CONTRACTILE RESPONSE OF THE ISOLATED TRABECULAR MESHWORK AND CILIARY MUSCLE TO CHOLINERGIC AND ADRENERGIC AGENTS

To characterize the contractile properties of isolated trabecular mesh work strips, we measured the effect of various cholinergic and adrener gic substances on the contractility of trabecular meshwork (TM) strips in comparison with the effects on ciliary muscle (CM) strips. Using a n electromagnetic force-length transducer, we performed measurements o f isometric tension on isolated bovine TM and CM strips. Isolated stri ps were contracted by cholinergic agonists, the relative potency being carbachol > pilocarpine > acetylcholine. The half-maximal effective c oncentration was 2x10(-7) mol l(-1) for carbachol and 2x10(-6) mol l(- 1) for pilocarpine. To characterize muscarinic receptors, we tested se lective antagonists for M(1) (pirenzepine) and M(3) (4-DAMP). Pharmaco logically, the functional muscarinic receptors are of the M(3) subtype in TM as well as CM. The M(1) subtype seems to be less important. The al-agonist phenylephrine was more effective in inducing contractions in TM than in CM. The alpha(2)-agonist brimonidine induced contraction s only in TM. In precontracted tissues the beta-agonist isoproterenol induced a relaxation in both tissues. This relaxation could be inhibit ed by metipranolol. Epinephrine (or dipivefrin) induced small contract ions in TM and CM, which became more prominent, especially in TM, when the beta-adrenoreceptors were inhibited by metipranolol. The data ind icate the presence of functional muscarinic, alpha-adrenergic, and bet a-adrenergic receptors in bovine TM and CM. The contractile properties of TM and CM are differently modulated by the various drugs. Choliner gic and alpha-adrenergic agonists induced contraction, whereas beta-ag onists induced relaxation.