Bone tissue changes in rats during prolonged restriction of motor activity

The objective of this investigation was to measure the effect of prolonged restriction of motor activity (hypokinesia) of rats on the mass, density, mineral composition, reconstruction parameters and elemental composition of their bone tissue. The studies were done during 90 days of hypokinesia (HK) on 90 male Wistar rats equally divided into two groups: (1) vivarium control rats (VCR) and (2) hypokinetic rats (HKR). For the simulation of the hypokinetic effect the HKR group was kept for 90 days in small individual cages made of wood that restricted the movements of rats in all directions without hindering food and water intakes. During the prehypokinetic period of 15 days and during the hypokinetic period of 90 days bone mass, bone density, bone calcium and phosphorus concentrations, bone reconstruction parameters and elemental composition of bones were determined. During the same periods food intake and body weight losses were also measured. In the HKR group signs of osteoporosis in the spongy structures of the tubular bones were observed; they also showed significant decrease in rat femur weight, and in cross section of the rat femur, and in mineral concentrations of the femoral head when compared with the VCR group. The HKR group also show a significant decrease in food intake and body weight when compared with the VCR group. The corresponding parameters did not change significantly in the VCR group when compared with the baseline control values. It was concluded that prolonged exposure to HK induced osteoporosis and structural changes in bones. This apparently occurred due to inhibition of bone tissue formation in the HKR group.     

Daily magnesium supplementation on serum and urinary magnesium changes in rats during prolonged restriction of motor activity

The objective of this investigation was to determine whether a plentiful magnesium (Mg²⁺) supplementation might be used to normalize or prevent Mg deficiency. This is manifested by increased rather than decreased serum Mg²⁺ concentration as is observed during prolonged hospitalization, which is developed during prolonged hypokinesia (HK) (decreased motor activity). Eighty male Wistar rats with an initial body weight of 370–390 g were used to perform the studies: They were equally divided into four groups:

1. Unsupplemented control animals (UCA);
2. Supplemented control animals (SCA);
3. Unsupplemented hypokinetic animals (UHA); and
4. Supplemented hypokinetic animals (SHA).

For the simulation of the hypokinetic effect, the hypokinetic animals were kept in small individual cages made of wood, which restricted their movements in all directions without hindering food and water intake. The control and hypokinetic supplemental animals receive 0.9 mg/mL Mg sulfate daily with their drinking water. Prior to and during the experimental period, urinary excretions of Mg, calcium, and phosphate along with their concentrations in serum, water intake, and urine excretion, and body weight were determined in the control and hypokinetic animals. In the supplemental and unsupplemental hypokinetic rats, urinary excretions and serum concentrations of electrolytes increased significantly, whereas serum concentration and urinary excretion thereof remained unchanged in the supplemented and unsupplemented control animals. It was concluded that a daily intake of large amounts of Mg supplementation cannot be used to prevent or normalize Mg deficiency in rats during prolonged exposure to HK.     

Daily zinc supplementation effect on zinc deficiency in rats during prolonged restriction of motor activity

The objective of this investigation was to evaluate the effect of 47 mg zinc supplementation on deficiency of zinc in rats during 98 d of restriction of motor activity (hypokinesia), which appeared by higher plasma zinc concentration. One Hundred 13-week-old Sprague-Dawley male rats weighing 360–390 g were used to perform the studies: They were equally divided into four groups: 1. Unsupplemented control animals (UCA); 2. Unsupplemented hypokinetic animals (UHA); 3. Supplemented control animals (SCA); and 4. Supplemented hypokinetic animals (SHA). For the simulation of the effect of hypokinesia (HK), the UHA and SHA were kept in small individual cages made of wood, which restricted their movements in all directions without hindering food and water intake. The SCA and SHA received daily with their food an additional amount of zinc. Before and during the experimental period of 98 d, plasma, urinary and fecal zinc, balance of zinc, food intake, and body weight were determined at different intervals. In the SHA and UHA, the concentration of zinc in plasma, and the elimination of zinc in urine and feces increased significantly when compared with the SCA and UCA, whereas the balance of zinc was negative. The body weight and food intake decreased significantly in the SHA and UHA when compared with the SCA and UCA. The increased plasma concentration of zinc in both the SHA and UHA groups was in contrast to the observed hypozincnemia during prolonged immobilization as during prolonged hospitalization. This reaction suggests that there may be some other mechanisms that are affecting the process of control and regulation of zinc metabolism during prolonged HK. It was concluded that exposure to prolonged restriction of motor activity of rats induces significant increases in plasma concentration, fecal and urinary elimination of zinc in the presence of negative zinc balance and regardless the daily intake of large amounts of zinc with their food, leading to zinc deficiency.     

