Recent evidence suggested that Na can be stored in an osmotically inactive form. We investigated whether osmotically inactive Na storage is reduced in a rat model of salt-sensitive (SS) hypertension. SS and salt-resistant (SR) Dahl-Rapp rats as well as Sprague-Dawley (SD) rats were fed a high (8%)-or low (0.1%)-NaCl diet for 4 wk (n ϭ 10/group). Mean arterial pressure (MAP) was measured at the end of the experiment. Wet and dry weights, water content, total body Na (TBS), and bone Na content were measured by dessication and dry ashing. MAP was higher in both Dahl strains than in SD rats. In SS rats, 8% NaCl led to Na accumulation, water retention, and hypertension due to impaired renal Na excretion. There was no dietary-induced Na retention in SR and SD rats. TBS was variable; nevertheless, TBS was significantly correlated with body water and MAP in all strains. However, the extent of Na-associated volume and MAP increases was strain specific. Osmotically inactive Na in SD rats was threefold higher than in SS and SR rats. Both SS and SR Dahl rat strains displayed reduced osmotically inactive Na storage capacity compared with SD controls. A predisposition to fluid accumulation and high blood pressure results from this alteration. Additional factors, including impaired renal Na excretion, probably contribute to hypertension in SS rats. Our results draw attention to the role of osmotically inactive Na storage. salt sensitive; bone sodium; Dahl rats THE RELATIONSHIP BETWEEN SALT intake and blood pressure has been extensively studied in humans and provides evidence that subpopulations of humans are sensitive to alterations in salt intake. A well-established animal model for salt-sensitive (SS) hypertension is the Dahl rat. SS rats develop hypertension when fed a high-NaCl diet (6). Salt-resistant (SR) Dahl rats developed increased blood pressure after they received a transplanted kidney from an SS donor animal. Conversely, transplantation of SR donor kidneys into SS rats lowers blood pressure (5, 10). Despite the fact that the glomerular filtration rate is not different between both strains (2, 14), SS rats have an impaired ability to excrete Na (1, 2). However, this feature does not fully explain the development of SS hypertension (11). Thus the role of Na retention in the development of hypertension is unclear.Recent studies on long-term Na balance in humans showed that high dietary Na consumption with Na retention does not necessarily lead to expansion of the extracellular volume (8). This finding suggests that Na might be stored in an osmotically inactive form. We studied the relationship between osmotically inactive Na storage, total body Na (TBS), total body water (TBW), and hypertension in Dahl SS rats and control animals. Our initial primary hypothesis was that Dahl SS rats exhibit a reduced capacity for osmotically inactive Na storage that would predispose these animals to volume retention and thus lead to SS hypertension. The secondary hypothesis was that osmotically inactive Na storage is also deficient in...

Femoral neck anteversion (FNA), also called femoral torsion or femoral version, is the angle between the projection of two lines in the axial plane perpendicular to the femoral shaft; one line going through the proximal femoral neck region and the second one through the distal condylar region (Figure 1), indicating the degree of 'twist' of the femur. FNA affects the biomechanics of the hip, as moment arms and the line of action of muscles around the joint are altered. As a result, FNA is associated with differences in gait and is a risk factor for clinical problems

BackgroundMuscle mass and function are perturbed by immobilization and remobilization. When muscle mass changes, the quality and quantity of the extracellular matrix protein, particularly the collagens, change with it. In this study, we investigated the temporal profile of three peptide biomarkers derived from turnover of collagen type III and type VI in a long-term immobilization and remobilization study. We also compared individual biomarker levels with Lean body Mass (LBM) and changes therein, hypothesizing that these biomarkers would be biomarkers of the remodeling processes associated with immobilization and/or remobilization.MethodsIn the Berlin bed rest study, 20 young men were recruited and randomly assigned to 8-week’s strict bed rest with or without resistive vibration exercise countermeasure. We measured three neo-epitope ELISA kits in the serum samples of this study: Pro-C3, measured the synthesis of collagen type III; Pro-C6, measured the synthesis of collagen type VI; and C6M measured the degradation of collagen type VI induced by MMP-2 and MMP-9 cleavage.ResultsPro-C3 and Pro-C6 biomarkers are up-regulated with both immobilization and remobilization, whereas C6M is hardly affected at all. We found that Pro-C3 and C6M levels are related to LBM at baseline and that high levels of Pro-C6 are associated with smaller changes in muscle mass during both immobilization and remobilization.ConclusionThe Pro-C3 and–C6 biomarkers change likely reflect remodeling changes in response to unloading or reloading, whereas C6M does not appear to respond to unloading. Pro-C3 and C6M levels correlate with LBM at baseline, while Pro-C6 is related to the anabolic and catabolic responses to unloading and reloading.

An integrative evaluation of oxidative metabolism was carried out in 9 healthy young men (age, 24.1 ± 1.7 yr mean ± SD) before (CTRL) and after a 10-day horizontal bed rest carried out in normoxia (N-BR) or hypoxia (H-BR, FiO2 = 0.147). H-BR was designed to simulate planetary habitats. Pulmonary O2 uptake (V̇o2) and vastus lateralis fractional O2 extraction (changes in deoxygenated hemoglobin+myoglobin concentration, Δ[deoxy(Hb+Mb)] evaluated using near-infrared spectroscopy) were evaluated in normoxia and during an incremental cycle ergometer (CE) and one-leg knee extension (KE) exercise (aimed at reducing cardiovascular constraints to oxidative function). Mitochondrial respiration was evaluated ex vivo by high-resolution respirometry in permeabilized vastus lateralis fibers. During CE V̇o2peak and Δ[deoxy(Hb+Mb)]peak were lower (P < 0.05) after both N-BR and H-BR than during CTRL; during KE the variables were lower after N-BR but not after H-BR. During CE the overshoot of Δ[deoxy(Hb+Mb)] during constant work rate exercise was greater in N-BR and H-BR than CTRL, whereas during KE a significant difference vs. CTRL was observed only after N-BR. Maximal mitochondrial respiration determined ex vivo was not affected by either intervention. In N-BR, a significant impairment of oxidative metabolism occurred downstream of central cardiovascular O2 delivery and upstream of mitochondrial function, possibly at the level of the intramuscular matching between O2 supply and utilization and peripheral O2 diffusion. Superposition of hypoxia on bed rest did not aggravate, and partially reversed, the impairment of muscle oxidative function in vivo induced by bed rest. The effects of longer exposures will have to be determined.