six women bicycled for 90 min at 45% of peak [O.sub.2] consumption, during which time systemic and leg FFA kinetics ([9,10-[sup.3]H]palmitate) were measured. The catecholamine and hormonal responses to exercise were not different in men and women. The baseline systemic and leg palmitate release was 94 [+ or -] 15 vs. 114 [+ or -] 5 [micro]mol/min and 16 [+ or -] 2 and 20 [+ or -] 3 [micro]mol/min, respectively, in men and women [P = nonsignificant (NS)]. Systemic and leg palmitate release increased (both P [is less than] 0.001) to 251 [+ or -] 18 vs. 212 [+ or -] 16 [micro]mol/min and 73 [+ or -] 19 vs. 80 [+ or -] 12 [micro]mol/min in men and women, respectively, during the last 30 min of exercise (P = NS, men vs. women). We conclude that the systemic and leg adipose tissue lipolytic response to exercise is not different in nonobese men and women. lipolysis; body composition; indirect calorimetry

Zhou, Jun, Xiaolang Yan, Donna H. Ryan, and Ruth B. S. Harris. Sustained effects of repeated restraint stress on muscle and adipocyte metabolism in high-fat-fed rats. Am. J. Physiol. 277 (Regulatory Integrative Comp. Physiol. 46): R757-R766, 1999.--Repeated restraint stress 3 h/day for 3 days in rats causes a temporary hypophagia but a sustained weight loss. We investigated whether poststress changes in peripheral tissue metabolism contributed to these responses. One day after the last restraint, insulin sensitivity, measured by oral glucose tolerance test, was improved in restrained rats. Restraint and pair-fed rats weighed less than controls, but body fat content was the same in all groups. Muscle glucose uptake, measured in vitro, was not changed by treatment, whereas in vitro adipocyte glucose uptake was substantially inhibited only in restrained rats. Adipocytes from restrained rats had elevated rates of fatty acid oxidation but not fatty acid esterification, indicating a shift in energy supply from glucose to fatty acids. Five days after the last restraint, the reduced weight of restrained and pair-fed rats resulted from loss of both lean and fat tissue. These results demonstrate that restraint caused sustained, tissue-specific changes in metabolism that may contribute to changes in body composition and body weight of the rats. glucose tolerance; glucose transport; fatty acid oxidation; body composition