Stress distribution on the cusps of a polyurethane trileaflet heart valve prosthesis in the closed position.

In this paper, a finite element analysis of the stress distribution on the cusps of a polyurethane trileaflet heart valve prosthesis in the closed position is presented. The geometry of the valve was modified from a relationship proposed by Ghista and Reul (J. Biomechanics 10, 313-324, 1977). The effects of variations in stent height, leaflet thickness and coaptation area on the stress distribution were also analyzed. Analyses were performed with both rigid and flexible stents for the trileaflet valve in order to delineate the effect of stent flexibility on the leaflet stress distribution. The results showed that regions of stress concentration were present near the commissural attachment similar to those predicted with the bioprostheses. The stresses on the leaflets were reduced by increasing the stent height with both rigid and flexible stents. Selectively increasing the leaflet thickness near the commissures and also increasing the coaptation area did not prove to reduce the leaflet stresses when the stent flexibility was taken into account. The possible effect of high stresses on the structural integrity of polyurethane leaflets and its relationship with calcification is yet to be investigated.     

Crystal structure of cholestanyl caprylate and binary phase behavior with cholesteryl caprylate

The crystal structure of cholestanyl n-octanoate (caprylate) (C35H62O2) is monoclinic with space group A2 and cell dimensions a = 10.103(7), b = 7.646(7), c = 87.63(7) A, beta = 90.51(6) degrees; Z = 8 [two molecules (A, B) in asymmetric unit], V = 6769 A3, Dc = 1.010 g cm-3. Integrated X-ray intensities for 3798 reflections with I greater than 2 sigma (I) were measured with a rotating anode diffractometer at room temperature. The structure was determined using direct methods. Block diagonal least squares refinement gave R = 0.111. Molecules A and B have almost fully extended conformations, but differ significantly in the rotation about the ester bond and in the C17 chains. The molecular packing in the crystal structure of cholestanyl caprylate consists of stacked bilayers each having d002 = 43.8 A in thickness and within each bilayer, cholestanols pack with cholestanols and caprylate chains pack with caprylate chains. The crystal structure is very similar to that of cholesteryl myristate but is quite different from that of cholesteryl caprylate. The phase equilibria of the cholestanyl caprylate/cholesteryl caprylate binary system have been shown to involve limited mutual solubility of the two components and to have a eutectic point at 73% cholestanyl caprylate. The cholesteric mesophase is monotropic at all compositions except for a narrow range near the eutectic point where it is enantiotropic.     

ph1b基因在Aegilops有益基因直接遗传转移中利用的可能性

第一次用中国春和中国春ph1b突变体对(中国春phlb突变体×Ae.uariabilis)F_1和(中国春ph1b突变体×Ae.turcomenica)F_1回交获得了成功,并通过连续回交,把Ae.turcomenica的抗白粉基因转移到了普通小麦中。证实了利用ph1b基因从山羊草属的一些种“直接遗传转移”有益基因到普通小麦中的可能性。     

DM891129菌株对沙土鼠高胆固醇血症的影响

本项研究的目的是通过动物实验来观察由健康人分离出的肠球菌DM891129菌株的降血脂作用。本实验选42只沙土鼠(gerible),雌雄各半,随机分为3组,第1组13只为正常组;第2组13只,在正常饮食中 5％胆固醇饲喂1周;第3组16只,在第2组饮食的基础上,每天以肠球菌(DM891129)菌悬液(10~9个细菌/ml)0.5ml/次,Bid灌胃一周。3组沙土鼠以眼球采血,分别检测血清胆固醇、甘油三酯和胆酸水平及粪便中肠球菌和肠杆菌水平。结果表明:第2组胆固醇水平较第1组明显升高(P<0.001)。第3组胆固醇水平较第2组明显降低(P<0.001)。相应的、第3组鼠粪便肠球菌水平明显高于第1、2组(P<0.05),而1、2组之间无显著性差异,第2、3组肠杆菌水平明显高于第1组(P<0.02、P<0.05),2、3组肠杆菌水平无显著性差异。胆酸、甘油三酯水平3组之间无显著性差异。可见DM891129菌株对沙土鼠高胆固醇饮食所致的高胆固醇血症具有明显的降低作用而对血甘油三酯、胆酸水平无显著性影响。现在对DM891129菌株体内降血胆固醇水平的机制尚不清楚,有待于进一步研究。     

抑菌生的研究总结报告

本文报告一种由枯草杆菌制成的生态制剂,并命名为抑菌生(Subtilobiogen)。该制剂对创、烧伤感染有治疗作用。经过安全试验、急性毒性试验、Ames试验和微核试验证明,该制剂是一种无害、无毒和有致突变作用的活菌制剂。抑菌生有膏剂、乳剂及粉剂3种剂型。抑菌生在试管和体内对金黄色葡萄球菌、绿脓杆菌和大肠杆菌均具有抑菌作用。临床观察证明,将抑菌生喷洒在创面上,对浅Ⅱ°度、深Ⅱ°度及混合型烧伤感染均具有明显疗效。实验组(181例)与对照组(174例)相比较,在统计学上具有显著性差异。抑菌生的作用机制,经过初步试验证明,与营养争夺和占位性保护有关,因为枯草杆菌的生长速度超过金黄色葡萄球菌、绿脓杆菌和大肠杆菌的生长速度。     

pH-sensitive liposomes containing polymerized phosphatidylethanolamine and fatty acid.

With the ultimate aim of targeting cancer drugs to malignant tissues, liposomes containing polymeric phosphatidylethanolamine and a fatty acid were prepared. For this purpose diacetylenic phosphatidylethanolamine (DAPE), a phosphatidylethanolamine containing diacetylene, was synthesized. Liposomes containing DAPE, fatty acid, and either phosphatidylethanolamine (PE) or phosphatidylethanolamine-beta-oleoyl-gamma-palmitoyl (POPE) were then prepared. Polymerization of DAPE was effected by UV illumination. The polymeric liposomes so obtained were stable at physiological pH but became leaky below pH 6.5. Of various compositions studied, the greatest pH-sensitivity was found with liposomes composed of 35 mol% DAPE, 35 mol% POPE, and 30 mol% saturated fatty acid. The presence of blood plasma albumin decreased vesicle stability while apolipoprotein A-I (apo A-I) had the opposite effect and plasma as a whole had a slightly stabilizing effect.     

Centrally acting endogenous hypotensive substances in rats subjected to endotoxic shock.

Cerebroventricular perfusate (CVP) from rats subjected to endotoxic shock was infused into the lateral ventricle of the naive rat. This procedure produced a hypotensive response in the recipient rat which could be reversed by the intravenous injection of the opioid antagonist naltrexone. The degree of endotoxemic hypotension in the donor rat was attenuated by perfusing the cerebroventricular system with mock CSF. The results suggest the existence of endogenous hypotensive substances in rat central nervous system, possibly opioid in nature, which may play a critical role in the pathogenesis of endotoxic shock.