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Auditory, visual and somatosensory evoked potentials (EPs), recorded epidurally from 31 chronically implanted male Long-Evans rats, were studied to examine the pattern of sensory effects caused by hypercapnia. Recordings were obtained before exposures, 10-20 min after the beginning of exposure to CO2 in synthetic air, and 30 min after the end of exposure. Previous recordings revealed no substantial effects of the extended recording period itself. Blood pH during an average exposure of 18.8% CO2 was about 7.1. During this level of CO2 exposure the somatosensory response was almost completely abolished, but the latencies of early detectable components were not affected. In contrast, the latencies of all brainstem auditory evoked response components and the 1-5 interwave time increased, whereas amplitudes were only slightly affected. Amplitudes and latencies of early and late components of the flash EP were decreased and lengthened, but the after-discharge components appeared to be most sensitive to CO2. Concentration-response relationships were examined by exposure of rats to 8 and 16% CO2. The most sensitive EP parameter was average amplitude of the late somatosensory EP components. These results suggest that EPs might be useful for assessing acute metabolic disturbances as well as more commonly assessed neurologic disorders.

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Peak oxygen uptake (peak VO2) and basal total activity of lactic dehydrogenase (LDH-T) and its five isoenzymes were measured in seven men, 19-21 years old, before, during, and after three 2-week bed rest (BR) periods, each separated by 3-week recovery periods. For 1 h X d-1 during BR, they performed isometric (250 kcal X -1) leg exercise, or no exercise. LDH-T was reduced (p less than 0.05) with all three regimens by day 10 of BR, but the decrease occurred at different rates. The earliest significant (p less than 0.05) reduction in LDH-T with the no-exercise regimen was associated with the greatest decrease in peak VO2 of 12.3%; isotonic exercise was next with a peak VO2 decrease of 9.2%; finally, isometric exercise had the least decrease in peak VO2 at 4.8%. Irrespective of the exercise regimen during BR, the increases in isoenzyme activities occurred mainly in LDH-1 and LDH-2 (heart subunits). Isometric (aerobic) muscular strength training appears to maintain skeletal muscle integrity and, perhaps, oxygen uptake capacity better during bed rest than isotonic exercise training. Reduced hydrostatic pressure during bed rest, however, ultimately overrides effects of both moderate isometric and isotonic exercise training (metabolism) in the resulting decrease in LDH-T.

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Bleomycin is a primary fibrogenic agent which increases collagen content in a fibroblast system by a direct effect on fibroblasts. A mechanism for the increase in collagen content is an increase in the rate of collagen biosynthesis. This implies alteration of either collagen transcription or translation. Hyperoxia depresses collagen biosynthesis without changing collagen content. This implies that hyperoxia also depresses collagen degradation. The addition of phagocytes (macrophages) to hyperoxically exposed cells increases both collagen content and the rate of collagen biosynthesis. Hyperoxia is therefore a secondary fibrogenic agent. This suggests that mediators released from phagocytes alter collagen transcription or translation.

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Rats of similar age and size were exposed continuously to nitrogen dioxide (NO2) at a concentration of about 15 ppm in air for 1, 2, 3, and 4 wk and 2, 3, 4, 5, 7, 13, 15, and 17 months. Large increases in lung volume and lesions of the small airways and their epithelium and that of adjacent alveoli developed. The lesions in the terminal bronchioles involved hypersecretion and asggregation of cellular debris and free cells in their lumena. A calibrated grid fitted to an eyepiece was used to measure the diameters of all patent bronchioles at the proximal point of the first alveolar "break" in the respiratory bronchiole. The terminal bronchioles and their short respiratory bronchioles inthe NO2-exposed animals developed stenosis, which increased with time. The maximum change, occurring after 17 months of exposure, was a 45.6% reduction in bronchiolar diameter. Over-all constriction was underestimated because nonpatent sections of bronchioles were excluded The ratio of lung volume to bronchiolar diameter in exposed animals also increased with time as a result of the rising volume and the falling bronchiolar diameter. Probable are discussed.

