Skeletal musculature of rats during modeling of the physiological effects of weightlessness (morphological study)

In the experiment rats were suspended in the head-down position (at -15 to -20 degrees) for 21 days. To study the effect of this exposure on skeletal muscles of their fore- and hindlimbs, morphological and histochemical methods were used. Changes in the hindlimbs were similar to those seen in real weightlessness of similar duration. The two antigravitational muscles - soleus and gastrocnemius muscles - showed greatest changes, i.e. atrophic and metabolic shifts. The biceps brachii muscle that changes insignificantly in the weightless state developed a destructive process (with degradation of myofibers) that was later replaced with a reparative process. The changes in this muscle are assumed to be associated with hemodynamic disorders. It is recognized that the method of rat suspension is adequate for a ground-based study of morphological effects of weightlessness on hindlimbs and is unacceptable for that of forelimbs where the exposure induces microcirculation disorders.     

Effects of diet and exercise on the density and composition of the fat-free mass in obese women

PURPOSE: The purpose of this study was to determine whether the density (D(FFM)) and composition of the fat-free mass (FFM) and the accuracy of estimates of body composition from body density (%Fat(d)) are affected by diet and exercise. METHODS: Twenty-nine obese women (body mass index (BMI) = 25.0-43.7 kg x m(-2) and %Fat(d) = 35.7-47.1%) were assigned to one of three groups: diet only (DO, N = 9); diet and aerobic exercise (DE, N = 9); or control (C, N = 11). Measures of body density by hydrostatic weighing, body water by deuterium dilution, and bone mineral by whole-body dual-energy x-ray absorptiometry, and estimates of body composition from body density and from a four-component model were obtained before and after a 16-wk diet and exercise intervention. RESULTS: Mean (+/- SD) changes in body mass were -7.2 +/- 7.4, -3.9 +/- 3.3, and +1.2 +/- 2.8 kg for the DO, DE, and C, respectively. The density and composition of the FFM did not change significantly (P > 0.05) in any of the groups. Individual changes in D(FFM) (-0.011 to +0.011 g x mL(-1)), and differences between changes in %Fat estimated using a four-component model and %Fat(d) (-2.1 to +2.7% body mass) were not related to changes in body mass (r = -0.08). Individual changes in D(FFM) were most strongly related to changes in water fraction (r = -0.95) and protein fraction (r = +0.88), and were unrelated to changes in the mineral fraction (r = +0.04) of the FFM. CONCLUSIONS: We conclude that in obese women, the density and composition of the FFM are unaltered and densitometry correctly assesses group mean changes in body composition with moderate weight loss induced by diet or diet and aerobic exercise. However, individual deviations in D(FFM) from the assumed value of 1.1 g x mL(-1) are substantial, and a multi-component model in which body water is measured is needed to accurately assess individual body composition changes resulting from diet and exercise.     

颈椎Modic改变的MRI表现与临床意义

目的：探讨颈椎Modic改变的MRI表现与临床意义。方法回顾性分析116例颈椎Modic改变的MRI图像资料,记录Modic改变的类型、节段分布情况。结果116例患者中共计150个节段存在Modic改变,按照Modic分型,其中Ⅰ型23个节段,Ⅱ型110个节段,Ⅰ-Ⅱ混合型13个节段,Ⅲ型4个节段,发生率分别为15．3％、73．3％、8．7％、2．7％。按发生节段其中C5-6占57个节段,C6-7占41个节段,C4-5占29个节段,其余23个节段,分布情况与椎间盘突出好发部位相符。结论Modic改变是颈椎退行性病变中的一种常见表现,是引起颈痛的原因之一,并与椎间盘退变密切相关,MRI是首要检查方法。     

MR microscopy of perfused brain slices

To study the origins of signal changes in clinical MRI we have previously studied isolated single neuronal cells by MR microscopy. To account for the extracellular environment of the cells, we have developed a prototype perfusion chamber for MR microimaging of perfused rat hippocampal brain slices. To demonstrate the utility of this model, brain slices were initially perfused in isotonic solutions and then subjected to osmotic perturbations via perfusate exchange with 20% hypertonic and 20% hypotonic solutions. In diffusion weighted images, signal intensity changes of +16(σ_n-1 = 11)%(hypotonic) and -26(σ_n-1 = 10)% (hypertonic) were observed. No significant variation in response was observed across the slice when several subregions were examined. These observations are consistent with the view that contrast changes are driven primarily by changes in the intra- and extracellular compartmentation of water. This is the first report of MR microimaging of the isolated brain slice. The technique will enable the correlation of MR microimaging measurements with microscopic changes using other modalities and techniques to provide a better understanding of signals in clinical MRI.     

