乌拉地尔在大鼠小肠的在体灌流吸收研究

目的:研究乌拉地尔在大鼠小肠上、下部的吸收情况,为开发其缓释制剂提供依据。方法:采用大鼠在体小肠回流实验装置,利用高效液相色谱法分别测定酚红和乌拉地尔的含量。结果:乌拉地尔在大鼠小肠上、下段的吸收速度常数Ka分别为0.269、0.271,t1/2分别为2.6、2.58h,吸收率分别为27.29%、28.26%(P>0.05)。结论:乌拉地尔在大鼠小肠上、下段的吸收率无显著性差异,适合制备缓释制剂。     

苏子油乳剂小肠吸收动力学研究

以测定α 亚麻酸（α ＬＮＡ） 含量为指标,采用大鼠在体、离体小肠吸收实验方法,对苏子油乳剂小肠吸收动力学进行了研究．实验表明：苏子油乳剂小肠吸收较好,６ 小时吸收率为８６ ％ ,胆管结扎与不结扎对吸收率无明显影响;实验浓度下苏子油乳剂在小肠上、中、下段的吸收速率常数无显著差异;其吸收机制为被动扩散．     

药品和营养品中的面筋(谷朊)

乳糜泻(Celiac sprue)或非热带性口炎性腹泻是吸收不良综合症的一种,是以体重减轻、腹部肿胀、腹泻、脂肪痢及吸收功能异常为特征的遗传性疾病。患病者往往小肠结构异常,绒毛倒状和表面上皮发生变化,不能耐受小麦或其制品中的面筋(Gluten)。目前认为,面筋蛋白质通过两种机制引起吸收不良及组织结构改变。中毒机制认为,病人缺乏一种通常能将面筋水解成小肽和氨基酸的特异粘膜肽酶,由于毒性产物蓄积而导致脂肪痢和肠上皮脱落。免疫学机制则认为,HLA 型抗原量增加的易感性病人不能耐受食     

几种酶抑制剂对胰岛素肠道吸收的影响几种酶抑制剂对胰岛素肠道吸收的影响

目的研究酶抑制剂对胰岛素在大肠和小肠吸收的影响,初步探讨酶抑制剂在肠道各段的作用机制。方法采用原位肠袢法,设计肠道冲洗实验,测定胰岛素肠道吸收后的降血糖效应和血药浓度。结果胰岛素单用于小肠袢或大肠袢时,冲洗实验前后均无降血糖效应。与酶抑制剂合用时,冲洗实验前,小肠段无降血糖效应,冲洗实验后,小肠段降血糖效应有所提高;冲洗实验前后,大肠段均产生明显的降血糖效应。酶抑制剂作用与其种类、应用浓度和不同区段内蛋白水解酶的活性有关;各种酶抑制剂提高胰岛素降血糖效应的顺序为:亮肽素>甘氨胆酸钠>杆菌肽>抑氨肽酶素B>胱蛋白;其中甘氨胆酸钠和杆菌肽还具有渗透促进作用。结论合用酶抑制剂能显著改善胰岛素在大肠处的吸收。     

炎琥宁大鼠在体肠吸收实验研究

目的考察炎琥宁在大鼠小肠中的吸收状况,为炎琥宁口服肠溶制剂的制备提供理论依据。方法采用大鼠在体肠循环法,通过测定各时间点炎琥宁的剩余药量计算吸收速率。结果低、中、高(6μg.mL-1、1 mg.mL-1和1.4mg.mL-1)三种浓度炎琥宁溶液在小肠的吸收速率(Ka)分别为1.64×10-2、5.87×10-3和8.26×10-3;吸收率分别为89%、55%和69%。1 mg.mL-1炎琥宁溶液在小肠的不同部位(十二指肠、空肠、回肠)吸收速率分别为1.11×10-2、1.20×10-2和0,吸收率分别为86%、0.86%和0。结论炎琥宁在小肠有较好的吸收,低浓度吸收优于高浓度,因此,该药适合制备小肠定位释放的缓控释制剂。     

LC-MS/MS法对融合蛋白FP3的氨基酸全序列测定

运用液质联用、两种串联质谱对融合蛋白FP3的氨基酸全序列测定, 确证其一级结构。将样品还原烷基化后, 通过胰蛋白酶酶解蛋白, PNGase F去除多肽混合物中糖肽的糖基化, 将去糖后的总肽用于液质联用系统, 通过液相分离后, 运用Q-TOF和线性离子阱两种串联质谱测定各个肽段的b, y碎片离子, 分析测定融合蛋白FP3的氨基酸全序列。通过LC-ESI-Q-TOF完成了融合蛋白FP3的76%氨基酸序列测定, 通过LC-ESI-Trap完成余下24%氨基酸序列测定。液质联用、串联质谱法测定蛋白质氨基酸序列快速、灵敏、准确, 是对重组蛋白结构分析和确证的重要手段。     

