The metabolism of cyanide and sulphur in the toxic optic neuropathies

Pettigrew, Alan R (1972) The metabolism of cyanide and sulphur in the toxic optic neuropathies. MSc(R) thesis, University of Glasgow.

Abstract

This work is an attempt to provide a biochemical rationale for any clinical changes which may occur during the treatment of patients suffering from the toxic amblyopias, particularly tobacco amblyopia and Leber's hereditary optic atrophy. Cyanide is presumed to be an important cause of the visual failure found in these conditions, and the patients may have a defect in the mechanism for the detoxification of cyanide. The major metabolite of cyanide is thiocyanate, and measurements of plasma and urinary thiocyanate therefore provide a convenient guide to the patients metabolism of cyanide. The previously unsatisfactory colorimetrio procedure for thiocyanate has been improved following the suggestions of Bark & Higson (1964). The method for cyanide estimation is still not completely satisfactory, but is now greatly improved by the intro-duction of a microdiffusion technique, using the Barke & Higson colour reaction. Measurements were made of plasma thiocyanate levels in a group of 20 normal smokers, and were significantly higher than those in a group of 10 normal non-smokers (P< 0.025). The levels of plasma thiocyanate in 18 untreated tobacco amblyopia patients and in 12 untreated Leber's hereditary optic atrophy patients were found to be significantly lower than those found in the normal smokers (P < 0.001). An impairment of thiocyanate excretion was also observed in these patients. After 4 months intramuscular hydroxocobalamin therapy, the plasma thiocyanate levels of these patients rose significantly and approached those of the normal smokers. There were also increases in urinary thiocyanate, improvement in thiocyanate excretion and improvements in vision. Seven tobacco amblyopia patients were treated with an oral preparation of hydroxocobalamin. After 4 months, 3 of the group showed increases in plasma and urinary thiocyanate similar to that obtained with the intramuscular therapy. Six tobacco amblyopia patients were treated with an oral cystine preparation at a dose of 4.0 gm. per day. After 4 months treatment, there were similar increases in plasma and urinary thiocyanate, and satisfactory visual improvement in 3 of the group. Using a fluorometric procedure, red. cell glutathione levels were measured in 32 tobacco amblyopia patients and were found to be significantly lower than those found in 34 normal (non-alriblyopic) subjects of similar ages (P < 0.01). Sequential measurements of red cell glutathione and plasma thiocyanate were made in patients receiving treatment, and the results suggest a possible relation-ship between these two factors.

• Item Type: Thesis (MSc(R))
• Qualification Level: Masters
• Additional Information: Adviser: R MS Smellie
• Keywords: Physiology, Ophthalmology
• Date of Award: 1972
• Depositing User: Enlighten Team
• Unique ID: glathesis:1972-73087
• Copyright: Copyright of this thesis is held by the author.
• Date Deposited: 14 Jun 2019 08:56
• Last Modified: 14 Jun 2019 08:56
• URI: https://theses.gla.ac.uk/id/eprint/73087