The use of solid soft silicone rubber exoplants in retinal detachment surgery

A method of retinal detachment surgery utilizing soft solid silicone rubber exoplants is described along with its use in typical cases. Solid silicone rubber, long used as a scleral implant, is a well-tolerated exoplant scleral buckling material which has been found to provide excellent long-term results. The surgical procedure described is relatively short in duration and has a minimum of operative and postoperative complications.     

Reactive distillation for methyl acetate production

We describe a hierarchy of methods, models, and calculation techniques that support the design of reactive distillation columns. The models require increasingly sophisticated data needs as the hierarchy is implemented. The approach is illustrated for the production of methyl acetate because of its commercial importance, and because of the availability of adequate published data for comparison. In the limit of reaction and phase equilibrium, we show (1) the existence of both a minimum and a maximum reflux, (2) there is a narrow range of reflux ratios that will produce high conversions and high purity methyl acetate, and (3) the existence of multiple steady states throughout the entire range of feasible reflux ratios. For finite rates of reaction, we find (4) that the desired product compositions are feasible over a wide range of reaction rates, up to and including reaction equilibrium, and (5) that multiple steady states do not occur over the range of realistic reflux ratios, but they are found at high reflux ratios outside the range of normal operation. Our calculations are in good agreement with experimental results reported by Bessling et al., [Chemical Engineering Technology 21 (1998) 393].     

Differentiating between parthenogenetic and "positive development" embryos in turkeys by molecular sexing

In mated or inseminated turkeys, 5 to 15% of eggs set for incubation show only rudimentary development. Most of these embryos die during the first 24 to 48 h of incubation and contain only unorganized sheets of tissue. This abnormal development is termed "positive development" (PD). Turkey eggs also show incidence of parthenogenesis and the resulting progeny is believed to be always male. As both types of embryos are morphologically similar at the early stage of incubation, it has been speculated that PD embryos may in fact be parthenogens. By identifying the sex at the blastodermal stage with the help of DNA markers, we have differentiated between the PD embryos and parthenogens. Parthenogenetic embryos were obtained from eggs laid by uninseminated or virgin Beltsville Small White (BSW) hens, and the PD embryos were obtained from eggs of inseminated Nicholas and British United Turkeys of America (BUTA) hens. DNA was extracted from blastoderms of parthenogenetic and PD embryos. Turkey W-chromosome specific DNA probe and primers were used to detect females in all samples by Southern blot and polymerase chain reaction (PCR), respectively. No female was detected among the 35 parthenogens examined, whereas there were 3 females among the 11 PD embryos. The presence of both males and females among PD embryos suggests that they are products of fertilization, and that at least these 3 female embryos, if not all the 11 PD embryos, are not of parthenogenetic origin. It is concluded, therefore, that PD embryos result from errors in fertilization or from early embryonic mortality following successful fertilization, and that they are unlikely to be of parthenogenetic origin.     

The role of blood stem cells in hematopoietic cell renewal

It has been the purpose of this keynote address to review available evidence for the notion that the stem and progenitor cells circulating in the peripheral blood play a decisive role in the homeostasis of blood cell formation distributed throughout dozens of bone marrow units in the skeleton. Furthermore, if this notion is correct, one could speculate that the quantity and quality of stem and progenitor cells in the blood should reflect the functional state of the hematopoietic stem cell system throughout the skeletal bone marrow and provide a new tool for the evaluation of alteration in blood cell production. On this basis, the following questions are considered: A) What do we know about the quality and quantity of blood stem cells in steady-state conditions? B) In what way do blood stem cells respond to perturbations of the "steady-state" of blood cell formation? C) Which role do blood stem cells play during hemopoietic development assuming that the establishment of bone marrow hemopoiesis requires the "seeding" of blood stem cells into an appropriate cellular environment? D) What is the role of blood stem cells in hemopoietic regeneration after partial body irradiation with a small volume of marrow (and hence stem cells) protected? and E) What are the mechanisms and/or kinetics of hemopoietic recovery if stem cells introduced into the circulation were collected from exogenous (autologous or allogeneic) sources? In this review presentation, experimental work of our group and of other members of the scientific community is summarized. It becomes obvious that blood stem and progenitor cells play a key role in hematopoietic homeostasis. Furthermore, their physiology and pathophysiology deserve rigorous experimental studies in order to develop a novel tool in the diagnosis and prognosis of neoplastic and non-neoplastic disorders of blood cell formation.     

Coronary atherosclerosis or diabetic cardiomyopathy? Pathoanatomic changes of blood vessels, nerves and myocardium in patients with diabetes mellitus

In patients with diabetes mellitus, heart disease is more common that in the background populations and has a more serious prognosis. The reasons are only partially understood. Whether patients with diabetes mellitus have a more diffuse and pronounced coronary atherosclerosis has been the subject of many investigations with diverging results. However, the larger studies suggest that coronary atherosclerosis is more pronounced and diffuse in diabetics compared with non-diabetic patients. The pathoanatomic picture of the atherosclerotic process seems to be identical in patients with and without diabetes mellitus. A number of structural abnormalities in the intramural vessels and interstitial tissue of the heart have been demonstrated in diabetics. However, similar abnormalities have also been reported in non-diabetic patients. With respect to where "diabetic cardiomyopathy" is a specific entity, the existing data are not confirmative. Whether diabetes mellitus per se induces functional changes in the coronary vascular system leading to myocardial ischaemia and dysfunction is a subject for future investigations.     

Phosphorylation of a twitchin-related protein controls catch and calcium sensitivity of force production in invertebrate smooth muscle

"Catch" is a condition of prolonged, high-force maintenance at resting intracellular Ca2+ concentration ([Ca2+]) and very low energy usage, occurring in invertebrate smooth muscles, including the anterior byssus retractor muscle (ABRM) of Mytilus edulis. Relaxation from catch is rapid on serotonergic nerve stimulation in intact muscles and application of cAMP in permeabilized muscles. This release of catch occurs by protein kinase A-mediated phosphorylation of a high (approximately 600 kDa) molecular mass protein, the regulator of catch. Here, we identify the catch-regulating protein as a homologue of the mini-titin, twitchin, based on (i) a partial cDNA of the purified isolated protein showing 77% amino acid sequence identity to the kinase domain of Aplysia californica twitchin; (ii) a polyclonal antibody to a synthetic peptide in this sequence reacting with the phosphorylated catch-regulating protein band from permeabilized ABRM; and (iii) the similarity of the amino acid composition and molecular weight of the protein to twitchin. In permeabilized ABRM, at all but maximum [Ca2+], phosphorylation of twitchin results in a decreased calcium sensitivity of force production (half-maximum at 2.5 vs. 1.3 microM calcium). At a given submaximal force, with equal numbers of force generators, twitchin phosphorylation increased unloaded shortening velocity approximately 2-fold. These data suggest that aspects of the catch state exist not only at resting [Ca2+], but also at higher submaximal [Ca2+]. The mechanism that gives rise to force maintenance in catch probably operates together, to some extent, with that of cycling myosin crossbridges.