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Biomedical subjects

W M Kohrt

Publications and source records attributed to W M Kohrt.

At least 73 records · Page 4Linked to original sources
PubMed1993

Age-related differences in body composition by hydrodensitometry and dual-energy X-ray absorptiometry.

To determine whether percent body fat (%BF) is overestimated in older people by hydrodensitometry (HD) because of an age-related decrease in bone mineral content (BMC), body composition of 113 women and 72 men (21-81 yr) was assessed by HD and dual-energy X-ray absorptiometry (DEXA). DEXA provides an estimate of %BF adjusted for differences in BMC. HD %BF and DEXA %BF were not different in young people [21-39 yr; 17.6 +/- 6.4 (SD) vs. 17.6 +/- 7.2%, NS], were slightly, but significantly, different in middle-aged people (40-59 yr; 25.5 +/- 6.4 vs. 24.1 +/- 6.7%, P < 0.05), and showed the largest disparity in older people (> or = 60 yr; 34.9 +/- 7.9 vs. 30.8 +/- 8.7%, P < 0.05). The discrepancy in older people was apparently not due to mineral loss, however, inasmuch as correction of HD %BF for variance in BMC as a fraction of fat-free mass resulted in only small adjustments (approximately 1%) of %BF. Assessment of DEXA %BF was further evaluated in nine subjects with packets of lard (2-3 kg) overlying either the thigh or the trunk region. Only 55% of the exogenous fat was identified as fat when it was in the trunk region compared with 96% when it was positioned over the legs. These data suggest that the age-related increase in upper body adipose tissue is underestimated by DEXA.

Absorptiometry, Photon↗
PubMed1993

Differences in cardiovascular adaptations to endurance exercise training between older men and women.

Recent studies have shown that people in their seventh decade are able to adapt to exercise training with an increase in maximal O2 uptake (VO2max) similar in relative magnitude to that observed in young people. The purpose of this study was to determine the relative contributions of increases in stroke volume and O2 extraction to the training-induced increase in VO2max in older men and women. Fifteen men [63 +/- 3 (SE) yr] and 16 women (64 +/- 3 yr), in good health, participated in 9-12 mo of endurance exercise training at 70 to 85% of maximal heart rate for 45 min/day, 4 days/wk. VO2max increased 19% (2.35 +/- 0.1 to 2.8 +/- 0.1 l/min; P < 0.01) in the men and 22% (1.36 +/- 0.1 to 1.66 +/- 0.1 l/min; P < 0.01) in the women in response to training. In the men, stroke volume during maximal exercise was 15% higher after training, and this increase accounted for 66% of the increase in VO2max. The remainder of the increase in VO2max was accounted for by a 7% greater arteriovenous O2 content difference during maximal exercise. In contrast, training resulted in no change in stroke volume in women, in whom the entire increase in VO2max was accounted for by a greater arteriovenous O2 content difference (12.2 +/- 0.4 before vs. 14.4 +/- 0.4 ml O2/100 ml blood after; P < 0.01) during maximal exercise. There were no changes in these variables in the control subjects. The mechanisms responsible for the training-induced increase in VO2max in the older men were similar to those found in young people.(ABSTRACT TRUNCATED AT 250 WORDS)

Adaptation, Physiological↗
PubMed1993

Effects of age, adiposity, and fitness level on plasma catecholamine responses to standing and exercise.

The plasma norepinephrine (NE) and epinephrine (E) responses to a variety of stressors are influenced by age, adiposity, and exercise training status. The objectives of this study were to 1) compare basal levels as well as posture- and exercise-induced changes in plasma NE and E concentrations in young [25 +/- 1 (SE) yr; n = 24] and older (64 +/- 1 yr; n = 106) people and examine the associations of the responses with adiposity and maximal O2 uptake (VO2max) and 2) determine the extent to which the NE and E responses are altered by exercise training in older people. We found no significant differences in basal NE and E levels between young and older subjects. However, the NE response to standing was exaggerated in older people (696 +/- 39 vs. 512 +/- 61 pg/ml; P < 0.05), whereas NE and E responses to exercise requiring approximately 78% of VO2max were attenuated in older people (NE: 1,444 +/- 74 vs. 1,983 +/- 222 pg/ml; E: 109 +/- 10 vs. 228 +/- 29 pg/ml; both P < 0.01). Increments in NE and E during exercise were more closely associated with age (NE: r = -0.38; E: r = -0.46; both P < 0.05) and VO2max (NE: r = 0.43; E: r = 0.52; both P < 0.05) than with adiposity (NE: r = -0.29; E: r = -0.25; both P < 0.05). In 48 older subjects who completed 9 mo of exercise training, the increases in NE and E during exercise at the same absolute intensity were 39 and 57% lower, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Adipose Tissue↗
PubMed1993

Exercise training decreases plasma cholesteryl ester transfer protein.

