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PubMed2002

Endocytosis in tobacco pollen tubes: visualisation and measurement of plasma membrane retrieval during different gravity conditions indicates gravity-dependence of endocytosis.

We studied the effect of microgravity on endocytosis in growing tobacco pollen tubes by measuring the plasma membrane retrieval employing the fluorescent phospholipid bis-Bodipy FL C11- phosphatidylcholine as marker. Time course experiments under 1xg condition revealed a localised and relatively fast plasma membrane retrieval in the pollen tube tip region within the first minutes after lipid application. The rate of endocytotic bis-Bodipy FL C11- PC-modified plasma membrane retrieval is inhibited by hyper-g conditions achieved by centriftigal forces. In contrast, during the microgravity phase of a parabolic rocket flight the retrieval of the fluorescently-marked plasma membrane is distinctly enhanced. Our results show that microgravity exerts an unspecific physiological response in pollen tubes, most likely involving the cytoskeleton as inhibitor experiments indicate under 1xg condition.

Journal Article↗
PubMed2004

[Biology of size and gravity].

Gravity is a force that acts on mass. Biological effects of gravity and their magnitude depend on scale of mass and difference in density. One significant contribution of space biology is confirmation of direct action of gravity even at the cellular level. Since cell is the elementary unit of life, existence of primary effects of gravity on cells leads to establish the firm basis of gravitational biology. However, gravity is not limited to produce its biological effects on molecules and their reaction networks that compose living cells. Biological system has hierarchical structure with layers of organism, group, and ecological system, which emerge from the system one layer down. Influence of gravity is higher at larger mass. In addition to this, actions of gravity in each layer are caused by process and mechanism that is subjected and different in each layer of the hierarchy. Because of this feature, summing up gravitational action on cells does not explain gravity for biological system at upper layers. Gravity at ecological system or organismal level can not reduced to cellular mechanism. Size of cells and organisms is one of fundamental characters of them and a determinant in their design of form and function. Size closely relates to other physical quantities, such as mass, volume, and surface area. Gravity produces weight of mass. Organisms are required to equip components to support weight and to resist against force that arise at movement of body or a part of it. Volume and surface area associate with mass and heat transport process at body. Gravity dominates those processes by inducing natural convection around organisms. This review covers various elements and process, with which gravity make influence on living systems, chosen on the basis of biology of size. Cells and biochemical networks are under the control of organism to integrate a consolidated form. How cells adjust metabolic rate to meet to the size of the composed organism, whether is gravity responsible for this feature, are subject we discuss in this article. Three major topics in gravitational and space biology are; how living systems have been adapted to terrestrial gravity and evolved, how living systems respond to exotic gravitational environment, and whether living systems could respond and adapt to microgravity. Biology of size can contribute to find a way to answer these question, and answer why gravity is important in biology, at explaining why gravity has been a dominant factor through the evolutional history on the earth.

Adaptation, Physiological↗
PubMed1994

Artificial gravity in space and in medical research.

The history of manned space flight has repeatedly documented the fact that prolonged sojourn in space causes physiological deconditioning. Physiological deterioration has raised a legitimate concern about man's ability to adequately perform in the course of long missions and even the possibility of leading to circumstances threatening survival. One of the possible countermeasures of physiological deconditioning, theoretically more complete than others presently used since it affects all bodily systems, is artificial gravity. Space stations and spacecrafts can be equipped with artificial gravity, but is artificial gravity necessary? The term "necessary" must be qualified because a meaningful answer to the question depends entirely on further defining the purpose of space travel. If man intends to stay only temporarily in space, then he must keep himself in good physical condition so as to be able to return to earth or to land on any other planetary surface without undue exposure to major physiological problems resulting from transition through variable gravitational fields. Such a situation makes artificial gravity highly desirable, although perhaps not absolutely necessary in the case of relative short exposure to microgravity, but certainly necessary in interplanetary flight and planetary landings. If the intent is to remain indefinitely in space, to colonize space, then artificial gravity may not be necessary, but in this case the consequences of long term effects of adaptation to weightlessness will have to be weighed against the biological evolutionary outcomes that are to be expected. At the moment, plans for establishing permanent colonies in space seem still remote. More likely, the initial phase of exploration of the uncharted solar system will take place through successive, scope limited, research ventures ending with return to earth. This will require man to be ready to operate in gravitational fields of variable intensity. Equipping spacecrafts or space stations with some means of artificial gravity in this initial phase is, therefore, necessary without question. In a strict sense artificial gravity is conceived as a means of replacing natural gravity in space by the centripetal acceleration generated by some sort of rotating device. Rotating devices create an inertial force which has effects on bodies similar to those caused by terrestrial gravity, but artificial gravity by a rotation device is not the same as terrestrial gravity, as we shall see. Present research in artificial gravity for space exploration is projected in two main directions: artificial gravity for whole space stations and artificial gravity produced by short arm centrifuges designed for human use in space.

