Resistance Training Threshold for Elevating Bone Mineral Density in Growing Female Rats

The purpose of this study was to determine the minimum amount of resistance exercise that would stimulate bone formation yielding an elevation in bone mineral density (BMD) during the growth period in female rats. Female rats were randomly divided into: Control (Con, n=8), 3 ladder climb resistance-trained group (3LC, n=8), 4 ladder climb resistance-trained group (4LC, n=8), 5 ladder climb resistance-trained group (5LC, n=8), and 6 ladder climb resistance-trained group (6LC, n=8). All exercised groups were conditioned to climb a vertical ladder with weights appended to their tail 3 days/wk for a total of 6 wks. After 6 wks, left tibia BMD (g/cm²) was significantly greater for 4LC (0.197±0.003), 5LC (0.200±0.004) and 6LC (0.202±0.003) when compared to Con (0.185±0.006). Left femur BMD (g/cm²) was significantly greater for 4LC (0.260±0.005), 5LC (0.269±0.004) and 6LC (0.272±0.006) when compared to Con (0.244±0.006). There were no significant differences in tibia and femur BMD between 4LC, 5LC, and 6LC groups. The results suggest that during growth, a high volume of resistance exercise was required to elicit an elevation in BMD in females.

Better cognitive control of emotional information is associated with reduced pro-inflammatory cytokine reactivity to emotional stress

Stress is strongly associated with several mental and physical health problems that involve inflammation, including asthma, cardiovascular disease, certain types of cancer, and depression. It has been hypothesized that better cognitive control of emotional information may lead to reduced inflammatory reactivity to stress and thus better health, but to date no studies have examined whether differences in cognitive control predict pro-inflammatory cytokine responses to stress. To address this issue, we conducted a laboratory-based experimental study in which we randomly assigned healthy young-adult females to either an acute emotional stress (emotionally evocative video) or no-stress (control video) condition. Salivary levels of the key pro-inflammatory cytokines IL-1β, IL-6, and IL-8 were measured before and after the experimental manipulation, and following the last cytokine sample, we assessed participants' cognitive control of emotional information using an emotional Stroop task. We also assessed participants' cortisol levels before and after the manipulation to verify that documented effects were specific to cytokines and not simply due to increased nonwater salivary output. As hypothesized, the emotional stressor triggered significant increases in IL-1β, IL-6, and IL-8. Moreover, even in fully adjusted models, better cognitive control following the emotional (but not control) video predicted less pronounced cytokine responses to that stressor. In contrast, no effects were observed for cortisol. These data thus indicate that better cognitive control specifically following an emotional stressor is uniquely associated with less pronounced pro-inflammatory cytokine reactivity to such stress. These findings may therefore help explain why superior cognitive control portends better health over the lifespan.

Training-induced Increase in Bone Mineral Density between Growing Male and Female Rats

The purpose of this study was to determine the existence of sex differences in the resistance training-induced elevation in bone mineral density (BMD) and bone strength (Fmax) during the growth period in rats. 16 male (M) and 16 female (F) rats (approx. 8 weeks old) were randomly divided into sedentary control (MC=8, FC=8), and resistance-trained (RT) groups (M-RT=8, F-RT=8). The RT groups were conditioned to climb a vertical ladder 4 consecutive times (per exercise session) with weights attached to their tail 3 days per week for a total of 6 weeks. After 6 weeks, there were no interaction effects (sex×exercise). The main effect of sex indicated no difference in tibial BMD (in g/cm(2)) for males (0.226±0.005) compared to females (0.221±0.004). However, Fmax (in Newtons) was significantly greater for males (131.3±5.3) compared to females (89.9±3.0). The main effect of exercise indicated that tibial BMD and Fmax were significantly greater for RT groups (0.234±0.004 g/cm(2) and 120.9±7.4 Newtons) compared to controls (0.212±0.003 g/cm(2) and 100.3±5.1 Newtons). The results indicate that during growth, there were no sex differences in the training-induced elevation in BMD and bone mechanical properties.

Prevalence of vitamin D3 deficiency in orange county residents

With the prevalence of sunlight exposure in Orange County, California, one would expect it to be rare and unusual to find high incidence of Vitamin D deficiencies among its residents. This study evaluated the concentration of Vitamin D3 as part of a larger study to evaluate bone health in Orange County residents. Our preliminary data shows that 19.2% of the 151 subjects evaluated had low Vitamin D3 (<30 pg/ml) and illuminates a growing problem in the United States. We speculate that the widespread sensitivity to skin cancer and sun exposure, the increased use of sun-screens and the filtering of UV waves in automobile glass has put the public at risk for low Vitamin D.