To assess the effect of exercise on the plasma concentration of cholesterol ester transfer protein (CETP) and its possible influence in mediating the exercise-associated redistribution of cholesterol among plasma lipoproteins, we measured plasma CETP in 57 healthy normolipidemic men and women before and after 9 to 12 months of exercise training. The training protocol resulted in significant changes in VO2max (mean +/- SD, +5.3 +/- 3.5 mL.kg-1 x min-1), body weight (-2.5 +/- 3.5 kg), plasma triglycerides (-25.7 +/- 36.3 mg/dL), high-density lipoprotein cholesterol (HDL-C) (+2.6 +/- 6.2 mg/dL), and ratios of total cholesterol to HDL-C (-0.30 +/- 0.52) and low-density lipoprotein cholesterol (LDL-C) to HDL-C (-0.18 +/- 0.45) (all P < or = .05) but no change in lipoprotein(a). CETP concentration (in milligrams per liter) fell significantly in response to training in both men (n = 28, 2.47 +/- 0.66 to 2.12 +/- 0.43; % delta = 14.2%; P < .005) and women (n = 29, 2.72 +/- 1.01 to 2.36 +/- 0.76; % delta = 13.2%; P < .047). The CETP change was observed both in subjects who lost weight (n = 28, delta mean weight = -5.0 kg; delta CETP = -0.42 +/- 0.79; % delta = 15.4%; P < .009) and in those who were weight stable (n = 29, delta mean weight = -0.12 kg; delta CETP = -0.29 +/- 0.78; % delta = 10.4%; P < .055).(ABSTRACT TRUNCATED AT 250 WORDS)

Aged↗
PubMed1993

Insulin resistance in aging is related to abdominal obesity.

Studies have shown that insulin resistance increases with age, independent of changes in total adiposity. However, there is growing evidence that the development of insulin resistance may be more closely related to abdominal adiposity. To evaluate the independent effects of aging and regional and total adiposity on insulin resistance, we performed hyperinsulinemic euglycemic clamps on 17 young (21-33 yr) and 67 older (60-72 yr) men and women. We assessed FFM and total and regional adiposity by hydrodensitometry and anthropometry. Insulin-stimulated GDRs at a plasma insulin concentration of approximately 450 pM averaged 45.6 +/- 3.3 mumol.kg FFM-1 x min-1 (mean +/- SE) in the young subjects, 45.6 +/- 10.0 mumol.kg FFM-1 x min-1 in 24 older subjects who were insulin sensitive, and 23.9 +/- 11.7 mumol.kg FFM-1 x min-1 in 43 older subjects who were insulin resistant. Few significant differences were apparent in skin-fold and circumference measurements between young and insulin-sensitive older subjects, but measurements at most central body sites were significantly larger in the insulin-resistant older subjects. Waist girth accounted for > 40% of the variance in insulin action, whereas age explained only 10-20% of the total variance and < 2% of the variance when the effects of waist circumference were statistically controlled. These results suggest that insulin resistance is more closely associated with abdominal adiposity than with age.

Adult↗
PubMed1992

Exercise training improves fat distribution patterns in 60- to 70-year-old men and women.

Changes in body composition and fat distribution in response to endurance exercise training were compared in 47 men and 46 women, aged 60 to 70 yr. Body composition was assessed by hydrodensitometry and fat distribution was evaluated with skinfold thickness and circumference measures. The 9- to 12-mo exercise program consisted primarily of walking and/or jogging for 46 +/- 5 min.d-1, 4.0 +/- 0.6 d.wk-1, at 80 +/- 5% of maximal heart rate. Although men lost more weight during the exercise program than women (men, -3.4 +/- 4.4 kg; women, -1.6 +/- 3.8 kg), relative changes were not significantly different, averaging -3.7 +/- 4.1% and -2.7 +/- 2.9% of body weight in men and women, respectively. The changes in body weight reflected fat loss, as fat-free mass did not change. The reductions in skinfold thickness and circumferences were similar in men and women, and in both groups the largest absolute and relative changes occurred in the truncal area, indicating a preferential loss of fat from the central regions of the body. The results of this study indicate that endurance exercise training can favorably modify the abdominal fat distribution profile that is typical of older men and women in the United States and thus, perhaps, reduce the risk of the diseases associated with abdominal obesity.