Adolescent↗
PubMed2006

A modeling study of the effect of gravity on airflow distribution and particle deposition in the lung.

Inhalation of particles generated as a result of thermal degradation from fire or smoke, as may occur on spacecraft, is of major health concern to space-faring countries. Knowledge of lung airflow and particle transport under different gravity environments is required to addresses this concern by providing information on particle deposition. Gravity affects deposition of particles in the lung in two ways. First, the airflow distribution among airways is changed in different gravity environments. Second, particle losses by sedimentation are enhanced with increasing gravity. In this study, a model of airflow distribution in the lung that accounts for the influence of gravity was used for a mathematical description of particle deposition in the human lung to calculate lobar, regional, and local deposition of particles in different gravity environments. The lung geometry used in the mathematical model contained five lobes that allowed the assessment of lobar ventilation distribution and variation of particle deposition. At zero gravity, it was predicted that all lobes of the lung expanded and contracted uniformly, independent of body position. Increased gravity in the upright position increased the expansion of the upper lobes and decreased expansion of the lower lobes. Despite a slight increase in predicted deposition of ultrafine particles in the upper lobes with decreasing gravity, deposition of ultrafine particles was generally predicted to be unaffected by gravity. Increased gravity increased predicted deposition of fine and coarse particles in the tracheobronchial region, but that led to a reduction or even elimination of deposition in the alveolar region for coarse particles. The results from this study show that existing mathematical models of particle deposition at 1 G can be extended to different gravity environments by simply correcting for a gravity constant. Controlled studies in astronauts on future space missions are needed to validate these predictions.

Airway Resistance↗
PubMed2002

Microtubule self-organisation and its gravity dependence.

The molecular processes by which gravity affects biological systems are poorly, if at all, understood. Under equilibrium conditions, chemical and biochemical reactions do not depend upon gravity. It has been proposed that biological systems might depend on gravity by way of the bifurcation properties of certain types of non-linear chemical reactions that are far-from-equilibrium. In such reactions, the initially homogenous solution spontaneously self-organises by way of a combination of reaction and diffusion. Theoreticians have predicted that the presence or absence of an external field, such as gravity, at a critical moment early in the self-organising process may determine the morphology that subsequently develops. We have found that the formation in vitro of microtubules, a major element of the cellular skeleton, shows this type of behaviour. The microtubule preparations spontaneously self-organise by way of reaction and diffusion, and the morphology of the state that forms depends upon gravity at a critical bifurcation time early in the process. Experiments carried out under low gravity conditions show that the presence of gravity at the bifurcation time actually triggers the self-organising process. This is an experimental demonstration of how a very simple biochemical system, containing only two molecules, can be gravity sensitive. At a microscopic level the behaviour results from an interaction of gravity with the concentration and density fluctuations that arise from processes of microtubule shortening and elongation. We have developed a numerical reaction-diffusion scheme, based on the chemical dynamics of a population of microtubules, that simulate self-organisation. These simulations provide insight into how self-organisation occurs at a microscopic level and how gravity triggers this process. Recent experiments on cell lines cultured in space suggest that microtubule organisation may not occur properly under low gravity conditions. As microtubule organisation is essential to cellular function, it is quite plausible that the type of processes described in this article provide an underlying explanation for the gravity dependence of living systems at a cellular level.

Diffusion↗
PubMed2000

Exploring dynamic similarity in human running using simulated reduced gravity.

