Resistance Exercise In Rats Research Articles

Milk kefir therapy improves the skeletal response to resistance exercise in rats submitted to glucocorticoid-induced osteoporosis.

Glucocorticoid-induced osteoporosis (GIO) has emerged as a challenge after long-term glucocorticoids (GCs) administration. Exercise has been an important non-pharmacological option, while medications modulate bone remodeling despite adverse effects. In this way, milk Kefir (MK) therapy stands out as a safe alternative to improve bone metabolism. Our study aimed to investigate the effect of MK associated to resistance exercise on bone loss in rats with GIO. For this, sixty male Wistar rats were divided into 2 groups: normal (N) and subjected to GIO, which was subdivided into 4 groups: control (C), milk kefir therapy (K), Exercise (Ex), and Exercise+K (ExK). GIO was induced by dexamethasone (7mg/kg - i.m.; 1×/wk, 5wk). MK was administered daily (1×/day; 0.7ml/animal) and the climb exercise with load was performed 3×/wk; both for 16wk. Femur was collected for assessment of bone microarchitecture, quality and metabolism. GIO markedly reduced trabecular bone volume density (BV/TV) (-35%), trabecular thickness (Tb.Th) (-33%), mineral content of femur (-26%) as well as bone collagen content (-56%). Bone strength and its biomechanical properties given by flexural strength (-81%), fracture load (-80%), and the number of osteocytes (-84%) were lowered after GIO. GCs reduced osteoblast number and function while increased osteoclast number, altering bone remodeling (p<0.05). On the other hand, ExK significantly improved bone microarchitecture and quality, marked by fractal dimension increase (+38%), cortical volume (+34%), BV/TV (+34%), Tb.Th (+33%), mineral content and collagen maturity, while reduced the space between trabecula (-34%). The Ex and ExK increased the number of osteocytes (p<0.05) and they were able to reverse the lower osteoblast number. Both treatments used alone significantly enhanced bone biomechanical properties, but the ExK showed a more significant improvement. ExK ameliorated bone strength and biomechanics (p<0.05) and stimulated bone formation and modulated bone remodeling (p<0.05). MK and exercise administered isolated or in association increased the percentage of collagen bone filling after GIO (p<0.05), but only ExK improved collagen maturity. Our results showed that MK associated to resistance exercise enhanced bone microarchitecture, quality and metabolism, being therefore an interesting tool to improve skeletal response during GIO.

Repeated bouts of resistance exercise in rats alter mechanistic target of rapamycin complex 1 activity and ribosomal capacity but not muscle protein synthesis.

What is the central question of this study? Is muscle protein synthesis (MPS) additionally activated following exercise when ribosomal capacity is increased after repeated bouts of resistance exercise (RE)? What is the main finding and its importance? Skeletal muscles with increased ribosome content through repeated RE bouts showed sufficient activation of MPS with lower mechanistic target of rapamycin complex 1 signalling. Thus, repeated bouts of RE possibly change the translational capacity and efficiency to optimize translation activation following RE. Resistance exercise (RE) activates ribosome biogenesis and increases ribosome content in skeletal muscles. However, it is unclear whether the increase in ribosome content subsequently causes an increase in RE-induced activation of muscle protein synthesis (MPS). Thus, this study aimed to investigate the relationship between ribosome content and MPS after exercise using a rat RE model. Male Sprague-Dawley rats were categorized into three groups (n=6 for each group): sedentary (SED) and RE trained with one bout (1B) or three bouts (3B). The RE stimulus was applied to the right gastrocnemius muscle by transcutaneous electrical stimulation under isoflurane anaesthesia. The 3B group underwent stimulation every other day. Our results revealed that 6 h after the last bout of RE, muscles in the 3B group showed an increase in total RNA and 18S+28S rRNA content per muscle weight compared with the SED and 1B groups. In both the 1B and 3B groups, MPS, estimated by puromycin incorporation in proteins, was higher than that in the SED group 6h after exercise; however, no significant difference was observed between the 1B and 3B groups. In the 1B and 3B groups, phosphorylated p70S6K at Thr-389 increased, indicating mechanistic target of rapamycin complex 1 (mTORC1) activity. p70S6K phosphorylation level was lower in the 3B group than in the 1B group. Finally, protein synthesis per ribosome (indicator of translation efficiency) was lower in the 3B group than in the 1B group. Thus, three bouts of RE changed the ribosome content and mTORC1 activation, but not the degree of RE-induced global MPS activation.

