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Inhibition of hepatic deiodination of thyroxine is caused by selenium deficiency in rats. 总被引:4,自引:2,他引:2
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Selenium (Se) deficiency produced up to a 14-fold decrease in hepatic tri-iodothyronine (T3) production from thyroxine (T4) in vitro. The T3 production rate could not be restored by the addition of a variety of cofactors, nor by the addition of control homogenate. The impairment in hepatic T3 production observed in Se deficiency was reflected in the concentrations of thyroid hormones circulating in plasma, T4 being increased approx. 40% and T3 being decreased by 30%. However, the fall in plasma T3 concentrations was smaller than might be expected in view of the marked decreased in T3 production. Se deficiency had no measurable effect on plasma reverse-tri-iodothyronine concentrations. The data suggest that Se deficiency produces an inhibition of both 5- and 5'-deiodination, consistent with the widely held view that these reactions are catalysed by the same enzyme complex. The mechanism of inhibition appears not be mediated by changes in thiol levels, but a direct role of Se in the activity of the deiodinase complex cannot be excluded. 相似文献
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Beckett W. S.; Freed A. N.; Turner C.; Menkes H. A. 《Journal of applied physiology》1988,64(2):605-610
Because it is relatively insoluble, the oxidant gas O3 may penetrate to small peripheral airways when it is inhaled. Increased responsiveness in large airways after O3 breathing has been associated with the presence of inflammatory cells. To determine whether O3 produces prolonged hyperresponsiveness of small airways associated with the presence of inflammatory cells, we exposed the peripheral lungs of anesthetized dogs to 1.0 ppm O3 for 2 h using a wedged bronchoscope technique. A contralateral sublobar segment was simultaneously exposed to air as a control. In the O3-exposed segments, collateral resistance (Rcs) was increased within 15 min and remained elevated approximately 150% throughout the 2-h exposure period. Fifteen hours later, the base-line Rcs of the O3-exposed sublobar segments was significantly elevated, and these segments demonstrated increased responsiveness to aerosolized acetylcholine (100 and 500 micrograms/ml). There were no differences in neutrophils, mononuclear cells, or mast cells (numbers or degree of mast cell degranulation) between O3 and air-exposed airways at 15 h. The small airways of the lung periphery thus are capable of remaining hyperresponsive hours after cessation of localized exposure to O3, but this does not appear to be dependent on the presence of inflammatory cells in the small airway wall. 相似文献
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Airway responsiveness to inhaled cholinergic agonist during the early stage of pulmonary O2 toxicity was examined to determine whether normobaric hyperoxia alters airway function. Eight healthy nonsmoking males with moderate base-line methacholine responsiveness breathed normobaric O2 (greater than or equal to 95%) over 12 h and on another occasion breathed air in an identical protocol. Vital capacity, expiratory flow, airway responsiveness to methacholine, and respiratory symptoms were measured at 0, 4, 8, and 12 h while subjects breathed O2 and 12 h afterwards. After 12 h, forced vital capacity was significantly decreased with O2 breathing but not with air breathing. At 4, 8, or 12 h of exposure and 12 h after exposure, there was no difference in methacholine sensitivity or reactivity between O2 and air-exposure trials. The earliest manifestations of pulmonary normobaric O2 toxicity in normal adults include diminished vital capacity and the onset of respiratory symptoms, but early O2 toxicity does not produce altered responsiveness to inhaled methacholine. 相似文献
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Beckett W. S.; Vroman N. B.; Nigro D.; Thompson-Gorman S.; Wilkerson J. E.; Fortney S. M. 《Journal of applied physiology》1986,61(3):919-925
Pulmonary function was assessed in supine subjects before, during, and after three separate bed-rest studies of 11 and 12 days duration. Forced vital capacity (FVC) increased during bed rest in each subject. Total lung capacity (TLC) was measured by helium dilution in one bed-rest study and increased in each subject, while residual volume and functional residual capacity of the respiratory system did not change. No change in FVC was found in an ambulatory control group using identical measurement techniques. Maintaining base-line plasma volume during one bed rest by the use of exogenous estrogen did not prevent an increase in FVC, and decreasing plasma volume with diuretics in ambulatory subjects to the same degree as seen in the bed rests did not cause an increase in FVC. We conclude that prolonged bed rest results in a small significant increase in TLC and that this change is not dependent on alterations in plasma volume. 相似文献
7.
Relationship between CO and transit times for dye and thermal indicators in central circulation 总被引:1,自引:0,他引:1
We investigated two factors that may influence the estimation of lung water by the thermal-dye double-indicator-dilution method: 1) changes in cardiac output (CO), and 2) thermal equilibration with cardiac tissue. In theory, the difference between mean transit times of thermal and dye indicators (delta MTT) is proportional to the extravascular volume of distribution of the thermal indicator (VODev) and inversely related to CO. The delta MTT also includes a time element DT due to the difference in response times of the measuring instruments such that delta MTT = VODev/CO + DT. In nine anesthetized dogs we recorded 286 aortic thermal and dye curves following left atrial (LA) and right atrial (RA) injections as CO was increased from 2.35 to 6.65 ml X s-1 X kg-1 by isoproterenol infusion, and a regression of delta MTT on CO-1 was performed. DT was measured in vitro for comparison with the y-intercept. In six of nine dogs the slope of the regression for LA injections was not different from zero, indicating that there is no measurable volume of distribution for thermal indicator in cardiac tissue. For RA injections the relationship between delta MTT and CO-1 was linear in all experiments, with an average correlation coefficient of 0.97 +/- 0.01 (SE), indicating that the VODev was constant over a threefold increase in CO. Although the in vitro measurement of DT agreed closely with the average of the y-intercepts of the regressions, small between-subject differences in DT can lead to apparent flow-related changes in extravascular thermal volume computed in the conventional fashion using the in vitro estimate of DT. 相似文献
8.
Blood pressure within the corpus cavernosum penis of the bull 总被引:1,自引:0,他引:1
J E Lewis D F Walker S D Beckett R I Vachon 《Journal of reproduction and fertility》1968,17(1):155-156
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Selenium (Se) deficiency decreased by 8-fold the activity of type 1 iodothyronine 5'-deiodinase (ID-I) in hepatic microsomal fractions from rats. Solubilized hepatic microsomes from rats injected with 75Se-labelled Na2SeO3 4 days before killing were found by chromatography on agarose gels to contain a 75Se-containing fraction with ID-I activity. PAGE of this fraction under reducing conditions, followed by autoradiography, revealed a single 75Se-containing protein (Mr 27,400 +/- 300). This protein could also be labelled with 125I-bromoacetyl reverse tri-iodothyronine, an affinity label for ID-I. The results suggest that hepatic ID-I is a selenoprotein or has an Se-containing subunit essential for activity. 相似文献