Validation of a radiotelemetry system for continuous blood pressure and heart rate monitoring in dogs.

A blood pressure telemetry system with catheter placement in the femoral artery was evaluated over a 119-day period in eight mongrel dogs. Every 3 weeks, the pressures recorded by telemetry were compared with direct, simultaneously recorded blood pressures measured from a femoral artery catheter implanted on the contralateral side. One telemetry device failed within 1 week of implant and was replaced before the beginning of data collection. Continuous blood pressure measures were accurate for a minimum of 17 weeks in all eight dogs. Acute changes in blood pressure and heart rate were not evaluated. Validation by simultaneous recording with a physiological monitor indicated that there was no drift in the telemetry blood pressure or heart rate during the 17-week period. Heart rates recorded by telemetry and a physiological monitor were identical, as were mean arterial pressures. The systolic pressure measured by the physiological monitor was consistently higher than that measured by telemetry. This may have been due to differences in the compliance of the catheter material in the two systems. Two devices failed within approximately 6 months of implant, apparently because of exhaustion of the battery. These findings indicate that this telemetry device can be used for periods of up to 17 weeks without appreciable drift or attenuation of the blood pressure signal. The results also describe a validation procedure for monitoring the accuracy of the telemetry system over extended periods of use. We conclude that this telemetry device can be used for the long-term assessment of blood pressure and heart rate in the dog.

Autonomic control of blood pressure and heart rate in obese hypertensive dogs.

Autonomic control of cardiovascular function was evaluated in nine dogs before and after a high-fat overfeeding regimen. Body weight increased significantly (from 19.8 +/- 0.9 to 29.5 +/- 2.1 kg; P < 0.01) with overfeeding. Mean arterial pressure (MAP) increased from 94.6 +/- 2.1 to 105.5 +/- 3.7 mmHg (P < 0.05), and heart rate (HR) increased from 94.8 +/- 3.5 to 112.3 +/- 5.6 beats/min (P < 0.01). After ganglionic blockade with chlorisondamine, dose response of MAP and HR to methoxamine (alpha-agonist) or isoproterenol (beta-agonist) was evaluated. Peak MAP response to methoxamine was blunted in obese dogs. HR response to isoproterenol was not different between lean and obese dogs. Atropine in the presence of propranolol increased HR from 80.8 +/- 7 to 202.8 +/- 8.9 beats/min in lean dogs and from 113.8 +/- 12.1 to 131.7 +/- 18.2 in obese dogs. These data suggest the increase in HR observed in obese dogs may be due to a decrease in parasympathetic inhibition rather than an increase in sympathetic stimulation. The blunted response to methoxamine in obese hypertensive dogs suggests that the sympathetic control of peripheral vascular resistance is altered in obesity.

Conjugated linoleic acid persistently increases total energy expenditure in AKR/J mice without increasing uncoupling protein gene expression.

AKR/J mice fed a high fat diet were treated with a 1% (1 g/100 g) admixture of conjugated linoleic acids (CLA) for 5 wk and compared with control mice. Body weights, energy intakes and energy expenditure (EE) determined by indirect calorimetry were measured weekly. CLA treatment reduced adipose depot weights by approximately 50% but had no significant effects on either body weight or energy intake. CLA increased EE persistently by an average of 7.7% throughout the 5-wk experiment. This greater EE, despite no difference in energy intake, was sufficient to account for the lower body fat stores in the CLA-treated mice. De novo fatty acid biosynthesis in adipose tissue, measured by incorporation of deuterium-labeled water, was not decreased by CLA treatment and therefore did not explain the lower adipose lipid in these mice. Expression of uncoupling protein (UCP) in skeletal muscle, white adipose tissue and kidney was not affected by CLA treatment. In brown adipose tissue, UCP1 expression was not affected by CLA treatment. However, UCP2 expression, although quite low, was significantly greater in CLA-fed mice. We conclude that CLA acts to reduce body fat stores by chronically increasing metabolic rate. This effect on metabolic rate is likely not due to increased UCP gene expression. Furthermore, the reduced body fat is not due to decreased de novo fatty acid synthesis in white adipose tissue.