Abdomen↗
PubMed1992

Eccentric exercise induces transient insulin resistance in healthy individuals.

Euglycemic-hyperinsulinemic clamps were performed on six healthy untrained individuals to determine whether exercise that induces muscle damage also results in insulin resistance. Clamps were performed 48 h after bouts of predominantly 1) eccentric exercise [30 min, downhill running, -17% grade, 60 +/- 2% maximal O2 consumption (VO2max)], 2) concentric exercise (30 min, cycle ergometry, 60 +/- 2% VO2max), or 3) without prior exercise. During the clamps, euglycemia was maintained at 90 mg/dl while insulin was infused at 30 mU.m-2.min-1 for 120 min. Hepatic glucose output (HGO) was determined using [6,6-2H]glucose. Eccentric exercise caused marked muscle soreness and significantly elevated creatine kinase levels (273 +/- 73, 92 +/- 27, 87 +/- 25 IU/l for the eccentric, concentric, and control conditions, respectively) 48 h after exercise. Insulin-mediated glucose disposal rate was significantly impaired (P less than 0.05) during the clamp performed after eccentric exercise (3.47 +/- 0.51 mg.kg-1.min-1) compared with the clamps performed after concentric exercise (5.55 +/- 0.94 mg.kg-1.min-1) or control conditions (5.48 +/- 1.0 mg.kg-1.min-1). HGO was not significantly different among conditions (0.77 +/- 0.26, 0.65 +/- 0.27, and 0.66 +/- 0.64 mg.kg-1.min-1 for the eccentric, concentric, and control clamps, respectively). The insulin resistance observed after eccentric exercise could not be attributed to altered plasma cortisol, glucagon, or catecholamine concentrations. Likewise, no differences were observed in serum free fatty acids, glycerol, lactate, beta-hydroxybutyrate, or alanine. These results show that exercise that results in muscle damage, as reflected in muscle soreness and enzyme leakage, is followed by a period of insulin resistance.

Adult↗
PubMed1992

Plasma glucose kinetics during exercise in subjects with high and low lactate thresholds.

The purpose of this study was to test the hypothesis that the rate of plasma glucose oxidation during exercise is inversely related to muscle respiratory capacity. To this end, 14 subjects were studied: in 7 of these subjects, the blood lactate threshold (LT) occurred at a relatively high intensity [i.e., at 65 +/- 2% of peak cycle ergometer oxygen uptake (VO2 peak)], whereas in the other 7 subjects, LT occurred at a relatively low intensity (i.e., at 45 +/- 2% of VO2 peak). VO2peak did not differ between the two groups, but citrate synthase activity in the vastus lateralis muscle was 53% higher (P < 0.05) in the high LT group. A primed continuous infusion of [U-13C]glucose was used to quantify rates of glucose appearance (Ra), disappearance (Rd), and oxidation (R(ox)) during 90 min of exercise at 55% VO2peak. Although both absolute and relative rates of oxygen uptake during exercise were similar in the two groups, mean Ra and Rd were 17% lower (P < 0.001) in the high LT group, and mean R(ox) was 25% lower (21.0 +/- 2.6 vs. 27.9 +/- 2.6 mumol.min-1.kg-1; P < 0.001). The percentage of total energy derived from glucose oxidation was inversely related to muscle citrate synthase activity (r = -0.85; P < 0.01). These data support the concept that skeletal muscle respiratory capacity has a major role in determining the metabolic response to submaximal exercise.

Adult↗
PubMed1992

Effects of aging, sex, and physical training on cardiovascular responses to exercise.

