Effects Of Simulated Weightlessness By Tail-suspension On Pancreatic Secretions And Hsp70Expression In Rat Pancreas

Background and Objective: Recent researches have showed that agravity orsimulated weightlessness have some influence on respiratory system, cardiovascularsystem, endocrine system, immune system, genital system, etc., and even causepathological changes. The pancreas is one of the important endocrinal organs whichcould also be affected by agravity or simulated weightlessness. This study investigatedthe stress effects of simulated weightlessness by tail-suspension upon pancreaticsecretions and Hsp70expression in rat pancreas.Methods:(1) The experiments were performed after approval by the Hospital’s EthicsCommittee. Sixty-four adult male Wistar rats were randomly divided into8experimental groups (n=8) including suspended for6h,12h,1d,2d,3d,5d,7d and0h (control). Tail-suspension was used as the method to establish the animal model ofsimulated weightlessness.(2) At the end of the experiment, animals were anesthetizedwith chloral hydrate (300mg/kg) and the peripheral vein blood samples were acquiredin each group，then the body and tail of pancreas obtained from control and suspendedanimals were immediately frozen in liquid nitrogen at-80℃until analysis, andthe headof pancreas were preserved in zinc-buffered formalin.(3) The levels of glucose, insulin,glucagon, C-peptide, serum amylase and lipase in venous blood samples were examedby using radioimmunoassay and biochemical analysis.(4) Hsp70protein and Hsp70mRNA in pancreas were detected by using immunohistochemistry, western blot assay,and RT-PCR technique respectively. Results:(1) Compared with the control group, the level of blood glucose fluctuatedduring the7days experiment, and the level of insulin was increased in the early phasewith peak value at6-hours’, then decreased along with C-peptide showing a trough at3-day’s, while the level of glucagon maintained above the normal. The serum amylaseand lipase were increased transiently at the early hours of the suspension. Pancreaticsecretions altered noticeably in the early phase of the suspension, and recovered to someextent in the later phase of the experiment.(2) The immunohistochemistry showed thatHsp70protein was stained as brown particles. The nuclei of pancreatic islet cells weredeeply stained in the early hours of suspension followed by the stain of the cytoplasm ofpancreatic acinar cells and islet cells. The expression of Hsp70protein was obviouslyweakened in the rat pancreas of3d to5d suspension groups.(3) Western blotting assayshowed that Hsp70expression in rat pancreas was significantly up-regulated comparedwith controls in the early stage of suspension (P＜0.05), and was recovered to normalranges in the late phase of suspension.(4) The semi-quantitative PCR analysis showedthat the Hsp70mRNA in rat pancreas was also significantly up-regulated at the earlyphase of suspension as compared with the control group (P＜0.05), and fluctuatednotably all through the experiment.Conclusions:(1) The pancreatic secretions were altered under the condition ofsimulated weightlessness by tail-suspension, and the level of serum glucose fluctuatednoticeably during the7days experiment.(2) The simulated weightlessness acted as acellular insult or stressor that elevated Hsp70expression both at protein and mRNAlevels in the suspended rat pancreas, and the results suggested that Hsp70playedimportant roles in the stress response of rat pancreas to the simulated microgravity.