Systemic and intraocular uptake of spantide, a tachykinin antagonist, following topical application to the rabbit eye.

Previous observations have indicated that topical application to the rabbit eye of tachykinin antagonists, including spantide, effectively prevents the miosis and the disruption of the blood-aqueous barrier consequent to ocular injury. The present study shows that spantide is taken up into the rabbit eye following topical application. This was established by determination of spantide in the aqueous humor by radioimmunoassay. The concentrations reached in the aqueous humor were those that could be expected to block tachykinin receptors. The elimination of spantide from the aqueous humor was found to be slow. From HPLC analysis it seemed that spantide in the aqueous humor is degraded to smaller products, predominantly spantide 5-11. Some of the topically applied peptide appeared in the general circulation. Here the rate of elimination was rapid by comparison. Very small amounts of spantide appeared in the cerebrospinal fluid after intravenous injection.