T. Krupin et al., PROLONGED INTRAOCULAR-PRESSURE REDUCTION FOLLOWING INTRAVITREAL BARIUM INJECTION IN RABBITS, Experimental Eye Research, 62(3), 1996, pp. 231-235
The isolated ciliary epithelium contains barium-inhibitable potassium
channels. The present study was aimed at testing the in vivo effects o
f barium on aqueous humor dynamics in rabbits. BaCl2 was administered
to one eye by topical delivery or intravitreal injection. Dynamic meas
urements included intraocular pressure, outflow facility, episcleral v
enous pressure and aqueous flow (fluorophotometry). Barium dynamics we
re studied using Ba-133. Intraocular pressure was not altered after to
pical administration of BaCl2. Ba-133 was not detected in the aqueous
after delivery of eyedrops containing the radiochemical. Intraocular p
ressure decreased following intravitreal injection of BaCl2 (0.15 mu g
). The onset of this pressure reduction was 12 to 16 hr, the maximum d
ecrease (-11.3 mmHg) occurred at 2 days, and the effect persisted (-4.
2 mmHg) for approximately 12, days after the injection. Outflow facili
ty and episcleral venous pressure were not altered. However, aqueous h
umor flow 5 to 6 days after the injection was decreased by 42% to 63%
as determined by fluorophotometry or calculated tonographic data. The
injection was not associated with findings of intraocular inflammation
, Radioactivity was detected in the vitreous within the first 3 days a
fter the injection; however, activity was present in the ciliary body,
equally distributed between the cell membrane and soluble fractions,
seven days after the injection. Intravitreally injected BaCl2 results
in a prolonged intraocular pressure decrease relating to reduced aqueo
us formation. While the mechanism(s) for the BaCl2-induced decrease in
pressure are not clear, possibilities include a Ba2+ interaction with
ciliary epithelial K+ or N-type Ca2+ channels. (C) 1996 Academic Pres
s Limited