BACKGROUND: The relative contributions of decreases in maximal heart rate, stroke volume, and oxygen extraction and of changes in body weight and composition to the age-related decline in maximal oxygen uptake (VO2max) are unclear and may be influenced by sex and level of physical activity. METHODS AND RESULTS: To investigate mechanisms by which aging, sex, and physical activity influence VO2max, we quantified VO2, cardiac output, and heart rate during submaximal and maximal treadmill exercise and assessed weight and fat-free mass in healthy younger and older sedentary and endurance exercise-trained men and women. For results expressed in milliliters per kilogram per minute, a three-to-four-decade greater age was associated with a 40-41% lower VO2max in sedentary subjects and a 25-32% lower VO2max in trained individuals (p less than 0.001). A smaller stroke volume accounted for nearly 50% of these age-related differences, and the remainder was explained by a lower maximal heart rate and reduced oxygen extraction (all p less than 0.001). Age-related effects on maximal heart rate and oxygen extraction were attenuated in trained subjects (p less than 0.05). After normalization of VO2max and maximal cardiac output to fat-free mass, age- and training-related differences were reduced by 24-47% but remained significant (p less than 0.05). For trained but not sedentary subjects, maximal cardiac output and stroke volume normalized to fat-free mass were greater in men than in women (p less than 0.05). CONCLUSIONS: A lower stroke volume, heart rate, and arteriovenous oxygen difference at maximal exercise all contribute to the age-related decline in VO2max. Effects of age and training on VO2max, maximal cardiac output, and stroke volume cannot be fully explained by differences in body composition. In sedentary subjects, however, the sex difference in maximal cardiac output and stroke volume can be accounted for by the greater percentage of body fat in women than in men.

Adult↗
PubMed1992

Body composition of healthy sedentary and trained, young and older men and women.

This study examined the effects of age and physical activity on body composition and fat distribution by comparing differences between young and older endurance trained men and women with differences between young and older sedentary people. Although indices of total body adiposity (fat mass, percent body fat) were higher in the older than in the young people in both the trained and the sedentary groups, the magnitude of the difference was markedly less in the trained group (P less than 0.01). The average differences in fat mass between young and old sedentary men and women were 10.1 kg and 12.2 kg, respectively, but only 4.3 kg and 5.5 kg in trained men and women. Skinfold thicknesses were approximately 24% and approximately 47% larger at all sites (triceps, thigh, subscapula, pectoralis, umbilicus, suprailiac) in the older than in the young trained men and women, respectively. Similar differences were found between young and older sedentary people except at central, upper body sites, where the relative differences in skinfold thicknesses between young and older sedentary people were 2- to 6-fold greater than in trained people. Thus, people who exercise regularly appear to accumulate less adipose tissue in upper, central body regions as they get older, potentially reducing the risk for the metabolic disorders associated with upper body obesity.

Adipose Tissue↗
PubMed1991

Ageing, exercise and food restriction: effects on skeletal muscle glucose uptake.

We investigated the effects of ageing, exercise and food restriction on glucose uptake by muscles perfused with physiological concentrations of insulin and glucose in male Long-Evans rats. The rate of glucose uptake by hindlimb muscles perfused with medium containing 50 microU@ml insulin and 8 mM glucose was the same in 9-10 month-, 18 month-, and 24-month-old rats. Rats exercised by means of swimming 3 h/day, 5 days/week, had significantly higher rates of muscle glucose uptake than did the sedentary freely eating rats. Paired-weight sedentary rats, that were food restricted so as to keep their weights in the same range as those of the swimmers, had a hindlimb glucose uptake rate similar to that of the swimmers, and greater than that of the sedentary freely eating rats. The 24-month-old sedentary freely eating rats showed a trend toward a higher plasma glucose response and a lower plasma insulin response to a glucose tolerance test. The 24-month-old swimmers showed no deterioration in glucose tolerance compared to the 9-10 month-old rats. Our findings argue against the concept that ageing results in skeletal muscle insulin resistance in rats.

Aging↗
PubMed1991

Plasma glucose kinetics in a well-trained cyclist fed glucose throughout exercise.

We hypothesized that when plasma glucose availability is maintained by carbohydrate (CHO) ingestion, trained cyclists can utilize plasma glucose at very high rates during the later stages of prolonged exercise (10). To test this hypothesis, a well-trained male cyclist was studied during exercise to fatigue at 70% VO2max when ingesting glucose throughout exercise. A primed continuous infusion of [U-13C]glucose was begun after 60 min of exercise to measure rates of plasma glucose appearance (Ra), disappearance (Rd), and oxidation (R(ox)). Ra and Rd rose progressively throughout exercise, peaking at 6.85 and 6.99 mmol/min, respectively, at fatigue (i.e., 133 min). Most (93%) of this glucose was oxidized; during the final 30 min of exercise, R(ox) averaged 6.10 mmol/min and accounted for approximately half of total CHO oxidation. These results support the hypothesis that trained cyclists can oxidize plasma glucose at very high rates during the later stages of prolonged exercise when fed CHO.

