Aging and aerobic exercise are two conditions known to interfere with health and quality of life, most likely by inducing oxidative stress to the organism. We studied the effects of aging on the morphological and functional properties of skeletal, cardiac, and intestinal muscles and their corresponding oxidative status in C57BL/6 mice and investigated whether a lifelong moderate exercise program would exert a protective effect against some deleterious effects of aging. As expected, aged animals presented a significant reduction of physical performance, accompanied by a decrease of gastrocnemius cross-sectional area and cardiac hypertrophy. However, most interesting was that aging dramatically interfered with the intestinal structure, causing a significant thickening of the ileum muscular layer. Senescent intestinal myocytes displayed many mitochondria with disorganized cristae and the presence of cytosolic lamellar corpuscles. Lipid peroxidation of ileum and gastrocnemius muscle, but not of the heart, increased in aged mice, thus suggesting enhanced oxidative stress. With exception of the intestinal muscle responsiveness, animals submitted to a daily session of 60 min, 5 days/wk, at 13 up to 21 m/min of moderate running in treadmill during animal life span exhibited a reversion of all the observed aging effects on intestinal, skeletal, and heart muscles. The introduction of this lifelong exercise protocol prevented the enhancement of lipid peroxidation and sarcopenia and also preserved cellular and ultracellular structures of the ileum. This is the first time that the protective effect of a lifelong regular aerobic physical activity against the deleterious effects of aging on intestinal muscle was demonstrated.

Rosa EF, Takahashi S, Aboulafia J, Nouailhetas VL, Oliveira MG. Oxidative stress induced by intense and exhaustive exercise impairs murine cognitive function. J Neurophysiol 98: 1820 -1826, 2007. First published July 11, 2007 doi:10.1152/jn.01158.2006. It has been shown that exercise is helpful against brain disorders. However, this may not be true for intense exercise (IE). Because it is easy to misadjust exercise intensity with physical condition, it is essential to know the effects of IE on cognitive process because it may have important consequences on people skills and work skills. We investigated the effects of IE on male C57Bl/6 mice, 3-mo-old, undergoing 10 days of intense and exhaustive running program on cognition and its possible relationship with brain oxidative stress. Cognition was evaluated by three different cognitive tests: passive avoidance task, contextual fear conditioning, and tone fear conditioning, performed 24 h after the last exercise session. Brain oxidative stress was evaluated by lipid peroxidation and protein oxidation. There was a remarkable memory reduction of exercised animals in comparison with the control group, associated with increase in the brain oxidative stress, with no alterations in shock sensitivity, locomotion and anxiety parameters. Concurrent vitamin C and E supplementation fully prevented the memory decrement induced by IE and partially recovered both the increased the brain lipid peroxidation and the protein oxidation. In conclusion, IE-induces a high index of brain oxidative stress and impairs memory in murine model that was prevented by vitamin C and E supplementation.

This study investigated the influence of a moderate exercise training program on the intestinal contractility based on the hypothesis that this organ may endure repetitive periods of ischemia-reperfusion events during moderate aerobic training (10, 25, 40, and 55 days of 60-min treadmill running at 13-21 m/min, 5 days/week). The adaptation of the animal to this program was assessed by significant increase of animal physical performance associated with a mild increase in the wet heart mass-to-body mass ratio. The endurance exercise training caused functional changes of the C57BL/6 ileum contractility, mainly causing a significant reduction of the efficacy of both the electro- (KCl) and pharmacomechanical (acetylcholine, [2-lysine]-angiotensin II, and bradykinin) couplings after 55 days of moderate treadmill running. The level of ileum lipid peroxidation, evaluated by an indirect method, significantly decreased after 10 days of moderate aerobic training, remaining at this lower level throughout the 55 days of training. Altogether, these data demonstrate that the murine ileum is an important target for aerobic moderate exercise training program by causing impairment of the contractility in response to either agonists or depolarization, and that endurance exercise exerts a remarkable protective effect against tissue oxidative stress.

Several gastrointestinal symptoms associated with prolonged intense exercise (IE) have been reported, although the mechanisms underlying its effects on the intestine remain poorly understood. The aim of the present study was to investigate whether IE may induce oxidative stress in the intestine, as well as its possible relationship with intestinal signaling impairments, leading to contractile disturbances. C57BL/6 mice were submitted to 4 days (EX.4D) and 10 days (EX.10D) of IE. The daily exercise session consisted of a running session until exhaustion, with the treadmill speed set at 85% of each animal's maximum velocity. The decrease in exhaustion time was exponential, and the reduction in the maximum velocity, as assessed by an incremental test, was higher in EX.4D than in EX.10D animals. The ileum mucosa layer was partially destroyed after 4 days of IE, where 37% and 11% muscle layer atrophies were observed in EX.4D and EX.10D animals, respectively. Ileum contractility was significantly impaired in the EX.4D animal group, with reduced efficacy for carbachol, bradykinin, and KCl signaling associated with a decrease in lipid peroxidation and with no alteration of protein oxidation. Intestinal myocytes from EX.10D animals displayed areas containing structurally disorganized mitochondria, which were associated with increased levels of protein oxidation, without alteration of contractility, except for a reduction in the potency of bradykinin signaling. Finally, no clear relationship between ileum contractility and oxidative stress was shown. Together, these results argue in favor of significant functional, biochemical, and morphological disturbances caused by exercise, thus demonstrating that intestinal tissue is very sensitive to exercise.