SASCUBE: An Updated Method of Cubes for Calculation of the Intensity of X-Ray Scattering by Biopolymers in Solution

Biophysics - Abstract—This work describes an updated method of cubes, which allows calculation of the SAS curves for biopolymers in solution on the basis of the coordinates of their atoms...     

Magnesium loading effect on magnesium deficiency in endurance-trained subjects during prolonged restriction of muscular activity

The aim of this study was to evaluate the effect of magnesium (Mg) loading (10.0 mg Mg/kg body wt) and daily Mg supplements (5.0 mg Mg/kg body wt) on Mg deficiency shown by increased and not by decreased serum Mg concentration during hypokinesia (decreased km number/d). The studies were done during 30 d of prehypokinesia and 364 d of hypokinesia (HK) periods. Forty endurance-trained volunteers aged 22–26 yr with a peak VO2 max of 66.3 mL·kg⁻¹ min⁻¹ and with an average 15.0 km/d running distance were chose as subjects. They were equally divided into four groups:

Daily hyperhydration effect on electrolyte deficiency of endurance-Trained subjects during prolonged hypokinesia

The aim of this study was to evaluate the effect of a daily intake of fluid and salt supplementation (FSS) on the deficiency of electrolytes, which is characterized by higher rather than lower plasma concentration of electrolytes during prolonged hypokinesia (HK) (decreased number of km taken per day). Forty long distance runners aged 22–25 yr with a peak V0₂ 65.4 mL min^-1 kg^-1 with an average 14.2 km d running distance were selected as subjects. They were equally divided into four groups: 1) unsupplemented control subjects (UCS); 2) unsupplemented hypokinetic subjects (UHS); 3) supplemented hypokinetic subjects (SHS), and 4) supplemented control subjects (SCS). During the investigation of 364 d, groups 2 and 3 maintained an average running distance of less than 4.7 km per day, groups 1 and 4 did not experience any modification in their normal training routines and diets. During the preexperimental period of 60 d and during the experimental period of 364 d urinary excretion of electrolytes and concentrations of sodium, potassium, calcium, and magnesium in plasma were determined. Whole blood hemoglobin, hematocrit index, plasma osmolality, and plasma protein concentration were measured. In the UHS plasma concentration of electrolytes and urinary excretion thereof, fluid elimination, hematocrit, whole blood hemoglobin, plasma osmolality, and plasma protein concentration increased significantly (p < 0.05) when compared with the UCS, SCS, and SHS groups. In the SHS plasma concentration of electrolytes and urinary excretion thereof, fluid excretion, whole blood hemoglobin, hematocrit, plasma osmolality, and plasma protein concentration decreased when compared with the UHS and increased insignificantly when compared with the UCS and SCS groups. It was concluded that FSS may be used to prevent or minimize electrolyte deficiency in endurance-trained volunteers during prolonged restriction of muscular activity.     

Systemic and Cellular Responsiveness of the CNS to Hypoxia

We review some of the existing data on the problem of the influence of hypoxia (low partial O₂ pressure) on the state of the CNS. The sensitivity of various structures (in the brain cortex, diencephalon, brainstem, and spinal cord) is compared. Indications for a mosaic pattern of the adaptation processes in different compartments of the CNS are analyzed. It is emphasized that the sensitivity of certain CNS structures to insufficient oxygen supply is most probably governed by a phylogenetic vertical rather than an anatomical vertical principle. It is demonstrated that reactions of the neuron–glia complexes at the molecular and supramolecular levels form the basic level determining the pattern of responses of CNS structures to the dosed hypoxia; these reactions are reflected in changes in the states of the membrane and cytosol developing against the background of the expression activity in the genome apparatus together with corresponding changes in the synthesis of transmitters (nitric oxide, glutamate, other excitatory amino acids, etc.) and other biologically active substances, which determine transport of the substrates to tissues, control of intracellular transport, and oxygen consumption.     