Equal BMD after daily or triweekly exercise in growing rats

The purpose of this study was to examine the efficacy of continuous resistance training (3 days/wk) compared to interrupted resistance training where 20-24 h separated an exercise bout (i. e. 6 days/wk) for enhancing bone mineral density (BMD) in growing male rats. The total volume of work performed per week between the two resistance training programs was equivalent by design. Young male rats were randomly divided into Control (Con, n=9), 3 days/wk resistance trained group (RT3, n=9), and 6 days/wk resistance trained group (RT6, n=9). The RT3 and RT6 groups were conditioned to climb a vertical ladder with weights appended to their tail for a total of 6 wks. After 6 wks, BMD (assessed via DXA) from the left tibia was significantly greater for RT3 (0.242+/-0.004 g/cm (2)) and RT6 (0.244+/-0.004 g/cm (2)) compared to Con (0.226+/-0.003 g/cm (2)). Further, serum osteocalcin (oc, in ng/ml) was significantly greater for RT3 (75.8+/-4.4) and RT6 (73.5+/-3.8) compared to Con (53.4+/-2.4). There was no significant difference in BMD or serum OC between RT3 and RT6 groups. The results indicate that both resistance training programs were equally effective in elevating bone mineral density in young, growing rats.

Interrupted resistance training and BMD in growing rats

A resistance training program, where the exercise was uninterrupted (UT, i.e. continuous repetitions) was compared against another resistance training program where the exercise was interrupted (IT, i.e. 2 exercise sessions during a training day) for enhancing bone modeling and bone mineral density (BMD) in maturating animals. The total volume of work performed between the two resistance training programs was equivalent by design. Young male rats (approximately 8 weeks old) were randomly divided into Control (Con, n=8), UT (n=8) and IT (n=7) resistance trained groups. The UT and IT groups were conditioned to climb a vertical ladder with weights appended to their tail 3 days/week for 6 weeks. After the 6 week training regimen (Mean+/-SD), tibial BMD (assessed via DXA) was significantly greater for UT (0.237+/-0.008 g/cm(2)) and IT (0.238+/-0.005 g/cm(2)) compared to Con (0.223+/-0.004 g/cm(2)). Further, serum osteocalcin (OC) was significantly greater for UT (45.65+/-2.83 ng/ml) and IT (46.33+/-4.60 ng/ml) compared to Con (37.86+/-4.04 ng/ml). There was no significant difference in BMD or serum OC between UT and IT groups. The results indicate that both resistance training programs were equally effective in elevating BMD in growing animals.

Sex differences in hepatic gluconeogenic capacity after chronic alcohol consumption

Alcohol-induced hypoglycemia has traditionally been attributed to the amount of ethanol consumed rather than any inherent decline in glucose output capacity by the gluconeogenic organs and/or an increase in skeletal muscle glucose uptake. Further, while the potential for sex differences that might impact glucose homeostasis following chronic alcohol consumption has been recognized, direct evidence has been noticeably absent. This paper will provide a brief review of past and present reports of the potential for sex differences in glucose homeostasis following chronic ethanol consumption. This paper will also provide direct evidence from our laboratory demonstrating sex differences from chronic alcohol consumption resulting in a decrement in glucose appearance and more importantly, a specific decline in hepatic gluconeogenic (HGN) capacity in the absence and presence of ethanol. All our studies involved 8 weeks of chronic alcohol consumption in male and female Wistar rats, as well as a 24 to 48 hour fast to deplete hepatic glycogen stores. Under the conditions of chronic alcohol consumption and an acute dose of ethanol, we provide in vivo evidence of an early decline in whole body glucose appearance in females fed an ethanol diet compared to controls. While the decline was also observed in males fed the alcohol diet, it occurred much later compared to ethanol fed females. The site for the decline in whole body glucose production (i.e., either the kidneys or the liver) was beyond the scope of our prior in vivo study. In a follow-up study using the in situ perfused liver preparation, we provide additional evidence for a specific reduction in HGN capacity from lactate in ethanol fed females compared to ethanol fed males in the absence of alcohol in the perfusion medium. Finally, employing the isolated hepatocyte technique, we report decrements in HGN from lactate in ethanol fed females compared to ethanol fed males in the presence of ethanol in the incubation medium. The mechanism for the specific decline in HGN within the liver of ethanol fed females remains to be determined. To the extent that our observations in animals can be extrapolated to humans, we conclude that alcoholic women are more susceptible to ethanol-induced hypoglycemia compared to alcoholic men.

Resistance training and bone mineral density during growth

This study examined the efficacy of two different resistance training programs in enhancing bone modeling and bone mineral density (BMD) in maturating rats. One exercise mode involved lifting a lighter weight with more repetitions (LI), while the other regimen involved lifting a heavier weight with fewer repetitions (HI) where the total volume of work between exercise programs was equivalent by design. Twenty-three male rats were randomly divided into control (Con, n = 8), LI (n = 7), and HI (n = 8) groups. The LI and HI groups were conditioned to climb a vertical ladder with weights appended to their tail 4 days/wk for 6 wks. After training, serum osteocalcin (OC) was significantly (p < 0.05) higher in both HI (45.2 +/- 1.7 ng/ml) and LI (39.1 +/- 2.2 ng/ml) when compared to Con (29.9 +/- 0.9 ng/ml). Left tibial BMD was significantly (p < 0.05) greater for HI (0.231 +/- 0.004 g/cm (2)) when compared to both LI (0.213 +/- 0.003 g/cm (2)) and Con (0.206 +/- 0.005 g/cm (2)) with no significant difference between LI and Con. The results indicate that both HI and LI are effective in elevating serum OC, implicating an osteogenic response; however, only HI resulted in a significant elevation in BMD.