大蒜油及其包合物小肠吸收的研究

本文以大蒜油为测定指标，采用大鼠在体小肠回流的方法，对大蒜油及其包合物的小肠吸收情况进行对比实验。结果表明大蒜油或包合物在体小肠循环2．5h的吸收速度常数（Ka）分别为0．9665h-1和0．2568h-1，吸收半衰期（t1／2）分别为43．13min和2．65h，吸收率分别为94．87％和51．05％，包合物经小肠循环6h吸收率接近80％。吸收曲线表明，包合物比大蒜油的吸收缓慢平稳持久，病理学检查表明，包合物能明显降低大蒜油对肠道的刺激性和毒性。     

尼莫地平自微乳化液大鼠小肠吸收动力学研究

以测定尼莫地平含量为指标，采用大鼠在体小肠吸收实验方法，对尼莫地平自微乳化液大鼠小肠吸收动力学进行了研究。实验表明：尼莫地平自微乳化液大鼠小肠吸收较好，循环灌流3h后．胆管结扎的大鼠小肠药物吸收百分率为84．74％，胆管未结扎的大鼠小肠药物吸收百分率为81．54％，胆管结扎与不结扎对吸收率无显著影响。     

在体单向肠灌流模型研究帕拉米韦拟肽类衍生物的大鼠小肠吸收特性

目的研究帕拉米韦及其拟肽类衍生物的大鼠小肠吸收机制,筛选出膜渗透性最大的衍生物。方法采用大鼠在体单向灌流法研究帕拉米韦拟肽类衍生物的小肠吸收,采用高效液相色谱法测定药物和酚红的浓度。建立lgD预测值和lgP之间的关系。结果帕拉米韦拟肽类衍生物的膜渗透系数都比帕拉米韦高,其中帕拉米韦L-异亮氨酸衍生物具有最高的膜渗透性;寡肽转运蛋白(PEPT1)典型底物甘氨酰肌氨酸能显著降低帕拉米韦拟肽类衍生物的小肠吸收,而L-缬氨酸不具有这种能力。结论帕拉米韦拟肽类衍生物是PEPT1的底物,它们在大鼠小肠内的吸收是PEPT1介导的主动转运过程。     

大黄总蒽醌大鼠在体胃肠吸收

目的:研究大黄总蒽醌在大鼠胃、肠的吸收性质。方法:采用大鼠在体胃、肠吸收模型,以高效液相色谱法测定胃、肠灌注液中大黄总蒽醌的含量,并考察离子浓度增加对吸收的影响。结果:大黄总蒽醌在大鼠小肠2h累积吸收率为66.99%,在结肠中2h累积吸收率为23.54%,增加离子强度对吸收没有影响。结论:大黄总蒽醌在大肠吸收相对较少。提示根据其泻下作用机制,可以将大黄总蒽醌制备成口服结肠定位给药形式。     

Direct photoaffinity labelling of binding proteins for beta-lactam antibiotics in rabbit intestinal brush border membranes with [3H]benzylpenicillin

Brush border membrane vesicles from rabbit small intestine were used to study the intestinal uptake system for beta-lactam antibiotics. Benzylpenicillin inhibited the H+-dependent uptake of alpha-aminocephalosporins in a concentration-dependent manner suggesting a common transport system for alpha-aminocephalosporins and benzylpenicillin. Benzylpenicillin is therefore a suitable probe to characterize this transport system. Irradiation of [3H]benzylpenicillin using light sources having their maximum of radiation at 300 or 254 nm resulted in a covalent incorporation of radioactivity into penicillin binding proteins as was shown with serum albumin. Hence [3H]benzylpenicillin can be used for direct photoaffinity labeling of penicillin binding proteins in different cells and tissues. In brush border membrane vesicles from rabbit small intestine predominantly a membrane polypeptide with an apparent molecular weight of 127,000 was labeled by [3H]benzylpenicillin. Competition labeling experiments demonstrated that beta-lactam antibiotics--penicillins and cephalosporins--specifically interact with this protein, whereas amino acids, sugars or bile acids had no effect on the labeling pattern. Compounds which decreased the labeling of the 127,000 molecular weight membrane polypeptide also inhibited the H+-dependent uptake of the alpha-aminocephalosporin cephalexin into intestinal brush border membrane vesicles. These results suggest that a polypeptide of molecular weight 127,000 in the brush border membrane from rabbit small intestine is a constituent of a common transport system responsible for the uptake of orally effective beta-lactam antibiotics and dipeptides. beta-Lactam antibiotics which are not absorbed from the small intestine also bind from the luminal site to this transport system, but are not transported across the brush border membrane.     

