American journal of physiology. Regulatory, integrative and comparative physiology
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Am. J. Physiol. Regul. Integr. Comp. Physiol. · Mar 2007
Randomized Controlled TrialIncreased fatigue resistance of respiratory muscles during exercise after respiratory muscle endurance training.
Respiratory muscle fatigue develops during exhaustive exercise and can limit exercise performance. Respiratory muscle training, in turn, can increase exercise performance. We investigated whether respiratory muscle endurance training (RMT) reduces exercise-induced inspiratory and expiratory muscle fatigue. ⋯ Similarly, cycling endurance in POST(EXH) did not improve after RMT (P = 0.071), while a significant improvement was seen in the subgroup with >10% of diaphragm fatigue after PRE(EXH) (P = 0.017), but not in the sham training group (P = 0.674). However, changes in cycling endurance did not correlate with changes in respiratory muscle fatigue. In conclusion, RMT decreased the development of respiratory muscle fatigue during intensive exercise, but this change did not seem to improve cycling endurance.
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Am. J. Physiol. Regul. Integr. Comp. Physiol. · Feb 2007
Leptin antagonist reveals that the normalization of caloric intake and the thermic effect of food after high-fat feeding are leptin dependent.
High-fat (HF) feeding induces a transient increase in caloric intake and enhances energy expenditure. We hypothesized that leptin is necessary for homeostatic restoration of the HF-enhanced caloric intake and may mediate the increase in uncoupling protein-1 (UCP1) in brown adipose tissue (BAT). We employed a leptin antagonist to examine the role of leptin in these biological processes. ⋯ HF feeding elevated caloric intake, which nearly normalized by day 7, whereas in the presence of the antagonist, caloric intake remained elevated. Moreover, the HF-mediated augmentation in UCP1 in BAT was prevented by the antagonist. These results demonstrate that leptin is essential for the homeostatic restoration of caloric intake after HF feeding and that this leptin antagonist is able to block central leptin signaling and leptin-mediated UCP1 elevation.
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Am. J. Physiol. Regul. Integr. Comp. Physiol. · Jan 2007
The median preoptic nucleus is involved in the facilitation of heat-escape/cold-seeking behavior during systemic salt loading in rats.
Systemic salt loading has been reported to facilitate operant heat-escape/cold-seeking behavior. In the present study, we hypothesized that the median preoptic nucleus (MnPO) would be involved in this mechanism. Rats were divided into two groups (n = 6 each): one group had the MnPO lesion with ibotenic acid (4.0 mug) and the other was the vehicle control. ⋯ However, in the MnPO-lesion group, counts of the behavior were similar between the hypertonic- and isotonic-saline injection trials (10 +/- 2 and 8 +/- 1 at 35 degrees C, and 17 +/- 1 and 16 +/- 1 at 40 degrees C, respectively). T(core) increased (P < 0.05) in the heat in both trials (36.8 +/- 0.1 degrees C and 37.4 +/- 0.1 degrees C at 26 degrees C and 37.4 +/- 0.2 degrees C and 37.8 +/- 0.2 degrees C at 40 degrees C in the hypertonic- and isotonic-saline injection trials, respectively). These results may suggest that, at least in part, the MnPO is involved in the facilitation of heat-escape/cold-seeking behavior during osmotic stimulation.
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Am. J. Physiol. Regul. Integr. Comp. Physiol. · Jan 2007
Insulin sensitivity, fat distribution, and adipocytokine response to different diets in lean and obese cats before and after weight loss.
Obesity is a major health problem in cats and a risk factor for diabetes. It has been postulated that cats are always gluconeogenic and that the rise in obesity might be related to high dietary carbohydrates. We examined the effect of a high-carbohydrate/low-protein (HC) and a high-protein/low-carbohydrate (HP) diet on glucose and fat metabolism during euglycemic hyperinsulinemic clamp, adipocytokines, and fat distribution in 12 lean and 16 obese cats before and after weight loss. ⋯ Lean cats and cats during weight loss, but not obese cats, adapted to the varying dietary carbohydrate/protein content with changes in substrate oxidation. We conclude that diet HP is beneficial through maintenance of normal insulin sensitivity of fat metabolism in obese cats, facilitating the loss of fat during weight loss, and increasing heat production in lean cats. These data also show that insulin sensitivity of glucose and fat metabolism can be differentially regulated in cats.
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Am. J. Physiol. Regul. Integr. Comp. Physiol. · Nov 2006
Role of brain IL-1beta on fatigue after exercise-induced muscle damage.
Brain cytokines, induced by various inflammatory challenges, have been linked to sickness behaviors, including fatigue. However, the relationship between brain cytokines and fatigue after exercise is not well understood. Delayed recovery of running performance after muscle-damaging downhill running is associated with increased brain IL-1beta concentration compared with uphill running. ⋯ Injection of IL-1beta significantly decreased wheel running activity in uphill runners (P<0.01), whereas IL-1ra improved wheel running in downhill runners (P<0.05). Similarly, IL-1beta decreased and Il-1ra increased run time to fatigue in the uphill and downhill runners, respectively (P<0.01). These results support the hypothesis that increased brain IL-1beta plays an important role in fatigue after muscle-damaging exercise.