Habitual high-protein diet does not influence muscle protein synthesis in response to acute resistance exercise in rats.

Resistance training combined with consumption of a high-protein diet (HPD) is typically recommended to increase muscle mass, as both acute resistance exercise (RE) and dietary protein intake stimulate mechanistic target of rapamycin complex 1 (mTORC1) and muscle protein synthesis (MPS). However, the effect of chronic HPD consumption on MPS response to an acute RE remains to be determined. Male Sprague-Dawley rats aged 10 wk were fed HPD (50 kcal % protein, for 4 wk) or normal protein diet (NPD; 20 kcal % protein). After the 4-wk dietary intervention, the rats were fasted overnight and the right gastrocnemius muscle was subjected to percutaneous electrical stimulation to mimic acute RE, whereas the left gastrocnemius muscle served as control. The rats were sacrificed 6 h after exercise and the tissues were sampled immediately. The HPD group showed significantly lower fat mass and higher skeletal muscle mass than the NPD group without affecting body weight. Resting mTORC1 activity did not differ between the groups. Additionally, resting MPS was also unchanged after HPD. Acute RE significantly increased mTORC1 activity and MPS in both groups. However, differences in diet did not influence the response of mTORC1 activation to acute RE. Furthermore, HPD did not affect the response of MPS to acute RE. The present results suggested that although 4 wk of HPD reduces body fat and increases skeletal muscle mass, it does not affect muscle protein synthesis at basal state, and in response to acute RE.

Identification of the force-velocity curve on dynamic resistance exercise for rats.

The aim of this study was to identify force-velocity and power-velocity curves in climbing activity protocols, used as dynamic resistance exercise in rats. Eighteen 45-day-old male Wistar rats (weight = 211.9 ± 5.2 g) were evaluated. After familiarization to the climbing procedure, the animals performed an incremental climbing test (load relative to 75% of the body mass at first stage, followed by 30 g increments with and 120 s recovery between climbs) to determine the maximum carrying capacity (MCC). After this, the animals climbed with different loads (without load, 10%, 20%, 30%, 40%, 50%, 75%, 90%, and 100% of MCC) with 120 s recovery between climbs. Time for each climb was recorded to calculate the mechanical power. The peak power was reached at 30% of MCC. For the force-velocity curve, an inversely proportional relation was observed between force and velocity, as expected, greater forces were expressed in lower velocities. Therefore, our results suggest that training at 30% of MCC should be encouraged aiming the target for greater power output and 90%-100% of MCC should be the load aiming for strength training in climbing activities for rats.

L-arginine modulates inflammation and muscle regulatory genes after a single session of resistance exercise in rats.