Alcohol-induced suppression of gluconeogenesis is greater in ethanol fed female rat hepatocytes than males

The impact of alcohol-induced suppression on hepatic gluconeogenesis (HGN) after chronic ethanol consumption between males and females is unknown. To determine the effects of chronic alcohol consumption (8 weeks) on HGN, the isolated hepatocyte technique was used on 24 h fasted male and female Wistar rats. Livers were initially perfused with collagenase and the hepatocytes were isolated. Aliquots of the cell suspension were placed in Krebs-Henseleit buffer and incubated for 30 min with lactate, [U -14C]lactate, and nine different concentrations of ethanol (EtOH). Dose-effect curves were generated for the determination of maximal and half-maximal alcohol-induced inhibition on HGN. There was no significant difference in HGN (lactate only and no EtOH) between males and females fed the control diet (88.5 +/- 5.1 nmol/mg protein/30 min). Similarly, the HGN (lactate only and no EtOH) in males fed the ethanol diet (ME) were not significantly different (82.8 +/- 3.5 nmol/mg protein/30 min) compared to controls. In contrast, the females chronically fed the ethanol diet (FE) had significantly (P < .05) lower HGN (67.8 +/- 4.6 nmol/mg protein/30 min) compared to both ME and controls. With alcohol in the incubation medium, the HGN significantly (P<.05) declined in all groups. While alcohol suppressed HGN to a larger (P < .05) extent in ME (45.8 +/- 3.7 nmol/mg protein/30 min) compared to controls (64.0 +/- 3.8 nmol/mg protein/30 min), the inhibition was even greater (P < .05) in FE (32.7 +/- 3.2 nmol/mg protein/30 min). The more pronounced effect of chronic alcohol consumption on HGN in the presence of ethanol in female hepatocytes was supported by the concomitant decreases (P < .05) in 14C-lactate incorporation into 14C-glucose, lactate uptake, and 14C-lactate uptake. The results suggest that chronic alcohol consumption elicits a greater reduction on HGN in the presence of ethanol in the hepatocytes of females compared to males.

Lactate delivery (not oxygen) limits hepatic gluconeogenesis when blood flow is reduced

The purpose of this study was to determine, using the isolated liver perfusion technique, whether the limiting factor for hepatic gluconeogenesis (GNG) from lactate was precursor delivery or oxygen availability during reduced flow rates of 0.85 or 0.60 ml.min(-1).g liver(-1). After a 24-h fast, three different experimental protocols were employed. Protocol 1 examined the impact on GNG when reservoir lactate concentration was maintained but oxygen delivery was elevated via increases in hematocrit (Hct). Elevating the Hct from 22.5+/- 0.8% to 30.9+/- 0.4% at a blood flow of 0.89+/- 0.01 ml.min(-1).g liver(-1) increased the oxygen consumption (Vo(2)) but did not augment GNG. Similarly, when the Hct was elevated from 22.5+/- 0.8% to 41.5+/- 0.7% at 0.59+/- 0.04 ml.min(-1).g liver(-1), Vo(2) was increased, but GNG was unaffected. Protocol 2 examined the impact on GNG when Hct was maintained but precursor delivery was elevated via increases in reservoir lactate concentration ([LA]). Specifically, elevating the [LA] from 2.31+/- 0.07 to 3.61+/- 0.33 mM at a flow rate of 0.82+/- 0.04 ml.min(-1).g liver(-1) significantly increased GNG. Similarly, elevating the [LA] from 2.31+/- 0.07 to 4.24+/- 0.37 mM at a flow rate of 0.58+/- 0.02 ml.min(-1).g liver(-1) increased GNG. Finally, we examined the impact of increasing both the oxygen and lactate delivery (Protocol 3). Again, Vo(2) was elevated with increased oxygen delivery, but GNG was not augmented beyond that observed with elevations in lactate delivery alone, i.e., Protocol 2. The results indicate that, during decrements in blood flow, GNG is limited primarily by precursor delivery, not oxygen availability.

Impact of flow rate on lactate uptake and gluconeogenesis in glucagon-stimulated perfused livers

The impact of reduced hepatic flow on lactate uptake and gluconeogenesis was examined in isolated glucagon-stimulated perfused livers from 24-h-fasted rats. After surgical isolation, livers were perfused (single pass) for 30 min with Krebs-Henseleit (KH) bicarbonate buffer, fresh bovine erythrocytes (hematocrit approximately 20%), and no added substrate. After this "washout" period, steady-state perfusions were initiated with a second reservoir containing the KH buffer, bovine erythrocytes, [U-(14)C]lactate (10,000 dpm/ml), lactate (2.5 mM), and glucagon (250 microg/ml). Perfusion flow rate was adjusted to one of five rates (i.e., 1.8, 2.7, 3.9, 7.4, and 11.0 ml.min(-1).100 g body wt(-1)). After the perfusion, the liver was dissected out and weighed so as to establish the actual flow rate per gram of liver. The resulting flow rates ranged from 0.52 to 4.03 ml.min(-1).g liver(-1). As a function of flow rate, lactate uptake rose in a hyperbolic fashion to an apparent plateau of 2.34 micromol.min(-1).g liver(-1). Fractional extraction (FX) of lactate from the perfusate demonstrated an exponential decline with increased flow rates (r=0.97). At flow rates above 1.0 ml.min(-1).g liver(-1), adjustments in FX compensated for changes in lactate delivery, resulting in steady rates of lactate uptake and gluconeogenesis. Below 1.0.min(-1).g liver(-1) the increased FX was unable to compensate for the decline in lactate delivery and lactate uptake declined rapidly. Gluconeogenesis demonstrated similar kinetics to lactate uptake, reflecting its dominant role among pathways for lactate removal under the current conditions.

