Partial depletion of the taurine content in the rat retina was accompl
ished for up to 22 weeks by introduction of 1.5% guanidino-ethanesulfo
nate (GES) in the drinking water. Taurine levels decreased by 50% afte
r 1 week of GES treatment and by 80% at 16 weeks. Replacement of GES b
y taurine to the GES-treated rats from week 16 to 22 returned their ta
urine content to the control value. Whereas addition of taurine (1.5%)
to the drinking water of control rats from week 16 to 22 elevated the
retinal taurine content to 118% of the control value, the administrat
ion of untreated water to GES-treated animals for the 16 to 22 week ti
me period increased the retinal taurine content to only 76% of the con
trol value. The amplitude of the electroretinogram (ERG) b-wave was de
creased by 60% after GES-treatment for 16 weeks and maintained this re
duced level for up to 22 weeks. Administration of taurine in the drink
ing water from week 16 to 22 returned the b-wave amplitude to a range
not statistically different from the control values whereas the admini
stration of untreated water produced less improvement. After 6 weeks o
f GES treatment when the retinal taurine content was reduced by 70% an
d the amplitude of the b-wave was reduced by 50% (extrapolated from Fi
gure 1), phosphorylation of a specific protein with an approximate mol
ecular weight of 20K was increased by 94%. The increased phosphorylati
on of the similar to 20K protein observed after GES treatment was reve
rsed when the animals were treated with taurine (1 1/2%) in the drinki
ng water for an additional 6 weeks. There was no change in the phospho
rylation of the similar to 20K protein when animals were treated with
taurine for 6 weeks. The data obtained support the theory that taurine
may have a regulatory effect on retinal protein phosphorylation.