The Effect Of Tannins On The Lipids Metabolism Of Plateau Pikas (Ochotona Curzoniae)

A variety of plants in the Qinghai-Tibet alpine ecosystems contain high levels of phenolic secondary compounds, because they exposured to special environment, such as strong ultraviolet, high altitude, low oxygen, cold and drought, etc. And the level of the phenolic compounds varies depending on the season. Plateau pika is the herbivorous mammals inhabiting in the Qinghai-Tibet plateau. Many studies showed that plants can resist the predation of herbivorous animals through increasing the plant secondary compounds content such as tannins, and so on, while animals will adapt to these changes. In order to elucidate the co-evolution between animals and plants in plateau, wild animals were captured in different time (May, June. July and August) to observe the seasonal change of TC (Total cholesterol), TG (Triglyceride), PL (Phospholipid), FFA (Free fatty acid) and HDL-C (High density lipoprotein cholesterol) in pikas.And the levels of lipids in pikas were also determined after they were ig(Intragastrical) given0(control),10(low dose),20(medium dose) and40(high dose) mg/kg BW of tannin acid for different days (1d,4d and8d). The cDNA fragment of HMG-CoA reductase, the key enzyme of cholesterol synthesis, in liver of plateau pikas was cloned, and the fluorescence quantitative real-time PCR was used to quantify the mRNA of this enzyme, we also detected the changes of the content of this enzyme with Western blot method. The results were as follows.1) The partial cDNA sequences of HMG-CoA reductase gene in the liver of plateau pikas was obtained, it was798bp, encoding266amino acid residues. When aligned the sequence with gene of HMG-CoA reductase of rabbit, rat, mouse and human, their homology were99.6%,98.9%,99.2%and99.2%, respectively.2) Tannin acid had different effects on different lipids. There was no change of the content of serum TC when pikas were given low dose of tannin acid for1day, but the content of TC were significantly higher than control after given low or medium dose for4days. After given tannin acid for8days, only low dose increased the TC level in pikas.After giving medium and high dose of tannin acid for1day, the serum HDL-C level increased significantly.When treated for4days, only high dose increased the HDL-C1evel.But after they were treated for8days, both of the medium and high dose significantly decreased the HDL-C level in pikas.The serum TG reduced after given medium and high dose of tannin acid for1day or high dose for4days, while all doses of tannin acid made animals have higher TG after they were treated for8days.The serum PL decreased after animals were given high dose of tannin acid for1or4days.The most obvious change was found in FFA, because except for given low dose of tannin acid for1day, all of low, medium and high doses could make the FFA decrease after animal were treated for1,4and8days.3) The effect of tannin acid on the gene expression of HMG-CoA reductase was very clear. Both of the content and the mRNA level of this enzyme incresased after pikas were given low or medium dose for short time and decreased when administrated with high dose for any days.4) In field, the levels of all kinds of lipids in pikas changed from month to month. Compared to the serum contents in May, serum TC in pikas was much lower in July and August. HDL-C decreased firstly and had lowest level in June, then, became higher in August. TG increased firstly and then showed a downward trend, and reached its highest levels in June. PL got its highest point in July.5) The gene expression of HMG-CoA reductase also changed seasonally in filed. Compared to May, both of the content and the mRNA level of this enzyme were higher in June and lower in July or August.So, all of the results suggested that tannins affect the metabolism of lipids in pikas. The expression of HMG-CoA reductase and the content of cholesterol in pikas were enhanced when animals gave lower tannins, but inhibited when animals treated with higher tannins; In field, the expression of HMG-CoA reductase in pikas were increased when animals took lower tannins, but reduced when animals got higher tannins. This conclusion will be helpful to elucidate the co-evolution between pikas and the plants they feeding on.