Opposing effects of chronic alcohol consumption on hepatic gluconeogenesis for female versus male rats

BACKGROUND

The impact of chronic alcohol consumption on hepatic gluconeogenesis (HGN) between males and females is unknown. To determine the effects of chronic alcohol consumption (8 weeks) on HGN, the isolated liver perfusion technique was used on 24-hr-fasted male and female Wistar rats.

METHODS

After surgical isolation, livers were perfused (single pass) for 30 min with Krebs-Henseleit bicarbonate buffer and fresh bovine erythrocytes with no added substrate (washout period). After the washout period, livers were perfused with lactate (10 mM) and [U-14C]lactate (15,000 dpm/ml) using the recirculation method.

RESULTS

There was no significant difference in HGN between males and females fed the control diet. In contrast, the females chronically fed the ethanol diet (FE) had significantly lower HGN rates (2.73 +/- 0.37 micromol/min x g liver protein(-1)), whereas males fed the ethanol diet (ME) had significantly higher HGN rates (4.99 +/- 0.45 micromol/min x g liver protein(-1)) than controls (3.83 +/- 0.34 micromol/min x g liver protein(-1)). Concomitant decreases were also observed for both 14C-lactate incorporation into 14C-glucose and rates of lactate uptake for FE, while corresponding increases were observed for 14C-lactate incorporation into 14C-glucose for ME. The livers from ME were able to convert a greater percentage of the lactate into glucose, resulting in the elevation in gluconeogenic capacity.

CONCLUSION

Chronic alcohol consumption lowers the hepatic gluconeogenic capacity from lactate in females and elevates HGN in males.

Differential effects of alcohol upon gluconeogenesis from lactate in young and old hepatocytes

The purpose of this study was to determine the effect of age upon hepatic gluconeogenesis (HGN) from lactate in the presence of various concentrations of alcohol from young (3 months) and old (24 months) male rats. After a 24-hour fast, livers were perfused with collagenase and the hepatocytes were isolated. Aliquots of the cell suspension were placed in Krebs-Henseleit buffer and incubated with lactate, [U-(14)C]lactate, and nine different concentrations of ethanol (EtOH) for 30 min. Dose-effect curves were generated for the determination of maximal and half-maximal alcohol-induced inhibition on gluconeogenesis. There were no significant differences in basal HGN (lactate only and no EtOH) between young and old hepatocytes, 86.9+/-6.3 nmol/mg protein/30 min. The addition of ethanol significantly reduced HGN from lactate in both groups. At the highest ethanol concentration (15 mM), the glucose production was inhibited more from old, 46.1+/-1.2 nmol/mg protein/30 min, compared to young hepatocytes, 56.0+/-1.6 nmol/mg protein/30 min. The greater age-related reduction in HGN was confirmed by the minimal glycogenolysis, and the concomitant decline in [U-(14)C]glucose production, lactate uptake, and [U-(14)C]lactate uptake. The results suggest that alcohol elicits a greater inhibition upon HGN from lactate in old compared to young liver cells.

Chronic alcohol consumption yields sex differences in whole-body glucose production in rats

AIMS

The effects of chronic alcohol consumption (8 weeks) on glucose kinetics, in the absence (water, 4 g/kg) and presence of an acute ethanol dose (4 g/kg), were examined in 48 h fasted male and female Wistar rats.

METHODS

Primed continuous infusions of [6-3H]- and [U-14C]glucose were employed to assess rates of glucose appearance (Ra), glucose disappearance (Rd), and apparent glucose carbon recycling.

RESULTS

After injecting the male and female controls with water, there were no significant alterations in glucose kinetics. Compared to controls, chronic alcohol-fed female animals (injected with water) demonstrated significantly lower: glucose Ra, blood glucose concentration, and apparent glucose carbon recycling for a majority of the experimental period. In separate groups injected with ethanol, the glucose Ra fell by 31% for male rats fed the control diet (MC), 43% for male rats fed the ethanol diet (ME), 29% for female rats fed the control diet (FC), and 42% for female rats fed the ethanol diet (FE). Further, compared to controls (MC and FC), the blood glucose concentration was significantly lower prior to and following the ethanol injection for FE. In addition, FE animals had significantly lower rates of glucose Ra and glucose carbon recycling compared to controls prior to and after the ethanol injection. ME animals demonstrated similar declines in glucose Ra (compared to FE), but only after the ethanol injection. Conversely, ME were able to match the decrease in glucose Ra with comparable declines in glucose Rd resulting in blood glucose concentrations that did not differ from controls.