Physiological responses to a 6-d taper in middle-distance runners: influence of training intensity and volume

PURPOSE: This study examined some physiological and performance responses to a 6-d taper, and the influence of training intensity and volume on these responses. METHODS: After 15 wk of training, 8 well-trained male middle-distance runners were randomly assigned to either a moderate volume taper (MVT, N = 4) or a low volume taper (LVT, N = 4), consisting of either a 50% or a 75% progressive reduction in pretaper low intensity continuous training (LICT) and high intensity interval training (HIIT). Blood samples were obtained and 800-m running performance was measured before and after taper. RESULTS: Performance was not significantly enhanced by either taper protocol (post- vs pre-taper times 124.9 +/- 4.5 vs 126.1 +/- 4.2 s with LVT, 126.2 +/- 8.0 vs 125.7 +/- 6.6 s with MVT). For the entire group of 8 subjects, red cell count, hemoglobin (Hb), mean corpuscular volume and mean corpuscular Hb concentration significantly decreased with taper, while reticulocyte count increased. Performance changes for all subjects correlated with changes in postrace peak blood lactate concentration (r = 0.87, P < 0.01). Taper LICT correlated with changes in Hb (r = 0.77), hematocrit (r = 0.81), reticulocyte count (r = 0.73), creatine kinase (r = 0.72), and total testosterone (r = -0.78), and with posttaper red cell distribution width (r = -0.75) and lymphocyte count (r = -0.82). Taper HIIT correlated nonsignificantly with changes in red cell count (r = -0.66) and total testosterone (r = 0.68). CONCLUSION: It is concluded that taper-induced physiological changes in trained middle-distance runners are mainly hematological, and that distinct physiological changes are elicited from LICT and HIIT during taper. Middle-distance runners can progressively reduce their usual training volume by at least 75% during a 6-d taper.     

CT analysis of lung density changes in patients undergoing total body irradiation prior to bone marrow transplantation

Sequential changes in lung density measured by CT are potentially sensitive and convenient monitors of lung abnormalities following total body irradiation (TBI). Methods have been developed to compare pre- and post-TBI CT of lung. The average local features of a cross-sectional lung slice are extracted from three peripheral regions of interest in the anterior, posterior, and lateral portions of the CT image. Also, density profiles across a specific region may be obtained. These may be compared first for verification of patient position and breathing status and then for changes between pre- and post-TBI. These may also be compared with radiation dose profiles through the lung. A preliminary study on 21 leukemia patients undergoing total body irradiation indicates the following: (a) Density gradients of patients' lungs in the antero-posterior direction show a marked heterogeneity before and after transplantation compared with normal lungs. The patients with departures from normal density gradients pre-TBI correlate with later pulmonary complications. (b) Measurements of average peripheral lung densities have demonstrated that the average lung density in the younger age group is substantially higher: pre-TBI, the average CT number (1,000 scale) is -638 +/- 39 Hounsfield unit (HU) for 0-10 years old and -739 +/- 53 HU for 21-40 years old. (c) Density profiles showed no post-TBI regional changes in lung density corresponding to the dose profile across the lung, so no differentiation of a radiation-specific effect has yet been possible. Computed tomographic density profiles in the antero-posterior direction are successfully used to verify positioning of the CT slice and the breathing level of the lung.     

Estimation of early postmortem intervals by a multiple regression analysis using rectal temperature and non-temperature based postmortem changes

Five general methods based on rectal temperature and a multiple regression analysis using rectal temperature and non-temperature based postmortem changes were applied to 212 postmortem cases of within 24h postmortem (PM) intervals. Non-temperature based postmortem changes of rigidity, hypostasis and corneal turbidity were numerically categorized and used with rectal temperatures as four statistical variables in the multiple regression analysis. The correlation coefficient values between true and calculated postmortem intervals were 0.78-0.82 in the five general methods based on rectal temperature. The multiple regression analysis produced a multiple correlation coefficient value of 0.89 and according to the error ranges of the PM intervals, 72% of the cases were estimated within the error of +/-1.0 h and 92% within +/-5.0 h. Although assessments of non-temperature based PM changes are mostly subjective and have a wide variation, the present study demonstrated a usefulness of non-temperature based PM changes in the estimation of PM intervals.     

