| Abstract: | 過去已知高濃度之葡萄糖及穀氨醯氨同時存在下造成胰島素標的(Target)組織對胰島素調控之葡萄糖運輸系統(GTS)發生去敏感作用,且可能因而抑制胰島素所調控之其他生理功能。活化之淋巴細胞表現胰島素接受器,且其對葡萄糖之利用受胰島素之調節。此外,胰島素對於活化之淋巴細胞的複制能力具有關鍵性的影響。故本研究以in vitro研究方法,觀察活化的T淋巴細胞GTS胰島素敏感性及高濃度葡萄糖與穀氨醯氨對其GTS活性之影響,並觀察這些細胞GTS活性之變化與其複製能力之關係。實驗方法係取大白鼠頸部淋巴結,經密度梯度以1.077kg/m/sup 3/溶液離心得到淋巴細胞,將淋巴細胞經24小時Concanaval in A(Con A)活化後,以Silicon oil-layer技術追蹤[/sup 3/H] 2-deoxyglucose運送至胞內的速率測定細胞攝取葡萄糖之速率。並以[6-/sup 3/H]thymidine併入經Con A活化之細胞DNA之速率做為複製能力指數。 研究結果顯示,雖然活化淋巴細胞之葡萄糖利用率受胰島素之作用而增加,但其葡萄糖運輸系統活性並未受胰島素之影響。另一方面,不論在正常(10mmol/L)或高(30mmol/L)濃度葡萄糖濃度下,10mmol/L穀氨醯氨之添加均比無穀氨醯氨添加時有較高之細胞GTS活性;且不論有無胰島素存在,高濃度葡萄糖(30mmol/L)與高濃度穀氨醯氨(10mmol/L)顯著抑制細胞對葡萄糖之攝取(與正常濃度葡萄糖(10mmol/L)與高濃度穀氨醯氨(10mmol/L)相比)。此外,在淋巴細胞的複製功能方面,於固定葡萄糖濃度下(10、30或50mmol/L)加入不同濃度穀氨醯氨(0-10mmol/L),則細胞功能性約在穀氨醯氨濃度0.5-2mmol/L達尖峰,然後隨即下降,且葡萄糖濃度愈高則在愈低的穀氨醯氨濃度即開始下降;而於固定穀氨醯氨濃度下(2、6或10mmol/L),隨著葡萄糖濃度之增加(10、30或50mmol/L),淋巴細胞之複製率亦隨之降低。 本研究結果指出胰島素對活化之淋巴細胞葡萄糖代謝調控發生於胞內而非葡萄糖運輸器。且高濃度葡萄糖與高濃度穀氨醯氨可能影響其非胰島素調控之葡萄糖運輸及/或代謝途徑。此外,高濃度葡萄糖與穀氨醯氨在抑制活化之淋巴細胞複製功能上具有協同作用,但此作用與葡萄糖運輸系統活性並無相關性。
It has been known for sometime that the presence of high concentrations of both glucose and glutamine desensitizes the glucose transport system (GTS) of insulin target tissues/cells, consequently, the physiological function of these tissues may be affected. Activated lymphocytes express insulin receptor and the utilization of glucose in these cells are regulated by insulin. In addition, insulin plays an crucial role on the proliferative ability of activated lymphocytes. Therefore, the present study carried out an in vitro investigation on the sensitivity of GTS in activated T-lymphocytes and the effect of high concentrations of both glucose and glutamine on the activity of this system. The effects of high concentrations of both glucose and glutamine on lymphocyte proliferation were also investigated. Lymphocytes were prepared from rat cervical lymph node by first tear the organ with a stainless steel grinder and the cells released were layered on a density gradient solution (d=1.077kg/m/sup 3/). The cells were then washed and activated with Con A for 24h before use for the investigation of GTS activity with [/sup 3/H]2-deoxyglucose. The rate of [6-/sup 3/H]thymidine incorporated into Con A activated lymphocytes were determined as the index of proliferative ability of these cells. Results of the present study show that although insulin regulated the utilization rate of glucose in activated lymphocytes, the transport of glucose into these cells were not affected by insulin. On the other hand, no matter whether normal (10mmol/L) or high (30mmol/L) concentration of glucose presence, the addition of glutamine (10mmol/L) increased the GTS activity in these cells compared to the condition where no glutamine was added. In addition, independently from the action of insulin, the presence of high concentrations of both glucose (30mmol/L) and glutamine (10mmol/L) significantly inhibited the uptake of glucose by these cells (compared with cells in the presence of normal concentration of glucose (10mmol/L) and high concentration of glutamine (10mmol/L). Furthermore, in the presence of a certain concentration of glucose (10, 30 or 50mmol/L), the addition of various concentrations of glutamine (0-10mmol/L) into the culture medium firstly increased and then decreased the proliferation rate of lymphocytes. Peaks in all investigations appeared at 0.5-2mmol/L of glutamine. The higher concentration of glucose presented, the lower concentration of glutamine was required to start inhibiting the proliferation rate. Similarly, in the presence of a certain concentration of glutamine (2, 6 or 10mmol/L), the proliferation rate of lymphocytes were suppressed dose-dependently by the concentrations of glucose (10, 30 or 50mmol/L). Thus, the results of the present study indicated that insulin regulate the utilization of glucose in activated lymphocytes via intracellular mechanisms rather than via the regulation of GTS. The presence of high concentrations of glucose and glutamine suppresses glucose utilization independently from the action of insulin. Finally, the present study indicated that the suppressing effect of high concentrations of both glucose and glutamine on the function of lymphocytes was independent from the activity of GTS in these cells. |
