Experimental dog model for assessment of fasting and postprandial fatty acid metabolism: pitfalls and feasibility.

The dog is a widely-used model for conducting metabolic studies. This is mainly due to its large size and its physiology which is relatively similar to that of humans. Here, we attempted to optimize a postprandial metabolic study protocol used in dogs. Following acclimatization, female mongrel dogs underwent 9 h profiling for time-course baseline plasma data on triglyceride, adrenocorticotropic hormone (ACTH) and cortisol levels. One week later, carotid and jugular catheters were surgically inserted for sampling and infusions. Initial post-operative care, based on the literature (Protocol 1), consisted of analgesia (buprenorphine every 8-12 h and 2-3 doses/day of acepromazine), restriction by Pavlov harness within cages, and a two- to three-day recovery period. Throughout the experiment, dogs received a lipid tracer diluted in 5% bovine serum albumin (BSA). Compared with baseline, animals vomited (n = 6/6) and exhibited high ACTH + cortisol levels (stress biomarkers), resulting in blunted triglyceride peak levels. To avoid these undesirable effects, post-operative care was modified (Protocol 2) as follows: animals (n = 19) were given a single dose of buprenorphine and no acepromazine, were unrestrained and free to move within cages, the recovery period was extended to seven days, and the lipid tracer was diluted in 0.002% versus 5% BSA. Using this modified protocol, postprandial plasma-triglyceride and ACTH/cortisol patterns were similar to baseline values. Controlling for stressors, as well as for factors which may alter proper digestion, is critical for all postprandial metabolic studies. Our results show that an optimized postprandial metabolic protocol used in dogs reduces experimental variability, while improving animal care and comfort.

Relationship between total and high molecular weight adiponectin levels and plasma nonesterified fatty acid tolerance during enhanced intravascular triacylglycerol lipolysis in men.

CONTEXT: Increased plasma nonesterified fatty acid (NEFA) appearance during enhanced intravascular triacylglycerol (TG) lipolysis is a marker of metabolic adipose tissue dysfunction and may lead to the development of insulin resistance. The relationship between total and high molecular weight (HMW) adiponectin levels, NEFA appearance, and total TG lipolytic capacity has not been previously studied in humans. OBJECTIVES: Our objective was to determine whether total and HMW adiponectin plasma levels are associated with plasma NEFA level and appearance, and with total TG lipolytic rate during enhanced intravascular TG lipolysis in men. DESIGN: This was a cross-sectional metabolic study. SETTING: The study was performed at an academic clinical research center. PARTICIPANTS: There were 15 healthy men (mean +/- sd body mass index 25.5 +/- 4.7 kg/m(2)) aged 21-50 yr (mean +/- sd 31.1 +/- 10.2) without first-degree relatives with type 2 diabetes included in the study. INTERVENTIONS: Pancreatic clamps and iv infusion of stable isotopic tracers ([1,1,2,3,3-(2)H(5)]glycerol and [U-(13)C]palmitate) were performed, whereas intravascular TG lipolysis was clamped by iv infusion of heparin plus Intralipid at low (fasting) and high insulin levels. Total and HMW adiponectin levels were measured using an ELISA. MAIN OUTCOME MEASURES: Levels of total and HMW adiponectin, palmitate appearance (plasma palmitate appearance rate), and glycerol appearance (plasma glycerol appearance rate) were calculated. RESULTS: During heparin plus Intralipid infusion, total and HMW adiponectin was inversely correlated with plasma palmitate appearance rate (r = -0.65; P = 0.01), but this association was lost when expressed per nonlean weight. Adiponectin levels were positively associated with plasma glycerol appearance rate per nonlean weight (r = 0.71 and r = 0.66, respectively; P < or = 0.01). CONCLUSIONS: Increased adipose tissue mass likely explains the association between low adiponectin and reduced NEFA tolerance. Adiponectin level is a marker of total TG lipolytic rate per adipose tissue mass in men.

Impaired plasma nonesterified fatty acid tolerance is an early defect in the natural history of type 2 diabetes.

CONTEXT: Abnormal plasma nonesterified fatty acid (NEFA) metabolism may play a role in the development of type 2 diabetes. OBJECTIVES: Our objectives were to demonstrate whether there is a defect in insulin-mediated suppression of plasma NEFA appearance (RaNEFA) and oxidation (OxNEFA) during enhanced intravascular triacylglycerol lipolysis early in the natural history of type 2 diabetes, and if so, to determine whether other mechanisms than reduced insulin-mediated suppression of intracellular lipolysis are involved. DESIGN: These are cross-sectional studies. SETTING: The studies were performed at an academic clinical research center. PARTICIPANTS: Nine healthy subjects with both parents with type 2 diabetes (FH+) and nine healthy subjects with no first-degree relatives with type 2 diabetes (FH-) with similar anthropometric features were included in the studies. INTERVENTIONS: Pancreatic clamps and iv infusion of stable isotopic tracers ([1,1,2,3,3-(2)H5]-glycerol and [U-(13)C]-palmitate or [1,2-(13)C]-acetate) were performed while intravascular triacylglycerol lipolysis was simultaneously clamped by iv infusion of heparin plus Intralipid at low (fasting) and high insulin levels. Oral nicotinic acid (NA) was used to inhibit intracellular lipolysis. MAIN OUTCOME MEASURES: RaNEFA and OxNEFA were determined. RESULTS: During heparin plus Intralipid infusion at high plasma insulin levels, and despite similar intravascular lipolytic rates, FH+ had higher RaNEFA and OxNEFA than FH- (RaNEFA: 17.4+/-6.3 vs. 9.2+/-4.2; OxNEFA: 4.5+/-1.8 vs. 2.3+/-1.5 micromol/kg lean body mass/min), independent of NA intake, gender, age, and body composition. In the presence of NA, insulin-mediated suppression of RaNEFA was still observed in FH-, but not in FH+. CONCLUSIONS: Increased RaNEFA and OxNEFA during intravascular lipolysis at high insulin levels occur early in the natural history of type 2 diabetes.

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.

UNLABELLED: 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 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.