EFFECT OF SIMULATED MICROGRAVITY ON THE BIOCHEMICALS, MINERALS AND THYROID HORMONE PROFILES IN RATS

Abstract

Change in ambient temperature are compensated by the rats either by altering the metabolic activity, by thermogenesis, evaporative cooling, altering peripheral circulation Rodent being the non-sweating animal, on increase in room or environmental temperature may respond either altering its respiration rate followed by changes in metabolic profiles. The thermoneutral zone for a rat to grow and reproduce has been documented to be between 20°C to 26°C. Exposure to high temperature may result in high corticosteroid concentration, modulate immune function, changes lymphocytes migratory pattern to impairment of lactation as well as testicular atrophy. On the other hand, cold stress may increase nor-epinephrine and epinephrine, to combat this via stimulation of neuro- endocrine mechanism. In the present study, two hundreds and forty healthy albino young (n=120) and old (n=120) rats were used during winter and summer season. Rats were divided into four groups in each season i.e. young and old, consisting of male (n=30) and female (n=30) in each age category. In each age × sex matched rats, three subgroups were made and has been given the name as control group (CC), horizontal restrained group (HR) and head down suspended group (HDS). For winter season, the room temperature of experimental period was from 20°C to 23°C and for summer season, the experimental room temperature in ranged from 30°C to 33°C. No extra efforts were made to change the laboratory condition i.e. facilitating with heater during winter and air conditioning during summer seasons. A 12 hours light/12 hours dark cycle with ad libitum food offered each day to an individual rats as well as fresh water (at normal temperature) were provided every day from 9-10 h (morning). Body weight of these rats were taken on weekly basis, while food and water were offered ad libitum and daily intake by the individual rats was taken into account on day to day basis from 9-11 h. Rats were decapitated on day 7th (n=5) and day 28th (n=5) of experimental period from all groups to collected the organs and blood for the collection of serum. Serum was collected in small aliquots in ependorff and preserved at -20°C for further analysis of biochemicals, electrolytes, minerals and thyroid hormones. Appropriate statistical analysis was performed to estimate the difference between age, days, treatments and their possible interactions during each season. The analysis of variance tables showing these effect with their significance level has been presented in appendix from 4.1 to 4.102. Other data tabulated showing the mean and overall mean values of each parameter at different days has been shown in their respective text in the result section. Pearson’s correlation was also estimated and result has been presented in discussion section of this dissertation. Present study was designed to adopt a rat model that has been tested for many to weightlessness studies and estimated the response and complexity of weightlessness. The challenge of exposure to different environmental temperature namely winter and summer for separately for one month. During winter and summer seasons, male and female rats did show a significant decrease in the weight of liver, percent of lymphocytes, serum glucose, cholesterol, proteins and albumin concentration, serum sodium, potassium, magnesium, manganese, copper, selenium and T3 concentration in the HR and HDS group as compared to control group. A significant increase in the adrenal weight, neutrophils percent and serum calcium concentration was also observed in the HR and HDS groups. Kidney weight of male rats did increase in HR and HDS groups and in female of HDS group during winter seasons. Pituitary weight did increase significantly in male and female HR and HDS groups during winter, however, during summer, pituitary weight was significantly high in female of HR and HDS groups. Testis weight did decrease significantly in male of HDS group only in the present study. Serum concentration of AST did increase significantly in male of HDS group during winter season, while during summer, it did increase significantly in male of HR and HDS groups and female of HDS group. On the other hand, serum concentration of ALT did increase significantly in male and female rats of HR and HDS groups during winter while during summer, the increase was only significantly in male and female of HDS rats. Serum iron concentration was significantly high in male HR and HDS rats during winter and summer season while in female, it was significantly low in HR and HDS during summer season. Serum thyroxin concentration did decrease significantly in male and female HR and HDS group in winter season and during summer, male rats did show a significant decrease during summer season.