ALBERT

Description: Testes from flight rats on COSMOS 2044 and simulated-launch, vivarium, or caudal-elevation control rats (5/group) were analyzed by subjective and quantitative methods. On the basis of observations of fixed tissue, it was evident that some rats had testicular abnormalities unassociated with treatment and probably existing when they were assigned randomly to the four treatment groups. Considering rats without preexisting abnormalities, diameter of seminiferous tubules and numbers of germ cells per tubule cross section were lower (P less than 0.05) in flight than in simulated-launch or vivarium rats. However, ratios of germ cells to each other or to Sertoli cells and number of homogenization-resistant spermatids did not differ from values for simulated-launch or vivarium controls. Expression of testis-specific gene products was not greatly altered by flight. Furthermore, there was no evidence for production of stress-inducible transcripts of the hsp7O or hsp9O genes. Concentration of receptors for rat luteinizing hormone in testicular tissue and surface density of smooth endoplasmic reticulum in Leydig cells were similar in flight and simulated-launch rats. However, concentrations of testosterone in testicular tissue or peripheral blood plasma were reduced (P less than 0.05) in flight rats to less than 20% of values for simulated-launch or vivarium controls. Thus spermatogenesis was essentially normal in flight rats, but production of testosterone was severely depressed. Exposure to microgravity for more than 2 wk might result in additional changes. Sequelae of reduced androgen production associated with microgravity on turnover of muscle and bone should be considered.

Description: No abstract available

Description: No abstract available

Description: Ventilation-perfusion (VA/Q) inequality has been shown to increase with exercise. Potential mechanisms for this increase include nonuniform pulmonary vasoconstriction, ventilatory time constant inequality, reduced large airway gas mixing, and development of interstitial pulmonary edema. We hypothesized that persistence of VA/Q mismatch after ventilation and cardiac output subside during recovery would be consistent with edema; however, rapid resolution would suggest mechanisms related to changes in ventilation and blood flow per se. Thirteen healthy males performed near-maximal cycle ergometry at an inspiratory PO2 of 91 Torr (because hypoxia accentuates VA/Q mismatch on exercise). Cardiorespiratory variables and inert gas elimination patterns were measured at rest, during exercise, and between 2 and 30 min of recovery. Two profiles of VA/Q distribution behavior emerged during heavy exercise: in group 1 an increase in VA/Q mismatch (log SDQ of 0.35 +/- 0.02 at rest and 0.44 +/- 0.02 at exercise; P less than 0.05, n = 7) and in group 2 no change in VA/Q mismatch (n = 6). There were no differences in anthropometric data, work rate, O2 uptake, or ventilation during heavy exercise between groups. Group 1 demonstrated significantly greater VA/Q inequality, lower vital capacity, and higher forced expiratory flow at 25-75% of forced vital capacity for the first 20 min during recovery than group 2. Cardiac index was higher in group 1 both during heavy exercise and 4 and 6 min postexercise. However, both ventilation and cardiac output returned toward baseline values more rapidly than did VA/Q relationships. Arterial pH was lower in group 1 during exercise and recovery. We conclude that greater VA/Q inequality in group 1 and its persistence during recovery are consistent with the hypothesis that edema occurs and contributes to the increase in VA/Q inequality during exercise. This is supported by observation of greater blood flows and acidosis and, presumably therefore, higher pulmonary vascular pressures in such subjects.

Description: Matrix vesicles isolated from fourth-passage cultures of chondrocytes were tested for their ability to induce hydroxyapatite formation in a gelatin gel in order to gain insight into the function of matrix vesicles in in situ mineralization. These matrix vesicles did not appear to be hydroxyapatite nucleators per se since the extent of mineral accumulation in the gel diffusion system was not altered by the presence of matrix vesicles alone, and in the vesicle containing gels, mineral crystals were formed whether associated with vesicles or not. In gels with these matrix vesicles and beta-glycerophosphate, despite the presence of alkaline phosphatase activity, there was no increase in mineral deposition. This suggested that in the gel system these culture-derived vesicles did not increase local phosphate concentrations. However, when known inhibitors of mineral crystal formation and growth (proteoglycan aggregates [4 mg/ml], or ATP [1 mM], or both proteoglycan and ATP) were included in the gel, more mineral was deposited in gels with the vesicles than in comparable gels without vesicles, indicating that enzymes within these vesicles were functioning to remove the inhibition. These data support the suggestion that one function of the extracellular matrix vesicles is to transport enzymes for matrix modification.

Description: Decreased postural stability is observed in most astronauts immediately following spaceflight. Because ataxia may present postflight operational hazards, it is important to determine the incidence of postural instability immediately following landing and the dynamics of recovery of normal postural equilibrium control. It is postulated that postflight postural instability results from in-flight adaptive changes in central nervous system (CNS) processing of sensory information from the visual, vestibular, and proprioceptive systems. The purpose of the present investigation was to determine the magnitude and time course of postflight recovery of postural equilibrium control and, hence, readaptation of CNS processing of sensory information. Thirteen crew members from six spaceflight missions were studied pre- and postflight using a modified commercial posturography system. Postural equilibrium control was found to be seriously disrupted immediately following spaceflight in all subjects. Readaptation to the terrestrial environment began immediately upon landing, proceeded rapidly for the first 10-12 hours, and then proceeded much more slowly for the subsequent 2-4 days until preflight stability levels were reachieved. It is concluded that the overall postflight recovery of postural stability follows a predictable time course.

