title: The effects of 3,4,3'-triiodo-l-thyronine on didehydroretinol synthesis by isolated coho salmon retinal pigment epithelial cells.
abstract: The effects of thyroid hormone on the production of vitamin A(2) retinoids from vitamin A(1) precursor were investigated in retinal pigmented epithelial (RPE) cells obtained from juvenile coho salmon. Specifically, changes in the production of both the storage and the free forms of radiolabeled 3,4-didehydroretinoids were measured after 24 and 48 h incubation with [11,12-(3)H]all-trans-retinol with (or in the absence of) exogenous 3,4,3'-triiodo-l-thyronine (T(3)). RPE cells incubated with radiolabeled all-trans-retinol showed double the production of radiolabeled 3,4-didehydroretinoids (both storage and free forms) after 48 h compared to 24 h incubation. The addition of T(3) had no significant effect on the production of didehydroretinyl esters (storage form) after 24 h incubation, but did have a significant effect after 48 h, with a ca. 50% reduction in the amount of labeled didehydroretinyl produced compared to the amount produced by the controls after 48 h. Essentially the same observation was made for the production of radiolabeled didehydroretinol (free form) where, after 48 h of incubation with T(3), there was a ca. 50% reduction in the amount of labeled didehydroretinol produced compared to the amount produced by the controls after 48 h. The reduction in both the storage and the free forms of didehydroretinoids indicates that T(3) probably had the effect of altering the activity of the "terminal ring dehydrogenase" enzyme which acts on the outer ring of retinoids. The scope of this experiment, however, does not indicate whether the production of didehydroretinoids is specific to the free or to the storage forms as retinoids within the RPE can shuttle between both forms. The results of this experiment do indicate that the in vitro observations of this experiment may be extended to in vivo and field observations. In vitro, T(3) by itself altered the production of didehydro-derivatives of retinoids. The changes in visual pigment complement seen in salmonids, which are due to changes in relative proportions of 11-cis-retinal and 11-cis-3,4-didehydroretinal in the photoreceptors, may also be the result of T(3) acting by itself on the RPE cells.
authors.affiliation: Department of Biological Science, Simon Fraser University, Burnaby, British Columbia, V5A 1S6, Canada. georgea@basalmed.uio.no
authors.forename: G
authors.initials: G
authors.lastname: Alexander
authors.forename: R
authors.initials: R
authors.lastname: Sweeting
authors.forename: B A
authors.initials: BA
authors.lastname: McKeown
mesh_terms: D000818:Animals; D002851:Chromatography, High Pressure Liquid; D017684:Oncorhynchus kisutch / Q000378:metabolism*; D010857:Pigment Epithelium of Eye / Q000187:drug effects* / Q000378:metabolism*; D012172:Retinaldehyde / Q000031:analogs & derivatives* / Q000096:biosynthesis*; D014284:Triiodothyronine / Q000494:pharmacology*; D014316:Tritium; D014801:Vitamin A / Q000378:metabolism
chemical_list: D014284:Triiodothyronine; D014316:Tritium; D014801:Vitamin A; C017184:dehydroretinal; D012172:Retinaldehyde