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The amount of nitric oxide (NO) in the blood of residents of urban and suburban areas was measured under steady-state conditions by isotopic dilution with N15O, followed by field-ionization mass spectrometry. Approximately 20 nmoles of NO per ml of blood was characteristic of both smokers and nonsmokers, except for one of the eight subjects who had a significantly lower level. Monkeys (Macaca speciosa) had values comparable to those of seven human subjects, and rats had values like that of the unique human subject. Whether the origin of the NO was endogenous or exogenous was not determined.

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The purpose of this study was to determine the effects of sulfuric acid (H(2)SO(4)) alone and with ozone (O(3)) on rats. To accomplish this, rats were exposed for 8 hours daily to an atmosphere containing either nebulized H(2)SO(4), H(2)SO(4) plus 0.9 ppm O(3), or 0.9 ppm O(3). The atmosphere in the exposure chambers was maintained at a fairly constant temperature and humidity. Nebulized H(2)SO(4) was delivered uniformly to provide a particle size of about 0.3 micron mass median diameter (MMD) and a mass concentration of 2 mg/m(3). In preliminary experiments, animals exposed to 2 mg/m(3) of H(2)SO(4) daily for 82 days showed very slight morphologic injury to the respiratory tract. In contrast, biological effects were readily demonstrable in rats exposed to H(2)SO(4) plus O(3) or to O(3) alone, possibly with some enhancement of effect in animals exposed to the mixture. The effects observed were characteristic of the response to O(3) alone.

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To determine the cause of the body weight loss during bed rest (BR), fluid balance and anthropometric measurements were taken from seven men (19-21 yr) during three 2-wk BR periods which were separated by 3-wk ambulatory recovery periods. Caloric intake was 3,073 +/- 155 (SD) kcal/day. During two of the three BR periods they performed supine isotonic exercise at 68% of VO2max on the ergometer for 1 h/day; or supine isometric exercise at 21% of maximal leg extension force for 1 min followed by a 1-min rest for 1 h/day. No prescribed exercise was given during the other BR period. During BR, body weight decreased slightly with no exercise (-0.43 kg, NS), but decreased significantly (P less than 0.05) by -0.91 kg with isometric and by -1.77 kg with isotonic exercise. About one-third of the weight reduction with isotonic exercise was due to fat loss (-0.69 kg) and, the remainder, to loss of lean body mass (-0.98 kg). It is concluded that the reduction in body weight during bed rest has two major components: First, a loss of lean body mass caused by assumption of the horizontal body position that is independent of the metabolic rate. Second, a loss of body fat content that is proportional to the metabolic rate.

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Fluid and electrolyte shifts were measured in seven men (19-21 yr) during three 2-wk bed rest (BR) periods, each of which was separated by a 3-wk ambulatory recovery period. During two of the three BR periods they performed isometric exercise and isotonic exercise. No prescribed exercise was given during the other BR period. On day 4 of BR, plasma volume decreased (P less than 0.05) 441 ml (-12.6%) with no exercise, 396 ml (-11.3%) with isometric, and 262 ml (-7.8%) with isotonic exercise; the decreases (NS) of extracellular volume were -4.4%, -2.6%, and -2.7%, respectively. By day 13 of BR, plasma volume stabilized at the lower level with isometric and isotonic exercise and continued to decline with no exercise; but the extracellular volume returned to or above control levels due to an overshoot of the interstitial volume of +320 to +430 ml (2.0-2.7%) that was about equal to the plasma volume loss. During BR there were isocontent losses from the plasma of protein, albumin, globulin, urea N2, uric acid, creatinine, Na, Cl, osmolarity, P, and glucose that were not influenced by either exercise regimen. However, the blood, red blood cell, and plasma volumes, and the Ca and K contents were stabilized during BR by both exercise regimens. The results suggest that during BR, preservation of the extracellular volume takes precedence over maintenance of the plasma volume, and this mechanism is independent of the effects of isometric or isotonic exercise.

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