Diffusion tensor imaging and MR spectroscopy in hypertension and presumed cerebral small vessel disease.

In patients with cerebral small vessel disease (SVD) diffusion tensor imaging (DTI) is sensitive to white matter damage and correlates better with cognitive function than conventional imaging. It has been proposed as a surrogate marker for treatment trials. However, the pathological changes underlying DTI are not known. The purpose of this study was to use magnetic resonance spectroscopy (MRS) to determine the pathological changes underlying DTI abnormalities in a range of patients from asymptomatic white matter hyperintensities to symptomatic cerebral SVD. 29 SVD patients, 63 hypertensive subjects, and 42 normotensive controls were recruited. The relationship between the DTI and MRS parameters in the centrum semiovale white matter was determined. There was a significant reduction in N-acetylaspartate (NAA; 2.067 +/- 0.042 vs 2.299 +/- 0.029 and 2.315 +/- 0.036, P = 9 x 10(-6)) and increase in mean diffusivity (mm2/s x 10(-3); 0.942 +/- 0.123 vs 0.822 +/- 0.064 and 0.792 +/- 0.057, P = 1 x 10(-8)) in symptomatic SVD patients compared with the other two groups. DTI parameters correlated with NAA in all three groups, in a graded manner depending on severity of disease (r -SVD -0.827, hypertensive subjects -0.457, controls -0.317). NAA is a marker of axonal loss/dysfunction. These findings are consistent with axonal loss/dysfunction being the principal process causing the DTI changes found in cerebral SVD and ageing.     

Energy absorption, lean body mass, and total body fat changes during 5 weeks of continuous bed rest

Inactivity causes profound changes. We determined the nature of the body composition changes due to inactivity, and sought to determine if these changes are secondary to changes in energy absorption. Volunteers were 15 healthy males who lived on a metabolic research ward under close staff supervision for 11 weeks. Subjects were ambulatory during the first 6 weeks and remained in continuous bed rest for the last 5 weeks of the study. Six male volunteers (age 24-61 years, height 175.7 +/- 4.2 cm) were selected for body composition measurements. Nine different male volunteers (age 21-50 years, height 177.7 +/- 5.0 cm) were selected for energy absorption measurements. The volunteers were fed weighed conventional foods on a constant 7-d rotation menu. The average daily caloric content was 2,592 kcal. Comparing the 5 weeks of continuous bed rest with the previous 6 weeks of ambulation we observed: no change in energy absorption or total body weight during bed rest, but a significant decrease in lean body mass and a significant increase in total body fat (p less than 0.05).     

Sequential MRI changes in Wilson's disease with de-coppering therapy: a study of 50 patients

Wilson's disease (WD) is clinically and radiologically a dynamic disorder. However, there is a paucity of studies involving sequential MRI changes in this disease with or without therapy This study looked at serial MRI changes and their clinical correlate in patients with WD The severity of MRI changes using 1.5 T MRI in 50 patients with WD was graded based on alteration in signal intensity of focal lesions and atrophy. Details of clinical manifestations, Schwab and England Activities of daily living (MSEADL) score, Neurological Symptom Score (NSS) and Chu staging were recorded. Clinical severity and disability scores were correlated with MRI scores using SPSS v10 The mean age at onset of illness and diagnosis was 12.8+/-5.6 years and 14.4+/-6.0 years, respectively. At the time of first MRI, patients had been treated for 49.0+/-77.3 months. At a follow-up of 24.2+/-12.2 months, clinically 36 patients had improved, 9 remained the same and 5 had worsened. Serial imaging revealed an improvement in MRI parameters in 35 patients, no significant changes in 10, worsening in 4 and an admixture of resolving and evolving changes in 1. The overall MRI score improved from 8.2+/-5.7 to 5.9+/-6.6. There was an improvement in measures of disability and impairment in all: Chu stage, 11.5+/-0.7 to 1.3+/-0.6; MSEADL score (%), 79.7+/-27.6 to 88.0+/-25.4; NSS, 10.6+/-11.2 to 8.0+/-11.6, with good clinico-radiological correlation. Patients with extensive changes, white-matter involvement and severe diffuse atrophy had a poor prognosis In conclusion, the majority of patients with WD showed variable improvement in clinical and MRI features when treated.     

