High-performance liquid chromatographic assay of sulfapyridine and acetylsulfapyridine in biological fluids

A high-pressure liquid chromatographic method for the sensitive, rapid, and specific determination of sulfapyridine and its N-acetyl derivative in plasma and saliva was developed. A cyano-bonded, reversed-phase, high efficiency column was used. The system detected these sulfonamides in serum to 0.25 mg/liter and within only 6 min. Sulfapyridine was separated from its acetyl derivative with little interference from other drugs. The assay reproducibility was within 3%. The assay was highly useful for routine monitoring of patients receiving sulfasalazine for inflammatory bowel disease.

Identification of words and letters within words

Three experiments were designed to examine the way letters are identified when they are presented within the context of a word. The first two experiments demonstrated that identification speed is facilitated if the within-word letter position of the target location. If the locational information is specified before the word is displayed (e.g., it is always the first letter), but if the locational information is presented along with the display (e.g., the target position is underlined) reaction time is considerably slower. A model of the identification process was described which assumed that subjects first identify the word, then analyze the contents of all the letter positions in order to encode each letter. Finally, the identification can occur when subjects shift their attention to the target location. If the locational information is given before the display, the attention shift can occur as the letter positions are being analyzed and encoded, but the shift must be delayed until after the analysis if the locational information is part of the display. An implication of the model is that prior to identifying the contents of the target position, the subject should always have an encoding of all the letters in the word, and the results of the third experiment supported that expectation.

Retinal glycogen content during ischaemia

In the normal rabbit retina glycogen particles were only observed in the Müller cell. The glycogen was evenly distribution throughout the cytoplasm. The inner retina contained large amounts of Müller cell cytoplasm and consequently possessed substantial quantities of glycogen. The outer retina contained little Müller cell cytoplasm and only small amounts of Glycogen. Following total acute ischaemia induced by high intraocular pressure, the amount of glycogen in the retina fell rapidly so that by 45-60 min of ischaemia it was absent from the Müller cell. In the rabbit, ischaemia preferentially damaged the outer retina and especially the visual cells. This pattern of damage was thought to be a reflection of the amount of glycogen present in the different regions of the retina.

Light damage to the retina

The retinae of anaesthetised Dutch rabbits were exposed to light of various known intensities for a period of 1 h. After this period the animals were sacrificed and tissue taken for investigation by light and electron microscopy. Changes were apparent in the visual cells and retinal pigment epithelium only at the highest intensities employed. The retinal pigment epithelium and the outer nuclear layer exhibited mild oedematous changes. The major components to be affected were the visual cell outer segments. Marked disruption and vesiculation were features of the cone outer segments, which was in distinct contrast to the focal damage observed in the rod outer segments.

Effect of photocoagulation on the barrier function of the pigment epithelium. II. A study by electron microscopy

The healing of retinal photocoagulation burns and their permeability to colloidal carbon and horseradish peroxidase was studied by electron microscopy. Recent burns showed disruption of intercellular junctions in the pigment epithelium. By 2 days there was infiltration of the burn by proliferating pigment epithelial cells, and by 7 days the burn was composed of a mass of interconnected cells of pigment epithelial and Müller cell origin. Fresh photocoagulation burns result in complete disruption of the blood-ocular barrier, permitting particles as large as colloidal carbon to pass between disrupted pigment epithelial cells. Healed photocoagulation burns remain permeable to smaller tracers such as horseradish peroxidase.

Observations on the retinal pigment epithelium and retinal macrophages in experimental retinal detachment

After experimental retinal detachment in rabbits macrophages are a prominent feature in the subretinal space or within the retina. Two sources for these macrophages are identified. The retinal pigment epithelium (RPE) may undergo metaplasia and actively 'bud'; the evolving macrophage is then formed by a vitreal protrusion of the cytoplasm of an RPE cell which is 'nipped off' by lateral protrusions from adjacent cells. In addition, in regions of RPE proliferation, blood-borne cells were found in Bruch's membrane and among the mass of proliferated RPE cells, suggesting that blood-borne cells may pass from the choroidal circulation through Bruch's membrane and the RPE layer.

Post-mortem changes in the rabbit retina. A study by light microscopy

The course of post-mortem changes in rabbit retina has been followed. Short post-mortem periods are accompanied by degenerative changes limited mainly to the visual cells and retinal pigment epithelium. Long post-mortem periods are associated with degenerative changes throughout the retina. Retinal tissue maintained at room temperature was less affected than that kept at body temperature (37degreesC). Post-mortem changes are similar to those observed following periods of pressure induced ischaemia and it is thought that the mechanical effects of pressure on retinal tissue are minimal at the level of resolution afforded by light microscopy.

The occurrence of macrophages in the ischaemic rabbit eye

Mature macrophages involved in the removal of outer segment material were found between the visual cells and retinal pigment epithelium of the ischaemic rabbit retina. The mature macrophages were evident after only 15 min of ischaemia and the cells became progressively more numerous with increasing periods of ischaemia. A quantitative study was undertaken into the occurrence of the macrophages. These cells were probably of retinal pigment epithelial origin.

Phagocytosis in the choroidal endothelium of the ischaemic rabbit eye

Phagosomes containing membranous debris were found in the choroidal endothelium of rabbits following periods of acute pressure ischaemia and also accompanying periods of post-ischaemic recovery. The membranous debris may be of visual cell origin and pass into the choroid by a transpigment epithelial route. Ischaemia may be a sufficient stimulus to induce the vascular endothelium to engulf this material. The phagosomes were found only in ischaemic or post-ischaemic tissue.