We investigated the regulation of the Ca2+-activated K+(maxi-K+) channel by angiotensin II (ANG II) and its synthetic analog, [Lys2]ANG II, in freshly dispersed intestinal myocytes. We identified a maxi-K+ channel population in the inside-out patch configuration on the basis of its conductance (257 ± 4 pS in symmetrical 150 mM KCl solution), voltage and Ca2+ dependence of channel opening, low Na+-to-K+and Cl−-to-K+permeability ratios, and blockade by external Cs+ and tetraethylammonium chloride. ANG II and [Lys2]ANG II caused an indirect, reversible, Ca2+- and dose-dependent activation of maxi-K+ channels in cell-attached experiments when cells were bathed in high-K+ solution. This effect was reversibly blocked by DUP-753, being that it is mediated by the AT1 receptor. Evidences that activation of the maxi-K+ channel by ANG II requires a rise in intracellular Ca2+concentration ([Ca2+]i) as an intermediate step were the shift of the open probability of the channel-membrane potential relationship to less positive membrane potentials and the sustained increase in [Ca2+]iin fura 2-loaded myocytes. The preservation of the pharmacomechanical coupling of ANG II in these cells provides a good model for the study of transmembrane signaling responses to ANG II and analogs in this tissue.

Intense and exhaustive exercise (IEE) is associated with oxidative stress in skeletal muscle, and we recently reported that intestine is sensitive to IEE. In the present study, we investigated the possible relationship between the effects of IEE on morphology and oxidative markers in the ileum and isolated mitochondria. C57BL/6 mice were ascribed either to a control group comprising two subgroups, one sedentary and another exercised for 10 days (E10), or to a corresponding supplemented control group again comprising two subgroups, one sedentary and another exercised for 10 days (E10-V). The IEE program consisted of a single daily treadmill running session at 85% of V(max), until animal exhaustion. Vitamins C (10 mg/kg) and E (10 mg/kg) were concurrently intraperitoneally administered 2 h before the exercise sessions. IEE was shown to cause 1) impairment of ileum internal membrane mitochondria verified by ultramicrography analysis; 2) increase in ileum carbonyl content (117%) and reduction in antioxidant capacity (36%); 3) increase in mitochondria carbonyl content (38%), increase in the percentage of ruptured mitochondria (25.3%), increase in superoxide dismutase activity (186%), and reduction in citrate synthase activity (40.4%) compared with control animals. Observations in the vitamin-supplemented exercised animals (E10-V) were 1) healthy appearance of myocyte mitochondria; 2) decrease in ileum carbonyl content (66%) and increase in antioxidant capacity (53%); 3) decrease in mitochondria carbonyl content (43%), decrease in the percentage of ruptured mitochondria (30%), slight increase in superoxide dismutase activity (7%), and significant increase in citrate synthase activity (121%) compared with E10 animals. Therefore, the present results strongly corroborate the hypothesis that IEE leads to marked disturbances in intestinal mitochondria, mainly in redox status, and affects whole intestinal redox status.

The role of ion fluxes in angiotensin II (AII) desensitization (tachyphylaxis) was investigated by studying Na+ and Ca2+ translocation in cultured vascular smooth muscle cells from the rat aorta. The effects of AII were compared to those of [1-sarcosine]-AII (Sar1-AII), an analogue which also induces tachyphylaxis, and [2-lysine]-AII (Lys2-AII), an analogue that does not show this property. Maximally effective concentrations of the three peptides induced a rapid and transient increase in 45Ca2+ efflux, a rapid and sustained decrease in total cell Ca2+ and an increased Na+ permeability. Repeated treatments, at short intervals, with either of the three peptides abolished the effect on Ca2+ efflux, and this desensitization was slowly reversible. A 30-min rest period was sufficient for full recovery of the response of cells that were desensitized by Lys2-AII, whereas the recovery from AII or Sar1-AII-desensitization was still not complete after 60 min. Our results suggest that the difference in the behaviour of the "tachyphylactic" AII and Sar1-AII and the "non-tachyphylactic" Lys2-AII lays not in the production of different signals upon binding to the receptor, but in a difference in the hormone-receptor interaction itself.

Single-channel currents were recorded in excised inside-out and cell-attached patches of cultured cells from the longitudinal smooth muscle of the guinea pig ileum. In the presence of symmetrical high-K+ solutions, we identified a voltage-dependent 12-pS channel. It was reversibly blocked by addition of either Ba2+ or Cs+ at the cellular side of the patch but was insensitive to Ca2+ or ATP. This channel had poor selectivity concerning cations (PLi > PK = PNa = PCa, where P is permeability) and low permeability to anions. Isosmotic substitution of NaCl for KCl in the solution facing the cellular side enhanced the channel activity by increasing NPo values where N is number of channels and Po is open probability. In the cell-attached configuration, the channel was also activated by addition of angiotensin II in the bath solution. We propose that this nonselective cation channel might play a role in the control of the membrane potential during the contractile response of the guinea pig ileum to agonists by keeping the voltage-sensitive Ca2+ channels open.