Effect of mental stress on left ventricular ejection fraction and its relationship to the severity of coronary artery disease

To evaluate the relationship between the mental stress-induced decrease in left ventricular ejection fraction (LVEF) and the severity of exercise-induced ischaemia, 20 patients with stable coronary artery disease (CAD) underwent radionuclide ventriculography during mental stress testing and stress myocardial perfusion single-photon emission tomography (SPET). We also examined whether changes in haemodynamic and neurohormonal parameters are related to changes in LVEF during mental stress. The LVEF decreased from 54.8% +/- 17.7% to 49.8% +/- 16.2% with mental stress (P < 0.0005). Ten of the 20 patients (50.0%) had a > or = 5% decrease in LVEF The remaining ten patients had no or a <5% decrease in LVEF There was a significant correlation between the change in LVEF during mental stress and the size of the reversible defect on stress myocardial perfusion SPET (r = -0.80, P < 0.0005), with close regional correspondence (75% identical). This correlation was less strong in the 12 patients with a total defect score at rest of <10 (r = -0.69, P = 0.014) than in the eight patients with a total defect score at rest of > or = 10 (r = -0.94, P = 0.001). The changes in blood pressure and heart rate were not significantly correlated with the change in LVEF, but the percent change in adrenaline concentration correlated with the change in LVEE It is suggested that mental stress impairs systolic function by inducing transient myocardial ischaemia. The effect of neurohormonal responses during mental stress on LV systolic function may also be important in patients with CAD.     

The role of physical activity in changes in walking mechanics with age

While age-related declines in walking mechanics have been documented, it remains unclear if changes in walking mechanics with age occur as a natural consequence of aging and to what extent these changes are related to a reduction in fitness and physical activity with aging. The study aim was to determine if the walking mechanics of an older (>50) yet highly active population are different from a younger population (<40). Gait mechanics data for 79 middle-aged (50-64 yrs) and 54 older (65-80 yrs) individuals with ≥ 7500 steps/day, based on a 7 day activity monitoring history, and 33 younger adults (ages 18-40) were collected. The older subjects did not reduce self-selected walking speed relative to the younger subjects. However, the walking speed was maintained by increasing cadence while reducing stride-length for middle-aged and older subjects. Middle-aged and older adults had less ankle dorsi-flexion landing at heel-strike and older adults also had less plantar flexion at toe-off. Small decreases in the ankle dorsi-flexion moments (p=0.019, p=0.008) and increases in the hip extension moments (p=0.004, p=0.005) were found for two normalized walking speeds for the middle-aged and older adults compared to the young adults. These results provide quantitative evidence that increased activity with aging can mitigate declines in walking performance and mechanics with age. The high volume of walking activity in the older subjects did not fully prevent changes in gait mechanics, but may have minimized the magnitude of age-related changes on ambulatory function relative to other reports of older inactive subjects.     

Stability of radionuclide left ventricular volume measurements

Left ventricular volume measurements are useful in the evaluation of cardiac function and are important in the long-term management of patients with various cardiac diseases. Although there are many methods of measuring left ventricular volumes, a non invasive and reproducible method relies on radionuclide techniques. The errors in estimation of left ventricular volumes have previously been well studied. To date there is little information on the reproducibility of left ventricular volume measurements made by this technique at different points in time. This study evaluated 61 patients with stable coronary artery disease over a period of approximately 1 year. All patients had two resting radionuclide gated blood pool studies. Patients had no changes in symptoms, electrocardiographic findings or medication between studies. Using +/- 2 SD as 95% confidence limits for a true change, an end diastolic volume index change greater than -34 ml m-2 and +38 ml m-2 or an end systolic volume index change greater than -24 ml m-2 and +26 ml m-2 are required to state with confidence that a change has occurred between two examinations. These data provide guidelines to assess whether interval changes in left ventricular volumes are real or are due to variations within the technique.     

Changes at the base of skull and cervical spine in Down syndrome

Lateral films of the skull base and upper cervical spine in flexion, extension, and neutral positions in 165 patients with Down syndrome, ranging in age from 16 to 60 years, were analyzed. There is a 20% incidence of atlantoaxial subluxation with a marked preponderance in men (24% incidence compared to 15% in women). In addition, there is a high incidence of degenerative changes at the C2-3 and C3-4 cervical interspaces, especially in patients over 37 years of age; these are unusual sites when compared to the normal population in which the degenerative changes are most often at the C5-6 and C6-7 levels. Four patients demonstrated subluxation at cervical interspaces other than C1-2 and six had congenital fusion of either vertebral bodies or facets in the cervical region. Several patients also had flattening of cervical vertebrae; 20% of patients had nonaeration of the sphenoid sinus and 46% had partial aeration.     