Conjugated linoleic acid rapidly reduces body fat content in mice without affecting energy intake.

Recent reports have demonstrated that conjugated linoleic acid (CLA) has effects on body fat accumulation. In our previous work, CLA reduced body fat accumulation in mice fed either a high-fat or low-fat diet. Although CLA feeding reduced energy intake, the results suggested that some of the metabolic effects were not a consequence of the reduced food intake. We therefore undertook a study to determine a dose of CLA that would have effects on body composition without affecting energy intake. Five doses of CLA (0.0, 0.25, 0.50, 0.75, and 1.0% by weight) were studied in AKR/J male mice (n = 12/group; age, 39 days) maintained on a high-fat diet (%fat 45 kcal). Energy intake was not suppressed by any CLA dose. Body fat was significantly lower in the 0.50, 0.75, and 1.0% CLA groups compared with controls. The retroperitoneal depot was most sensitive to the effects of CLA, whereas the epididymal depot was relatively resistant. Higher doses of CLA also significantly increased carcass protein content. A time-course study of the effects of 1% CLA on body composition showed reductions in fat pad weights within 2 wk and continued throughout 12 wk of CLA feeding. In conclusion, CLA feeding produces a rapid, marked decrease in fat accumulation, and an increase in protein accumulation, at relatively low doses without any major effects on food intake.

Changes in skeletal muscle vascular resistance with weight gain: associations with insulin and sympathetic activity.

OBJECTIVE: This study was designed to characterize changes in peripheral vascular resistance with weight gain, and whether these changes are correlated with insulin and/or sympathetic activity. RESEARCH METHODS AND PROCEDURES: Femoral vascular resistance (FVR), mean arterial pressure, heart rate, and plasma insulin were measured before and during overfeeding in seven dogs with unilateral lumbar ganglionectomy (L3 to L6). Measurements were taken standing and while walking on a treadmill. RESULTS: There was a significant main effect of weight gain to increase mean arterial pressure (16.5+/-8.4 mmHg and 12.5+/-6.8 mmHg increase for standing and walking baseline, respectively) and heart rate (increase from week 1 of 31.6+/-10.6 beats/minute standing and 38.3+/-9.1 walking beat/minute). FVR increased immediately with overfeeding/ weight gain [standing: denervated (DNX):1.32+/-0.3 to 2.34+/-0.5; intact: 0.88+/-0.17 to 1.9+/-0.33 mmHg/mL.min(-1)], but returned to baseline with continued weight gain. Return of FVR to baseline occurred between weeks 2 and 3 of overfeeding in the DNX limb, but did not return to baseline until week 6 in the innervated limb. These changes were not correlated with plasma insulin levels. DISCUSSION: These data suggest that vascular resistance may be normal in the obese, but increases in vascular resistance occur early with weight gain (before changes in arterial pressure). This initial increase in vascular resistance could initiate the series of events leading to obesity-associated hypertension. Additionally, changing vascular resistance during weight gain may be influenced by sympathetic activity, because DNX limb FVR returned to baseline approximately 3 weeks earlier than the innervated limb.

Composition of dietary fat affects blood pressure and insulin responses to dietary obesity in the dog.

Cardiovascular and metabolic parameters were evaluated in 15 female spayed dogs before and after they became obese on either a saturated fat (LD, lard, n=8) or unsaturated fat (CO, corn oil, n=7) diet. Body weight and body fat increased significantly in both groups, although no differences occurred between diet groups. Dogs receiving the LD diet exhibited a greater increase in mean arterial pressure than those receiving the CO diet (p<0.01; 15.9 +/- 2.1 vs. 9.8 +/- 3.3 mm Hg increase). The CO diet stimulated a greater increase in heart rate than the LD diet (p<0.05; 32.8 +/- 7.8 vs. 14.1 +/- 5.8 bpm increase). Ganglionic blockade with chlorisondamine caused an increase in HR in both lean groups and in the obese CO group, but not the obese LD group, consistent with a decrease in parasympathetic tone to the heart in the dogs overfed saturated fat. Obesity enhanced the heart rate response to beta-adrenergic stimulation by isoproterenol in the LD, but not CO group. The LD diet increased circulating insulin and decreased insulin sensitivity, whereas the CO diet had no effect on either parameter. These findings suggest that the composition of dietary fat can modulate the autonomic and metabolic adaptations induced by dietary obesity.