Biologically active dietary peptides

A large variety of peptides are generated in the gut lumen during normal digestion of dietary proteins. Large quantities of small peptides (ie. dipeptides and tripeptides) are absorbed through the gut mucosa and represent the primary mechanism for absorption of dietary nitrogen. However, larger peptide fragments are also absorbed with absorption decreasing with increasing chain length. Many of these dietary peptides have been shown to have biologic activity and many are active in microgram quantities. These peptides may modulate neural, endocrine, and immune function. In this report, we review normal protein digestion and absorption. We then discuss the biological actions of the amino acids arginine and glutamine and the biologic actions of a variety of dietary derived peptides. We concentrate on the immune effects of these peptides. We illustrate the potency of dietary peptides with a discussion of the cardiovascular effects of carnosine. We also review biologic effects of different protein sources, which generate different peptide profiles during digestion. The implications of dietary peptides for modulation of disease are discussed.     

The effect of L-leucine on the absorption of levodopa, studied by regional jejunal perfusion in man.

1. A new method for perfusing a 10 cm segment of jejunum in humans has been used in seven subjects to study the effect of the amino acid L-leucine (40 mM) on the intestinal absorption of levodopa (2.5 mM). The tube contains six channels and has two inflatable balloons, which enable a perfusion of a closed and defined segment of the proximal small intestine. 2. L-leucine decreased the intestinal absorption of levodopa from 40 +/- 19 to 21 +/- 15% but was without effect on the absorption of antipyrine, benserazide and D-glucose. 3. We confirm that levodopa is absorbed by the active transport system normally responsible for the absorption of large neutral amino acids (LNAA) in humans. Oral absorption by passive diffusion, probably by the paracellular route, might also occur for levodopa in the proximal part of the small intestine.     

大鼠在体单向肠灌流法对核黄素肠吸收的研究

目的：研究核黄素在大鼠肠道的在体吸收情况。方法应用大鼠在体肠灌流技术中的重量法研究核黄素在大鼠的十二指肠、空肠、回肠的吸收情况,用高效液相色谱法测定肠灌流液中核黄素的含量,计算核黄素的有效渗透系数（Pef）及药物吸收速率常数（Ka ）。结果核黄素在大鼠各肠段的 Pef（×10－4 cm·s －1）按十二指肠、空肠、回肠顺序依次分别为1.002±0.630、0.818±0.386、0.796±0.372;Ka （×10－3 s －1）依次为1.114±0.625、0.905±0.452、0.873±0.369。结论核黄素在大鼠肠段不同部位吸收存在差异,核黄素在十二指肠的吸收显著高于空肠和回肠段。     

Bestatin as an experimental tool in mammals

Bestatin, an antibiotic of microbial origin, is a potent inhibitor of some, but not all aminopeptidases. It can be administered, with low toxicity, to cultured cells, intact animals and humans. It has become a useful tool in elucidating the physiological role of some mammalian exopeptidases in the regulation of the immune system, in the growth of tumors and their invasion of surrounding tissues, and in the degradation of cellular proteins. Bestatin-sensitive enzymes play important roles in the digestion and absorption of peptides in the brush border of the intestine and the kidney, in the reproductive system, and in the metabolism of opioid peptides and leukotrienes. Aminopeptidase N emerges as the major target for the effects of bestatin on the immune system and some of its effects on tumor growth and the endometrium. It is also the major bestatin-sensitive enzyme involved in the degradation of oligopeptides on the surface of intestine and kidney brush borders, and the inactivation of enkephalins in the brain. Bestatin-sensitive cytosolic exopeptidases are important in the degradation to amino acids of di- and tripeptides generated in most cells by cellular protein degradation, as well as those absorbed through the brush border of intestine and kidney. Inhibition of one of these exopeptidases, cytosol alanine aminopeptidase, results in apoptosis. Bestatin-sensitive cystinyl aminopeptidase is abundant in placenta. Two bestatin-sensitive enzymes, aminopeptidase B and nardilysin, are particularly abundant in late spermatids. Finally bestatin-sensitive LTA4 hydrolase generates the potent chemotactic agent, LTB4.     