Adult↗
PubMed1991

Effects of treadmill exercise to exhaustion on the insulin response to hyperglycemia in untrained men.

The effects of a single bout of exercise to exhaustion on pancreatic insulin secretion were determined in seven untrained men by use of a 3-h hyperglycemic clamp with plasma glucose maintained at 180 mg/100 ml. Clamps were performed either 12 h after an intermittent treadmill run at approximately 77% maximum O2 consumption or without prior exercise. Arterialized blood samples for glucose, insulin, and C-peptide determination were obtained from a heated hand vein. The peak insulin response during the early phase (0-10 min) of the postexercise clamp was higher (81 +/- 8 vs. 59 +/- 9 microU/ml; P less than 0.05) than in the nonexercise clamp. Incremental areas under the insulin (376 +/- 33 vs. 245 +/- 51 microU.ml-1.min) and C-peptide (17 +/- 2 vs. 12 +/- 1 ng.ml-1.min) curves were also greater (P less than 0.05) during the early phase of the postexercise clamp. No differences were observed in either insulin concentrations or whole body glucose disposal during the late phase (15-180 min). Area under the C-peptide curve was greater during the late phase of the postexercise clamp (650 +/- 53 vs. 536 +/- 76 ng.ml-1.min, P less than 0.05). The exercise bout induced muscle soreness and caused an elevation in plasma creatine kinase activity (142 +/- 32 vs. 305 +/- 31 IU/l; P less than 0.05) before the postexercise clamp. We conclude that in untrained men a bout of running to exhaustion increased pancreatic beta-cell insulin secretion during the early phase of the hyperglycemic clamp. Increased insulin secretion during the late phase of the clamp appeared to be compensated by increased insulin clearance.

Adult↗
PubMed1991

Effects of gender, age, and fitness level on response of VO2max to training in 60-71 yr olds.

The adaptive response of maximal aerobic power (VO2max) to endurance exercise training was compared in 53 men and 57 women, aged 60-71 yr. The subjects were healthy and had been sedentary for at least 2 yr. Pretraining VO2max was measured during graded treadmill walking on two occasions. These values were reproducible (24.4 +/- 4.7 vs. 24.4 +/- 4.6 (SD) ml.min-l.kg-1; r = 0.96). Subjects trained primarily by walking and running for 9-12 mo, averaging 3.9 +/- 0.6 days/wk and 45 +/- 5 min/day at 80 +/- 5% of maximal heart rate (HRmax). Average improvement in VO2max (ml.min-1.kg-1) was 24 +/- 12% (range 0-58%). Relative improvement was not significantly different in men and women (26 +/- 12 vs. 23 +/- 12%, ml.min-1.kg-1; 21 +/- 10 vs 19 +/- 10%, l/min). When subjects were divided into three groups by age (60-62, 63-66, 67-71 yr), there were no significant differences among the groups in the relative increase in VO2max (21% vs. 19% vs. 18%, 1/min). Correlation analysis also yielded a nonsignificant relationship between improvement and age (r = -0.13). To examine the effect of initial fitness level on the adaptive response to exercise, pretraining VO2max was correlated with the absolute improvement in VO2max. This relationship was not significant in either men (r = 0.04) or women (r = -0.23). In conclusion, in healthy people aged 60-71 yr, VO2max adapts to endurance exercise training to the same relative extent as in young people, and this adaptation is independent of gender, age, and initial level of fitness.

Adaptation, Physiological↗
PubMed1991

Effects of aging, gender, and physical training on peripheral vascular function.

