Hara H, Nishi T, Kasai T
Department of Bioscience and Chemistry, Faculty of Agriculture, Hokkaido University, Sapporo, Japan.
Proc Soc Exp Biol Med. 1995 Dec;210(3):278-84. doi: 10.3181/00379727-210-43950.
Previously, we have shown that, in rats that have had bile-pancreatic juice (BPJ) diverted from the proximal small intestine for 7 days, the exocrine pancreatic secretion was enhanced after they were fed a casein, fat-free diet. This demonstrates that the pancreatic secretion is stimulated by dietary protein with a pancreatic protease-independent pathway. To examine the chemical structure of casein responsible for the enhancement of pancreatic secretion, we prepared chemically modified casein in which lysine residues were guanidinated. Secretion of protein, amylase, and chymotrypsin in the chronic BPJ-diverted rat was increased much more after the rats were fed a diet containing guanidinated casein (250 g/kg diet) than after they were fed a diet containing intact casein (250 g/kg diet). In normal rats whose diverted BPJ was returned to the duodenum, the increases in the pancreatic secretion after consuming the guanidinated casein diet were comparable to those after consuming the intact casein diet. In vitro digestibility of guanidinated casein by trypsin and chymotrypsin was much lower than that of intact casein. Also, guanidinated casein inhibited tryptic hydrolysis of benzoyl-L-arginine p-nitroanilide to a lesser extent than did intact casein as determined by an in vitro assay. These results demonstrate that guanidinated casein is less sensitive to trypsin than is intact casein and that the structure that is sensitive to trypsin is not involved in the stimulation of pancreatic secretion in diverted rats. The results evidence that masking luminal trypsin activity does not predominantly contribute to the enhancement of pancreatic secretion in 7-day BPJ-diverted rats. Also, in normal rats, the luminal protease-independent mechanism may play a role partly in increasing the pancreatic secretion by dietary protein.
此前，我们已经表明，在将胆汁胰液（BPJ）从小肠近端改道7天的大鼠中，给它们喂食酪蛋白无脂饮食后，外分泌性胰腺分泌增强。这表明胰腺分泌是由膳食蛋白质通过一种不依赖胰腺蛋白酶的途径刺激的。为了研究负责增强胰腺分泌的酪蛋白的化学结构，我们制备了赖氨酸残基被胍基化的化学修饰酪蛋白。与喂食含有完整酪蛋白（250 g/kg饮食）的大鼠相比，慢性BPJ改道大鼠在喂食含有胍基化酪蛋白（250 g/kg饮食）的饮食后，蛋白质、淀粉酶和胰凝乳蛋白酶的分泌增加得更多。在将改道的BPJ恢复到十二指肠的正常大鼠中，食用胍基化酪蛋白饮食后胰腺分泌的增加与食用完整酪蛋白饮食后的增加相当。胍基化酪蛋白在体外被胰蛋白酶和胰凝乳蛋白酶的消化率远低于完整酪蛋白。此外，通过体外测定，胍基化酪蛋白对苯甲酰-L-精氨酸对硝基苯胺的胰蛋白酶水解的抑制程度低于完整酪蛋白。这些结果表明，胍基化酪蛋白对胰蛋白酶的敏感性低于完整酪蛋白，并且对胰蛋白酶敏感的结构不参与改道大鼠胰腺分泌的刺激。结果证明，在7天BPJ改道的大鼠中，掩盖肠腔胰蛋白酶活性并非胰腺分泌增强的主要原因。此外，在正常大鼠中，肠腔蛋白酶非依赖机制可能在一定程度上参与膳食蛋白质增加胰腺分泌的过程。