Absorption of iothalamate after oral administration and absorption enhancement by amino acids in dogs and rats

The oral absorption of iothalamate and the effect of amino acids on its absorption were studied in 6 dogs and 6 rats using a simple HPLC assay. The results showed that iothalamate was absorbed in dogs, averaging 9.9, 8.5, and 10.0 per cent following the administration of 40 and 100 mg kg-1 of iothalamic acid capsules and 50 mg kg-1 of sodium iothalamate solution, respectively. The absorption from the capsule was slower and more sustained than that from the solution. In rats, the absorption appeared to be dose-independent (averaging about 4.2 per cent) in the dose range of 20-800 mg kg-1. The low bioavailability obtained was mainly due to the high polarity of iothalamate molecules as suggested by the GI recovery and in vitro partition studies. Among several amino acids tested as possible ion-pair formers, only homoarginine hydrochloride increased the partition of iothalamate into chloroform layer. However, both homoarginine hydrochloride and arginine hydrochloride at the amino acid/iothalamate molar ratio of 25 were found to significantly enhance (about 70 per cent) the iothalamate absorption in dogs. The in situ rat small intestinal loop study indicated that the absorption-enhancing effect of arginine was sodium dependent. At the sodium chloride concentration of 0.09 M, no significant increase in the absorption was observed, while at the concentration of 0.3 M or higher, a marked increase (about twofold) was obtained in both upper and lower intestine. Thus, the mechanism of the amino acids in facilitating the iothalamate absorption may be more closely related to the active amino acid transport system rather than the possible increase in lipophilicity of the ion-pair formed. The potential use of such naturally occurring, relatively non-toxic amino acids for increasing the GI absorption of water-soluble weak acids or bases through ion-pair formation remains to be fully investigated.     

Absorption of 3-nitropropanol and 3-nitropropionic acid from the digestive system of sheep

When 3-nitropropanol (NPOH) was injected into the rumen (30 mg/kg), abomasum (10 mg/kg) or small intestine (10 mg/kg) of sheep, it was rapidly absorbed and converted to 3-nitropropionic acid (NPA). The reticulo-rumen was the major site of absorption for the miserotoxin aglycone but the abomasum and the small intestine also had the capacity to absorb NPOH. When NPA was injected into different regions of the alimentary tract, the reticulo-rumen was also the major site of absorption. Absorption of NPA or NPOH from the small intestine was much more rapid than from the abomasum. Plasma levels of NPA and inorganic nitrite were higher after dosing with NPOH than with NPA indicating a more rapid rate of uptake of the aglycone.     

Direct assignment of disulfide bonds by Edman degradation of selected peptide fragments

Disulfide linkages in peptides or proteins were analyzed by automated gas-phase Edman sequencing performed in minimized reducing agents. If cystine linkage was regulated at the same position in two peptides during peptide preparation, the diphenylthiohydantoin derivative of cystine was significantly recovered by Edman reaction. In contrast, when the crosslinked half cystines were present at different positions in the peptides, the derivative could be poorly detected. Upon direct sequence analysis of intact bovine insulin, the PTH derivatives of cystine from both Cys-A7 and Cys-B7 were significantly released after Edman cycle 7 and gave approximately 20% recovery of common PTH amino acids. However, Cys-Al1 linked to Cys-A6 was poorly detectable after Edman cycle 11. For general use of this method, proteins need to be subjected to several sets of proteolytic or chemical cleavages in the hope that at least one of the fragments will have cystine linkage at the same position. This method was applied to several fragments of platelet-derived growth factor B chain and brain-derived neurotrophic factor.     

Oral uptake and persistence of the FnAb-8 protein characterized by in situ radio-labeling and PET/CT imaging

The absorption of peptides and proteins delivered orally is minimum because of the intestine epithelial barrier. There are few known active transport mechanisms for macromolecules including the neonatal Fc Receptor (FcRn) for the absorption and secretion of IgGs in infant and adult intestine. We had previously described the FnAb-8 protein that could bind to hFcRn tightly at pH 6.0 but barely at pH 7.4. In this study, we examined its uptake, biodistribution and pharmacokinetics after peroral administration in both wild-type and human FcRn transgenic (Tg) mice. FnAb-8 was modified to contain trans-cyclooctene (TCO) which could interact with ¹⁸F labeled tetrazine in situ via the bioorthogonal inverse-electron-demand Diels−Alder reaction. We showed that FnAb-8 had a tendency to distribute and persist in the Tg mice intestine for an extended duration of time. It could also be absorbed into the circulation and distributed systemically over a long period of time up to 172 h. The improvement in oral uptake and concentration in the intestine tissue may be valuable for designing oral delivery of biopharmaceuticals, especially for diseases involving the gastric intestinal tissue.