We investigated the skeletal muscle adaptation to l-arginine supplementation prior to a single session of resistance exercise (RE) during the early phase of muscle repair. Wistar rats were randomly assigned into non-exercised (Control), RE plus vehicle (RE); RE plus l-arginine (RE+L-arg) and RE plus aminoguanidine (RE+AG) groups. Animals received four doses of either vehicle (0.9% NaCl), l-arg (1g/b.w.), or AG (iNOS inhibitor) (50mg/b.w.). The animals performed a single RE session until the concentric failure (ladder climbing; 80% overload) and the skeletal muscles were harvested at 0, 8, 24, and 48hours post-RE. The RE resulted in increased neutrophil infiltrate (24hours post-RE) (3621 vs 11852; P<.0001) associated with enhanced TNF-α (819.49 vs 357.02; P<.005) and IL-6 (3.84 vs 1.08; P<.0001). Prior, l-arginine supplementation attenuates neutrophil infiltration (5622; P<.0001), and also TNF-α (506.01; P<.05) and IL-6 (2.51, P<.05) levels. AG pretreatment mediated an inhibition of iNOS levels similar to levels found in RE group. RE animals displayed increased of atrogin-1 (1.9 fold) and MuRF-1 (3.2 fold) mRNA levels, reversed by l-arg supplementation [atrogin-1 (0.6 fold; P<.001); MuRF-1 (0.8-fold; P<.001)] at 24hours post-RE. MyoD up-regulated levels were restricted to l-arg treated animals at 24hours (2.8 vs 1.5 fold; P<.005) and 48hours post-RE (2.4 vs 1.1 fold; P<.001). AG pretreatment reversed these processes at 24hours [atrogin-1 (2.1 fold; P<.0001); MuRF-1 (2.5 fold; P<.0001); MyoD (1.4 fold)]. l-arginine supplementation seems to attenuate the resolution of RE-induced muscle inflammation and up-regulates MyoD expression during the early phase of muscle repair.

Co-ingestion of carbohydrate and whey protein increases fasted rates of muscle protein synthesis immediately after resistance exercise in rats.

The objective of the study was to investigate whether co-ingestion of carbohydrate and protein as compared with protein alone augments muscle protein synthesis (MPS) during early exercise recovery. Two months old rats performed 10 repetitions of ladder climbing with 75% of body weight attached to their tails. Placebo (PLA), whey protein (WP), or whey protein plus carbohydrate (CP) was then given to rats by gavage. An additional group of sedentary rats (SED) was used as controls. Blood samples were collected immediately and at either 1 or 2 h after exercise. The flexor hallucis longus muscle was excised at 1 or 2 h post exercise for analysis of MPS and related signaling proteins. MPS was significantly increased by CP compared with PLA (p<0.05), and approached significance compared with WP at 1 h post exercise (p = 0.08). CP yielded a greater phosphorylation of mTOR compared with SED and PLA at 1 h post exercise and SED and WP at 2 h post exercise. CP also increased phosphorylation of p70S6K compared with SED at 1 and 2 h post exercise. 4E-BP1 phosphorylation was inhibited by PLA at 1 h but elevated by WP and CP at 2 h post exercise relative to SED. The phosphorylation of AMPK was elevated by exercise at 1 h post exercise, and this elevated level was sustained only in the WP group at 2 h. The phosphorylation of Akt, GSK3, and eIF2Bε were unchanged by treatments. Plasma insulin was transiently increased by CP at 1 h post exercise. In conclusion, post-exercise CP supplementation increases MPS post exercise relative to PLA and possibly WP, which may have been mediated by greater activation of the mTOR signaling pathway.

Whey protein increases muscle weight gain through inhibition of oxidative effects induced by resistance exercise in rats

Whey protein (WP) is known for its nutritional value and antioxidant properties. The aim of this study was to evaluate whether the antioxidant properties of WP could contribute to muscle weight gain in response to resistance exercise (RE). We hypothesized that WP ingestion could increase muscle weight gain in rats subjected to an RE program, through inhibition of oxidative effects induced by high-intensity RE. Thirty-two male Fischer rats were randomly assigned to control sedentary, control exercised, WP sedentary, and WP exercised groups (n=8/group). The RE consisted of inducing the rats to perform sets of jumps for 8 weeks. Body and muscle weight gains, muscle glutathione content, histopathology, muscle antioxidant enzyme activities, and gene expression were evaluated. Body and muscle weight gains of exercised rats fed WP were higher than those of control exercised rats. Concomitantly, RE induced an increase in phagocyte infiltration, protein oxidation, and down-regulation of glutathione peroxidase and gamma-glutamylcysteine synthetase messenger RNA expression in gastrocnemius muscle (P<.05), effects that were inhibited by WP ingestion. Cytosolic superoxide dismutase and catalase messenger RNA expression were reduced only by RE (P<.05), and muscle glutathione content was increased only by WP (P<.05) with no significant interaction observed (P>.05). These findings suggest that differences in body and muscle weight gain in exercised rats fed control or WP diets were mediated, in part, by the antioxidant properties of WP, and indicate that when associated with RE, WP represents a nutritional aid to support muscle growth.