CONCLUSIONS

Chronic alcohol consumption results in sex differences in whole-body glucose production and glucose regulation.

Effect of endurance training and fasting on renal gluconeogenic enzymes in the rat

The purpose of this study was to examine the effects of chronic exercise training (running 30 m/min, 10% grade, 90 min/d for 8-10 weeks) on specific renal enzyme activities involved with the gluconeogenic pathway in the fed and 24-hr fasted state in rats. A portion of the kidney (containing the cortex and medulla) was homogenized from which cytosolic (c) and mitochondrial (m) fractions were separated. Maximal gluconeogenic enzyme activities were assessed for: phosphoenolpyruvate carboxykinase (cPEPCK), fructose 1,6-bisphosphatase (cFBP), pyruvate carboxylase (mPC), aspartate aminotransferase (cAspAT), alanine aminotransferase (cAlaAT), and lactate dehydrogenase (cLDH). In the fed state, there was no significant difference between groups in any of the enzymes examined (nmoles/min x mg protein-1): cPEPCK (25.8+/- 1.7), cFBP (106.8+/- 7.1), mPC (20.7+/- 1.8), cAspAT (1047.1 +/- 38.6), cAlaAT (52.3 +/- 4.3), and cLDH (1728.6+/- 163.2). After the 24-hr fast, there was a significant increase in cPEPCK (52.4+/- 2.9 and 52.0 +/- 2.1) and mPC (44.6 +/- 4.3 and 47.6 +/- 4.9), control and trained, respectively. These results suggest that the maximal enzyme activities for cPEPCK and mPC can be augmented as a result of fasting that was independent of the training status.

Effect of age and endurance training on the capacity for epinephrine-stimulated gluconeogenesis in rat hepatocytes

The effects of endurance training on hepatic glucose production (HGP) from lactate were examined in 24-h-fasted young (4 mo) and old (24 mo) male Fischer 344 rats by using the isolated-hepatocyte technique. The liver cells were incubated for 30 min with 5 mM lactate ([U-14C]lactate; 25000 dpm/ml) and nine different concentrations of epinephrine (Epi). Basal HGP (with lactate only and no Epi) was significantly greater for young trained (T) (99.6 +/- 6.2 nmol/mg protein) compared with young controls (C) (78.2 +/- 6.0 nmol/mg protein). The basal HGP was also significantly greater for old T (97.3 +/- 5.9 nmol/mg protein) compared with old C (72.2 +/- 3.9 nmol/mg protein). After the incubation with the various concentrations of Epi, Hanes-Woolf plots were generated to determine kinetic constants (Vmax and EC50). Maximal Epi-stimulated hepatic glucose production (Vmax) was significantly greater for young T (142.5 +/- 6.5 nmol/mg protein) compared with young C (110.9 +/- 4.8 nmol/mg protein). Similarly, the Vmax was significantly greater for old T (138.2 +/- 5.0 nmol/mg protein) compared with old C (103.9 +/- 2.5 nmol/mg protein). Finally, there was an increase in the EC50 from the hepatocytes of old T (56.2 +/- 6.2 nM) compared with young T (32.6 +/- 4.9 nM). In like manner, there was an increase in the EC50 from the hepatocytes of old C (59.7 +/- 5.8 nM) compared with young C (33.1 +/- 2.7 nM). The results suggest that training elevates HGP in the basal and maximally Epi-stimulated condition, but with age there is a decline in EC50 that is independent of training status.

Hepatic gluconeogenic capacity from various precursors in young versus old rats

Hepatic gluconeogenic capacity was studied in young (4 months of age) and old (24 months of age) male Fischer 344 rats fasted for 24 hours using the isolated hepatocyte technique. Following the isolation of liver cells, the following precursors were added to the cell suspensions and incubated for 30 minutes: lactate (5 mmol/L), pyruvate (5 mmol/L), alanine (5 mmol/L), glutamine (5 mmol/L), oxaloacetate (5 mmol/L), glycerol (5 mmol/L), dihydroxyacetone (10 mmol/L), fructose (10 mmol/L), or saline (no precursor addition). To confirm that glucose production reflects gluconeogenic capacity, there was significant depletion of hepatic glycogen after the 24-hour fast and minimal alterations in glycogen content once substrates were added. Adjusting the gluconeogenic rates to reflect 100% cell viability resulted in no difference between young and old animals for any substrate used with the sole exception of fructose. The hepatic glucose production from fructose was 34% greater for young versus old animals. The results suggest that following a period of starvation the basal glucose production rates from hepatocytes, incubated with precursors entering the gluconeogenic pathway prior to fructose-6-phosphate, are equivalent in young and old rats.

