Florant G L, Richardson R D, Mahan S, Singer L, Woods S C
Department of Biology, Temple University, Philadelphia, Pennsylvania 19122.
Am J Physiol. 1991 Apr;260(4 Pt 2):R712-6. doi: 10.1152/ajpregu.1991.260.4.R712.
Plasma insulin (PI) reportedly crosses the blood-brain barrier in mammals and acts with the central nervous system (CNS) to reduce food intake. Animals that hibernate (hibernators) eat little or no food from early winter (November) to spring (April). This lack of food intake may be due to elevated PI concentrations acting within the CNS. In this study, we determined whether hibernators have altered insulin levels within the CNS at different times during the circannual cycle of metabolism and feeding. Plasma and cerebrospinal fluid (CSF) immunoreactive insulin concentrations were measured in marmots (Marmota flaviventris) during the feeding phase of the body weight cycle and during the fasting period (hibernation). Basal plasma and CSF samples were collected in September, November, January, and April. In addition, plasma and CSF insulin levels were monitored during a 2-h intravenous infusion of glucose (20% wt/vol) that stimulated pancreatic B-cell production of insulin. During the spring feeding period, we found that as PI levels rise, so do CSF insulin concentrations. However, in fall and winter when marmots are fasting, very little insulin entered the CSF even when PI levels were significantly elevated. Furthermore, the longer the fast, the lower was the CSF insulin under both basal and infusion conditions. These results lead us to conclude that elevated CSF insulin is not a likely cause of suppressed food intake in fasting marmots.
据报道，血浆胰岛素（PI）可穿过哺乳动物的血脑屏障，并与中枢神经系统（CNS）共同作用以减少食物摄入量。冬眠动物（冬眠者）从初冬（11月）到春天（4月）几乎不吃或根本不吃东西。这种食物摄入量的缺乏可能是由于中枢神经系统内升高的PI浓度所致。在本研究中，我们确定了冬眠者在代谢和进食的年度周期的不同时间点中枢神经系统内的胰岛素水平是否发生了变化。在体重周期的进食阶段和禁食期（冬眠）期间，测量了土拨鼠（黄腹土拨鼠）的血浆和脑脊液（CSF）免疫反应性胰岛素浓度。在9月、11月、1月和4月采集基础血浆和脑脊液样本。此外，在静脉输注葡萄糖（20%重量/体积）2小时以刺激胰腺B细胞产生胰岛素的过程中，监测血浆和脑脊液胰岛素水平。在春季进食期，我们发现随着PI水平升高，脑脊液胰岛素浓度也升高。然而，在秋季和冬季土拨鼠禁食时，即使PI水平显著升高，进入脑脊液的胰岛素也很少。此外，禁食时间越长，基础和输注条件下脑脊液胰岛素水平越低。这些结果使我们得出结论，脑脊液胰岛素升高不太可能是禁食土拨鼠食物摄入量受抑制的原因。