The Nitric oxide/CGMP/KATP pathway mediates systemic and central antinociception induced by resistance exercise in rats

Resistance exercise (RE) is characterized to increase strength, tone, mass, and/or muscular endurance and also for produces many beneficial effects, such as blood pressure and osteoporosis reduction, diabetes mellitus control, and analgesia. However, few studies have investigated endogenous mechanisms involved in the RE-induced analgesia. Thus, the aim of this study was evaluate the role of the NO/CGMP/KATP pathway in the antinociception induced by RE. Wistar rats were submitted to acute RE in a weight-lifting model. The nociceptive threshold was measured by mechanical nociceptive test (paw-withdrawal). To investigate the involvement of the NO/CGMP/KATP pathway the following nitric oxide synthase (NOS) non-specific and specific inhibitors were used: N-nitro-l-arginine (NOArg), Aminoguanidine, N5-(1-Iminoethyl)-l-ornithine dihydrocloride (l-NIO), Nω-Propyl-l-arginine (l-NPA); guanylyl cyclase inhibitor, 1H-[1,2,4]oxidiazolo[4,3-a]quinoxalin-1-one (ODQ); and KATP channel blocker, Glybenclamide; all administered subcutaneously, intrathecally and intracerebroventricularly. Plasma and cerebrospinal fluid (CSF) nitrite levels were determined by spectrophotometry. The RE protocol produced antinociception, which was significantly reversed by NOS specific and unspecific inhibitors, guanylyl cyclase inhibitor (ODQ) and KATP channel blocker (Glybenclamide). RE was also responsible for increasing nitrite levels in both plasma and CSF. These finding suggest that the NO/CGMP/KATP pathway participates in antinociception induced by RE.

Fos expression on medullary and hypothalamic areas after resistance exercise in rats.

The acute effects of exercise are generated by alterations in the autonomic nervous system that is mediated through the integration of multiple nuclei of autonomic control. The aim of this study was to evaluate the Fos protein expression on the hypothalamic and medullary areas of cardiovascular control after a single bout of resistance exercise (RE). Were used Wistar rats (250g–300g) divided into two groups: sham (SH) and resistance exercise (RE). The animals performed the RE protocol (10 sets of 10 repetitions with 2 min for recovery) in a squat apparatus with 60% of 1RM. The animals were anesthetized, perfused, the brain was removed and sliced in a cryostat for immunohistochemistry method. The brain sections were subjected to immunofluorescence protocol. Fos protein immunoreactivity increase when compared to SH in the nucleus tractus solitary (RE = 15.3 ± 0.6 vs. SH = 1.6 ± 0.6), in the caudal ventrolateral region of the medulla (RE = 23.3 ± 0.8 vs SH 1.3 ± 0.3) and in the paraventricular nucleus of the hypothalamus (RE = 59.3 ± 4.2 vs SH 1.3 ± 0.3), we showed that after RE there is an intense activation of important brain areas for cardiovascular control during the post exercise period. Suggesting mobilization and possible interaction of specifics nuclei of brain to correct homeostatic changes produced by RE. Research support: CAPES, Fapitec.