Lactate removal is not enhanced in nonstimulated perfused skeletal muscle after endurance training

The effects of endurance training (running 40 m/min grade for 60 min, 5 days/wk for 8 wk) on skeletal muscle lactate removal was studied in rats by utilizing the isolated hindlimb perfusion technique. Hindlimbs were perfused (single-pass) with Krebs-Henseleit bicarbonate buffer, fresh bovine erythrocytes (hematocrit approximately 30%), 10 mM lactate, and [U-14C]lactate (30,000 dpm/ml). Arterial and venous blood samples were collected every 10 min for the duration of the experiment to assess lactate uptake. During perfusions, no significant differences in skeletal muscle lactate uptake were observed between trained (7.31 +/- 0.20 micromol/min) and control hindlimbs (6.98 +/- 0.43 micromol/min). In support, no significant differences were observed for [14C]lactate uptake in trained (22,776 +/- 370 dpm/min) compared with control hindlimbs (21,924 +/- 1,373 dpm/min). Concomitant with these observations, no significant differences were observed between groups for oxygen consumption (4.93 +/- 0.18 vs. 4.92 +/- 0.13 micromol/min), net skeletal muscle glycogen synthesis (7.1 +/- 0.4 vs. 6.5 +/- 0.3 micromol x 40 min(-1) x g(-1)), or 14CO2 production (2,203 +/- 185 vs. 2,098 +/- 155 dpm/min), trained and control, respectively. These findings indicate that endurance training does not affect lactate uptake or alter the metabolic fate of lactate in quiescent skeletal muscle.

Strength training does not alter the effects of testosterone propionate injections on high-density lipoprotein cholesterol concentrations

The purpose of the study was to examine the long-term effects of a high-volume strength training program (vertical ladder climbing) and testosterone propionate injections (intraperitoneal) on serum lipid and lipoprotein concentrations in male Sprague-Dawley rats. The animals were randomly divided into a testosterone (T)-treated group (dose per injection, 2.5 mg/kg testosterone propionate solubilized in 1 mL safflower oil) and a control (C) group (injected with an isovolumic amount of safflower oil alone). Animals were further divided into a strength-trained group (E) and a sedentary group (S). The 10-week resistance training program consisted of weights (100% of body mass) appended to the tail as the animal climbed an 85-cm ladder to volitional fatigue. Following 10 weeks of strength training and testosterone injections, body weight was not significantly different between the main effects of strength training exercise (TE + CE v TS + CS) and testosterone injections (TE + TS v CE + CS) or between groups. Testicular mass (mean +/- SE) was measured as a relative indicator of testosterone effects. Both TE and TS had significantly reduced testicular mass (2.56 +/- 0.04 and 2.38 +/- 0.03 g, respectively) compared with CE and CS (3.49 +/- 0.03 and 3.49 +/- 0.04 g, respectively). No significant differences were observed between groups for total serum cholesterol, serum triglycerides, or serum low-density lipoprotein cholesterol (LDL-C). In contrast, significant decreases in high-density lipoprotein cholesterol (HDL-C) were observed for both TE (26.7 +/- 1.6 mg/dL) and TS (27.5 +/- 1.3 mg/dL) compared with CE (48.7 +/- 2.9 mg/dL) and CS (43.5 +/- 2.6 mg/dL). As a result, the total cholesterol to HDL-C ratio was significantly greater for TS + TE (4.7 +/- 0.1) compared with CS + CE (2.9 +/- 0.2). These observations suggest that in animals, a 10-week program of high-volume strength training does not elicit any beneficial effect on the lipid or lipoprotein status, nor does it attenuate the altered lipoprotein profile induced by testosterone propionate injections.

Temporal effects of testosterone propionate injections on serum lipoprotein concentrations in rats

The chronic abuse of androgenic anabolic steroids, a group of synthetic derivatives of testosterone, to improve athletic performance have demonstrated compromised serum lipoprotein concentrations reflecting an elevated risk for cardiovascular disease. While the detrimental alterations in the lipoprotein profile have been reported consistently for orally administered androgenic anabolic steroids, the reports examining the effects of parenteral administration of testosterone upon the lipid profile remain equivocal.

PURPOSE

The purpose of this study was to determine whether compromised serum lipoprotein concentrations would be manifest in rats receiving testosterone injections (twice per week) over the time course of 7 wk.

METHODS

Male rats were randomly assigned to either an experimental group (dose per injection, 3 mg x kg(-1) testosterone propionate solubilized in 1 mL of safflower oil) or a control group (injected with an isovolumic amount of safflower oil alone). The effects of the steroid regimen on the serum lipoprotein profiles were followed after 1, 3, 5, and 7 wk of injections. To assess the relative effects of testosterone propionate, testicular mass was determined at the time of sacrifice.

RESULTS

Testicular mass (mean +/- SE) was significantly lower (P<0.01) in the experimental group, 3.08+/-0.03 g, compared with that in controls, 3.82+/-0.05 g, by week 3 and continued to decline for the remainder of the steroid regimen, reaching a nadir of 2.70+/-0.01 g at week 5. No significant differences were observed between groups for total serum cholesterol, serum triacylglycerols, or serum low density lipoprotein (LDL)-C at any time point. However, at week 7, serum high density lipoprotein (HDL)-C (mean +/- SE) was significantly lower (P<0.02) in the testosterone treated animals, 32+/-2 mg x dL(-1), compared with that in controls, 47+/-2 mg x dL(-1). As a result, the ratio of total cholesterol to HDL-C (mean +/- SE) significantly increased (P<0.02) by the seventh week in the testosterone treated group, 3.5+/-0.2, versus controls, 2.5+/-0.2.