Description: A new technique for simultaneously recording continuous electrocardiographic (ECG) data and walking step rate (cadence) is described. The ECG and gait signals are recorded on 2 channels of an ambulatory Holter monitor. Footfall is detected using ultrathin, force-sensitive foot switches and is frequency modulated. The footfall signal provides an indication of the subject's activity (walking or standing), as well as the instantaneous walking rate. Twenty-three young and elderly subjects were studied to demonstrate the use of this ECG and gait recorder. High-quality gait signals were obtained in all subjects, and the effects of walking on the electrocardiogram were assessed. Initial investigation revealed the following findings: (1) Although walking rates were similar in young and elderly subjects, the elderly had both decreased heart rate (HR) variability (p 〈 0.005) and increased cadence variability (p 〈 0.0001). (2) Overall, there was an inverse relation between HR and cadence variability (r = -0.73). Three elderly subjects with no known cardiac disease had HR and cadence variability similar to those of the young, whereas elderly subjects with history of congestive heart failure were among those with the lowest HR variability and the highest cadence variability. (3) Low-frequency (approximately equal to 0.1 Hz) HR oscillations (frequently observed during standing) persisted during walking in all young subjects. (4) In some subjects, both step rate and HR oscillated at the same low frequency (approximately equal to 0.1 Hz) previously identified with autonomic control of the baroreflex.(ABSTRACT TRUNCATED AT 250 WORDS).

Description: It is not known whether the asymptotic behavior of whole body O2 consumption (VO2) at maximal work rates (WR) is explained by similar behavior of VO2 in the exercising legs. To resolve this question, simultaneous measurements of body and leg VO2 were made at submaximal and maximal levels of effort breathing normoxic and hypoxic gases in seven trained male cyclists (maximal VO2, 64.7 +/- 2.7 ml O2.min-1.kg-1), each of whom demonstrated a reproducible VO2-WR asymptote during fatiguing incremental cycle ergometry. Left leg blood flow was measured by constant-infusion thermodilution, and total leg VO2 was calculated as the product of twice leg flow and radial arterial-femoral venous O2 concentration difference. The VO2-WR relationships determined at submaximal WR's were extrapolated to maximal WR as a basis for assessing the body and leg VO2 responses. The differences between measured and extrapolated maximal VO2 were 235 +/- 45 (body) and 203 +/- 70 (leg) ml O2/min (not significantly different). Plateauing of leg VO2 was associated with, and explained by, plateauing of both leg blood flow and O2 extraction and hence of leg VO2. We conclude that the asymptotic behavior of whole body VO2 at maximal WRs is a direct reflection of the VO2 profile at the exercising legs.

Description: Insights into muscle energetics during exercise (e.g., muscular efficiency) are often inferred from measurements of pulmonary gas exchange. This procedure presupposes that changes of pulmonary O2 (VO2) associated with increases of external work reflect accurately the increased muscle VO2. The present investigation addressed this issue directly by making simultaneous determinations of pulmonary and leg VO2 over a range of work rates calculated to elicit 20-90% of maximum VO2 on the basis of prior incremental (25 or 30 W/min) cycle ergometry. VO2 for both legs was calculated as the product of twice one-leg blood flow (constant-infusion thermodilution) and arteriovenous O2 content difference across the leg. Measurements were made 3-5 min after each work rate imposition to avoid incorporation of the VO2 slow component above the lactate threshold. For all 17 subjects, the slope of pulmonary VO2 (9.9 +/- 0.2 ml O2.W-1.min-1) was not different (P greater than 0.05) from that for leg VO2 (9.2 +/- 0.6 ml O2.W-1.min-1). Estimation of "delta" efficiency (i.e., delta work accomplished divided by delta energy expended, calculated from slope of VO2 vs. work rate and a caloric equivalent for O2 of 4.985 cal/ml) using pulmonary VO2 measurements (29.1 +/- 0.6%) was likewise not significantly different (P greater than 0.05) from that made using leg VO2 measurements (33.7 +/- 2.4%). These data suggest that the net VO2 cost of metabolic "support" processes outside the exercising legs changes little over a relatively broad range of exercise intensities. Thus, under the conditions of this investigation, changes of VO2 measured from expired gas reflected closely those occurring within the exercising legs.

Description: Pulmonary intravascular macrophages (PIMs) are lung macrophages found apposed to the endothelium of pulmonary capillaries. In many species, they are responsible for the clearance of blood-borne particulates and pathogens; however, little else is known about their roles as immunologic effector cells. We compared PIMs with pulmonary alveolar macrophages (PAMs) to determine the relative immunological activities of these two cell populations. Our results suggested that both populations possess similar phagocytic and bactericidal activities. In assays measuring cytotoxicity, PIMs were more cytotoxic than PAMs against virally infected target cells; however, differences between these macrophage populations were not as marked when noninfected targets were used. LPS-stimulated PIMs produced more T-cell proliferative cytokines than PAMs, and both populations of nonstimulated macrophages produced similar amounts of the cytokines. In contrast, PAMs produced more TNF alpha and NO2- than PIMs when both populations were stimulated with LPS; however, nonstimulated PAMs and PIMs produced similar amounts of TNF alpha and NO2. These data suggest that bovine PIMs are immunologically active. Differences between the degrees of activity of PIMs and PAMs indicate that these macrophage populations may have different roles in lung surveillance.