The Positive Impact of Vitamin D on Glucocorticoid-Dependent Skeletal Muscle Atrophy

(1) The study aimed to investigate whether vitamin D₃ supplementation would positively affect rats with glucocorticoids-induced muscle atrophy as measured by skeletal muscle mass in two experimental conditions: chronic dexamethasone (DEX) administration and a model of the chronic stress response. (2) The study lasted 28 consecutive days and was performed on 45 male Wistar rats randomly divided into six groups. These included two groups treated by abdominal injection of DEX at a dose of 2 mg/kg/day supplemented with vegetable oil (DEX PL; n = 7) or with vitamin D₃ 600 IU/kg/day (DEX SUP; n = 8), respectively, and a control group treated with an abdominal injection of saline (CON; n = 6). In addition, there were two groups of rats chronically stressed by cold water immersion (1 hour/day in a glass box with 1-cm-deep ice/water mixture; temperature ~4 °C), which were supplemented with vegetable oil as a placebo (STR PL; n = 9) or vitamin D₃ at 600 IU/kg/day (STR SUP; n = 9). The last group was of sham-stressed rats (SHM; n = 6). Blood, soleus, extensor digitorum longus, gastrocnemius, tibialis anterior, and quadriceps femoris muscles were collected and weighed. The heart, liver, spleen, and thymus were removed and weighed immediately after sacrifice. The plasma corticosterone (CORT) and vitamin D₃ metabolites were measured. (3) We found elevated CORT levels in both cold water-immersed groups; however, they did not alter body and muscle weight. Body weight and muscle loss occurred in groups with exogenously administered DEX, with the exception of the soleus muscle in rats supplemented with vitamin D₃. Decreased serum 25(OH)D₃ concentrations in DEX-treated rats were observed, and the cold water immersion did not affect vitamin D₃ levels. (4) Our results indicate that DEX-induced muscle loss was abolished in rats supplemented with vitamin D₃, especially in the soleus muscle.

The effects of ryanodine receptor (RYR1) mutation on natural killer cell cytotoxicity, plasma cytokines and stress hormones during acute intermittent exercise in pigs

Stress susceptibility has been mapped to a single recessive gene, the ryanodine receptor 1 (RYR1) gene or halothane (Hal) gene. Homozygous (Hal(nn)), mutated pigs are sensitive to halothane and susceptible to Porcine Stress Syndrome (PSS). Previous studies have shown that stress-susceptible RYR1 gene mutated homozygotes in response to restraint stress showed an increase in natural killer cell cytotoxicity (NKCC) accompanied by more pronounced stress-related hormone and anti-inflammatory cytokine changes. In order to determine the relationship of a RYR1 gene mutation with NKCC, plasma cytokines and stress-related hormones following a different stress model - exercise - 36 male pigs (representing different genotypes according to RYR1 gene mutation: NN, homozygous dominant; Nn, heterozygous; nn, homozygous recessive) were submitted to an intermittent treadmill walking. During the entire experiment the greatest level of NKCC and the greatest concentrations of interleukin (IL-) 6, IL-10, IL-12, interferon (IFN-)γ and tumor necrosis factor-α and stress-related hormones (adrenaline, prolactin, beta-endorphin) were observed in nn pigs, and the greatest concentration of IL-1 and growth hormone in NN pigs. Immunostimulatory effects of intermittent exercise on NKCC in nn pigs were concomitant with increases in IL-2, IL-12 and IFN-γ, the potent NKCC activators. Our findings suggest that stress-susceptible pigs RYR1 gene mutated pigs develop a greater level of NKCC and cytokine production in response to exercise stress. These results suggest that the heterogeneity of immunological and neuroendocrine response to exercise stress in pigs could be influenced by RYR1 gene mutation.

Natural killer cell cytotoxicity, cytokine and neuroendocrine responses to opioid receptor blockade during prolonged restraint in pigs

This study evaluated porcine natural killer cell cytotoxicity (NKCC), plasma cytokines including interleukin (IL) 1β, IL-6, IL-10, IL-12 and tumor necrosis factor-α and plasma stress-related hormones including prolactin (PRL), growth hormone (GH), β-endorphin (BEND), ACTH and cortisol (COR) during a 4h restraint and recovery phase after saline or naloxone (1mg/kg BW) administration. The restraint preceded with saline altered NKCC and IL-12 concentration (an early from 15 to 60 min increase followed by a decrease) and increased other measured cytokines and hormones concentrations. Naloxone pretreatment blocked the suppressive effects of the restraint on NKCC and IL-12 and altered IL-10, IL-6, TNF-α, PRL and ACTH concentrations. Furthermore, in naloxone-injected pigs, a positive correlation was found between NKCC and all measured cytokines (with the exception of IL-6) and BEND, ACTH and COR. Results suggest that naloxone-sensitive opioid pathways could influence the mechanisms underlying the immune system (including NKCC) response during stress.

Restraint effects on stress-related hormones and blood natural killer cell cytotoxicity in pigs with a mutated ryanodine receptor

A mutation in the ryanodine receptor gene (RYR1) of the calcium release channel is responsible for increased stress susceptibility in pigs. In the present study, the relation of a mutation in RYR1 with the neuroendocrine (stress-related hormone) response and the immune defense represented by natural killer cell cytotoxicity (NKCC) during a 4-h restraint and recovery phase in 60 male pigs was investigated. Blood samples were collected from pigs previously divided into RYR1 genotypes (nn, Nn, NN), based on PCR amplification and restriction analyses. The blood samples collected during the restraint and recovery phases of the experiment were used to determine NKCC ((51)Cr-release assay), large granular lymphocyte number (hematologic method), and plasma concentrations of prolactin (PRL), GH, ACTH, and cortisol (COR) (by specific RIA). The greatest degree of NKCC response (P < 0.05) to restraint stress relative to controls was observed for the stress-susceptible homozygote group (nn). Measures of stress-related hormones were positively correlated with NKCC during the entire experimental period (P < 0.001 for all investigated hormones) in the nn group. Immunostimulatory effects in the early (0-60 min) phase of restraint were associated with increased hormone responses, especially PRL and GH. In the late (180-240 min) phase of stress and the recovery phase (480 min), a decrease in immune response was accompanied by an elevated COR response in all RYR1 genotypes. Moreover, divergent responses of both PRL (greatest in nn, P < 0.001) and GH (greatest in NN, P < 0.001) to the 4-h restraint were observed. Our results suggest that stress-susceptible RYR1-mutated homozygotes develop a greater level of immune defense, including cytotoxic activity of NK cells, and accompanied by more pronounced stress-induced changes in neuroendocrine response than stress-resistant heterozygous (Nn) and homozygous (NN) pigs.