Participation of endogenous opioids in the antinociception induced by resistance exercise in rats

Exercise is a low-cost intervention that promotes health and contributes to the maintenance of the quality of life. The present study was designed to investigate the influence of different resistance exercise protocols on the nociceptive threshold of rats. Female Wistar rats were used to perform exercises in a weight-lifting exercise model. The following groups were examined (N = 6 per group): untrained rats (control group); an acute protocol group consisting of rats submitted to 15 sets of 15 repetitions of resistance exercise (acute group); rats exercised with 3 sets of 10 repetitions, three times per week for 12 weeks (trained group), and a group consisting of trained rats that were further submitted to the acute protocol (trained-acute group). The nociceptive threshold was measured by the paw-withdrawal test, in which the withdrawal threshold (escape reaction) was measured by an apparatus applying force to the plantar surface of the animal paw. The opioid antagonist naloxone (2 mg/kg) was administered subcutaneously 10 min before the exercise protocols. The trained group demonstrated antinociception only up to day 45 of the 12-week training period. A significant increase (37%, P < 0.05) in the nociceptive threshold was produced immediately after exercise, decreasing to 15% after 15 min, when the acute exercise protocol was used. Naloxone reversed this effect. These data show that the acute resistance exercise protocol was effective in producing antinociception for 15 min. This antinociceptive effect is mediated by the activation of opioid receptors.

Modulation of Insulin Signaling via Resistance Exercise

Resistance exercise in rats has been shown to substantially elevate S6K1 phosphorylation for up to 36 hr post exercise. Genetically increasing the activity of S6K1 can alter insulin sensitivity by inhibition of IRS‐1 expression and function. We hypothesized that lengthening contractions would increase S6K1 phosphorylation and down regulate the expression and function of IRS‐1. Wistar rats underwent unilateral lengthening contractions of the right Tibialis Anterior muscles and were collected at 0 mins, 30 mins, 3 hrs, 18 hrs and 48 hrs. S6K1389 phosphorylation was elevated by 751 ± 208 %, 3197 ± 1144 %, 10041 ± 2209 % (p &lt; 0.05), at 0 min, 30 min, 3 hr, respectively. IRS‐1636/639 phosphorylation was significantly increased at 30 mins and 18 hrs by 715 ± 160 % and 170 ± 38 %, respectively. IRS‐1 associated P85 was significantly reduced at 30 min and 3 hrs by 57 ± 7 % and 55 ± 7 %, respectively. Due to the time course of the S6K1389 and IRS‐1636/639 phosphorylation we concluded that S6K1 was the most likely kinase mediating the response. To test this further we pretreated female Wistar rats with rapamycin and collected tissues 30 mins post stimulation. We found that rapamycin reduced the increase in IRS‐1636/639 phosphorylation and partially rescued the reduction in IRS‐1 associated P85. We conclude that increased S6K1 activity after resistance exercise enhances IRS‐1 serine phosphorylation, decreasing IRS‐1 associated P85.

Phosphorylation of Ser535 on eIF2B&amp;epsiv; may be Important for Elevations in Muscle Protein Synthesis After Resistance Exercise in Rats

1256 Purpose: Rates of skeletal muscle protein synthesis are consistently reported to be elevated after an acute bout of resistance exercise, however the mechanisms responsible for this response remain unclear. Methods: Several potential regulators of the initiation of mRNA translation, a key rate-controlling step in protein synthesis, were examined in gastrocnemius muscle of rats 16 hr after moderate intensity resistance exercise. Results: Rates of protein synthesis were elevated after exercise, but at the time point examined no change was observed in phosphorylation of glycogen synthase kinase-3β, phosphorylation of Thr389 on p70S6K, or the phosphorylation pattern for total p70S6K. In contrast, the phosphorylation state of eIF2α on Ser 51 and eIF2Bε on Ser535 was reduced in exercised animals compared to sedentary control animals. Conclusions: These results suggest that phosphorylation of initiation factors that affect eIF2B activity (eIF2Bε and eIF2α) changes with resistance exercise in a manner compatible with an anabolic state.

Phosphorylation of Ser535 on eIF2B&amp;epsiv; may be Important for Elevations in Muscle Protein Synthesis After Resistance Exercise in Rats

Phosphorylation of Ser535 on eIF2B&amp;epsiv; may be Important for Elevations in Muscle Protein Synthesis After Resistance Exercise in Rats

Eukaryotic initiation factors and protein synthesis after resistance exercise in rats.

