| Weightlessness, stress and ionic radiation on space flight can induce metabolic and endocrinal disturbance of human body, and thus influence the health of astronauts. A great deal of Researches have been concerned on cardiovascular, bone and blood system alterations after weightlessness, but little attention has been paid to the effect of simulated weightlessness on digestive system. Stomach is the pivotal organ of digestive system. Research have shown that apart from the primary digestion to the food intake, the stomach can synthesizes and secretes many kinds of gut hormones(brain-gut peptide), and participate in the endocrinal regulation of human body. Thus stomach is an important endocrinal organ. Leptin was first isolated from mammalian adipose tissue, it is a polypeptide containing 146 amino acids. Leptin has a variety of biological activity, It is involved in the regulation of energy balance, fatty metabolization, neuro-endocrinal regulation, reproduction and haematopoiesis. Leptin play it's role through leptin receptor, Lep-R belong to the member of type I cytokine receptor family, and Janus kinase-signal transducer and activators of transcription(JAK-STAT) pathway is the key signal transduction approach of Lep-R. Besides, mitogen activated protein kinase(MAPK) and phosphatidylinositol 3-kinase (PI-3K) are the other two signal transduction pathway of leptin.Recent studies have shown that the gastric mucosas can synthesizes and secretes leptin, and gastric mucous cells can express Lep-R. Thus leptin was considered as a new gut hormone. It may play an important role in regulating gastrointestinal tract function. In the present study, the changes of the leptin and its receptor expression in rat gastric mucosas during simulated weightlessness was investigated on the following respects:⑴The changes of Lep and Lep-R expressing cell numbers after 28 day tail–suspended rats was observed by immunohistochemistry;⑵The contents of leptin in rat serum and gastric mucosa was determined by enzyme-link immunoassay(ELISA) . The main results and findings are as follows: 1. Twenty two Sprague-Dawley rats were divided into 28 day tail-suspension group (n=12) and in-phase normal control group (n=10). Localization and expression of leptin and OB-R in rat gastric mucosa was observed by immunohistochemistry, and the density of leptin and OB-R immunoreactive cells in both groups were compared. The results have showed that Leptin and OB-R immunoreactive cells were distributed in the middle and low part of the fundic gastric gland, and the positive staining signals were mainly located in chief as well as parietal cell. Leptin immunoreactive cell density in the 28 day tail-suspension group were significantly increased compared with the in-phase normal control group(P<0.01). While OB-R immunoreactive cell density in the 28 day tail-suspension rats were increased than those of control rats, but the difference was not statistically significant(P>0.05).2. Twenty Sprague-Dawley rats were divided into 28 day tail-suspension group (n=10) and in-phase normal control group (n=10). by using ELISA method, the rat serum and gastric mucosa levels of leptin in two groups was measured and compared. The results showed that the gastric mucous leptin level was significantly increased in 28 day tail-suspension group compared with that of the in-phase normal control group(382.6±44.8ng/g vs 257.3±31.6ng/g, P<0.05). And the serum leptin in the 28 day tail-suspension group was also increased statistically compared with that of the in-phase normal control group(133.5±15.1ng/ml vs 76.2±12.6ng/ml, P<0.05).By using immunohistochemistry and ELISA method in this study, we systemic observed and analyzed the changes of leptin and its receptor in gastric mucosa and serum of ground simulated weightlessness rats. To the best of our knowledge, this is first report that 28 day tail-suspension can lead to the enhanced expression of leptin and Lep-R in rat gastric mucosa, and this finding suggested that leptin might be involved in the regulation of digestive system disfunction during simulated weightlessness. Our results also found that the serum leptin level was higher in simulated weightlessness rats than that of in-phase normal control rats, this high level leptin may enter the centre nerve system through systemic circulation, act on the food intake centrum in the hypothalamus, results in reduction of appetite and bodyweight in simulated weightlessness rats. In summary, our present study provide experimental evidence for further studying the effects of leptin on simulated weightlessness induced digestive system disfunction.
|
PDF Full Text Request