Regulation of fatty acid composition of Cl. perfringens type A cells by hydrogen and hydroxyl ions

The composition of the fatty acid profiles of Cl. perfringens type A, grown on media with initial pH values from 5.5 to 9.0, was determined by the method of gas-liquid chromatography. The fatty acid profiles are stabilized in 18- to 24-h cultures. Hydrogen ions stimulate the synthesis of cyclopropane carboxylic fatty acids and "desaturase" activity; hydroxyl ions inhibit these processes. The content of saturated fatty acids in the bacteria is regulated by the initial acid-alkaline conditions of the medium. An increase in biomass accumulation under the influence of hydroxyl ions is coupled with a decrease in the energy supply of the bacteria. Possible mechanisms of the development of resistance to hydrogen and hydroxyl ions during the cultivation of Clostridia on a period growth medium are discussed.     

Myofibrillar disruption in hypocontractile myocardium showing perfusion-contraction matches and mismatches

Chronically instrumented dogs underwent 2- or 5-h regional reductions in coronary flow that were followed, respectively, by balanced reductions in myocardial contraction and O(2) consumption ("hibernation") and persistently reduced contraction despite normal myocardial O(2) consumption ("stunning"). Previously unidentified myofibrillar disruption developed during flow reduction in both experimental models and persisted throughout the duration of reperfusion (2-24 h). Aberrant perinuclear aggregates that resembled thick filaments and stained positively with a monoclonal myosin antibody were present in 34 +/- 3.8% (SE) and 68 +/- 5.9% of "hibernating" and "stunned" subendocardial myocytes in areas subjected to flow reduction and in 16 +/- 2.5% and 44 +/- 7.4% of subendocardial myocytes in remote areas of the same ventricles. Areas of myofibrillar disruption also showed glycogen accretion and unusual heterochromatin clumping adjacent to the inner nuclear envelope. The degrees of flow reduction employed were sufficient to reduce regional myofibrillar creatine kinase activity by 25-35%, but troponin I degradation was not evident. The observed changes may reflect an early, possibly reversible, phase of the myofibrillar loss characteristic of hypocontractile myocardium in patients undergoing revascularization.     

Urinary and plasma calcium changes in endurance trained volunteers during exposure to acute and rigorous bed rest conditions

The purpose of the present study was to evaluate the effect of acute (abrupt restriction of muscular activity) and rigorous bed-rest conditions on urinary and plasma calcium changes in endurance trained volunteers. The studies were performed on 30 long distance runners ages 23–25 who had a peak oxygen uptake of 66.0 mL/min/kg and had run 14.0 km/d on the average prior to their participation in the study. The volunteers were divided into three groups: The volunteers in the first group were under normal ambulatory conditions (control subjects), the second group was subjected to an acute bed-rest regime (acute bedrested subjects), and the third group was submitted to a rigorous bed-rest regime (rigorous bedrested subjects). The second and third groups of volunteers were kept under a rigorous bed rest regime for 7 d. During the pre-bed-rest period and during the actual bed-rest periods (acute and rigorous bed-rest periods), urinary excretion of calcium and plasma calcium and parathyroid hormone (PTH) concentrations were determined. During the 1st d of acute and rigorous bed-rest periods, urinary excretion and plasma concentration of calcium increased significantly (P≤0.05), while plasma parathyroid hormone content decreased significantly (P≤0.05). On the 3rd d of the experimental period, urinary excretion and plasma calcium concentration decreased somewhat, during the 7th d, calcium in urine and plasma increased further, while parathyroid hormone content in plasma increased somewhat on the 3rd d and decreased again on the 7th d of the experimental period. The changes were more pronounced in the volunteers who were subjected to acute bed-rest conditions than in the volunteers who were submitted to rigorous bed-rest conditions. It was concluded that exposure to acute bed-rest conditions induces significantly greater urinary and serum calcium changes than rigorous bed-rest conditions in endurance trained volunteers.