The Froude number (a ratio of inertial to gravitational forces) predicts the occurrence of dynamic similarity in legged animals over a wide range of sizes and velocities for both walking and running gaits at Earth gravity. This is puzzling because the Froude number ignores elastic forces that are crucial for understanding running gaits. We used simulated reduced gravity as a tool for exploring dynamic similarity in human running. We simulated reduced gravity by applying a nearly constant upward force to the torsos of our subjects while they ran on a treadmill. We found that at equal Froude numbers, achieved through different combinations of velocity and levels of gravity, our subjects did not run in a dynamically similar manner. Thus, the inertial and gravitational forces that comprise the Froude number were not sufficient to characterize running in reduced gravity. Further, two dimensionless numbers that incorporate elastic forces, the Groucho number and the vertical Strouhal number, also failed to predict dynamic similarity in reduced-gravity running. To better understand the separate effects of velocity and gravity, we also studied running mechanics at fixed absolute velocities under different levels of gravity. The effects of velocity and gravity on the requirements of dynamic similarity differed in both magnitude and direction, indicating that there are no two velocity and gravity combinations at which humans will prefer to run in a dynamically similar manner. A comparison of walking and running results demonstrated that reduced gravity had different effects on the mechanics of each gait. This suggests that a single unifying hypothesis for the effects of size, velocity and gravity on both walking and running gaits will not be successful.

Animals↗
PubMed2003

Calcium signaling in plant cells in altered gravity.

Changes in the intracellular Ca2+ concentration in altered gravity (microgravity and clinostating) evidence that Ca2+ signaling can play a fundamental role in biological effects of microgravity. Calcium as a second messenger is known to play a crucial role in stimulus-response coupling for many plant cellular signaling pathways. Its messenger functions are realized by transient changes in the cytosolic ion concentration induced by a variety of internal and external stimuli such as light, hormones, temperature, anoxia, salinity, and gravity. Although the first data on the changes in the calcium balance in plant cells under the influence of altered gravity have appeared in 80th, a review highlighting the performed research and the possible significance of such Ca2+ changes in the structural and metabolic rearrangements of plant cells in altered gravity is still lacking. In this paper, an attempt was made to summarize the available experimental results and to consider some hypotheses in this field of research. It is proposed to distinguish between cell gravisensing and cell graviperception; the former is related to cell structure and metabolism stability in the gravitational field and their changes in microgravity (cells not specialized to gravity perception), the latter is related to active use of a gravitational stimulus by cells presumebly specialized to gravity perception for realization of normal space orientation, growth, and vital activity (gravitropism, gravitaxis) in plants. The main experimental data concerning both redistribution of free Ca2+ ions in plant cell organelles and the cell wall, and an increase in the intracellular Ca2+ concentration under the influence of altered gravity are presented. Based on the gravitational decompensation hypothesis, the consequence of events occurring in gravisensing cells not specialized to gravity perception under altered gravity are considered in the following order: changes in the cytoplasmic membrane surface tension --> alterations in the physicochemical properties of the membrane --> changes in membrane permeability, ion transport, membrane-bound enzyme activity, etc. --> metabolism rearrangements --> physiological responses. An analysis of data available on biological effects of altered gravity at the cellular level allows one to conclude that microgravity environment appears to affect cytoskeleton, carbohydrate and lipid metabolism, cell wall biogenesis via changes in enzyme activity and protein expression, with involvement of regulatory Ca2+ messenger system. Changes in Ca2+ influx/efflux and possible pathways of Ca2+ signaling in plant cell biochemical regulation in altered gravity are discussed.

Calcium↗
PubMed1995

Does Paramecium sense gravity?

In order to get an insight into the cellular mechanisms for the integration of the effects of gravity, we investigated the gravitactic behaviour in Paramecium. There are two main categories for the model of the mechanism of gravitaxis; one is derived on the basis of the mechanistic properties of the cell (physical model) and the other of the physiological properties including cellular gravireception (physiological model). In this review article, we criticized the physical models and introduced a new physiological model. Physical models postulated so far can be divided into two; one explaining the negative gravitactic orientation of the cell in terms of the static torque generated by the structural properties of the cell (gravity-buoyancy model by Verworn, 1889 and drag-gravity model by Roberts, 1970), and the other explaining it in terms of the dynamic torque generated by the helical swimming of the cell (propulsion-gravity model by Winet and Jahn, 1974 and lifting-force model by Nowakowska and Grebecki, 1977). Among those we excluded the possibility of dynamic-torque models because of their incorrect theoretical assumptions. According to the passive orientation of Ni(2+)-immobilized cells, the physical effect of the static torque should be inevitable for the gravitactic orientation. Downward orientation of the immobilized cells in the course of floating up in the hyper-density medium demonstrated the gravitactic orientation is not resulted by the nonuniform distribution of cellular mass (gravity-buoyancy model) but by the fore-aft asymmetry of the cell (drag-gravity model). A new model explaining the gravitactic behaviour is derived on the basis of the cellular gravity sensation through mechanoreceptor channels of the cell membrane. Paramecium is known to have depolarizing receptor channels in the anterior and hyperpolarizing receptors in the posterior of the cell. The uneven distribution of the receptor may lead to the bidirectional changes of the membrane potential by the selective deformation of the anterior and posterior cell membrane responding to the orientation of the cell in the gravity field; i.e. negative- and positive-going shift of the potential due to the upward and downward orientation, respectively. The orientation dependent changes in membrane potential with respect to gravity, in combination with the close coupling of the membrane potential and the ciliary locomotor activity, may allow the changes in swimming direction along with those in the helical nature of the swimming path; upward shift of axis of helix by decreasing the pitch angle due to hyperpolarization in the upward-orienting cell, and also the upward shift by increasing the pitch angle due to depolarization in the downward-orienting cell. Computer simulation of the model demonstrated that the cell can swim upward along the "super-helical" trajectory consisting of a small helix winding helically an axis parallel to the gravity vector, after which the model was named as "Super-helix model". Three-dimensional recording of the trajectories of the swimming cells demonstrated that about a quarter of the cell population drew super-helical trajectory under the unbounded, thermal convection-free conditions. In addition, quantitative analysis of the orientation rate of the swimming cell indicated that gravity-dependent orientation of the swimming trajectory could not be explained solely by the physical static torque but complementarily by the physiological mechanism as proposed in the super-helix model.

