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Biomedical subjects

A Bill

Publications and source records attributed to A Bill.

At least 73 records · Page 4Linked to original sources
PubMed1980

Cholinergic vasoconstrictor effects in the rabbit eye: vasomotor effects of pentobarbital anesthesia.

Oculomotor nerve stimulation causes vasoconstriction in the anterior uvea, which is due partly to a muscarinic mechanism and partly to a non-sympathetic aminergic mechanism. The labelled microsphere method was used to analyze the effect of pentobarbital anesthesia on the resting cholinergic vasomotor tone in the anterior uvea and to determine the relationship between stimulation frequency and vasomotor response. An attempt was made also to ascertain whether the aminergic part of the vasoconstriction is caused by release of 5-hydroxytryptamine or norepinephrine. Induction of pentobarbital anesthesia caused a marked vasodilation in the iris and the ciliary processes and a subsequent muscarinic blockade had no effect on the blood flow. A similar result was obtained in the optic nerve. In the choroid plexus, heart muscle, pineal body and coecum, pentobarbital anesthesia caused vasodilation and a subsequent muscarinic blockade caused vasoconstriction. In the brain pentobarbital anesthesia caused a marked reduction in the blood flow of the grey matter and a moderate reduction in the white matter. After a muscarinic blockade there was some increase in the blood flow of the grey matter. Stimulation of the oculomotor nerve caused near maximum vasomotor responses at 10-20 Hz; maximum effect on the pupil size was obtained at 40-50 Hz. Depletion of 5-hydroxytryptamine with fenfluramine did not prevent the aminergic part of the vasoconstriction and a marked vasoconstriction was also observed after pretreatment with reserpine. The results indicate the pentobarbital anesthesia abolishes most of the spontaneous cholinergic vasoconstrictor tone of the anterior uvea and that the aminergic part of the oculomotor nerve induced vasoconstriction is caused by the stimulation of phentolamine-sensitive receptors by a mechanism probably not involving release of norepinephrine or 5-hydroxytryptamine.

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PubMed1980

Vasomotor effects of facial nerve stimulation: noncholinergic vasodilation in the eye.

The effect of facial nerve stimulation on ocular blood flow was studied in rabbits. The intracranial part of the facial nerve was stimulated electrically and the regional blood flow was measured with labelled microspheres. Effects on the intraocular pressure were determined in a separate series of experiments. Stimulation increased choroidal blood flow by about 200%. The blood flow of the iris and the ciliary processes also increased. The blood flow of the eyelids and the nictitating membrane increased by approximately 1000%, and the blood flow of Harder's gland increased by about 200%. The blood flow of the tongue and the submandibular gland also increased. The increase in the uveal blood flow could not be abolished by a cholinergic or ganglionic blockade. Ganglionic blockade abolished most of the increase in the blood flow of the eyelids, nictitating membrane and Harder's gland; the cholinergic blockade seemed less effective. The intraocular pressure increased with a mean value of 6 mmHg during optimal (20-30 Hz) stimulation. The increase could not be prevented by cholinergic blockade. Much of the increase in uveal blood flow seemed to be caused by stimulation of unconventional nerves. It is suggested that these nerves may be peptidergic using VIP as a transmitter and lacking a hexamethonium sensitive synapse between the site of stimulation and the eye. Their nature--afferent or efferent--remains unknown. A great part of the increase in blood flow of the eyelids, nictitating membrane and Harder's gland seemed to be due to other mechanisms involving nerves with a peripheral synapse.

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PubMed1980

Effects of intracameral Na2EDTA and EGTA on aqueous outflow routes in the monkey eye.

Intracameral perfusion with 4 to 6 mM Na2EDTA or 4 mM EGTA for 40 to 80 min caused a very large increase in gross outflow facility. This effect was partly reversible when followed by perfusion with mock aqueous humor. Eyes perfused with Na2EDTA were studied morphologically. In the trabecular meshwork the cells separated due to a splitting of the cell junctions. A distention of the cribriform meshwork, a wash-out of extracellular material , and a disintegration of the denuded trabecular cores were also noticed. The inner wall of Schlemm's canal protruded in a "balloonlike" manner into the lumen of the canal and showed frank ruptures, especially after prolonged perfusion times. The conventional outflow pathways beyond Schlemm's canal showed no abnormalities. In the uveoscleral outflow routes the anterior and middle part of the ciliary muscle demonstrated very wide intermuscular clefts and many degenerated muscle fibers. The posterior third of the muscle was normal. So were the ciliary epithelium, the choroid, and the retina. The pupillary sphincter also showed degeneration. The corneal endothelial cells separated, starting at the apical junctional complex.

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PubMed1980

Permeability of the intraocular blood vessels.

This paper reviews quantitative studies on the permeability of the ocular blood vessels. In the retina, where there are tight junctions between the endothelial cells of the microvessels, there is very low permeability even to sodium ions. Glucose is transported through the capillary wall by a carrier, net glucose extraction amounting to about 12 per cent. In the choroid and ciliary processes, where there are fenestrated capillaries, the permeability to plasma proteins is about five times that in the kidney (another tissue with fenestrated capillaries), and ten to thirty times that in heart and skeletal muscle, which has non-fenestrated capillaries without tight junctions. Capillary permeability to low molecular weight substances is high in the choroid; sodium permeability is probably about thirty times that in heart muscle and fifty times that in skeletal muscle. This high permeability results in a high glucose concentration in the tissue fluid enabling rapid glucose movement into the retina.

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PubMed1979

Drainage of microspheres and RBCs from the vitreous of aphakic and phakic eyes.