Effects of conjugated linoleic acid on body fat and energy metabolism in the mouse.

Conjugated linoleic acid (CLA) is a naturally occurring group of dienoic derivatives of linoleic acid found in the fat of beef and other ruminants. CLA is reported to have effects on both tumor development and body fat in animal models. To further characterize the metabolic effects of CLA, male AKR/J mice were fed a high-fat (45 kcal%) or low-fat (15 kcal%) diet with or without CLA (2.46 mg/kcal; 1.2 and 1.0% by weight in high- and low-fat diets, respectively) for 6 wk. CLA significantly reduced energy intake, growth rate, adipose depot weight, and carcass lipid and protein content independent of diet composition. Overall, the reduction of adipose depot weight ranged from 43 to 88%, with the retroperitoneal depot most sensitive to CLA. CLA significantly increased metabolic rate and decreased the nighttime respiratory quotient. These findings demonstrate that CLA reduces body fat by several mechanisms, including a reduced energy intake, increased metabolic rate, and a shift in the nocturnal fuel mix.

Differential metabolic effects of energy restriction in dogs using diets varying in fat and fiber content.

The role of dietary fat and fiber in energy restriction for the management of obesity was examined. Twelve male castrated dogs were energy restricted for 7 weeks by feeding 60% of their calculated maintenance energy requirements (MER = 1500 kcal/m2/d) for ideal body weight. Six dogs were restricted on a high-fat (35.4 kcal% from fat), low-fiber (2.9% dry matter basis [DMB]) diet while the other six dogs were restricted on a low-fat (24.5 kcal% from fat), high-fiber (27% DMB) diet. Compared with the high-fat, low-fiber diet, energy restriction on the low-fat, high-fiber diet resulted in significantly greater decreases in body fat (1472 +/- 166 vs. 853 +/- 176 g; p < 0.05) and total serum cholesterol concentrations (108.7 +/- 11.3 vs. 51.5 +/- 13.9 mg/dL; p < 0.005). Reductions in body weight (2.86 +/- 0.3 vs. 2.14 +/- 0.3 kg; p < 0.09), and mean arterial blood pressure (17.4 +/- 6.1 vs. 6.7 +/- 2.9 mmHg; p < 0.12) were also greater on the low-fat diet; however, these diet effects did not reach statistical significance. These data suggest that the fat and fiber content of the diet during energy restriction are important factors in the management of obesity.

Gene-environment interaction: a significant diet-dependent obesity locus demonstrated in a congenic segment on mouse chromosome 7.

We have previously reported suggestive evidence for a locus on Chromosome (Chr) 7 that affects adiposity in F2 mice from a CAST/Ei x C57BL/6J intercross fed a high-fat diet. Here we characterize the effect of a high-fat (32.6 Kcal% fat) diet on male and female congenic mice with a C57BL/6J background and a CAST/Ei-derived segment on Chr 7. Adiposity index (AI) and weights of certain fat pads were approximately 50% lower in both male and female congenic mice than in control C57BL/6J mice, and carcass fat content was significantly reduced. The reduction of fat depot weights was not seen, however, in congenic animals fed a low-fat chow diet (12 Kcal% fat). The congenic segment is approximately 25 cM in length, extending from D7Mit213 to D7Mit41, and includes the tub, Ucp2 and Ucp3, genes, all of which are candidate genes for this effect. Some polymorphisms have been found on comparing c-DNA sequences of the Ucp2 gene from C57BL/6J and CAST/Ei mice. These results suggest that one or more genes present in the congenic segment modulate the susceptibility to fat deposition on feeding a high-fat diet. We were unable to show any significant difference between the energy intakes of the congenic and the control C57BL/6J mice on the high-fat diet. Also, measurements of energy expenditure in male mice at 6 weeks of age, during the first 2 weeks of exposure to the high-fat diet, failed to show any differences between control and congenic animals.