Animals↗
PubMed2001

Factors associated with colostral specific gravity in dairy cows.

The objectives of this study were to identify factors associated with colostral specific gravity in dairy cows, as measured by a commercially available hydrometer (Colostrometer). Colostral specific gravity was measured in 1085 first-milking colostrum samples from 608 dairy cows of four breeds on a single farm during a 5-yr period. Effects of breed, lactation number, and month and year of calving on colostral specific gravity were determined, as were correlations between colostral specific gravity, nonlactating period length, and 305-d yields of milk, protein, and fat. For 75 multiparous Holstein cows, relationships between colostral specific gravity, colostral IgG1, protein, and fat concentrations, and season of calving were determined. Colostral specific gravity values were lower for Brown Swiss and Ayrshire cows than for Jersey and Holstein cows, and lower for cows entering first or second lactation than third or later lactations. Month of calving markedly affected colostral specific gravity values, with highest values occurring in autumn and lowest values in summer. In multiparous Holstein cows, colostral specific gravity was more strongly correlated with colostral protein concentration (r = 0.76) than IgG1 concentration (r = 0.53), and colostral protein concentration varied seasonally (higher in autumn than summer). Our results demonstrate that colostral specific gravity more closely reflects colostral protein concentration than IgG1 concentration and is markedly influenced by month of calving. These results highlight potential limitations of using colostral specific gravity as an indicator of IgG1 concentration.

Animals↗
PubMed2005

Reduced gravity evaluation of potential spaceflight-compatible flow cytometer technology.

BACKGROUND: The presence of a spaceflight-compatible flow cytometer onboard the International Space Station would be extremely beneficial for in-flight medicine and reduced gravity research. In the past, commercially available flow cytometers were not suitable for use during spaceflight due to their size, weight, power, and sheath fluid requirements. Recent advances in cytometer technology have enabled features that now make a spaceflight-compatible cytometer possible. We evaluated a small, robust novel cytometer with design features that minimize or eliminate many incompatibilities with spaceflight. This cytometer is highly miniaturized and lightweight, does not require sheath fluid, and uses a low-energy diode laser. The ability to achieve laminar particle flow without sheath fluid is important because an instrument using large liquid volumes and producing an equivalent amount of hazardous liquid waste would not meet spaceflight constraints. METHODS: For this study the cytometer was modified so that stained liquid cell samples could be delivered during reduced gravity. The cytometer was then evaluated onboard the NASA KC-135 reduced gravity research aircraft. The KC-135 uses a parabolic flight path to generate essentially zero gravity conditions for 30-s increments. Typically 40 parabolas are flown per mission, resulting in approximately 20 min of reduced gravity during which research may be performed. During this evaluation, bead-based cytometer precision, photomultiplier tube linearity, and leukocyte immunophenotype analysis were performed during reduced gravity. The flight data were then compared with ground-based control data and data generated using a reference cytometer (Beckman-Coulter XL). RESULTS: This novel cytometer functioned well during reduced gravity and produced data comparable to those of ground-based controls with only minor caveats. The reduced gravity cell immunophenotype data were indistinguishable from ground control data and reference cytometric data. Bead-based instrument precision (coefficient of variation) was slightly increased during reduced gravity operation, but not to a degree that would affect most common flow cytometric applications. The ability of the instrument to collect absolute cell counts was validated. CONCLUSIONS: This study represents the first generation of real-time flow cytometry data during zero gravity. With modifications, the evaluated cytometer technology could be the basis from which an operational spaceflight-compatible flow cytometer is developed.