The movements of plastic microspheres (7 to 10 mu in diameter) and autologous RBCs labeled with sodium chromate Cr 51 from the vitreous to the anterior chamber were studied in 24 rabbit eyes. Rabbits were made aphakic in one eye by intracapsular lens extraction of lensectomy via the pars plana, the fellow eyes serving as phakic controls. In phakic eyes the intravitreally injected microspheres and RBCs were retained inside the vitreous space, not gaining access to the anterior chamber. In aphakic eyes microspheres and RBCs moved to the anterior chamber and were usually seen on the corneal endothelium and in the chamber angle within two to ten days, although most particles remained in the vitreous for long periods of time. Removal of the lens thus improved forward drainage of particles from the vitreous space, but the structure of the vitreous seemed to preclude rapid clearance.

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PubMed1979

Effects of indomethacin on regional blood flow in conscious rabbits--a microsphere study.

In an attempt to reveal the importance of prostaglandins in the control of regional blood flow 20 mg/kg b.wt. indomethacin was given i.v. in conscious resting rabbits. Regional blood flow determinations were made before and 20 min after the injection using the labelled microsphere technique. The blood flow in the stomach wall was reduced by 0.75 +/- 0.17 g . min-1 . g-1 from a level of 1.64 +/- 0.24 g . min-1g-1. In jejunum the corresponding figures were 0.44 +/- 0.12 and 1.26 +/- 0.17 and in the brain 0.29 +/- 0.10 and 1.24 +/- 0.10. The blood flow in the liver via the hepatic artery increased by 0.20 +/- 0.02 g . min-1 . g-1 from a level of 0.13 +/- 0.02 g . min-1 . g-1. In the retina there was a reduction in blood flow by 2.75 +/- 1.03 mg . min-1 from a starting level of 15.1 +/- 2.3 mg . min-1. In a number of other tissues investigated there were no significant effects of the drug. The results suggest that under resting conditions prostaglandins play a role in the control of blood flow in the gastrointestinal tract, the brain and the retina--tissues which are likely to be rather active under such conditions.

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PubMed1979

Studies on ocular blood flow and retinal capillary permeability to sodium in pigs.

A surgical technique was developed in pigs that permits access to the retinal venous plexus surrounding the optic nerve. The effect of surgery on ocular blood flow and capillary permeability was evaluated. Blood flow, determined by the labelled microsphere technique, did not differ significantly between operated and control eyes. Increased intraocular pressure in the operated eye reduced blood flow through the choroid and the anterior uvea in proportion to the reduction in perfusion pressure, while in the retina a smaller reduction in blood flow occurred indicating that autoregulatory mechanisms are involved in the control of retinal blood flow. The capillary permeability to sodium was studied by the single injection technique, using albumin as a reference substance. The fractional initial extractions from the choroidal and the retinal vessels were 0.77 and -0.001 respectively. The absence of a sodium extraction from the retinal vessel indicates that this part of the blood-retinal barrier was intact and that the blood drained by the retinal plexus is not mixed with blood from other sources.

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PubMed1979

Regional lymph flow in unanesthetized rabbits.

Determinations were made of the 2-hour 22Na space and the 1 and 2 hour 51Cr EDTA spaces in a number of tissues. In regions where the two 51Cr-EDTA spaces were similar and smaller than or similar to the 22Na space the former spaces were regarded as measures of the extra-cellular volume. Using previously published data for plasma volumes, extravascular plasma-equivalent albumin and IgG spaces and the turnover rate constants for the extravascular proteins, it was possible to calculate extravascular protein concentrations and rates of net filtration from the capillaries or lymph flow in some tissues. The albumin concentrations, probably underestimated, were about 40% of the plasma concentrations in small intestine, lung and skeletal muscle, higher in heart muscle and lower in stomach wall. The net filtration or lymph flow, probably overestimated, was 0.81, 1.5, 0.53, 0.61 and 0.12 microliters/min per g in heart muscle, small intestine, lung, stomach wall and skeletal muscle, respectively.

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PubMed1978

The uptake of IgG and IgM coated sheep erythrocytes in perfused rabbit liver.

Erythrocytes sensitized with IgM and IgG (EA) are entrapped during perfusion of isolated rabbit liver. The binding of EIgG is of high affinity while that of EIgM is weak and partly reversible. Moreover, the binding of EIgM is dependent on the presence of Ca++ ions in the perfusion medium whilst the binding of EIgG is independent of divalent cations. No uptake of sensitized erythrocytes during perfusion of the inferior extremities of rabbits is found.

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PubMed1977

Trabeculo-electropuncture in cynomolgus monkeys (Macaca irus).

Trabeculo-electropuncture (TEP) was performed in one eye of ten cynomolgus monkeys. In five control eyes, the TEP probe was inserted into Schlemm's canal and withdrawn without causing a spark discharge. In another five control eyes,a scleral window was produced and the canal was opened, but no probe was inserted. The gross facility of outflow was determined prior to the operation and 2, 6, and 18 weeks postoperatively. TEP had no longlasting effect on the facility. Gonioscopy five months after the operation revealed marked changes in the anatomy of Schlemm's canal in treated eyes and in control eyes subjected to probe insertion. Control eyes without probe insertion appeared normal. Six months postoperatively three monkeys were killed and the eyes investigated. Light and electron microscopy indicated that insertion of the probe with or without spark discharge resulted in the formation of dense bridges between the inner and outer walls of Schlemm's canal. At the sites of TEP, the trabecular meshwork was replaced by dense scar tissue containing irregular, fine fibrillar material, elastic fibres and large amounts of curly collagen. There were no intertrabecular spaces in the scar tissue. In one eye, one lesion was covered by a thin endothelium resting on a basal membrane. The results indicate that the failure of TEP in monkey eyes was due to the formation of dense scar tissue occluding the openings initially produced by the spark discharge.

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