CONCLUSIONS

The results suggest that while testosterone propionate injections elicit a reduction in testicular mass within 3 wk, the lipoprotein profile is not altered until week 7. Further, the only compromised parameter under the conditions of this study is the decrease in serum HDL-C.

Training enhanced hepatic gluconeogenesis: the importance for glucose homeostasis during exercise

Endurance training has long been known to improve the individual's resistance to exercise-induced hypoglycemia. Traditionally attributed to a reduction in glucose uptake subsequent to enhanced fat oxidation, this issue has only recently been directly addressed. This paper briefly reviews the evidence for reduced glucose uptake versus enhanced glucose production in the improved hypoglycemic resistance following training. While whole body glucose removal and production may be reduced following training, this has only been demonstrated under exercising conditions in which glycemia demonstrates little deviation from rest. Under exercise conditions where untrained animals demonstrate substantial reductions in blood glucose, training enhanced hypoglycemic resistance has been shown to result entirely from enhanced glucose production via gluconeogenesis. Using the in situ perfused liver preparation, the authors have provided direct evidence for a training enhanced hepatic gluconeogenic capacity. The site of adaptation within the gluconeogenic pathway has now been constrained to below the level of the triose phosphates. Lack of evidence for suppressed skeletal muscle glucose uptake following training, a uniform observation for humans and rats, is also discussed. It is concluded that the improved hepatic gluconeogenic capacity of endurance trained individuals, at least in rats, is critical to their demonstrated resistance to exercise-induced hypoglycemia.

Enhanced hepatic gluconeogenic capacity for selected precursors after endurance training

The effects of endurance training (running 90 min/day, 30 m/min, approximately 10% grade) on hepatic gluconeogenesis were studied in 24-h-fasted rats by using the isolated liver perfusion technique. After isolation, livers were perfused (single pass) for 30 min with Krebs-Henseleit bicarbonate buffer and fresh bovine red blood cells (hematocrit 20-24%) with no added substrate. Alanine (10 mM), dihydroxyacetone (20 mM), or glutamine (10 mM) was then added to the reservoir, and perfusions continued for 60 min. No significant differences were observed in perfusate pH, hematocrit, bile production, or serum alanine aminotransferase effluxing from livers from trained or control animals for any perfusion. Livers from trained animals that were perfused with 10 mM alanine demonstrated significantly higher rates of glucose production compared with livers from control animals (0.51 +/- 0.04 vs. 0.40 +/- 0.02 micromol.min-1.g liver-1, respectively). Elevations of a similar magnitude were observed for rates of [14C]alanine incorporation into [14C]glucose in livers from trained vs. control animals (8,797 +/- 728 vs. 6,962 +/- 649 dpm.min-1.g liver-1, respectively). Significant increases were also observed in hepatic alanine uptake (30%), oxygen consumption (23%), urea release (22%), and 14CO2 production (29%) of livers of endurance-trained animals. In contrast, no significant differences between groups were observed for hepatic glucose output after perfusions with either dihydroxyacetone (1.75 +/- 0.06 micromol.min-1.g liver-1) or glutamine (0.62 +/- 0.04 micromol.min-1.g liver-1). Further, during perfusions with dihydroxyacetone and glutamine, training had no significant impact on precursor uptake, oxygen consumption, or urea output. The current findings indicate a training-induced adaptation for hepatic gluconeogenesis located below the level of the triose phosphates.

Training suppresses hepatic lactate dehydrogenase activity without altering the isoenzyme profile

A decrease in hepatic lactate dehydrogenase (LDH) activity following endurance training has been a consistent observation. In the present study, we sought to determine whether the training-induced decrease in hepatic LDH activity (pyruvate = substrate) was associated with a shift in the isoenzyme profile and/or alteration in other kinetic parameters. Animals (rats) were randomly assigned to either an endurance trained group (running 90 min at 30 m.min-1, 10% grade) or sedentary control group. Eight weeks of endurance training resulted in a significant decrease in maximal hepatic LDH activity for the forward reaction (pyruvate-->lactate), 107.3 +/- 5.5 mumol.min-1.g-1, when compared with control animals, 147.3 +/- 5.6 mumol.min-1.g-1. A similar decrease was observed for maximal LDH activity in the reverse reaction (lactate-->pyruvate), 49.8 +/- 2.1 vs 66.7 +/- 2.9 mumol.min-1.g-1, trained and controls, respectively. Training was also observed to decrease the Km for the reverse reaction, 5.18 +/- 0.78 mM vs 6.94 +/- 0.55 mM, for trained and controls, respectively. Km for the forward reaction was unaffected by training. Gel electrophoresis with densitometric evaluation revealed no shift in the isoenzyme pattern following endurance training. LDH5 accounted for 89% +/- 2%, whereas 6% +/- 0.5% was observed in LDH4, and 4% +/- 0.3% was observed in LDH3 for both groups. The densitometric area was approximately 34% lower from trained liver homogenates, a fractional decrease similar to that observed for maximal LDH activity. The decrease in hepatic LDH activity with endurance training appears attributable to a down regulation of enzyme content, with no significant alteration in isoenzyme distribution.

