Intravitreal clearance of tissue plasminogen activator in the rabbit
G. J. Jaffe, G. D. Green, B. S. McKay, A. Hartz and G. A. Williams
Department of Ophthalmology, Medical College of Wisconsin, Milwaukee.
The clearance of tissue plasminogen activator (t-PA) injected into the
midvitreous cavity was studied in the phakic, vitrectomized rabbit eye with
and without intravitreal fibrin clots. The quantity and activity of t-PA in
the vitreous, serum, and aqueous were determined at ten minutes and at 3,
6, 15, 24, and 48 hours after initial injection by an enzyme-linked
immunosorbent assay (ELISA) and a spectrophotometric solid-phase fibrin
assay (SOFIA). In eyes without an intravitreal fibrin clot, the estimated
half-life for t-PA was 4.3 hours by SOFIA and 5.8 hours by ELISA. In eyes
containing a vitreal fibrin clot, the half-life increased to 9.8 hours by
SOFIA and 11.9 hours by ELISA. Both of these half-lives were significantly
greater than the half-life for eyes without fibrin. Regardless of the
presence of fibrin, intravitreal t-PA activity was significantly less than
t-PA quantity, suggesting the presence of a t-PA inhibitor. A peak in
aqueous t-PA occurred before six hours, indicating that t-PA was cleared in
part through the anterior chamber. There was no measurable serum t-PA at
any of the sampling times.