Adult↗
PubMed2006

Recent results on modelling the spatial and temporal structure of the Earth's gravity field.

The Earth's gravity field plays a central role in sea-level change. In the simplest application a precise gravity field will enable oceanographers to capitalize fully on the altimetric datasets collected over the past decade or more by providing a geoid from which absolute sea-level topography can be recovered. However, the concept of a static gravity field is now redundant as we can observe temporal variability in the geoid due to mass redistribution in or on the total Earth system. Temporal variability, associated with interactions between the land, oceans and atmosphere, can be investigated through mass redistributions with, for example, flow of water from the land being balanced by an increase in ocean mass. Furthermore, as ocean transport is an important contributor to the mass redistribution the time varying gravity field can also be used to validate Global Ocean Circulation models. This paper will review the recent history of static and temporal gravity field recovery, from the 1980s to the present day. In particular, mention will be made of the role of satellite laser ranging and other space tracking techniques, satellite altimetry and in situ gravity which formed the basis of gravity field determination until the last few years. With the launch of Challenging Microsatellite Payload and Gravity and Circulation Experiment (GRACE) our knowledge of the spatial distribution of the Earth's gravity field is taking a leap forward. Furthermore, GRACE is now providing insight into temporal variability through 'monthly' gravity field solutions. Prior to this data we relied on satellite tracking, Global Positioning System and geophysical models to give us insight into the temporal variability. We will consider results from these methodologies and compare them to preliminary results from the GRACE mission.

Earth, Planet↗
PubMed1991

Mechanics of running under simulated low gravity.

Using a linear mass-spring model of the body and leg (T. A. McMahon and G. C. Cheng. J. Biomech. 23: 65-78, 1990), we present experimental observations of human running under simulated low gravity and an analysis of these experiments. The purpose of the study was to investigate how the spring properties of the leg are adjusted to different levels of gravity. We hypothesized that leg spring stiffness would not change under simulated low-gravity conditions. To simulate low gravity, a nearly constant vertical force was applied to human subjects via a bicycle seat. The force was obtained by stretching long steel springs via a hand-operated winch. Subjects ran on a motorized treadmill that had been modified to include a force platform under the tread. Four subjects ran at one speed (3.0 m/s) under conditions of normal gravity and six simulated fractions of normal gravity from 0.2 to 0.7 G. For comparison, subjects also ran under normal gravity at five speeds from 2.0 to 6.0 m/s. Two basic principles emerged from all comparisons: both the stiffness of the leg, considered as a linear spring, and the vertical excursion of the center of mass during the flight phase did not change with forward speed or gravity. With these results as inputs, the mathematical model is able to account correctly for many of the changes in dynamic parameters that do take place, including the increasing vertical stiffness with speed at normal gravity and the decreasing peak force observed under conditions simulating low gravity.

Adult↗
PubMed1998

First-morning urine specific gravity and enuresis in preschool children.

The object of the study was to determine whether a first-morning urine specific gravity of less than or equal to 1.015 was associated with enuresis in children 3 to 6 years old. Parents of preschool children seen at the Cleveland Clinic Foundation during a 5-month period completed a questionnaire concerning bed-wetting and voiding habits of their child and collected first-morning urine specimens for specific gravity analysis. Of 101 children, 12 had a urine specific gravity of less than or equal to 1.015 (11.9%), including seven of 73 (9.6%) nonbed-wetters, two of 19 (10.5%) bed-wetters by history (who did not wet their beds on the night of the study), and three of nine (33.3%) bed-wetters (who wet their beds on the night of the study). The 73 nonbed-wetters (72.3%) had a mean (+/- standard deviation) urine specific gravity of 1.022 (+/- 0.006); 19 bed-wetters by history (18.9%) had a mean urine specific gravity of 1.024 (+/- 0.006); and nine bed-wetters (8.9%) had a mean urine specific gravity of 1.019 (+/- 0.005). The groups' mean urine specific gravities were not significantly different (p = 0.10) and the enuretic children were not more likely to have first-morning-void urine specific gravity of less than or equal to 1.015 than nonenuretic children (p = 0.14). Enuretic children who wet their beds on the night of the study had lower mean urine specific gravity than nonbed-wetters although the difference was not significant. Therefore, we do not recommend routine use of first warning void urine specific gravity analysis for predicting presence or absence of enuresis.