Translational control of protein synthesis depends on numerous eukaryotic initiation factors (eIFs) and we have previously shown (Am. J. Physiol. Endocrinol. Metab. 276: E721-E727, 1999) that increases in one factor, eIF2B, are associated with increases in rates of protein synthesis after resistance exercise in rats. In the present study we investigated whether the eIF4E family of initiation factors is also involved with an anabolic response to exercise. Male Sprague-Dawley rats either remained sedentary (n = 6) or performed acute resistance exercise (n = 6), and rates of protein synthesis were assessed in vivo 16 h after the last session of resistance exercise. eIF4E complexed to eIF4G (eIF4E x eIF4G), eIF4E binding protein 1 (4E-BP1) complexed to eIF4E, and phosphorylation state of eIF4E and 4E-BP1 (gamma-form) were assessed in gastrocnemius. Rates of protein synthesis were higher in exercised rats compared with sedentary rats [205 +/- 8 (SE) vs. 164 +/- 5.5 nmol phenylalanine incorporated x g muscle(-1) x h(-1), respectively; P < 0.05]. Arterial plasma insulin concentrations were not different between the two groups. A trend (P = 0.09) for an increase in eIF4E x eIF4G with exercise was noted; however, no statistically significant differences were observed in any of the components of the eIF4E family in response to resistance exercise. These new data, along with our previous report on eIF2B, suggest that the regulation of peptide chain initiation after exercise is more dependent on eIF2B than on the eIF4E system.

Time course evaluation of protein synthesis and glucose uptake after acute resistance exercise in rats.

The temporal pattern for changes in rates of protein synthesis and glucose uptake after resistance exercise, especially relative to each other, is not known. Male Sprague-Dawley rats performed acute resistance exercise (n = 7) or remained sedentary (n = 7 per group), and the following were assessed in vivo 1, 3, 6, 12 and 24 h later: rates of protein synthesis, rates of glucose uptake, phosphatidylinositol 3-kinase (PI3-kinase) activity, and p70(S6k) activity. Rates of protein synthesis in mixed gastrocnemius muscle did not increase until 12 h after exercise (e.g., at 12 h, sedentary = 138 +/- 4 vs. exercised = 178 +/- 6 nmol phenylalanine incorporated x g muscle(-1) x h(-1), mean +/- SE, P < 0.05), whereas at 6 h after exercise rates of glucose uptake were significantly elevated (sedentary = 0.18 +/- 0.020 vs. exercised = 0.38 +/- 0.024 micromol glucose 6-phosphate incorporated x kg muscle(-1) x min(-1), P < 0.05). At 24 h after exercise, rates of protein synthesis were still elevated, whereas glucose uptake had returned to basal levels. Arterial insulin concentrations were not different between groups at any time. Non-insulin-stimulated activities of PI3-kinase and p70(S6k) were higher at 6, 12, and 24 h after exercise (P < 0.05), and, generally, these occurred when rates of protein synthesis (12 and 24 h) and glucose uptake were elevated (6 and 12 but not 24 h) by exercise. These data suggest that regulators of protein synthesis and glucose uptake may respond to the same contraction-generated signals with different kinetics or that they respond to different intra- or extracellular signals that are generated by exercise.

Severe diabetes prohibits elevations in muscle protein synthesis after acute resistance exercise in rats.

