Praissman M, Izzo R S
Endocrinology. 1986 Aug;119(2):546-53. doi: 10.1210/endo-119-2-546.
Pancreatic membrane receptors for cholecystokinin (CCK) in obese and nonobese Zucker rats were compared with the use of a biologically active [125I]iodo-CCK-8 radioprobe. Membrane homogenates from obese rats bound half the amount of radioligand in 2 h as did membranes from lean rats (specifically bound, 7.0% vs. 14.0%; P less than 0.001). The reduced binding in membranes from obese rats did not result from kinetic effects or radioligand degradation; similar rates of association and dissociation of [125I]iodo-CCK-8 were obtained in membrane preparations from both, and no differences were found in the extent of radioligand degradation in the two membrane preparations. These differences also did not reflect an effect of cell size, as pancreatic acinar cells from obese and nonobese rats had about the same perimeters (24.6 and 26.3 micron, respectively) and areas (30.1 and 34.2 micron 2, respectively). Scatchard-type plots of competitive displacement data for CCK-binding sites on pancreatic membranes from both genotypes were curvilinear and were analyzed by a two-site binding model. The Kd values for both the high (0.56 vs. 0.45 nM) and low (9.0 vs. 14 nM) affinity sites on membranes from nonobese and obese rats, respectively, were the same (P greater than 0.1), whereas the capacities for CCK in the high (365 vs. 165 fmol/mg protein) and low (1020 vs. 360 fmol/mg protein) affinity regions were significantly different (P less than 0.025). This difference in CCK receptor capacity was reflected by a reduced pancreatic protein secretory response in the obese rat. After injections of 40, 80, 160, and 320 ng CCK/kg BW, total pancreatic protein secretion in nonobese rats increased 5, 12, 19, and 21 times above basal levels, whereas the same doses caused 2-, 6-, 12-, and 13-fold increases in obese rats. Whereas the reduced secretion in the obese rat may reflect a difference in the intracellular machinery leading to protein secretion between the two genotypes, these data are more consistent with a direct mechanism, whereby reduced numbers of pancreatic receptors for CCK are responsible for reduced protein secretion.
利用具有生物活性的[125I]碘-CCK-8放射性探针，比较了肥胖和非肥胖 Zucker 大鼠中胆囊收缩素（CCK）的胰腺膜受体。肥胖大鼠的膜匀浆在2小时内结合的放射性配体量仅为瘦大鼠膜匀浆的一半（特异性结合量分别为7.0%和14.0%；P<0.001）。肥胖大鼠膜中结合减少并非源于动力学效应或放射性配体降解；在两种大鼠的膜制剂中，[125I]碘-CCK-8的结合和解离速率相似，且在两种膜制剂中放射性配体降解程度未发现差异。这些差异也不反映细胞大小的影响，因为肥胖和非肥胖大鼠的胰腺腺泡细胞周长（分别为24.6和26.3微米）和面积（分别为30.1和34.2平方微米）大致相同。两种基因型大鼠胰腺膜上CCK结合位点的竞争性置换数据的Scatchard型图呈曲线，并采用双位点结合模型进行分析。非肥胖和肥胖大鼠膜上高亲和力位点（分别为0.56和0.45 nM）和低亲和力位点（分别为9.0和14 nM）的Kd值相同（P>0.1），而高亲和力区域（分别为365和165 fmol/mg蛋白质）和低亲和力区域（分别为1020和360 fmol/mg蛋白质）中CCK的结合容量显著不同（P<0.025）。CCK受体容量的这种差异反映在肥胖大鼠胰腺蛋白质分泌反应降低上。在注射40、80、160和320 ng CCK/kg体重后，非肥胖大鼠的胰腺总蛋白分泌量比基础水平增加了5、12、19和21倍，而相同剂量在肥胖大鼠中仅引起2、6、12和13倍的增加。虽然肥胖大鼠分泌减少可能反映了两种基因型之间导致蛋白质分泌的细胞内机制差异，但这些数据更符合直接机制，即CCK胰腺受体数量减少导致蛋白质分泌减少。
