Summary
In the present study, a newly exposure technique of radon gas (29055±691 Bq/m3) has been fabricated to study the effects of radon inhalation in the male albino rats. Seventy two rats had been used, which were housed under standard laboratory conditions (12 h light: 12 h dark of photoperiod), 22±4 ºC temperature) and were given standard rat pellets and tap water ad libitum.
The study comprises two experiments. In the first experiment, rats were divided into seven groups; each group consisted of eight rats per cage. The control group was carried out without radon exposure, the other six rat groups were exposed to radon for different time periods starting from half hour to nine hours.
In this study, the absorbed doses were calculated using mathematical models, the lung dosimetry of radon progeny model was divided into 25 generations for rats. The airway generations can be grouped into the tracheobronchial (TB) and alveolar- interstitial (AI) regions. The TB region is further divided into the trachea and bronchi (BB region), and the bronchioles and terminal bronchioles (bb region). The AI region comprises the respiratory bronchioles, the alveolar ducts and sacs, and the interstitial connective tissues. This classification is consistent with the Human Respiratory Tract Model (HRTM) developed by the International Commission on Radiological Protection. The dose assessment and the effect of radon progeny on lung dosimetry have been studied through adopting two scenarios.
The annual effective dose was calculated for six different radon exposures time periods taking into account the radon activity concentration from the chamber of the present study. The radiation dose received is based on the radon exposure due to inhalation only (since the annual dose due to ingestion is not present) and in addition to the total annual effective dose measurements, the hereditary and cancer risk were estimated for different groups. The inhalation annual effective dose rates were varied from (0.01909 to 0.3436 Sv/y). The values of cancer risk ranged from 1.05×10–3 to 18.9×10-3. Other values of lifetime heredity effect varied from 0.381×10-4 to 6.872×10-4.
The current work included studying of the effects of radon exposure by inhalation on hemodynamic [blood pressure, electrocardiogram (ECG) diagram, (QRS) complex that represents the rapid depolarization of the right and left ventricles and (QT) interval is measured from the beginning of the QRS complex to the end of the T wave] and oxygen consumption rate (OCR) and some biochemical parameters (serum malondialdehyde MDA, tissue malondialdehyde MDA, tissue superoxide dismutase SOD, lung fibrosis marker hydroxyproline concentration, serum alanine aminotransferase ALT, aspartate aminotransferase AST, alkaline phosphate ALP) in male albino rats were investigated.
After one week of exposure, the results showed that radon inhalation significantly (P<0.05) increased systolic blood pressure (SBP) in a time dependent manner, also it increased serum malondialdehyde (MDA), liver and lung MDA tissues, moreover, it increased lung hydroxyproline concentration. Radon exposure decreased SOD activities in lung tissue, significantly increased serum transaminases ALT, AST and ALP activity, radon exposure prolonged the QRS and QT intervals, and decreased oxygen consumption rate when compared to the control group.
The second experiment was designed to study the effect of two doses of melatonin against the effects of radon exposure on hemodynamic, and some biochemical parameters ALT, AST and ALP activity in male albino rats. Rats of group six from the first experiment were considered as a positive control group which was exposed to radon exposure for six hours, and two further groups had exposed to radon exposure for the same time period after treatment by melatonin.
The decreases in lung SOD level in response to radon exposure was significantly (p<0.01) increased by melatonin and decreased by increasing the doses of melatonin. On the other hand, both doses of MEL administration decreased serum MDA level below the normal activity of the positive control rats. In addition, supplementation of positive control rats with both doses of MEL (60 and 120 mg / kg diet) caused significant reduction in lung MDA level; administration of melatonin prevented the increased liver MDA level and hydroxyproline concentration but doesn’t returned to the values in control group. Although, the supplementation of MEL prevented the increased serum transaminases activity (AST, ALT and ALP), but the high dose returned significantly the value of ALT to near of control group and low dose of melatonin returned the value of ALP to the control, while the high dose returned the ALP activity below of the control group.
Melatonin in dose of (120 mg / kg diet) successfully prevented the elevation in SBP that was produced by radon exposure and retuned the value of SBP to the control group. Furthermore, six hours of radon exposure resulted in a significant (P<0.05) increase in heart rate but MEL administration reduced the value of heart rate to the control group it also decreased the prolongation of QRS and QT intervals. Moreover, MEL increased the value of oxygen consumption rate near that of the control group.
posted : 12-6-2017