REGULATION OF OUTFLOW RATE AND RESISTANCE IN THE PERFUSED ANTERIOR SEGMENT OF THE BOVINE EYE

Contractile properties of isolated trabecular meshwork strips have rec ently been described. In the present paper we characterize the regulat ion of the outflow pathway in the isolated perfused anterior segment o f the bovine eye. Anterior segments of bovine eyes with detached iris, ciliary body and ciliary muscle were perfused at constant pressure of 8.8 mmHg. A constant outflow of approximately 6-8 mu l min(-1) could be obtained for at least 3 hr. The calculated outflow resistance was i n the range 1.1-1.4 mmHg min mu l(-1). The relative outflow was signif icantly reduced after application of carbachol, reaching a maximal inh ibition of 30%. EC(50) for carbachol was 3 x 10(-8) mol l(-1). Atropin completely blocked the effect of carbachol on outflow. Morphological examination of perfused anterior segments which were perfused with car bachol revealed an intact fine structure of the meshwork cells. Piloca rpine at 10(-5) mol l(-1) reduced outflow by 15%. Epinephrine at 10(-5 ) mol l(-1) reduced outflow, while epinephrine at 10(-6) mol l(-1) sli ghtly increased the outflow rate. This effect could be blocked by meti pranolol. Endothelin-1 in concentrations of 2 x 10(-9) and 2 x 10(-8) mol l(-1) inhibited relative outflow by > 30%. Carbachol, pilocarpine, endothelin and a high dose of epinephrine, which have been shown to i nduce contractions in isolated bovine trabecular meshwork and ciliary muscle strips, induced a reduction of outnow rate and an increase of o utflow resistance of the anterior segment. Thus, at least in the bovin e eye, the trabecular meshwork per se is directly involved in the regu lation of aqueous humor outflow. (C) 1995 Academic Press Limited