31P NMR characterization of graded traumatic brain injury in rats

Irreversible tissue injury following central nervous system trauma is believed to result from both mechanical disruption at the time of primary insult, and more delayed "autodestructive" processes. These delayed events are associated with various biochemical changes, including alterations in phosphate energy metabolism and intracellular pH. Using 31P NMR, we have monitored the changes in phosphorus energy metabolism and intracellular pH in a single hemisphere of the rat brain over an 8-h period following graded, traumatic, fluid percussion-induced brain injury. Following trauma the ratio of phosphocreatine to inorganic phosphate (PCr/Pi) declined in each injury group. This decline was transitory with low injury (1.0 +/- 0.5 atm), biphasic with moderate (2.1 +/- 0.4 atm) and high (3.9 +/- 0.9 atm) injury, and sustained following severe injury (5.9 +/- 0.7 atm). The initial PCr/Pi decline in the moderate and high injury groups was associated with intracellular acidosis; however, the second decline occurred in the absence of any pH changes. Alterations in ATP occurred only in severely injured animals and such changes were associated with marked acidosis and 100% mortality rate. After 4h, the posttraumatic PCr/Pi ratio correlated linearly with the severity of injury. We suggest that a reduced posttraumatic PCr/Pi ratio may be indicative of altered mitochondrial energy production and may predict a reduced capacity of the cell to recover from traumatic injury.     

Comparing genomic and histologic correlations to radiographic changes in tumors: a murine SCC VII model study

RATIONALE AND OBJECTIVES: To investigate the correlation between the temporal changes in T1- and T2-weighted contrast-enhanced magnetic resonance imaging (MRI), histologic evaluation, and genomic analysis using oligonucleotide microarrays in a murine squamous cell carcinoma tumor models. MATERIALS AND METHODS: The squamous cell carcinoma (SCC VII) cell line was used to initiate subcutaneous tumors in mice. This mouse model has been used as a model for human head and neck carcinomas. Animals were imaged using contrast enhanced MRI (CE-MRI). Different stages of tumor growth were defined based on changes in the T1- and T2-weighted MRI patterns. The contrast enhancing (CE) and nonenhancing (NE) regions of the tumors were marked and biopsied for oligonucleotide microarray and histologic analysis. Tumors with no differential contrast enhancement were used as controls. RESULTS: Distinct temporal stages of tumor progression can be defined using both T1- and T2-weighted CE-MRI and microarray analysis. The early stage tumors show a homogeneous contrast enhancement pattern in the T1- and T2-weighted images with no significant differential gene expression from the center and periphery of the tumor. The more advanced tumors that show discrete regions of contrast enhancement in the post-contrast T1-weighted MRIs and tissues from the CE and NE regions show distinctly differential gene expression profiles. Histologic analysis (hematoxylin-eosin stain) showed that the samples obtained from the periphery and center of the early stage tumors and the CE and NE regions from these more advanced tumors were similar. The gene expression profiles of late-stage tumors that showed changes in T2-weighted MRI signal intensity were consistent with tissue degradation in the NE region, which also showed characteristic signs of tissue necrosis in histologic analysis. CONCLUSION: These results show that temporal changes in T1- and T2-weighted CE-MRI are related to distinct gene expression profiles, and histologic analysis may not be sufficient to detect these detailed changes. As tumors progress, discrete regions of post-contrast T1 enhancement are identified; these regions have distinct gene expression patterns despite similar histologic features. In late-stage tumors, regions of T2 signal changes are observed which correspond with tissue necrosis.     

Validity of estimates of myocardial oxidative metabolism with carbon-11 acetate and positron emission tomography despite altered patterns of substrate utilization