BACKGROUND: Blood pressure and total peripheral resistance increase with age. However, the effect of age on vasodilatory capacity has not been characterized. METHODS AND RESULTS: To delineate the effects of aging, gender, and physical training on peripheral vascular function, we measured blood pressure during submaximal and maximal treadmill exercise and measured blood pressure, calf blood flow, and calf conductance (blood flow/mean blood pressure) at rest and during maximal hyperemia in 58 healthy sedentary subjects (men aged 25 +/- 5 and 65 +/- 3 years and women aged 27 +/- 5 and 65 +/- 4 years) and in 52 endurance exercise-trained subjects (men aged 30 +/- 3 and 65 +/- 4 years and women aged 27 +/- 3 and 65 +/- 3 years). Systolic and mean blood pressures were higher at rest, during maximal calf hyperemia, and during submaximal exercise of the same intensity in the older than in the younger subjects of the same gender and exercise training status (p less than 0.01). The magnitude of the age-related effect on blood pressure during exercise was greater in women than in men (p less than 0.01). Diastolic blood pressure during submaximal exercise was also higher in the older than in the younger subjects (p less than 0.05) but not in women treated with estrogen replacement. In contrast, systolic and mean blood pressures during submaximal work were lower in physically conditioned subjects than in sedentary age- and gender-matched subjects (p less than 0.05) but not in older women. Increased age was associated with reduced maximal calf conductance in women (p less than 0.01) but not in men. However, calf vasodilatory capacity was higher in trained than in untrained subjects (p less than 0.01), regardless of age and gender. There was a significant inverse relation between maximal calf conductance and systolic, diastolic, and mean blood pressures during submaximal exercise (r = -0.31 to -0.53, p less than 0.01) and a direct relation between maximal calf conductance and maximal oxygen uptake (r = 0.66, p less than 0.0001). CONCLUSIONS: Thus, for healthy subjects between the ages of 25 and 65 years, there is an interactive effect between age and gender and an independent effect of physical training on peripheral vascular function.

Adult↗
PubMed1990

The ratio of waist-to-hip circumference, plasma insulin level, and glucose intolerance as independent predictors of the HDL2 cholesterol level in older adults.

High plasma levels of HDL2, a subfraction of high-density lipoprotein (HDL) cholesterol, are associated with a reduced risk of coronary heart disease. To investigate the characteristics related to HDL2 cholesterol levels, we measured lipoprotein levels and several metabolic and anthropometric variables in 146 healthy subjects (77 men and 69 women) in the seventh decade of life. The level of HDL2 cholesterol was inversely correlated with the ratio of the waist-to-hip circumference (r = -0.335 for men; r = -0.370 for women; P less than 0.01) and the plasma insulin level (r = -0.400 for men; r = -0.398 for women; P less than 0.001). In a multiple regression model including both sexes, 41 percent of the variance in the HDL2 level was explained by the combined effect of the waist-to-hip ratio (P less than 0.0001), the plasma insulin level (P = 0.0003), and the degree of glucose tolerance indicated by the integrated area under the plasma glucose curve after an oral glucose-tolerance test (P = 0.05). The body-mass index, total percentage of body fat, maximal oxygen uptake, diet, and sex were not significant predictors of the HDL2 level when added to this model, whereas the original variables remained significant predictors. The HDL2 cholesterol level in subjects at the 25th percentile for waist-to-hip ratio was 153 percent of that in subjects at the 75th percentile. We conclude that HDL2 levels are inversely correlated with truncal fat, plasma insulin levels, and the presence of glucose intolerance and are not independently associated with sex or total body fat.

Abdomen↗
PubMed1990

Insulin secretory capacity in endurance-trained and untrained young men.

Insulin secretion in response to glucose stimulation is reduced in endurance-trained humans. In this study, a modified hyperglycemic clamp, with a superimposed arginine infusion and fat meal, was performed on eight endurance-trained and nine untrained men to determine whether insulin secretory capacity is reduced by exercise training. Raising the plasma glucose concentration to approximately 450 mg/dl resulted in a plasma insulin response in the trained men that was approximately 64% lower than that of the untrained (peak values: 54 +/- 8 vs. 149 +/- 35 microU/ml; P less than 0.001). When a primed continuous infusion of arginine was superimposed on the hyperglycemia, the plasma insulin response was also markedly lower (66%) in the trained subjects, reaching peak values of 333 +/- 68 and 974 +/- 188 microU/ml for trained and untrained subjects, respectively (P less than 0.005). When insulin secretion was further stimulated during the arginine-infused hyperglycemia by the ingestion of a high-fat meal, peak insulin concentrations averaged 989 +/- 205 microU/ml in the trained compared with 2,232 +/- 455 microU/ml in the untrained subjects (P less than 0.01). The response of gastric inhibitory polypeptide (GIP) to the fat meal was delayed and blunted, suggesting that some enteric factor(s) other than GIP mediated the insulinotropic effect of the fat meal. The reduced plasma insulin response in trained people to the stimuli investigated suggests that regular exercise produces either several adaptations within the beta-cell or a single alteration of the beta-cell that results in an attenuation of the insulin secretory response to glucose, arginine, and fat ingestion.

Adult↗