This study determined whether rates of protein synthesis increase after acute resistance exercise in skeletal muscle from severely diabetic rats. Previous studies consistently show that postexercise rates of protein synthesis are elevated in nondiabetic and moderately diabetic rats. Severely diabetic rats performed acute resistance exercise (n = 8) or remained sedentary (n = 8). A group of nondiabetic age-matched rats served as controls (n = 9). Rates of protein synthesis were measured 16 h after exercise. Plasma glucose concentrations were >500 mg/dl in the diabetic rats. Rates of protein synthesis (nmol phenylalanine incorporated. g muscle(-1). h(-1), means +/- SE) were not different between exercised (117 +/- 7) and sedentary (106 +/- 9) diabetic rats but were significantly (P < 0.05) lower than in sedentary nondiabetic rats (162 +/- 9) and in exercised nondiabetic rats (197 +/- 7). Circulating insulin concentrations were 442 +/- 65 pM in nondiabetic rats and 53 +/- 11 and 72 +/- 19 pM in sedentary and exercised diabetic rats, respectively. Plasma insulin-like growth factor I concentrations were reduced by 33% in diabetic rats compared with nondiabetic rats, and there was no difference between exercised and sedentary diabetic rats. Muscle insulin-like growth factor I was not affected by resistance exercise in diabetic rats. The results show that there is a critical concentration of insulin below which rates of protein synthesis begin to decline in vivo. In contrast to previous studies using less diabetic rats, severely diabetic rats cannot increase rates of protein synthesis after acute resistance exercise.

Attenuated insulin action on glucose uptake and transport in muscle following resistance exercise in rats.

A previous study reported elevations of insulin-mediated muscle protein synthesis following four days of resistance exercise in rats (Fluckey et al. 1996. Am J Physiol 270, E313-E319). The purpose of this study was to determine if insulin-stimulated muscle glucose uptake (a-v diff.) and 2-deoxyglucose (2-DG) transport were altered under similar conditions. The protocol consisted of squat-like exercises during four sessions with progressively increased weight (70-190 g). Each session consisted of 50 repetitions and sessions were separated by 48 h. Sixteen hours after the last exercise session, basal glucose uptake in perfused hindlimbs was not different (P > 0.05) between exercised (n=6) and non-exercised controls (n=6). However, there was a significant (P < 0.05) attenuation of insulin-stimulated (20 000 microU mL-1) glucose uptake in exercised vs. non-exercised rats (491 +/- 31 vs. 664 +/- 58 micromol glucose-1 g-1 [15-min insulin period]-1, respectively). Following resistance exercise, insulin-stimulated 2-DG transport, measured during the last 10 min of the perfusion period, was significantly reduced (P < 0.05) in the soleus, white gastrocnemius and extensor digitorum longus muscles. Additionally, GLUT-4 glucose transporter protein content was significantly reduced (P < 0.05) in white gastrocnemius and extensor digitorum longus muscles. These results demonstrate that insulin-stimulated glucose uptake and transport are reduced after resistance exercise. Furthermore, the applied resistance exercise protocol causes directionally opposite changes of insulin action in two major metabolic pathways, i.e. glucose transport and protein synthesis.

Pancreatic islet insulin secretion is increased after resistance exercise in rats.

The purpose of this study was to determine whether 4 days of resistance exercise facilitated insulin secretory adaptations at the level of the pancreatic islets. Eighteen male 400-g Sprague-Dawley rats were randomly assigned to two groups. All animals were operantly conditioned to engage in a resistance exercise protocol that required full extension of the hindlimbs. Resistance was applied to the animals via a leather-and-Velcro vest to which weighted pouches were attached. The acute (Acute, n = 9) group engaged in four exercise sessions (50 reps each) with increased resistance for each session (70-->120-->120-->190 g). Sessions were separated by 48 h of rest. The nonexercised (Nonex, n = 9) group engaged in the same protocol without resistance. Islets were dispersed 16 h postexercise, incubated for 48 h, and perifused (17-20 islets/rat) with a medium containing 10 mM L-arginine or 16 mM glucose as the insulin secretagogue. Basal insulin secretion from the islets before the introduction of L-arginine or 16 mM glucose was the same for the Acute and Nonex groups (P > 0.05). The total insulin response to 10 mM arginine was significantly higher for the Acute than for the Nonex group (1.16 +/- 0.30 and 0.31 +/- 0.10 ng insulin.islet-1.25 min-1, respectively, P < 0.05). There were no differences between groups for the overall insulin response to glucose (P > 0.05). However, the late-phase insulin response to glucose was higher for the Acute group (P < 0.05). These data suggest that insulin secretory adaptations occur at the level of the pancreatic islets after 4 days of resistance exercise.