Age Factors↗
PubMed2001

Ion channel are sensitive to gravity changes.

The effects of gravity on alamethicin doped planar lipid bilayers and on reconstituted porins of Escherichia coli outer membrane, respectively, have been investigated in this paper. The aim of the study was to find out whether and how gravity influences the highly stratified system: membrane-ion channel, in order to provide a novel approach to the explanation of gravity effects on living systems. This is necessary, as even single cells can react to gravity changes without having perceptive organelles. The mechanism of this detection is not clear yet. One possibility might be the detection of gravity by the membrane itself, or by the interaction of integral membrane proteins with gravity. Here we show for the first time that gravity directly influences the integral open state probability of native ion channels (porins) incorporated into planar lipid bilayers. Under hypergravity, especially the open state probability of porins is increased, whereas it is decreased in the microgravity case. The dependency is sigmoidal with the steepest region at 1 to 1.3 g. In the light of these experiments, a general effect of gravity on ion channels and membranes seems to be reasonable, possibly providing an explanation for several impacts of gravity on living systems.

Alamethicin↗
PubMed1997

Cytoplasmic streaming and gravity sensing in Chara internodal cells.

Since the nineteenth century, the merits of two alternate models for explaining the mechanism of plant gravity perception have been discussed. The gravitational pressure model states that plant cells perceive gravity by sensing their relative buoyancy to that of the surrounding medium, whereas the more popular starch-statolith model states that intracellular sedimenting particles act as gravity sensors. Vertically-oriented Chara internodal cells exhibit a gravity dependent polarity of cytoplasmic streaming such that the downwardly-directed stream moves ca. 10% faster than the upwardly-directed stream. This polarity of cytoplasmic streaming is not simply a consequence of gravity acting directly on the cytoplasm but is rather under physiological control. When Chara internodal cells are placed in a medium more dense than themselves, the gravity-induced polarity of cytoplasmic streaming is reversed. This phenomenon cannot be explained by a model which relies on intracellular sedimenting particles as gravity sensors but is consistent with the gravitational pressure model for gravity sensing. We propose that gravity causes the internodal cells to settle within the confines of the extracellular matrix resulting in a tension between the plasma membrane and the extracellular matrix at the top of the cell and a compression between the plasma membrane and the extracellular matrix at the bottom of the cell. These stresses are proposed to act upon peptides which span the plasma membrane/extracellular matrix interface at the ends of the cells and which subsequently activate Ca2+ channels which in turn may induce a polarity of cytoplasmic streaming.

Calcium↗
PubMed2001

Adjustment to concentration-dilution of spot urine samples: correlation between specific gravity and creatinine.

OBJECTIVE: Spot urine samples were investigated to determine correlations between urinary creatinine and specific gravity, and intra- and inter-day variations other than gender- and age-dependence of urinary concentrations. METHODS: Urinary creatinine concentrations and specific gravity were determined in 534 spot samples (385 from men and 149 from women). Subjects' ages ranged between 18 and 68 years. Spot urine samples were also collected from 14 male subjects before and after a 1-week work-shift for the evaluation of intra- and inter-day variations of creatinine and specific gravity. RESULTS: In spot samples, creatinine concentrations ranged between 0.16 and 4.36 g/l and specific gravity between 1.002 and 1.037. A high correlation (r = 0.82, P < 0.001) was observed between creatinine and specific gravity; male subjects showed significantly higher values of creatinine (P < 0.001) than did female subjects (1.90 +/- 0.74 and 1.41 +/- 0.72 g/l, respectively) and specific gravity (1.023 +/- 0.006 and 1.020 +/- 0.007, respectively). In addition, creatinine but not specific gravity significantly decreased (P < 0.02) in subjects older than 50 years, compared with those under 40. CONCLUSIONS: Results confirm the gender-dependence of creatinine concentrations in spot specimens and also show age-dependence, indicating the need for these aspects to be considered when the range of acceptable samples is to be set. No significant intra- or inter-day variations were observed for the two parameters. Lastly, the possibility of a comparison of differently adjusted values was indicated by a conversion formula derived from adjustments to creatinine and the corresponding specific gravity of a hypothetical urinary value, as follows: specific gravity adjusted values = 1.48 x creatinine adjusted values.

Adolescent↗