We recently demonstrated that the myocardial turnover rate constant (k) measured noninvasively with positron emission tomography (PET) after intravenous administration of [11C]acetate provides a reliable index of myocardial oxidative metabolism (MVO2) theoretically independent of the pattern of myocardial substrate use. However, because estimates of metabolism with other metabolic tracers are sensitive to substrate use, we measured k in 12 dogs during baseline conditions and again after infusion of either glucose (n = 8) or Intralipid (n = 4), interventions that raised arterial glucose or fatty acids by more than fivefold with concomitant changes in myocardial substrate use. Following glucose administration k increased, but no difference was detected after compensation for changes in hemodynamics and myocardial work induced by the infusion (0.18 +/- 0.03 min-1 (t1/2 = 3.9 min) at baseline compared with 0.22 +/- 0.06 min-1 (t1/2 = 3.2 min, p = N.S.). k was not affected by Intralipid infusion (k = 0.15 +/- 0.06 min-1 at baseline and 0.14 +/- 0.04 min-1 during infusion), and correlated closely with MVO2 measured directly (n = 19 comparisons, r = 0.89). The results indicate that estimates of MVO2 using [11C]acetate and PET are valid despite changes in the pattern of myocardial substrate utilization.     

Relationship of physical activity to eating behaviors and weight loss in women

PURPOSE: To examine whether change in physical activity is associated with compliance to changes in dietary intake and eating behaviors in an 18-month behavioral weight loss program, and to examine the contribution of exercise to weight loss when these other weight loss behaviors are also considered. METHODS: Data from 104 subjects who completed an 18-month behavioral weight loss program were analyzed in this study. All subjects were prescribed a reduced energy (1,200-1,500 kcal x d(-1)) and fat (20 to 30%) diet, and exercise progressed from 100 to 200 min x wk(-1). Subjects attended group behavioral lessons throughout the study. Weight, physical activity, energy intake, and weight loss eating behaviors were assessed at 0 and 18 months. RESULTS: Body weight decreased 7.8 +/- 7.5 kg and body mass index decreased 2.8 +/- 2.7 kg x m(-2) from 0 to 18 months ( < 0.05). Total energy intake (kcal x d(-1)) and macronutrient intake (g x d(-1)) decreased, whereas physical activity and eating behaviors associated with weight loss increased from 0 to 18 months ( < 0.05). Change in physical activity was significantly correlated with weight loss (r = 0.33), reductions in energy intake (r = 0.20), and improvements in eating behaviors associated with weight loss (r = 0.24) ( < 0.05). Regression analysis indicated that change in physical activity significantly improved weight loss after changes in energy intake and weight loss eating behaviors were considered in the analysis, with R(2)significantly improving by approximately 0.04 ( < 0.05). However, results from multiple regression showed weight loss was influence more by changes in eating behaviors than changes in physical activity (R(2) = 0.17 vs R(2) = 0.04). CONCLUSIONS: The combination of changes in eating and physical activity behaviors can improve long-term weight loss compared with either behavior alone. Interventions targeting both behaviors are recommended for improving long-term weight loss.     

Assessment of cerebral oxidative metabolism with breath holding and fMRI.

Carbon dioxide inhalation can be used to map changes in cerebral metabolic rate of oxygen (CMRO(2)) during neuronal activation with functional MRI (fMRI). A hypercapnic stress also can be achieved with a simple breath-holding test. Using this test as means of manipulating cerebral blood flow (CBF) independent of CMRO(2), we assessed changes in CMRO(2) during visual stimulation. With this task, CBF increased by 61 +/- 7%, whereas CMRO(2) changed by 2.43 +/- 4.97%. These results are in good agreement with previous positron emission tomographic (PET) data, indicating that changes in oxidative metabolism during focal neuronal activity can potentially be determined with the breath-holding test. This test could easily be performed during a routine MRI examination. Magn Reson Med 42:608-611, 1999.     

The effect of medium-wave UV-radiation on the photosynthetic apparatus and the productivity of higher plants

In laboratory and field experiments, the effect of medium-wave (290-320 nm) UV-radiation (UV-B) on the build-up of photosynthetic pigments, growth and productivity of higher plants was investigated. It was found that UV-B of 5-9 W/m2 in intensity applied daily (at a daily dose of 15-20 kJ/m2) or singly (at a daily dose of 24 or 36 kJ/m2) inhibited the formation of chloroplast pigments. The pattern and magnitude of changes depended on the plant species and leaf age. The degree of photosynthetic changes and plant resistance to UV-radiation were closely correlated. In field experiments (daily irradiation with 0.6 W/m2 at a dose of 12-13 kJ/m2/day), UV-B suppressed the growth and yield of cotton and soybean plants. This exposure modified chloroplasts of soybean plants and inhibited their growth to a greater extent than that of cotton plants. The factors responsible for the species-related specificity of UV-B resistance of higher plants are discussed and approaches to its evaluation based on the pigment apparatus of photosynthesis are described.