Showing papers by "University of Coimbra published in 1976"

The blood-retinal barriers.

Abstract: The Blood-Retinal Barrier (BRB) is a situation of restricted permeability which is present between the blood and the retina. This barrier has a well defined anatomic substrate, particular permeability characteristics and appears to play a role of major importance in the pathophysiology and therapeutics of retinal disease. The BRB phenomenon operates fundamentally at two levels, retinal vessels and chorioepithelial interface, forming which may be better called an inner BRB and an outer BRB. The main structures involved are, for the inner BRB, the endothelial membrane of the retinal vessels, and for the outer BRB, the retinal pigment epithelium. 'Zonulae occludentes' are present in these membranes forming complete belts around the cells, sealing off the spaces between them. Other structures appear to play an accessory role. Both barriers show an apparent predominance of processes of active transport over mechanisms of passive transfer, these being extremely restricted. Much information on the pathophysiology of the BRB mechanism has been obtained from studies of its experimental breakdown. In this way, a breakdown of the inner BRB may be induced by acute distension of the vessel walls, ischaemia, chemical influences, defects in the endothelial cells and failure of the active transport system, whereas experimental ischaemia, mechanical distension of the pigment epithelial membrane, defects in the pigment epithelium and failure of the active transport systems can cause a breakdown of the outer BRB. The increased permeability of the inner BRB, and of the outer BRB, appears to be related to changes in the vascular endothelial membrane and retinal pigment epithelium, respectively. In clinical ophthalmology there are two methods for the diagnosis of breakdown of the BRB, fundus fluorescein angiography and vitreous fluorophotometry. Vitreous fluorophotometry being capable of detecting functional alterations of the barrier before any pathological changes are apparent. There is evidence of an intimate relationship between breakdown of the BRB and almost every retinal disease, particularly the vascular retinopathies and the pigment epitheliopathies. Diabetic retinopathy, hypertensive retinopathy, retinal vein obstruction, blood diseases, trauma or surgery to the eye, temporary arterial obstruction, perivasculitis, Behcet's and Coats' diseases, retinoblastoma, hemangioblastoma and retinal neovascularization are examples of situations where a breakdown of the inner BRB has been demonstrated. On the other hand, examples of breakdown of the outer BRB include situations of choroidal ischaemia, detachment of the pigment epithelium, choroidal neovascularization, photocoagulation, retinal detachment, Koyanagi's disease, central serous choroidopathy, multifocal inner choroiditis and acute placoid pigment epitheliopathy.

Effect of heat treatment on the ATPase activity of various sarcoplasmic reticulum preparations.

Abstract: Ca2+-stimulated ATPase activity of sarcoplasmic reticulum (SR) preparations is activated after a short period of preincubation at temperatures between 40 and 45°C, but for temperatures higher than 48°C pronounced denaturation is observed. Heat denaturation is decreased if Mg2+ or K+ are present during heat treatment.

Synthesis of adenosine triphosphate during release of intravesicular and membrane-bound calcium ions from passively loaded sarcoplasmic reticulum

Abstract: Sarcoplasmic reticulum isolated from rabbit skeletal muscle and incubated in a medium containing Ca2+ in the absence of ATP retains intravesicular and/or membrane-bound Ca2+. The synthesis of ATP coupled with the release of intravesicular Ca2+ is totally inhibited by the ionophore X-537A. Release of the membrane-bound Ca2+, retained after short periods of incubation (10min) or after release of the intravesicular Ca2+ by ionophore X-537A, still supports some synthesis of ATP. The ratios of Ca2+ released to ATP synthesized are 2.5-3.2, when bound and intravesicular Ca2+ are released simultaneously, and 3.1-4.0, when only bound Ca2+ is released. The results show that the synthesis of ATP by sarcoplasmic reticulum during release of passively accumulated Ca2+ by EGTA [ethanedioxybis(ethylamine)tetra-acetic acid] is accompanied by a loss of membrane-bound Ca2+.

Effect of X-537A- on the phosphorylated protein in sarcoplasmic reticulum vesicles.

Abstract: The effect of the antibiotic X-537A on the phosphorylated ATPase (E∼P) was investigated. The results show that X-537A depresses the level of E∼P which is dependent on the Ca2+ gradient, while the Ca2+-independent E∼P is not affected.

Just two total graphs are complementary

Abstract: It is proved that there are just two non-trivial total graphs which are complementary, namely the triangle and its complement.

Lorazepam in the treatment of neurosis.

Abstract: An open study was carried out in 40 ambulatory neurotic patients with classical symptoms of anxiety to assess which of their symptoms responded most readily and favourably to treatment with lorazepam. Doses ranged from 2 mg to 15 mg daily and were adjusted to individual patient needs. The study period lasted 4 weeks and patients' individual symptoms were assessed weekly on a 4-point severity rating scale. The results showed a statistically significant and marked improvement during the first week for the majority of the 16 symptoms assessed, particularly emotional tension, irritability and apprehension. Symptoms with a cognitive element of anxiety were controlled to a lesser extent and were slower to respond. The few side-effects which were reported, mainly somnolence, appeared to be dose related and usually occurred during the first few days of treatment.