Endurance training fails to inhibit skeletal muscle glucose uptake during exercise

The effects of endurance training (running 30 m/min, 10% grade for 90 min, 5 days/wk for 12 wk) on skeletal muscle glucose uptake during steady-state exercise (running 20 m/min) were studied in fed rats. A bolus injection of 2-[1,2-3H]deoxyglucose was administered to assess the glucose metabolic index (R'g), an indicator of glucose uptake, in individual tissues of the animal. After 55 min of rest or moderate exercise, various tissues were analyzed for accumulation of phosphorylated 2-[1,2-3H]-deoxyglucose and/or glycogen content. No differences were observed between groups in the resting glycogen content for any of the muscle samples examined. Resting plasma glucose concentrations were not significantly different between groups. Furthermore, no significant differences were observed in R'g between groups for any of the muscle examined (tibialis anterior, extensor digitorum longus, soleus, white gastrocnemius, red gastrocnemius). During exercise, plasma glucose concentrations were not significantly different between groups. Exercise significantly elevated R'g above resting values in the tibialis anterior (5-fold), soleus (3-fold), and red gastrocnemius (7.5-fold). Despite an elevated R'g for specific muscles during exercise, no significant differences were observed in glucose uptake between groups for any tissue examined. Concomitantly, trained animals exhibited significantly less muscle glycogen depletion during exercise compared with control animals. Liver glycogen levels were also significantly higher post-exercise in trained vs. control animals.(ABSTRACT TRUNCATED AT 250 WORDS)

Enhanced gluconeogenesis from lactate in perfused livers after endurance training

The effects of endurance training (running 90 min/day at 30 m/min, 10% grade) on hepatic gluconeogenesis were studied in 24-h-fasted rats with use of the isolated liver perfusion technique. After isolation, the liver was perfused (single pass) for 30 min with Krebs-Henseleit bicarbonate buffer and fresh bovine erythrocytes (hematocrit 22-24%) with no added substrate. Subsequent to the "washout" period, the reservoir was elevated with various concentrations of lactate and [U-14C]lactate (10,000 dpm/ml) to assess hepatic glucose production. Relative flow rates were not significantly different between trained (1.94 +/- 0.05 ml/g liver) and control livers (1.91 +/- 0.05 ml/g liver). Furthermore, no significant differences were observed in perfusate pH, hematocrit, bile production, or serum alanine aminotransferase effluxing from trained or control livers. At saturating arterial lactate concentrations (> 2 mM), the maximal rate (Vmax) for hepatic glucose production was significantly higher for trained (0.91 +/- 0.04 mumol.min-1 x g liver-1) than for control livers (0.73 +/- 0.02 mumol.min-1 x g liver-1). That this reflected increased gluconeogenesis is supported by a significant elevation in the Vmax for [14C]glucose production from trained (13,150 +/- 578 dpm.min-1 x g liver-1) compared with control livers (10,712 +/- 505 dpm.min-1 x g liver-1). Significant increases were also observed in the Vmax for lactate uptake (25%), O2 consumption (19%), and 14CO2 production (23%) from endurance-trained livers. The Km for hepatic glucose output, approximately 1.05 mM lactate, was unchanged after endurance training. These findings demonstrate that chronic physical activity results in an elevated capacity for hepatic gluconeogenesis, as assessed in situ at saturating lactate concentrations.

Training improves glucose homeostasis in rats during exercise via glucose production

The effects of endurance training (running 1 h/day at 35 m/min, 10% grade) on glucose homeostasis during exercise (running 20 m/min) was studied in 30-h fasted rats. Primed-continuous infusion of [6-3H]- and [U-14C]glucose were employed to assess rates of appearance (Ra), disappearance (Rd), and apparent recycling. Training resulted in a 65% increase in skeletal muscle succinate dehydrogenase (SDH) activity but did not significantly influence body weight. Resting blood glucose concentrations were not significantly different between controls, 5.01 +/- 0.19 mM, and trained animals, 4.86 +/- 0.16 mM. Exercise resulted in a more rapid decline in blood glucose levels for control animals, reaching a value of 2.35 +/- 0.39 mM at 60 min, compared with 3.69 +/- 0.47 mM for trained animals. Glucose Ra was not significantly different between groups at rest, and rose for both groups during exercise. However, for controls Ra plateaued between 15 and 60 min of exercise at 11.03 +/- 0.73 mumol.100 g-1.min-1, whereas trained animals demonstrated a continuous rise to 17.13 +/- 1.18 mumol.100 g-1.min-1. Glucose Rd values were not significantly different between groups during the first 30 min of exercise but were significantly higher for trained animals during the final 30 min. As a result of the higher glucose Ra, trained animals demonstrated a smaller mean difference between Ra and Rd during exercise when compared with controls, -0.27 +/- 0.14 vs. -0.96 +/- 0.17 mumol.100 g-1.min-1. Trained animals further demonstrated significantly higher rates of glucose carbon recycling during the final 30 min of exercise.(ABSTRACT TRUNCATED AT 250 WORDS)